CSS 432: Global Internet 1

Global InternetTextbook Ch4.1

Instructor: Joe McCarthy

(based on Prof. Fukuda’s slides)

Routing (section 3.3)

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

CSS 432: Global Internet 2

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

Routing (section 3.3)

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 3

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

Internet Routing

CSS 432: Global Internet 4

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

Sep 2012: 430,000+ prefixes

430K << 4B…But do we want 430K entries in every router table?Traffic just for update messages?

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 5

Internet Routing

CSS 432: Global Internet 6

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

Sep 2012: 430,000+ prefixes Sep 2012: 40,000+ ASs

Hierarchical Routing 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 7

(Autonomous Systems aka Routing Domains)

Intra-domain Protocols

RIP: Route Information ProtocolDistributed with BSD UnixDistance-vector algorithmBased on hop-count

OSPF: Open Shortest Path FirstMore recent Internet standardUses link-state algorithmSupports authentication

CSS 432: Global Internet 8

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

CSS 432: Global Internet 9

Backbone service provider

Peeringpoint

Peeringpoint

Large corporation

Large corporation

Smallcorporation

“Consumer ” ISP

“Consumer” ISP

“ Consumer” ISP

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 10

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, 192.4.23

can be reached along the path (AS1, AS3) Speaker can cancel previously advertised paths

Backbone network(AS 1)

Regional provider A(AS 2)

Regional provider B(AS 3)

Customer P(AS 4)

Customer Q(AS 5)

Customer R(AS 6)

Customer S(AS 7)

128.96192.4.153

192.4.32192.4.3

192.12.69

192.4.54192.4.23

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 11

iGP + eGP Routing

CSS 432: Global Internet 12

CSS 432: Global Internet 13

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