Link State Protocol

Design byJignesh PatelPalanivel RathinamVishwesh Tendolkar

Overview

Representation of routers and networks Assumptions Routing protocol packets Implementation requirements Protocol data structures Implementation issues Protocol headers

Representation of routers and networks Each router will be a process identified by a

unique id No configuration files - command line arguments Port numbers play the role of interfaces

2000 2001

3000

RA

RB RC

Contd.

The command line arguments for the above network topology is

Router RA 2000 2001 Router RB 2000 3000 Router RC 2001 3000

Constraints: If a new node is to be added or an existing node is to be deleted, should restart the router process

Assumptions

No hierarchical routing All route processes run on the same machine Routing computation is decoupled from the

protocol

Routing protocol packets

There are five types of packets. Each packet is identified by the packet type in common header

Type 1 packet – Hello Type 2 packet – Database Description Type 3 packet – Link state request Type 4 packet – Link state update Type 5 packet – Link state acknowledgment

Implementation requirements Thread Timers

Single-shot Interval – avoid synchronization by adding small

random values LSA type – Router LSA List manipulation primitives

Protocol data structures

Router ID – 32 bit number Routing table Interface list Interface data structure

Type IP interface address IP interface mask Hello interval Router dead interval Delay Hello timer – fires hello packets every hello interval Neighbor router

Contd.

Interface data structure Interface output cost – expressed in link state

metric Retransmit interval – number of seconds between

LSA retransmissions Interface state (DOWN/UP)

Interface state machine DOWN

UP

Interface up

Contd.

Neighbor list Neighbor data structure

State Inactivity timer – single-shot timer whose length is router

dead interval Master/slave Database description sequence number Last DD packet received (DD header) Neighbor ID – router ID of neighboring router – this is

learned after receiving the hello packet Neighbor IP address

Contd.

List of router LSA (this is the link state information/database. This is generated for each router in the network)

Link state retransmission list Link state request list

Contd.

Neighbor state machineDOWN

INIT

EX-START2-WAY

EXCHANGE

LOADING FULL

HELLO RECEIVED

ONE-WAY RECEIVEDTWO -WAY RECEIVED

NEGOTIATION DONE

EXCHANGE DONE

LOADING DONE

Contd.

Routing table structure Destination type Destination ID Address mask Cost Next hop – router ID

Implementation issues

We are not using TCP based connection for information exchange, although some routing protocols use it (BGP)

Raw IP cannot be used to make processes communicate on the same machine. Since Raw IP is void of any transport layer protocol and hence the ports, processes should use the protocol number in IP to identify packets destined to them. This approach is not feasible

UDP although unreliable helps communication between multiple processes through ports. Also UDP has a built in checksum calculation

Contd.

Our link state protocol uses UDP for its communication

Presentation layer is binary Java is used as the programming language

Protocol headers

The link state protocol is layered. It has a common header which is given below

Version # = 1 Type = {1,…5}

Packet length (no. of words including header)

Router ID = R1

Contd.

Packet format for the hello protocol

Hello Interval = 10msec Dead time Interval = 5sec

Neighbor list = {R2,R3,R1}

…

Contd.

All link state messages share a common header which is depicted below

Age = 5 Sequence number = 3

Link state ID = 2000

Advertising Router = R1

Contd.

The link state advertisement includes information about the link and cost metric. We have used the metric from EIGRP to include delay, bandwidth and reliability

# links = 1

Link ID = R1

Link Data = 2000

Metric = w1 * cost + w2* delay + w3* bandwidth

Contd.

Link state updates. When a router receives a link state request packet during database synchronization or a multiple LSAs from neighbors, it sends a LSU. The packet format is shown below

# LSAs = 1

Link state advertisements

…

Contd.

The database description packet is shown below

Interface MTU = 512 MI M/SUNUSED

DD SEQUENCE NUMBER = time of day

LSA HEADER

Questions / Suggestions

?/ !

References

RFC 2328, OSPF v2 Routing in the Internet – by Christin Hieutema CS526 Manuscript – Dr. Deep Medhi &

Karthik Ramaswamy