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IP Routing: GGP and RIP. Network Protocols and Standards Autumn 2004-2005. IP Routing Protocols. Autonomous System Interior Gateway Protocols GGP RIP OSPF Exterior Gateway Protocols BGP EGP IP Multicast Routing MPLS. IP Routing Protocols. Autonomous Systems. Routing in the Internet.

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Ip routing ggp and rip

IP Routing: GGP and RIP

Network Protocols and Standards

Autumn 2004-2005

CS573: Network Protocols and Standards


Ip routing protocols
IP Routing Protocols

  • Autonomous System

  • Interior Gateway Protocols

    • GGP

    • RIP

    • OSPF

  • Exterior Gateway Protocols

    • BGP

    • EGP

  • IP Multicast Routing

  • MPLS

CS573: Network Protocols and Standards


Ip routing protocols1

IP Routing Protocols

Autonomous Systems

CS573: Network Protocols and Standards


Routing in the internet
Routing in the Internet

  • Routing Algorithms

    • Bellman-Ford

    • Dijkstra

  • Routing Protocols

    • Distance Vector

    • Link State

  • Routing Hierarchy

    • Interior Gateway Protocols (RIP, OSPF, IGRP)

    • Exterior Gateway Protocols (EGP, BGP, CIDR, Policy Routing)

    • Multicasting (IGMP)

CS573: Network Protocols and Standards


Internet from the start
Internet from the start

  • First, there was ARPANET

    • Routers had complete information about all the possible destinations – core routers

    • GGP (gateway-to-gateway) protocol was used for routing – a distance vector protocol

R

R

H

R

H

R

H

CS573: Network Protocols and Standards


Internet from the start1

ARPANET

R

R

Core Routers

R

LAN

LAN

LAN

Internet from the start

  • Then, LANs were connected to ARPANET

CS573: Network Protocols and Standards


Internet from the start2
Internet from the start

  • Problems with above configuration:

    • Routing overhead increased with the number of connected routers

      • Number of routes increased with the number of connected segments

      • Frequency of routing exchanges increased

      • Higher likelihood that something went wrong somewhere requiring updates

    • Number of different types of routers increased

    • Slow deployment of new versions of routing algorithms

CS573: Network Protocols and Standards


Internet from the start3
Internet from the start

Backbone Network

R1

Core Router

Local Network

R2

R3

R4

Local Network

Local Network

Local Network

CS573: Network Protocols and Standards


Autonomous system
Autonomous System

Backbone Network

R

R

Core Routers

R

AS

AS

AS

AS: Autonomous System

CS573: Network Protocols and Standards


Autonomous system1
Autonomous System

  • What is an autonomous system?

    • A set of routers and networks under the same administration. Examples:

      • A single router directly connecting one local network to the Internet

      • A corporate network linking several local networks through a corporate backbone

      • A set of client networks served by a single ISP

    • NOTE: From a routing point of view, all parts of an AS must remain connected

CS573: Network Protocols and Standards


Autonomous system2
Autonomous System

  • Internal connectivity within the AS means:

    • All routers must be connected

    • Parts of network connected through core AS (yes, core is an AS!) cannot form an AS

    • All routers must exchange routing information in order to maintain the connectivity (normally achieved by using a single routing protocol)

  • Routers inside an AS are called “interior gateway” and the protocol they use is called Interior Gateway Protocol (IGP)

CS573: Network Protocols and Standards


Autonomous system3
Autonomous System

  • In 1982, the IGP of choice was GGP

  • IGPs in use today are:

    • RIP

    • OSPF

    • IGRP

  • Each AS is identified by a 16-bit number

  • Number is assigned by the numbering authorities

CS573: Network Protocols and Standards


Autonomous system benefits
Autonomous System: Benefits

  • Routing overhead is lower

  • Network management becomes easy

  • Easier computation of new routes

  • Distribution of new software versions is easier

  • Failing elements can be isolated easily

  • AS use an Exterior Gateway Protocol to exchange information about reachability

CS573: Network Protocols and Standards


Ip routing protocols2

IP Routing Protocols

Gateway-to-Gateway Protocol

GGP

CS573: Network Protocols and Standards


GGP

  • The “old” ARPANET routing protocol

  • Defined in RFC 823

  • A distance-vector routing protocol

    • Only core routers participate in GGP

  • GGP messages travel in IP datagrams with protocol type = 3

  • GGP measures distance in router hops. i.e., the number of hops along a path refers to the number of routers

CS573: Network Protocols and Standards


Ggp message types
GGP Message Types

  • 4 types of GGP messages

    • GGP Routing Update message (type 12)

    • GGP Acknowledgment message (type 2/10)

    • GGP Echo Request or Reply (type 0 or 8)

CS573: Network Protocols and Standards


Ggp routing update
GGP Routing Update

  • A router sends this message to advertise the destination networks it knows how to reach

  • To keep the size of message small, networks are grouped by distance

    • In the message “Distance” is followed by a list of “Net” addresses that are at this distance

    • Contains a field that tells how many distance groups are being reported (3 in case below)

      • D1 – Net1, Net5, Net11

      • D2 – Net4, Net2, Net7, Net16

      • D3 – Net6, Net9

CS573: Network Protocols and Standards


Ip routing protocols3

IP Routing Protocols

Routing Information Protocol

RIP

CS573: Network Protocols and Standards


Routing information protocol
Routing Information Protocol

  • A distance vector based IGP

  • Similar to GGP

  • Designed at UC Berkeley

  • Based on Xerox XNS

  • Distributed with 4BSD UNIX (routed)

