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okay hi uh
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all right now we're on to ccna2 or
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second half of ccnt
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so uh chapter one is routing concepts
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so we're going to look at initial router
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configuration
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and so how we do that we'll look at how
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a router makes forwarding decisions for
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data packets
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and we're going to look at how routers
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operate in general
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okay so router configure uh
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functions so basically uh networks are
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relied on for
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web applications ip telephony video
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conferencing interactive gaming
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e-commerce and much more
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characteristics referred to when
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discussing networks are topology and so
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the topology is the design and so
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there's
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the physical topology and so that's
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where the physical devices are
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and so it's about cables and devices and
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computers
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and hosts all and all those kinds of
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things and so
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and how they connected together using
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wires cables or whatever
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logical uh topology is more about
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how things are organized and so
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who was directly connected to who and
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what
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now of course when it comes to a network
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i suppose the faster the better normally
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but of course the faster is normally the
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more expensive and so you
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you buy the speed you need and you can
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afford
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um then there's cost so again as i said
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the faster the more expensive typically
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so
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you know they're basically you know
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competing
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requirements basically and so uh of
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course security is another thing that's
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a hot topic these days and so uh
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original ip networks were not designed
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with security in mind at all it's been
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an add-on later but
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of course designing a network with
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security from the start does make it a
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bit better
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so availability basically is
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how much time is it available for use
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and so
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the more the better i suppose
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scalability means
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basically can this network grow
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without groaning um so it can it grow
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and then uh still handle the traffic
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uh and then reliability is you know of
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um basically you know
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do you have single points of failure so
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if a switch dies will everyone be gone
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or will just
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a small amount of people be affected or
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and so on and so forth and so
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as well as purchasing equipment that is
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more reliable with that with the own
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components of got
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redundancy and things like that and yeah
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and other things like
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we mean time between failures for the
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devices you buy so
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it's all things you can research so
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why routing so of course a router is
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used to connect one network to
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to another the term is the best route to
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the destination before forwarding
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traffic to the next router along the
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path
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uh it's responsible for routing traffic
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between networks
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and the routing table is used to make
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those
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to determine the best route for the
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packet to get to its destination
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um so a router is basically a
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specialized computer they've got a cpu
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they've got an operating
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system they've got permanent storage
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they've got volatile storage
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all the same things as the computer you
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sit down and type
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documents in some might be a little
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different so of course if you look in
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the specifics
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the operating system for a cisco router
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is ios internet work operating system
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and no
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apple didn't think of ios first
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when it comes to storage well ram pretty
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much the same
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but of course not many routers have a
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hard drive they used normally use flash
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just as their non-volatile storage um
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and a rom read only memory well pretty
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similar to at least how old a computer
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has worked
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um and of course the other major
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difference between routers and other
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computers is
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they will often have specialized ports
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for connecting networks together
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of course they're going to have more
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than one network port otherwise there's
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not much point to the router
