Global Internet Textbook Ch4.1

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Global InternetTextbook Ch4.1
Instructor Joe McCarthy (based on Prof. Fukudas
slides)
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Routing (section 3.3)
Example rows from (a) routing and (b) forwarding
tables

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

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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?

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Internet Routing
430K ltlt 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_Protoc
ol
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Internet, circa 1990

• Nationwide backbone (NSFNET)
• Regional networks (BARRNET, Westnet, )
• End-user sites (Stanford, Berkeley, )
• Each node is an Autonomous System (AS)

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Internet Routing
Sep 2012 430,000 prefixes
Sep 2012 40,000 ASs
http//en.wikipedia.org/wiki/Border_Gateway_Protoc
ol
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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)

(Autonomous Systems aka Routing Domains)
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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

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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

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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

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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.

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iGP eGP Routing
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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