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So my home router is connected to the Internet and can forward traffic onto the Internet even though

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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 and a small router wouldn't be able to handle that

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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 gonna telnet to route-server.ip.att.net.

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I'm told that I can log in with this username which gives me read-only access to the router and I'm

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gonna type show route summary. As you can see here there are 8.5 million odd routes in the

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routing table with 567,000 destinations.

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BGP summary will show me the BGP routing table BGP is the routing protocol used on the Internet.

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So total paths is 8.5 million, active paths is 567,000.

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As you can imagine a small router is not going to be able to handle this number of routes in this routing

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table.

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Here you can see examples of routes in the BGP routing table on this router and how long those routes

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have been in the routing table.

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Small routers aren't 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 pointing your device or router to a gateway of

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last resort.

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This is similar to the concept of a default gateway on a PC or a device such as an iPhone or iPad when

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the 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 as configured with the static default route. Another

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advantage of static routes is that you as the administrator determine explicitly where traffic flows.

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So rather than a routing protocol making the decision for you you decide and have control over where

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traffic goes or where packets are routed.

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But on the flip side, 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.

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Keep it up to date.

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Make sure that routes are not pointing to non-existent devices where networks go down.

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You would have to update the routing table and that's simply not scalable in large topologies.

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So hence dynamic routing protocols such as OSPF or EIGRP are used to dynamically add or remove routes

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from a routing table.

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BGP is mentioned is the routing protocol used on the internet for very large-scale implementations.

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The major advantage of dynamic routing protocols is that there is the dynamic or automatic adjustment of

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the routing table based on topology changes in your network.

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So rather than you having to manually adjust to a topology change the routing protocols update, insert

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or remove routes from the routing table based on changing conditions in the network.

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As soon as you enable a routing protocol such as OSPF or EIGRP the routers will form a neighbor or peer

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relationships with each other and exchange routes with one another.

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The routers will thus automatically learn about the networks available in the topology. Routers exchange

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information about routes using different methods.

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But as an example, OSPF uses link-state updates to advertise information about routes that are available

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in the network topology.

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This puts overhead on the network because additional traffic is sent and received by routers as they communicate

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with one another.

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However, as the network grows there is an exponential increase in the amount of work that would be required

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if static routes were used and thus because of the advantage that dynamic routing protocols put less

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overhead and workload on administrators to maintain routing tables.

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They are used in most networks today especially larger networks with the largest being the Internet which

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runs on BGP or border gateway protocol

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and once again dynamic routing protocols can adjust to changes in the topology automatically and without

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administrative intervention.