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so having a look at uh as we
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said the storage here uh ram
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exactly the same as computer you it's
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volatile
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that's where you put the operating
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system where it's running this
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configuration
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configuration works ends up there all of
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your working data ends up there as well
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so a lot of the routing table
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our tables packets can be stored there
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the whole lot so they're all
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uh that's pretty much the same purpose
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as your computer
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rom um well it's
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basically how the computer boots up it
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will go to rom first and then rom
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will do a postal power on self test
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diagnostic make sure everything it needs
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is there and then it will actually hunt
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for a full operating system
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with routers you actually do have a very
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basic ios
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built into rom and so they can talk on a
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network they won't be a router with just
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rom
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but they will be a host and you can
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actually then connect to other devices
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and maybe
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transfer a full operating system if it's
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been
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destroyed somehow or other now
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when it comes to uh non-volatile
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uh storage while on a computer we have a
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hard drive or a solid solid state drive
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or whatever might be with routers they
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have
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have two types so there's flash that's
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where you store the operating system
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uh you cannot store other files as well
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but you know storing files is not really
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a router's job
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and the most common files you might
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store is if you're doing intrusion
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prevention
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you'd have your signature files stored
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in flash as well
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um when it comes to the configuration
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um that's actually stored in what's
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called
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nvm nvram or non-volatile random access
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memory
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it's basically flash anyway but i've
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just given it a different name
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because it's organized separately okay
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when it comes to physically looking
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around this is a 1941 like
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what's in the rack in on the level three
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um you have usb ports so you can
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actually plug that in
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transfer files to and from and away your
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roll um
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we have network ports and so there's g00
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and g01
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you have a console port which i think
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we've discussed before that's how you do
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your initial configuration
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you can also use usb on these ones as
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well as a console port they've both got
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that light blue code
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auxiliary port is designed to plug a
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router
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and modem into and so you can actually
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do
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a little more remote administration with
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that and then here basically we have the
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h wix slots so high speed wan interface
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card slots and so of course in our rack
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we've actually got
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serial cards in there but you know you
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can put in
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dsl ports or whatever is required
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typically for your wan connection
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okay now of course routers as we said
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interconnect networks and so because
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they interconnect more than one network
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that's why they do the forwarding of
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packets between them
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multiple networks in a router require
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multiple interfaces that each belong to
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that different ip network
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and so the ethernet interfaces need to
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be configured
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to be on the lands they need to be and
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the lan ports of course
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you know probably hook into your isp or
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whatever it might be when a packet
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arrives on a router's interface the
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router might be
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the final destination or we might have
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to send it to another router to reach
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its final destination
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okay so routers choose the best paths
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and so they use a rounding table to do
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that
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so routers use the routing table like a
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map to discover the best path to a given
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network
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and so and so the primary function of a
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router is to determine the best path to
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send packets
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forward packets towards the destination
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when a router receives a packet examines
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the destination address of the packet
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and uses the routing table to look for
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the best
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part of that network when a match is
