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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

slide15
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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