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These are the user uploaded subtitles that are being translated: 1 00:00:00,000 --> 00:00:05,000 align:middle line:84% So my home router is connected to the Internet 2 00:00:05,000 --> 00:00:07,000 align:middle line:84% and can forward the traffic into the Internet 3 00:00:07,000 --> 00:00:10,000 align:middle line:84% even though it doesn’t know all the routes in the Internet 4 00:00:10,000 --> 00:00:13,000 align:middle line:84% Internet routing tables are growing all the time 5 00:00:13,000 --> 00:00:18,000 align:middle line:84% so there are more than 500,000 routes on the Internet 6 00:00:18,000 --> 00:00:24,000 align:middle line:84% and a small router wouldn't be able to handle that number of routes in its routing table. 7 00:00:24,000 --> 00:00:29,000 align:middle line:84% Now it’s possible to telnet to live BGP routers on the Internet. 8 00:00:29,000 --> 00:00:35,000 align:middle line:84% So in this example, I’m going to telnet to route-server.ip.att.net 9 00:00:35,000 --> 00:00:39,000 align:middle line:84% I’m told that I can log in with this user name 10 00:00:39,000 --> 00:00:43,000 align:middle line:84% which gives me read only access to the router 11 00:00:43,000 --> 00:00:49,000 align:middle line:84% and I’m going to type show route summary. 12 00:00:49,000 --> 00:00:54,000 align:middle line:84% As you can see here there are 8.5 million odd routes 13 00:00:54,000 --> 00:00:59,000 align:middle line:84% in the routing table with 567,000 destinations 14 00:00:59,000 --> 00:01:06,000 align:middle line:84% show bgp summary will show me the BGP routing table. 15 00:01:06,000 --> 00:01:09,000 align:middle line:84% BGP is the routing protocol used on the Internet. 16 00:01:09,000 --> 00:01:16,000 align:middle line:84% So total path is 8.5M active path is 567,000 17 00:01:16,000 --> 00:01:19,000 align:middle line:84% as you can imagine a small router 18 00:01:19,000 --> 00:01:24,000 align:middle line:84% is not going to be able to handle this number of routes in its routing table. 19 00:01:24,000 --> 00:01:28,000 align:middle line:84% Here you can see examples of routes in the BGP routing table 20 00:01:28,000 --> 00:01:34,000 align:middle line:84% on this router and how long thoses route have been in the routing table. 21 00:01:34,000 --> 00:01:39,000 align:middle line:84% Small routers aren't not going to handle that number of routes 22 00:01:39,000 --> 00:01:45,000 align:middle line:84% so you would typically use a default route pointing your router to a gateway of last resort. 23 00:01:45,000 --> 00:01:50,000 align:middle line:84% So a default route is a special type of static route 24 00:01:50,000 --> 00:01:55,000 align:middle line:84% pointing your device or router to a gateway of last resort. 25 00:01:55,000 --> 00:02:02,000 align:middle line:84% This is similar to the concept of a default gate way on a PC or a device 26 00:02:02,000 --> 00:02:04,000 align:middle line:84% such as an iPhone or iPad 27 00:02:04,000 --> 00:02:07,000 align:middle line:84% when a router doesn’t know where to send the traffic 28 00:02:07,000 --> 00:02:10,000 align:middle line:84% it simply sends it to the gateway of last resort. 29 00:02:10,000 --> 00:02:14,000 align:middle line:84% In other words, it will send it to this IP address 30 00:02:14,000 --> 00:02:18,000 align:middle line:84% as configured with the static default route. 31 00:02:18,000 --> 00:02:24,000 align:middle line:84% Another advantage of static routes is that you as the administrator 32 00:02:24,000 --> 00:02:27,000 align:middle line:84% determine explicitly where traffic flows. 33 00:02:27,000 --> 00:02:31,000 align:middle line:84% So rather than a routing protocol making the decision for you 34 00:02:31,000 --> 00:02:36,000 align:middle line:84% you decide and have control over where traffic goes 35 00:02:36,000 --> 00:02:40,000 align:middle line:84% or where packets are routed but on the flip side 36 00:02:40,000 --> 00:02:46,000 align:middle line:84% the burden of management and keeping things up to date also fall on your shoulders 37 00:02:46,000 --> 00:02:51,000 align:middle line:84% so you have to administer the routing table, keep it up to date 38 00:02:51,000 --> 00:02:55,000 align:middle line:84% make sure that routes are not pointing to non-existing devices 39 00:02:55,000 --> 00:02:59,000 align:middle line:84% where networks go down, you would have to update the routing table 40 00:02:59,000 --> 00:03:03,000 align:middle line:84% and that’s simply not scalable in large topologies 41 00:03:03,000 --> 00:03:06,000 align:middle line:84% so hence dynamic routing protocols 42 00:03:06,000 --> 00:03:14,000 align:middle line:84% such as OSPF or EIGRP are used to dynamically add or remove routes from a routing table. 43 00:03:14,000 --> 00:03:16,000 align:middle line:84% BGP as mentioned is the routing protocol 44 00:03:16,000 --> 00:03:21,000 align:middle line:84% used on the Internet for very large scale implementations. 45 00:03:21,000 --> 00:03:26,000 align:middle line:84% The major advantage of dynamic routing protocols is that 46 00:03:26,000 --> 00:03:31,000 align:middle line:84% there is the dynamic or automatic adjustment of the routing table 47 00:03:31,000 --> 00:03:34,000 align:middle line:84% based on topology changes in your network. 48 00:03:34,000 --> 00:03:39,000 align:middle line:84% So rather than you having to manually adjust to a topology change 49 00:03:39,000 --> 00:03:44,000 align:middle line:84% the routing protocols update, insert or removed routes 50 00:03:44,000 --> 00:03:50,000 align:middle line:84% from the routing table based on changing conditions in the network. 51 00:03:50,000 --> 00:03:52,000 align:middle line:84% As soon as you enable a routing protocol 52 00:03:52,000 --> 00:03:59,000 align:middle line:84% such as OSPF or EIGRP the routers will form a neighbor or peer relationships 53 00:03:59,000 --> 00:04:02,000 align:middle line:84% with each other and exchange routes with one another. 54 00:04:02,000 --> 00:04:07,000 align:middle line:84% The routers will does automatically learn about the networks available in the topology. 6572