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found the router encapsulates the packet
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into the data link frame for the
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outgoing
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interface and then forwards the packet
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out that interface towards its
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destination
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a router can handle different data link
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layer frame encapsulations
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as you can see on the router here you've
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got an ethernet lan here and you've got
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a serial port there
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that would be either hdlc or triple p
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typically and this would be ethernet
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two different layer two encapsulations
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and so
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you would actually strip the layer two
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off of it if it arrives from the
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ethernet and then
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put a different layer 2 on it to send it
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over the serial
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ok now of course
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they make um forwarding decisions and
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then it's actually
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switching that is what how it gets
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forwarded
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so the decision is where do i send it
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the switching is
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sending it so basically there's
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more than one way to forward packets and
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so there's process switching which
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basically
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is what this first one is here it
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arrives in interface
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uh and then it actually goes up through
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the cpu
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through ram the whole lot to be
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processed
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and then makes a decision now if
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um and so
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doing that is a slow way to do things
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but
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what you can do is if you've got fast
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switching as an option the first packet
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will always go through this process
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but it can actually update
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special registers so that well that's
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the first packet of a conversation
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um and so from there on in it can
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actually update those registers that all
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the subsequent packets
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will actually just be expressed through
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uh this the system and so it doesn't
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have to
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ram and be chugged on by the cpu for
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every packet
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um and so the first one is required
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to go through that process just so that
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the router can figure it out
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and then yeah it just sort of keeps that
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information in the cache
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so it knows how to forward the uh these
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subsequent frames or packets
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um and so with cisco
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express forwarding it's the fastest most
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recent and preferred packet forwarding
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um
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mechanism called ceph and so it
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builds a forwarding information base and
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an adjacency table
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table entry entries are not packet
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triggered like fast switching but
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change triggered when something changes
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in the topology
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when a network is converged the fib and
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adjacency tables contain all the
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information the router would
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have to consider when forwarding a
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packet the fob contains
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pre-computed reverse lookups next top
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information for routes including the
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interface and layer 2 information
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okay so how do we connect to a network
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and so based on your home home offices
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devices might connect as follows laptops
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and tablets may connect wirelessly
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to the home router the network printer
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consists of an uh
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connects maybe using an ethernet cable
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to a switch port
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the home router connects to the internet
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service provider by a cable modem or
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dsl or whatever it might be
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um and so of course the cable modem
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connects to the isp network so
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so branch site devices might connect as
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follows desktop pcs voip phones and
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corporate resources such as file servers
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and printers connect to allow to switch
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laptops and smart
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phones might connect wirelessly the
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wireless access points connect to
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switches using ethernet cables like two
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switches connect to an ethernet
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interface on the edge router using
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ethernet cables
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and the edge router connects to a wan
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service provider with whatever that is
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required
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central site devices might connect as
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follows the
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desktop pcs and voip phones cables again
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like two switches connect redundantly to
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a multi-layer three
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layer three switch layer three modular
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switches connect to an
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edge router using ethernet corporate
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website server connects to the edge
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router
