u Given packet header how to determine forwarding port u Topic for Thursday CSE

U given packet header how to determine forwarding

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u Given packet header, how to determine forwarding port u Topic for Thursday… CSE 222A – Lecture 3: Packet Forwarding 7
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Comparison Source routing Global addresses Virtual circuits Header size worst OK ~ large addrs best Router table size none # of hosts (prefixes) # of circuits Forward overhead best Prefix matching Pretty good Setup overhead none none High Error recovery Tell all hosts Tell all routers Tear down circuit and reroute CSE 222A – Lecture 3: Packet Forwarding 8
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Building a forwarding table u Computing paths between network elements u … and figuring out where the end-hosts are u … to map a destination address to an outgoing link How to find the hosts? u Learning/flooding u Injecting into routing protocol u Dissemination via different protocol u Directory service Finding the Hosts 9 CSE 222A – Lecture 3: Packet Forwarding
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Learning and Flooding When a frame arrives u Inspect the source address u Associate address with the incoming interface When the frame has an unfamiliar destination u Forward out all interfaces u … except for the one where the frame arrived A B C D Switch learns how to reach A. A B C D When in doubt, shout! Used in Ethernet LANs 10 CSE 222A – Lecture 3: Packet Forwarding
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Disseminate w/Other Protocol Distribute using another protocol u One router learns the route u … and shares the information with other routers learn a route to d (e.g., via BGP) disseminate route to other routers Internal BGP (iBGP) used in backbone networks 11 CSE 222A – Lecture 3: Packet Forwarding
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Directory Service Contact a service to learn the location u Lookup the end-host or subnet address u … and learn the label to put on the packet u … to get the traffic to the right egress point s d i e directory ± Host d is at egress e ² Encapsulate packet to send to egress e. Used in some data centers 12 CSE 222A – Lecture 3: Packet Forwarding
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To Each His Own… Ethernet LAN: spanning tree, MAC learning, flooding Enterprise: link-state routing, injecting subnet addresses Backbone: link-state routing inside, path-vector routing with neighboring domains, and iBGP dissemination Data centers: many different solutions, still in flux » E.g., link-state routing or multiple spanning trees » E.g., directory service or injection of subnets into routing protocol 13 CSE 222A – Lecture 3: Packet Forwarding
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  • Fall '08
  • Vahdat,A

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