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Global Internet Textbook Ch4.1. Instructor: Joe McCarthy (based on Prof. Fukuda’s slides). Routing (section 3.3). Example rows from (a) routing and (b) forwarding tables. What if every router needed an entry for every IP address?. Routing (section 3.3).

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global internet textbook ch4 1
Global InternetTextbook Ch4.1

Instructor: Joe McCarthy

(based on Prof. Fukuda’s slides)

CSS 432: Global Internet

routing section 3 3
Routing (section 3.3)

Example rows from (a) routing and (b) forwarding tables

  • What if every router needed an entry for every
    • IP address?

CSS 432: Global Internet

routing section 3 31
Routing (section 3.3)

Example rows from (a) routing and (b) forwarding tables

  • What if every router needed an entry for every
    • IP address? (232, or 4,000,000,000 possible hosts)
    • Network prefix?

CSS 432: Global Internet

internet routing
Internet Routing

430K << 4B

But do we want

430K entries in every router table?

Traffic just for update messages?

Sep 2012: 430,000+ prefixes

http://en.wikipedia.org/wiki/Border_Gateway_Protocol

CSS 432: Global Internet

internet circa 1990
Internet, circa 1990

Nationwide backbone (NSFNET)

Regional networks (BARRNET, Westnet, …)

End-user sites (Stanford, Berkeley, …)

Each node is an Autonomous System (AS)

CSS 432: Global Internet

internet routing1
Internet Routing

Sep 2012: 40,000+ ASs

Sep 2012: 430,000+ prefixes

http://en.wikipedia.org/wiki/Border_Gateway_Protocol

CSS 432: Global Internet

hierarchical routing
Hierarchical Routing

(Autonomous Systems aka Routing Domains)

  • Divide the routing problem in two parts:
    • Routing within a single AS
      • Intra-domain routing protocol (each AS selects its own)
    • Routing between ASs
      • Inter-domain routing protocol(Internet-wide standard)

CSS 432: Global Internet

intra domain protocols
Intra-domain Protocols
  • RIP: Route Information Protocol
    • Distributed with BSD Unix
    • Distance-vector algorithm
    • Based on hop-count
  • OSPF: Open Shortest Path First
    • More recent Internet standard
    • Uses link-state algorithm
    • Supports authentication

CSS 432: Global Internet

inter domain protocol

Large corporation

Consumer

ISP

Peering

point

Backbone service provider

Peering

point

Consumer

ISP

Consumer

ISP

Large corporation

Small

corporation

Inter-domain Protocol
  • Border Gateway Protocol, version 4 (BGP-4)
    • Internet is an arbitrarily interconnected set of ASs
    • Each AS has a Speaker (advertiser)
    • Goal: Reachability than optimality
  • Stub AS:
    • A single connection to another AS
    • Only carries local traffic
  • Multihomed AS:
    • Connections to multiple ASs
    • Refuses to carry transit traffic
  • Transit AS:
    • Connections to multiple ASs
    • Carries both transit & local traffic

CSS 432: Global Internet

bgp example

128.96

Customer P

192.4.153

(AS 4)

Regional provider A

(AS 2)

Customer Q

192.4.32

(AS 5)

192.4.3

Backbone network

(AS 1)

Customer R

192.12.69

(AS 6)

Regional provider B

(AS 3)

Customer S

192.4.54

(AS 7)

192.4.23

BGP Example
  • Speaker for AS2 advertises reachability to P and Q
    • Network 128.96, 192.4.153, 192.4.32 & 192.4.3can be reached directly from AS2
  • Speaker for AS1 (backbone) advertises
    • Networks 128.96, 192.4.153, 192.4.32, and 192.4.3 can be reached along the path (AS1, AS2)
    • Networks 192.12.69, 192.4.54, 192.4.23can be reached along the path (AS1, AS3)
  • Speaker can cancel previously advertised paths

CSS 432: Global Internet

routing areas
Routing Areas
  • AS divided into areas
  • Area 0
    • Known as the backbone area (connected to the backbone)
    • Area Border Routers (ABRs): R1, R2, R3
  • OSPF link state packets
    • Do not leave the area in which they originated (if they are not ABRs)
    • ABRs summarize routing information that they have learned from one area and make it available in their advertisements to other areas.

CSS 432: Global Internet

igp egp routing
iGP + eGP Routing

CSS 432: Global Internet

ip version 6
IP Version 6
  • Features
    • 128-bit addresses (classless)
    • multicast
    • real-time service
    • authentication and security
    • autoconfiguration
    • end-to-end fragmentation
    • protocol extensions
  • Header
    • 40-byte “base” header
    • extension headers (fixed order, mostly fixed length)
      • fragmentation
      • source routing
      • authentication and security
      • other options

CSS 432: Global Internet