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interface and the edge router connects
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to the wan
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service provider and also to an isp for
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backup purposes
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so that's for the bigger office
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okay so default gateways devices need
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the following information
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to be able to talk on an ip network so
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an ip address it's subnet mask and the
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default gateway
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when a host sends a packet to a device
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that is on the same ip network
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the packet has forwarded out the host
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interface to the destination device the
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router does not need to get involved
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when a host sends a packet to a device
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on a different ipa network the
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packet is forwarded to the default
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gateway because the host device cannot
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communicate with
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devices on other networks so the default
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gateway is the device that routes
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traffic from a local network
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to devices on remote networks such as
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devices on the internet
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and so all of these hosts would have
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this
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interface on the router as their default
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gateway
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and if you look at the addressing they
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are all members of the same
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subnet 1.21681
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this one here is a completely different
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router subnet because it's on a
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completely different site
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okay documenting and networking
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addressing so
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basically when you design a network
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addressing scheme
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don't just leave it in your head you
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should document it
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and so you should identify what devices
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uh using which interfaces and what ip
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addresses and subnet masks they use
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as well as their default gateways and so
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this is an example
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and so router one using this interface
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has this ip address or that mask
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the file gateway doesn't have one
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because it's a router
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and so on and so on so um routers of
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course will have multiple ip address
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entries because they have multiple
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interfaces
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while the host only has one interface
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they don't really need to specify it
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that's its ip address that's its mass
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that's its gateway which happens to be
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that one so pc1 connects to
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r1 as per the diagram and so you need to
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basically document all that information
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and so that handy later if you've left
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the company and someone else needs to
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find problems if they can find that
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documentation
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they can then figure things out that
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that bit easier
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now how do we get an eye a host to talk
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to ip
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now there's two major ways one is
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statically so that's where you
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have to type the ip address into the
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device
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and as long as you don't make any
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mistakes it works great
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but if you've got hundreds of devices
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that's when more mistakes are likely
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and well who really needs to do that
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and so dynamically is where you actually
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have a dhcp server
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the host when it boots up sends out a
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dhcp discover message saying hey is
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there a dhcp server out there
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i'd like an address please and so from
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there
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i get the address and they work nicely
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and there's much less chance of
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duplicate ip addresses and all kinds of
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stuff like that
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okay so probably should have been a few
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slides earlier but anyway
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device leds now host computers connect
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to a wide network using an rj45
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ethernet cable most network interface
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cards have one or more two led lights
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to tell you their status basically so
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green led
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normally means green is good um
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a blinking green one probably means that
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there's traffic moving at the moment
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no light probably means there's no cable
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plugged in or it's a bad cable
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um or it's been turned off so network
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infrastructure devices
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also use leds and so on and
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catalyst switch the green led indicates
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the switch is functionally normally
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amber means it indicates a malfunction
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cisco routers also use various led
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indicators as well
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and this of course is a uh indicator
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and so basically l means link s means
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speed
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and so ill you know green is good
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off is not good with the speed basically
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uh if it blinks once it's running at 10