  • First RFC was 1058, current RFC is 2453

  • Started off in small networks and then extended to larger networks

  • See Huitema, Chapter 5

CS573: Network Protocols and Standards


Rip details
RIP Details

  • Routers are active machines

    • Advertise their routes (IP NET, distance) to others

  • Hosts are passive machines

    • They listen and update their routes but do not advertise

  • RIP uses hop count metric

  • RIP messages are transmitted using UDP at port 520

CS573: Network Protocols and Standards


Rip route computation
RIP Route Computation

  • There is a cost associated with each link

    • Typically cost =1 i.e., number of hops

  • Each router receives route advertisements from its neighbors

    • Advertisements show distances to all destinations in the network

  • For each destination in the network:

    • The router takes each received advertisement and adds to it the cost to reach that neighbor who sent this advertisement; this gives the distance to the destination

    • The router selects lowest of these as path/cost to that destination

CS573: Network Protocols and Standards


Algorithm properties
Algorithm Properties

  • Convergence is guaranteed in a finite time given that topology remains static

  • Starting value of distance estimates to each destination can be any non-negative number

  • No assumption is made as to when the updates are sent or when the distances are computed

    • Each router can work based on its own clock and send its updates asynchronously

  • If the network changes, routes converge to a new equilibrium point

CS573: Network Protocols and Standards


Example
Example

Advertisement:

Distance to A is 2

Distance to B is 3

Distance to C is 5

Router

Advertisement:

Distance to A is 1

Distance to B is 4

Distance to C is 1

Cost = 1

Cost = 3

P1

P3

P2

Cost = 2

Advertisement:

Distance to A is 2

Distance to B is 1

Distance to C is 3

CS573: Network Protocols and Standards


Counting to infinity

1

A

C

1

1

10

Target

B

D

1

1

From

Via

Dist

Via

Dist

Via

Dist

Via

Dist

Via

Dist

Via

Dist

A

B

3

C

4

C

5

C

6

C

11

C

12

B

x

-

C

4

C

5

C

6

C

11

C

12

C

B

3

A

4

A

5

A

6

A

11

D

11

D

di

1

di

1

di

1

di

1

di

1

di

1

Counting to Infinity

Routes to Target:

A: route via B, distance 3

B: route via D, distance 2

C: route via B, distance 3

D: direct, distance 1

Assume that B to D link goes down, and B notices.

To reach target …

x = destination unreachable; di = directly connected

What if the link from C to D also goes down? Counting to Infinity!!!

CS573: Network Protocols and Standards


Some solutions
Some Solutions

  • Split Horizon

    • If A reaches a destination through B, it makes no sense for B to reach the same destination through A

    • Instead of broadcasting the same distance vector on all links, send different versions on each outgoing link by removing the entries for the destinations that are reachable through that link

  • Split Horizon with Poisonous Reverse

    • Include all the destinations in advertisements; even those which were missing in split horizon, but…

    • Set those vector distances to infinity that were missing in the simple version of split horizon

CS573: Network Protocols and Standards


Triggered updates
Triggered Updates

  • Split Horizon can work in loops with two gateways, but not with three or more

    • See example in book by Huitema

  • Another solution to deal with “count to Infinity” problem is triggered updates

    • A gateway is required to send an immediate update when any route changes. This reduces the occurrence of loops

    • Flood of triggered updates resolves loops faster when these happen

CS573: Network Protocols and Standards


Ripv2 message format
RIPv2 Message Format

8

16

24

31

COMMAND (1-5)

VERSION (2)

AS NUMBER

FFFF

AUTHENTICATION TYPE

AUTHENTICATION HEADER

FAMILY OF NET 1

MUST BE ZERO

ADDRESS OF NET 1

MASK

NEXT HOP

DISTANCE TO NET 1

… … … …

CS573: Network Protocols and Standards


Message format
Message Format

CS573: Network Protocols and Standards


Ripv2 message format1
RIPv2 Message Format

  • Address format is not limited to TCP/IP

  • RIP can be used with multiple network protocol suites

  • Family of net i:

    • Identifies the protocol family under which the network address should be interpreted

    • IP addresses are assigned value 2

  • Next hop

    • The sending router can specify another router’s IP address as next hop for the network

      • Set to 0.0.0.0 for sender itself

      • Solves similar problem (extra hop) as ICMP redirect

CS573: Network Protocols and Standards


Rip metrics and updates
RIP Metrics and Updates

  • By default, RIP uses hop count as the distance metric

    • Integers 1 through 15

    • 16 denotes infinity

  • Packets are normally sent every 30sec

  • If a route is not refreshed within 180 seconds, distance is set to infinity and later entry is removed

CS573: Network Protocols and Standards


Input processing
Input Processing

  • How to process incoming RIP packets?

    • Examine entries one by one

    • Validation check

      • Address is valid class A, B, or C

      • Network number is not 127

      • Host port is not a “broadcast” address

      • Metric is not larger than infinity (16)

    • Incorrect entries are ignored

      • And should be reported as errors

CS573: Network Protocols and Standards


Input processing1
Input Processing

  • Metric for entry is increased by link cost

  • Routing table is searched for an entry corresponding to the destination

    • If the entry is not present, it is added

    • If the entry is present but with a larger metric

      • Entry is updated and timer restarted

    • Entry is present and next hop router is sender of response message

      • Metric is updated and timer restarted

    • For all other cases, entry is ignored

CS573: Network Protocols and Standards


Rip responses
RIP Responses

  • A separate response is prepared for all connected interfaces/ports

    • Information sent on different ports may vary due to

      • Split Horizon processing

      • Subnet summarization

    • For triggered updates: may include only those entries that have been updated since last transmission

  • Maximum message size: 512 bytes (up to 25 entries)

    • Multiple messages have to be sent if more than 512 bytes

    • Source IP address is that of the interface on which the message is sent

    • Destination IP address is the broadcast address

CS573: Network Protocols and Standards


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