Transcript Global Internet

Global Internet
Textbook Ch4.1
Instructor: Joe McCarthy
(based on Prof. Fukuda’s slides)
CSS 432: Global Internet
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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,
 Network prefix?
or 4,000,000,000 possible hosts)
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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
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Internet, circa 1990

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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_Protocol
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Hierarchical Routing

Divide the routing
problem in two parts:
 Routing

Intra-domain routing
protocol
(each AS selects its own)
 Routing

within a single AS
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)

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Internet is an arbitrarily interconnected set of ASs
Each AS has a Speaker (advertiser)
Goal: Reachability than optimality
Large corporation
“Consumer ” ISP

Peering
point
Backbone service provider
“ Consumer” ISP
Large corporation
Peering
point

“Consumer”ISP
Stub AS:


Multihomed AS:


Small
corporation

Connections to multiple ASs
Refuses to carry transit traffic
Transit AS:


CSS 432: Global Internet
A single connection to another AS
Only carries local traffic
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 & 192.4.3
can be reached directly from AS2
Customer P
(AS 4)
128.96
192.4.153
Customer Q
(AS 5)
192.4.32
192.4.3
Customer R
(AS 6)
192.12.69
Regional provider A
(AS 2)
Backbone network
(AS 1)
Regional provider B
(AS 3)


Customer S
Speaker for AS1 (backbone) advertises
(AS 7)
 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
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192.4.54
192.4.23
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Routing Areas
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AS divided into areas
Area 0
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Known as the backbone area (connected to the backbone)
Area Border Routers (ABRs): R1, R2, R3
OSPF link state packets
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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
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