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megabit
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twice it's 100 three times it's gigabit
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so the console basically green is good
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our offers nothing and pretty much the
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same with
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usb as well
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so what ports and cables would we use
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now
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two hook a console cable into a
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router you would normally use the
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console port there
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with the rj45 end and then you would
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plug it into
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that nine pin serial port on the
00:18:03
computer of course
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some computers do not have those and so
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yeah legacy free so another option is
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usb port with a special cable
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into the usb console port
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now you need to load a specialized
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driver to actually get that to work on
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the computer
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and away your role then of course you
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need software
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now there's teraterm or putty they're
00:18:32
the free options available
00:18:34
hyperterminal used to be very popular as
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well but
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it's actually not available for free
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anymore
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um
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so yeah basically that's how you do your
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initial configuration is
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through some kind of console connection
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so either the console cable here
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or uh usb cable you can also do a usb to
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rs232 adapter
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uh which then plugs into that cable and
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away your roll
00:19:03
again you'll need a driver for that so
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ip on a switch
00:19:07
i switches don't actually need to have
00:19:09
an ip address
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um but of course you
00:19:15
if you wish to reconfigure that switch
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you don't necessarily need to want to go
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into the
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whatever room it might be in to
00:19:21
configure it then so some remote access
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so you can actually do it remotely is a
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good idea and so
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to configure it interface vlan 1 give it
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an ip address
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turn it on tell it who its gateway is
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that's all you need to do
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and that will actually configure the
00:19:39
switch virtual interface
00:19:41
and you'll be able to connect to the
00:19:42
switch from there as long as it's all
00:19:44
correct
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now routers and switches are same
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actually
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um enable secret
00:19:52
will of course be um
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that encrypted um
00:19:59
password encrypted well hashed with md5
00:20:04
um so that's
00:20:07
basically so you can get into privileged
00:20:08
exec mode
00:20:10
uh you can also set a console password
00:20:14
and so we've done cisco here then of
00:20:16
course you need to sell it
00:20:17
to use the password to log in line vty
00:20:21
again you can set a password and it
00:20:23
needs to be told it needs to log in
00:20:25
um and then of course these are plain
00:20:28
text passwords by default
00:20:30
but if you do service password
00:20:31
encryption it will actually
00:20:34
hash them and then that
00:20:37
someone's looking over your shoulder
00:20:39
when you do a show run they won't be
00:20:40
able to see what the password is
00:20:42
another thing you can do of course is do
00:20:45
the mana
00:20:46
banner motd which is banner message of
00:20:48
the day
00:20:49
and you should have something like
00:20:51
authorized access only or something like
00:20:53
that just so that
00:20:54
people know that they're entering a
00:20:56
system that you know we care about
00:20:58
um okay
00:21:02
now configuring ipv4 on a router
00:21:05
interface
00:21:06
is done on the physical interfaces so
00:21:08
you do it on a switch virtual interface
00:21:10
on a switch
00:21:11
but on a router we do it on the physical
00:21:13
interface and so in this case gigabit
00:21:15
ethernet zero zero
00:21:17
you can put it in the description which
00:21:19
is always a good idea
00:21:20
and then you put in the ip address turn
00:21:21
it on and away your roll that's all you
00:21:23
need to do per interface
00:21:26
um and so again this is probably a 1941
00:21:32
so it's got gigabit ethernet interfaces
00:21:35
uh you should always do show ip
00:21:37
interface brief or something like that
00:21:39
and it will tell you what interfaces are
00:21:41
on that particular router
00:21:47
ipv6 much the same process as ipv4 but
00:21:52
of course you do an ipv6 address
00:21:55
um and away your role
00:22:04
um how was that
00:22:12
now this clock rate command uh because
00:22:15
it's a serial interface you need to do
00:22:16
that on the dte
00:22:18
end um but on packet tracer it's
00:22:22
actually done automatically so
00:22:24
it's not a big challenge um
00:22:30
you can also of course do link local
00:22:32
addresses it talks about it here but it
00:22:34
doesn't show it
00:22:36
and so you know the fe-80 address you
00:22:38
can make that a little simpler
00:22:42
uh loopback interface um
00:22:46
different uses for different things you
00:22:48
might want to use it for ospf you might
00:22:50
actually use it with bgp
00:22:52
as well and things like that so
00:22:53
basically it's a
00:22:56
virtual interface as opposed to a
00:22:57
physical one
00:22:59
uh the advantage of that is it's always
00:23:02
going to be up if the router's up
00:23:03
and it's not depending on a cable
00:23:05
working and so that gives it some
00:23:07
reliability
00:23:08
and ospf does like having an interface
00:23:10
like that to use for certain things
00:23:12
um and bgp can use that as well as i
00:23:16
said
00:23:20
so as i said show ip interface brief is
00:23:22
a good way to see what you're into
00:23:23
what interfaces are on the machine and
00:23:25
also gives you their status so protocol
00:23:27
up
00:23:28
and physical interface up so that's
00:23:33
as good as you're going to get when it
00:23:34
comes to that
00:23:38
uh ip show ipv6 route
00:23:42
of course is the ipv6 routing table
00:23:45
and so you've got the source information
00:23:47
the destination network
00:23:49
and how to get it there these are all
00:23:52
directly connected so it's not a
00:23:53
challenge
00:24:01
when you do show commands you can
00:24:02
actually filter it say begin it gateway
00:24:05
or
00:24:05
show ip address show ip route begin
00:24:08
gateway so just
00:24:10
chops out all that in explanat
00:24:12
explanatory information
00:24:14
show running config you can just do
00:24:16
section or start or
00:24:18
will begin and things like that but i
00:24:21
don't think it's supported in packet
00:24:23
tracer so
00:24:23
yeah um command history of course you
00:24:27
can use the up arrow key or control p
00:24:28
for previous
00:24:32
and so it will show you by default the
00:24:35
last 10 commands
00:24:36
you can actually change the terminal
00:24:37
history size to be bigger or smaller
00:24:42
in this case 200 as opposed to 10
00:24:45
which is nice okay so how does a router
00:24:48
make
00:24:49
forwarding decisions and so basically
00:24:52
the primary function of router is the
00:24:53
four packets toward their destination
00:24:55
it uses a switching function which is a
00:24:57
process that accepts packet
00:25:00
packet on one interface forwards it to
00:25:02
another
00:25:03
interface and and so
00:25:06
that's the decision process then of
00:25:08
course the switching is actually where
00:25:10
it
00:25:11
gets the physical moving from port to
00:25:13
port
00:25:14
switching function also encapsulates the
00:25:15
packets in the appropriate data link
00:25:17
frame type for the outgoing interface
