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Berkeley ELENG 122 - TOC – Interdomain Routing

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TOC Interdomain Routing Review Why Hierarchical Routing Interconnections Big Picture Peering and Transit Reachability BGP TOC IP Routing Types Interdomain Review 44 B 66 B BGP 5 2 2 7 IntraDomain 4 Intradomain 8 RIP 3 3 6 13 13 11 2 10 OSPF IntraDomain 3 1 Formulate the routing problem as a Shortest Path Problem Link State v s Distance Vector Both work reasonably well in a well engineered network IntraDomain 13 IGRP A TOC IP Routing Types Interdomain Review 12 C Why Hierarchical Routing Is a natural way for routing to scale Size Network Administration Governance Allows multiple metrics at different levels of the hierarchy Exploits address aggregation and allocation 5 44 7 8 RIP 66 22 1 33 Inter Domain Routing IGRP TOC IP Routing Types Interdomain Why Hierarchical 11 10 13 13 OSPF 12 Interconnections The internet is an interconnection of unequal networks Interconnection arrangements drive the competitive landscape the robustness of the network End to end performance Interconnection is central to all large networks Voice Data Wireless Cable TOC IP Routing Types Interdomain Interconnections Interconnections www thelist com How many ISP s in the 415 area code That start with A C about 200 Just DSL that start with A C about 80 In the telephone network How many independent telephone companies in 1894 1902 in the US 3039 commercial companies 979 co operatives By controlling interconnection Bell got rid of them Interconnection is now regulated CLECs TOC IP Routing Types Interdomain Interconnections Big Picture Large ISP Large ISP Stub Small ISP Dial Up ISP Stub Access Network Stub The Internet contains a large number of diverse networks TOC IP Routing Types Interdomain Big Picture Peering Transit Peering The business relationship whereby ISPs reciprocally provide to each other connectivity to each others transit customers Transit The business relationship whereby one ISP provides usually sells access to all destinations in it s routing table William B Norton Internet Service Providers and Peering TOC IP Routing Types Interdomain Peering Transit Peering Transit Peering Figure from William B Norton Internet Service Providers and Peering West and East Peer with USNet but they can t reach each other TOC IP Routing Types Interdomain Peering Transit Peering Transit Transit Figure from William B Norton Internet Service Providers and Peering TOC IP Routing Types Interdomain Peering Transit Peering Transit Benefits of Transit v s Peering William B Norton Internet Service Providers and Peering TOC IP Routing Types Interdomain Peering Transit Peering Transit Moving from Transit to Peering William B Norton Internet Service Providers and Peering TOC IP Routing Types Interdomain Peering Transit Reachability Interdomain routing is about implementing policies of reachabilty Routing efficiency and performance is important but not essential ISPs could be competitors and do not want to share internal network statistics such as load and topology Use Border Gateway Protocol BGP Border routers communicate over TCP port 179 A Path Vector Protocol Communicate entire paths Route Advertisements A Router Can be involved multiple BGP sessions TOC IP Routing Types Interdomain Reachability BGP Border Gateway Protocol Concept I BGP E BGP Border Routers Sharing Routes Message Types Issues BGP Protocol TOC IP Routing Types Interdomain BGP Concept you can reach net A via me AS2 BGP AS1 R3 R2 traffic to A R1 table at R1 dest next hop A R2 A R border router internal router Share connectivity information across ASes TOC IP Routing Types Interdomain BGP Concept I BGP and E BGP IGP Interior Gateway Protocol Example OSPF I BGP R2 R3 IGP A AS1 E BGP announce B AS2 R1 AS3 R5 R4 R border router internal router TOC IP Routing Types Interdomain BGP I E B Border Routers Border Routers from the same AS speak IBGP from different AS s speak EBGP EBGP and IBGP are essentially the same protocol IBGP can only propagate routes it has learned directly from its EBGP neighbors All routers in the same AS form an IBGP mesh Important to keep IBGP and EBGP in sync TOC IP Routing Types Interdomain BGP Border Routers Sharing routes One router can participate in many BGP sessions Initially node advertises ALL routes it wants neighbor to know could be 50K routes Ongoing only inform neighbor of changes AS1 BGP Sessions AS3 AS2 TOC IP Routing Types Interdomain BGP Sharing Routes Message types 4 Open Session establishment id exchange Notification exception driven information Keep Alive soft state Update path vector information TOC IP Routing Types Interdomain BGP Messages Issues Advertising a Route Routing Table Scaling Update Message TOC IP Routing Types Interdomain BGP Issues Advertising a Route One router telling another one The prefix IP address of the next hop Path list of AS s that the announcement has passed through Since announcement propagates from destination this yields the path No refresh messages required The announcing router will follow the path itself TOC IP Routing Types Interdomain BGP Advertising BGP Routing Table Scaling Many small networks Aggregation hides a lot TOC IP Routing Types Interdomain BGP Scaling BGP Update Message Contains information about New Routes Withdrawn Routes No longer valid Path Attributes Path Weights Multple Exit Discriminators Local Preferences Etc Attribute information allows policies to be implemented TOC IP Routing Types Interdomain BGP Update BGP Protocol Path Vector Multi Homing Multi Exit Discriminators Routing Process Overview Attribute Choosing Best Route BGP Policies Transit vs Non Transit AS Customer Transit Problem BGP and Performance Skitter Summary TOC IP Routing Types Interdomain BGP Protocol Path Vector ner routes show ip bgp BGP table version is 6128791 local router ID is 4 2 34 165 Status codes s suppressed d damped h history valid best i internal Origin codes i IGP e EGP incomplete Network Next Hop Metric LocPrf Weight Path i3 0 0 0 4 0 6 142 1000 50 0 701 80 i i4 0 0 0 4 24 1 35 0 100 i12 3 21 0 23 192 205 32 153 0 50 0 7018 4264 6468 e128 32 0 0 16 192 205 32 153 0 50 0 7018 4264 6468 25 e 0 i Every route advertisement contains the entire AS path Generalization of distance vector Can implement policies for choosing best route Can detect loops at an AS level TOC IP Routing Types Interdomain BGP Protocol Path Multihoming B 5 44 IBGP 7 8 RIP 66 22 IBGP a 33 1 IGRP A Two or more interdomain connections between the same AS s Two or more interdomain connections between a customer and


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Berkeley ELENG 122 - TOC – Interdomain Routing

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