What are routing protocols? Routers use routing protocols. They exchange routing information with each other. We have two different types of routing protocols namely IGP which is used to refer to the process running on routers inside a network; anEGP which is used to refer to the process running between routers bordering directly connectednetworks. What is an IGP? IGP stands for InteriorGateway Protocol. this is used within an autonomous system and it carries information about internal infrastructure prefixes two widely used IGPs are OSPF which stand for Open choice Path First and IS-IS which stands for Intermediate System to System Why does the internet need an IGP? IGPs are needed for backbone scaling in RENs and ISPs. They provide hierarchy limits to the scope of failure and are only used for boosters infrastructure addresses and not end user addresses or anything else. The design goal of IGPs is to minimize the number of prefixes to aid in scalability and provide rapid convergence. IGPs also provide scalable internal routing for end-user networks. What is an EGP? EGP stands for Exterior Gateway Protocol. EGPs are used to convey routing information between ASes. EGPs are decoupled from IGPs. The only EGP currently in use is the Border Gateway Protocol known as BGP. Why does the internet need an EGP? EGPs are needed for scaling to large networks, they provide hierarchy and also limit the scope of failure. EGPs define administrative boundaries and they also provide policy in terms of controlling reachability of prefixes as well as merging separate organizations together and are also used for connecting multiple IGPs. Typical examples of EGP usage are RENs, ISPs and multi-homed end users What is the difference between interior versus exterior routing protocols? With interior routing protocols automatic neighbor discovery is usually enabled. You generally trust your IGP routers and prefixes go to all IGP routers. With exterior routing protocols you would need to specifically configure your peers you're connecting with outside networks and as such you would also have to set administrative boundaries. Finally the diagram on the screen talks about all the routing protocols we've been discussing in the previous slides. As you can see we have three separate networks. This is at the campus level, the REN level and at the end level or ISP level. At the campus level which is also your local internet you would typically connect with your REN using static or eBGP and within the REN level you would typically use your IGP which is OSPF or IS-IS or iBGP. And when you're connecting from the REN level to the ISP or NREN level you would typically use eBGP. The table on the screen shows you the default administrative distances utilized by the different vendors on their routers. Temember that the lower the value is preferred over the higher value. You can see that for connected interfaces all vendors are using the value of zero, whereas for static routes all the vendors are using one with the exception of Juniper and Huawei who are using 5 and 60 respectively. For external BGP routes you see that Cisco and Brocade and MikroTik are using 20 whereas Juniper and Nokia using 170 and Huawei is using 255. You're seeing similar things happening with OSPF routes whereas you have similar values that you have the same value for Cisco and Brocade and MikroTik, whereas Juniper and Huawei and Nokia have the same values. IS-IS also has the same scenario where Cisco and Brocade are using the same value, whereas Juniper and Nokia using 18 with while we're using 15. For iBGP routes you see that you still have the same thing where Cisco and Brocade and MikroTik are using 200 and you have Juniper using 170 and while we're using 255. Remember that these values are used in determining the best routes utilized in the global routing information base otherwise known as the "routing table".
© Produced by Philip Smith and the Network Startup Resource Center, through the University of Oregon.
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