00:25:19
and so as you can see this is the
00:25:21
sending host i'm assuming
00:25:24
so of course it goes down all seven
00:25:26
layers
00:25:27
once it's reached layer one it goes
00:25:28
across the piece of cable
00:25:30
then it's received at the router because
00:25:31
it's a remote host
00:25:35
uh the router only needs to look at
00:25:36
layout through information makes
00:25:37
forwarding decision doesn't worry about
00:25:38
the top four layers
00:25:41
or if it knows how to fold it then goes
00:25:43
down gets encapsulated and so on so
00:25:47
so the layer 3 as i said is the layer
00:25:49
that goes all the way through this is
00:25:51
from last
00:25:52
term layer 2 is changed at each step
00:25:54
along the way
00:25:59
um so when a router receives a packet
00:26:01
from one network that is destined for
00:26:02
another the router performs following
00:26:04
three steps it decapsulates the lathe
00:26:06
two frame header and the trailer and
00:26:08
exposes a lie3 packet
00:26:10
it examines the destination ip address
00:26:12
to find the best path
00:26:14
if the router finds a path to that
00:26:15
destination it encapsulates the layer 3
00:26:17
packet into a new layer 2 frame
00:26:19
and forwards it out the exit interface
00:26:21
as a packet travels from source device
00:26:23
destination device the last three ip
00:26:25
addresses do not change
00:26:26
however the layer 2 datalink addresses
00:26:28
will change at every hop
00:26:35
so for pc1 to send a packet to pc2 so
00:26:39
across um several router
00:26:42
hops it must determine if the
00:26:44
destination ip address is on the same
00:26:46
network as it
00:26:47
of course it isn't the pc1 will obtain
00:26:50
the mac address from its upcase
00:26:52
or use an art request because it's on a
00:26:54
different network it follows
00:26:55
forwards it to the default gateway so it
00:26:58
may need to send an art request about
00:26:59
the gateways ip address
00:27:03
to determine the mac address of the
00:27:05
default gateway
00:27:06
checks its art table or it will send out
00:27:08
a mark request as i said
00:27:09
when pc1 has the mac address of router 1
00:27:12
it can then forward the packet
00:27:14
when router 1 receives the ethernet
00:27:16
frame from pc1
00:27:17
it examines the destination mac address
00:27:19
and sees the
00:27:20
address for it um
00:27:25
and then of course it's got a type field
00:27:27
that tells it it's an ip packet
00:27:29
and so r1d encapsulates the ethernet
00:27:32
frame
00:27:32
because the destination ipv4 address is
00:27:35
not any of its ip addresses
00:27:37
it will then make a forwarding decision
00:27:39
and so we'll
00:27:41
look up the routing table in this case
00:27:44
it's looking for this network here
00:27:50
um and so it finds out the next top is
00:27:55
one nine two one six eight two two and
00:27:58
so that's
00:27:59
it will then of course need another mac
00:28:01
address on the next top
00:28:04
probably in its art table i'm assuming
00:28:06
that they talk to each other fairly
00:28:07
regularly
00:28:08
and so then because the x-interfaces on
00:28:11
an ethernet network r1 must resolve the
00:28:13
next stop
00:28:14
um when the r1 has the mac address it
00:28:17
can then
00:28:18
forward the frame out of fast ethernet
00:28:20
zero one
00:28:23
okay so then it will arrive at packet
00:28:26
router two
00:28:27
and basically the same process except
00:28:29
the outgoing interface
00:28:31
is not an ethernet it's a serial so
00:28:33
it'll either be
00:28:34
triple p or hdlc depending on what's
00:28:42
configured
00:28:49
because there are no mac addresses on
00:28:50
serial interfaces r2 sets the data link
00:28:52
destination address to
00:28:54
equivalent of a broadcast because on a
00:28:57
point of point there's only two hosts
00:28:58
itself and the other one so it arrives
00:29:01
at
00:29:02
r3 from that serial interface
00:29:06
triple p and so it decapulates the
00:29:09
triple p
00:29:09
frame searches in the routing table for
00:29:11
the destination oh that's a directly
00:29:13
connected network
00:29:14
so now it needs to know the mac address
00:29:17
of pc2
00:29:19
so it may or may not need to send an art
00:29:21
request
00:29:24
and then of course it will forward it
00:29:28
to pc2 it's gotten to its destination
00:29:32
okay so routing decisions primary
00:29:34
function of router is to determine the
00:29:36
best path to send packets
00:29:37
the rating table search results in one
00:29:39
of three path determinations you've got
00:29:41
a directly connected network
00:29:42
so basically um
00:29:46
yeah so it's learned it when it booted
00:29:48
because it's directly connected to it
00:29:50
you've got a
00:29:50
remote network and so that's either from
00:29:53
a static
00:29:54
route or a dynamic route learned from
00:29:56
another routing protocol
00:29:58
um and so we'll forward it to the next
00:30:01
hop router
00:30:02
along the path or if it doesn't know how
00:30:04
to find the destination
00:30:06
it will um
00:30:11
either center the gateway of last resort
00:30:14
so
00:30:14
basically if in doubt send it to there
00:30:17
so
00:30:17
in this case it could be your isp
00:30:19
whatever might be or
00:30:21
if there's no gateway of last resort it
00:30:23
would dump it
00:30:25
now determining the best path to a
00:30:26
destination network involves the
00:30:27
evaluation of multiple powers and
00:30:29
selecting the optimum and shortest path
00:30:31
to reach the network
00:30:32
the best path is selected based on the
00:30:34
met on a metric
00:30:35
or value that is used by the routing
00:30:37
protocol the best path to a network is
00:30:39
the path with the lowest metric
00:30:40
metric is a value that is used to
00:30:42
measure the distance to a given network
00:30:44
each dynamic rating protocol has their
00:30:46
own rules and metrics to build and
00:30:48
update rating tables
00:30:49
for example rip uses hop count ospf uses
00:30:52
cost
00:30:53
which is calculated from bandwidth and
00:30:55
there's eigrp which uses
00:30:57
bandwidth and delay and possibly load
00:30:59
and reliability
00:31:01
we'll talk about the igrp in cisco 3
00:31:05
if you continue on okay load balancing
00:31:08
is if a router has two or more parts
00:31:10
with identical metrics to the same
00:31:11
destination
00:31:12
the router will forward the packets
00:31:14
using both paths
00:31:16
the rating table contains a single
00:31:17
destination network
00:31:19
that has multiple exit interfaces um
00:31:22
it will do equal cost load balancing so
00:31:24
in other words
00:31:26
it will send the first packet on the
00:31:28
first part the second packet on the
00:31:29
second then the third on the first and
00:31:31
the fourth on the second and so on
00:31:35
now some writing protocols like eigrp
00:31:37
support unequal cost load balancing and
00:31:39
so
00:31:40
the the
00:31:45
a number of packets sent uh proportional
00:31:48
to the
00:31:49
uh desirability of the path basically
00:31:54
now there's different ways you can learn
00:31:56
destination
00:31:57
networks and so you need to have some
00:31:59
way of having a tie breaker
00:32:01
and so basically it's called
00:32:04
administrative distance
00:32:05
and so if you have a directly connected
00:32:08
network
00:32:09
that is extremely reliable so if you're
00:32:11
directly connected to a network
00:32:12
that's pretty damn reliable information
00:32:14
and so
00:32:15
the lower the admin distance the better
00:32:19
and so uh while rounding protocols are
00:32:22
basically routed as being
00:32:25
the most reliable to the least reliable
00:32:27
that's what they're saying
00:32:29
now i don't necessarily agree with all
00:32:30
their ratings but anyway but that's how
00:32:32
it works and so
00:32:33
basically how much do you trust the
00:32:35
route you can change the admin distance
00:32:36
as well
00:32:38
if you're feeling that way include
00:32:39
client and then there's rounding
00:32:41
uh router operation and so
00:32:44
of course a major part of that is the
00:32:46
routing table so
00:32:48
of course you get uh directly connected
00:32:50
routes
00:32:51
uh and so when an interface is up and
00:32:53
it's got an ipa address
00:32:55
it will have it will be in the routing
00:32:57
table
00:32:58
and then remote routes are either
00:32:59
learned by statically configuring them
00:33:01
or by learn
00:33:02
being learned by a dynamic writing
00:33:04
protocol a writing table is a data file
00:33:06
in ram that is used to store information
00:33:08
about directly connected and remote
00:33:10
networks
00:33:10
the routing table contains next top
00:33:12
associations for remote networks
00:33:14
association tells the router what the
00:33:16
next top is for that particular
00:33:18
destination network
00:33:23
so the sources available basically if
00:33:27
you do a show ip route
00:33:28
it will actually and i don't know why
00:33:30
they're showing us a
00:33:32
show running config but anyway um
00:33:35
if you look at a routing table these
00:33:37
these are some of the more common ones
00:33:38
you'll see so local
00:33:39
basically means the local interface and
00:33:42
so that will actually give you the
00:33:44
ip address of a local interface c means
00:33:46
it's a directly connected network
00:33:48
s means learns this route has been
00:33:51
learnt statically
00:33:52
d means it's been learned from eigrp and
00:33:55
o
00:33:56
means it's been learnt from ospf
00:34:00
so so here is an example of a routing
00:34:03
table entry
00:34:04
so d means it's been linked from an
00:34:05
eigrp
00:34:07
uh this is the destination network so 10
00:34:10
1 1
00:34:11
10 1 1 0 24.
