Original subtitles

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So my home router is connected to the Internet

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and can forward the traffic into the Internet

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even though it doesn’t know all the routes in the Internet

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Internet routing tables are growing all the time

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so there are more than 500,000 routes on the Internet

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and a small router wouldn't be able to handle that number of routes in its routing table.

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Now it’s possible to telnet to live BGP routers on the Internet.

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So in this example, I’m going to telnet to route-server.ip.att.net

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I’m told that I can log in with this user name

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which gives me read only access to the router

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and I’m going to type show route summary.

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As you can see here there are 8.5 million odd routes

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in the routing table with 567,000 destinations

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show bgp summary will show me the BGP routing table.

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BGP is the routing protocol used on the Internet.

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So total path is 8.5M active path is 567,000

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as you can imagine a small router

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is not going to be able to handle this number of routes in its routing table.

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Here you can see examples of routes in the BGP routing table

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on this router and how long thoses route have been in the routing table.

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Small routers aren't not going to handle that number of routes

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so you would typically use a default route pointing your router to a gateway of last resort.

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So a default route is a special type of static route

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pointing your device or router to a gateway of last resort.

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This is similar to the concept of a default gate way on a PC or a device

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such as an iPhone or iPad

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when a router doesn’t know where to send the traffic

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it simply sends it to the gateway of last resort.

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In other words, it will send it to this IP address

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as configured with the static default route.

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Another advantage of static routes is that you as the administrator

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determine explicitly where traffic flows.

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So rather than a routing protocol making the decision for you

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you decide and have control over where traffic goes

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or where packets are routed but on the flip side

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the burden of management and keeping things up to date also fall on your shoulders

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so you have to administer the routing table, keep it up to date

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make sure that routes are not pointing to non-existing devices

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where networks go down, you would have to update the routing table

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and that’s simply not scalable in large topologies

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so hence dynamic routing protocols

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such as OSPF or EIGRP are used to dynamically add or remove routes from a routing table.

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BGP as mentioned is the routing protocol

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used on the Internet for very large scale implementations.

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The major advantage of dynamic routing protocols is that

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there is the dynamic or automatic adjustment of the routing table

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based on topology changes in your network.

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So rather than you having to manually adjust to a topology change

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the routing protocols update, insert or removed routes

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from the routing table based on changing conditions in the network.

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As soon as you enable a routing protocol

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such as OSPF or EIGRP the routers will form a neighbor or peer relationships

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with each other and exchange routes with one another.

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The routers will does automatically learn about the networks available in the topology.