00:34:15
so here is that admin distance we're
00:34:16
talking about so eigrp's
00:34:18
admin distance is 90 this is the metric
00:34:21
so how far away is that destination
00:34:23
network so 10 1 1 0.
00:34:26
this is from router 1 and so 10 1 0 is
00:34:28
over here so that's
00:34:30
that's the distance so that is the next
00:34:33
hop
00:34:34
interface
00:34:37
this is how long since i've heard from
00:34:39
that neighboring router
00:34:41
so five seconds that's not long and this
00:34:43
is the exit interface for that
00:34:47
that route
00:34:54
so here we've got an empty routing table
00:35:00
so basically this router hasn't been
00:35:03
configured
00:35:04
enough for another thing because it
00:35:06
should have three entries at the very
00:35:07
minimum
00:35:08
for the three directly connected
00:35:09
networks so either the
00:35:12
cables aren't plugged in or the
00:35:14
information hasn't been put in yet
00:35:18
so new router without any configured
00:35:19
interfaces will have an empty routing
00:35:20
table as shown
00:35:21
before the interface state is considered
00:35:23
up and up uh
00:35:27
the interface must be assigned a valid
00:35:29
ipv4 ipv6 address
00:35:31
must be activated with the no shutdown
00:35:33
command and should have a carrier signal
00:35:35
from
00:35:36
neighbouring devices so you know to know
00:35:39
that the status of the cable is up
00:35:41
when interface is up the network of that
00:35:43
interface is added to the routing table
00:35:44
as a directly connected route
00:35:47
and so a directly connected route
00:35:50
especially with
00:35:51
ios version 15 you get two entries one
00:35:54
is the directly connected network
00:35:56
and one is the local link and so as you
00:35:59
can see
00:35:59
the local link is slash 32 which means
00:36:01
this is the host address
00:36:03
while this is the network number
00:36:06
24. and so directly connected and there
00:36:09
that's the physical interface
00:36:10
so you don't get as much information
00:36:12
because it's
00:36:14
you don't need it um
00:36:21
and so here you can see you've got your
00:36:24
cnl entries for the three
00:36:26
interfaces that are directly connected
00:36:28
so
00:36:31
as you learned last time router
00:36:33
interfaces by default are turned off
00:36:36
and so if you um
00:36:40
if you want to turn it on you actually
00:36:41
have to do no shutdown shutdown turns it
00:36:44
off no shutdown
00:36:45
turns it on now ipv6
00:36:50
uh again very similar
00:36:54
but of course the addressing is
00:36:56
different you still get your c
00:36:58
l entries
00:37:03
and it's not showing as a table okay um
00:37:06
now static and default routes so after
00:37:09
directly connected interface is
00:37:11
configured and added to the routing
00:37:12
table then static or dynamic routing
00:37:14
can be configured static routes are
00:37:16
manually configured and define an
00:37:17
explicit path between two networking
00:37:19
devices
00:37:20
if the network topology changes static
00:37:22
routes must be manually reconfigured
00:37:25
so what's the advantage of static routes
00:37:26
improved security and
00:37:28
reverse resource efficiency because um
00:37:31
routing protocols send information
00:37:33
across the networks so
00:37:35
that means it gives you a chance to be
00:37:37
intercepted
00:37:38
and of course resource efficiency you
00:37:40
don't need to send that information
00:37:43
and so you don't need a routing protocol
00:37:44
using ram and
00:37:47
bandwidth and all that as well but
00:37:50
it's not dynamic so there are two main
00:37:53
types of static routes static and
00:37:55
default static
00:37:56
so a static route is to a particular one
00:37:58
particular destination while the default
00:38:00
route is
00:38:01
if in doubt use this route
00:38:11
so of course the command is ip route
00:38:14
then it's a destination network
00:38:15
it's mask and then you can either use
00:38:18
next part p address or exit interface
00:38:20
now
00:38:21
next top ip address will always work the
00:38:23
exit interface will not always work
00:38:25
especially with the multi-access network
00:38:28
so a default route is basically the same
00:38:30
except the destination network is all
00:38:32
zeros and the mask is all zeros
00:38:34
and then you use an exit interface or
00:38:37
next top
00:38:38
and so basically this default gateway is
00:38:42
if i don't have a better route
00:38:43
i'll use this one
00:38:50
and here's an example ip route quad 0
00:38:52
quad 0
00:38:53
serial triple zero so that's how you
00:38:55
enter a default route
00:38:56
exit interface of 0 triple 0.
00:39:00
and so now you can see in the routing
00:39:01
table that there's this static entry
00:39:04
destination of quad zero and that's the
00:39:07
exit interface
00:39:08
now with ipv4 you also get a line saying
00:39:11
gateway of last resort is quad zero
00:39:14
and so that two indications that you get
00:39:16
a default route
00:39:18
that star means it's a candidate to be a
00:39:20
default route
00:39:24
um of course
00:39:27
this is a static route ip route one on
00:39:29
two one six eight ten zero
00:39:31
um 24 bit mask and then either an exit
00:39:36
interface
00:39:37
or a next top ip address
00:39:45
so ipv6 again is not greatly different
00:39:49
now when can you say an ipv6 address is
00:39:53
shorter when it's a default route
00:39:55
so ipv6 route two colons of course means
00:39:58
128 zeros
00:40:00
slash zero that's the subnet that's the
00:40:03
prefix and so then s triple zero so
00:40:06
that's actually
00:40:07
achieved the same as that quad zero ipv4
00:40:10
route
00:40:11
of course this is a static route and so
00:40:14
again you need
00:40:15
this is the destination network next top
00:40:18
ip address or
00:40:19
exit interface
00:40:25
now dynamic routing we will go into uh
00:40:27
in a later chapter
00:40:28
so basically the rating protocols are
00:40:30
used to for routers to share information
00:40:33
about the reachability and status of
00:40:35
remote networks rather than manually
00:40:37
configuring static routes dynamic rating
00:40:38
protocols use network discovery to share
00:40:41
information about the networks that it
00:40:42
knows about with other routers that are
00:40:44
using the same running protocol
00:40:46
routers automatically learn about remote
00:40:47
networks from the other routers
00:40:49
these networks and the best path to
00:40:50
which are added to the routing table of
00:40:52
the router
00:40:53
routers have converged after they finish
00:40:55
exchanging updating the rating tables
00:40:58
and the routers then maintain the
00:40:59
networks in their rating tables
00:41:03
so ipv4 rating protocols one of the
00:41:06
major advantages of dynamic
00:41:08
over static is um they can determine a
00:41:12
new best path
00:41:13
if the primary one fails dynamic random
00:41:16
protocols can adjust to topology changes
00:41:19
without involving a network
00:41:20
administrator
00:41:21
and so the ones that are still in use
00:41:23
these days eigrp which is
00:41:25
proprietary ospf which is standards
00:41:27
based iss is also standards based
00:41:29
and rip is standards based but a bit old
00:41:36
now if you do router question mark it'll
00:41:38
actually tell you what ones
00:41:42
are supported
00:41:47
okay so we've looked at
00:41:50
how to configure a router to route
00:41:52
between multiple uh directly connected
00:41:54
networks we've looked at how
00:41:55
routers use information and data packets
00:41:57
to forward make forwarding decisions in
00:41:59
a small and medium-sized business
00:42:01
i've explained how router learns about
00:42:02
remote networks when operating in a
00:42:04
small to medium-sized business network
00:42:07
there's the logo so of course
00:42:11
chapter two was also for this week
00:42:14
and so that video will follow have a
00:42:18
nice day
