eigrp routing protocol

EIGRP routing protocol

Omer ben-shalom024200164

Omer Ben-Shalom:

Must show how EIGRP is dealing with count to infinity problem

Omer Ben-Shalom:

Must show how EIGRP is dealing with count to infinity problem

Distance vector VS link state

Distance - shares all routes with neighbor routers and advertises many routes on one link change

Link state - shares only their own links but with all the routers in the AS/Area

Link state need not calculate before update so convergence is faster

Distance vector problems Uses periodic full route update

Routing loops Accept any neighbor with lower metric Could have learned this from you or

someone you announced to Could fool each other endlessly (Count to

infinity), therefore network diameter is limited

Some are classfull

Attempted solutions Split Horizon / Poison reverse

Do not advertise routes the way received (or) Set distance to on update Problematic in Non broadcast media

Hold down timers Hold update to routes with enlarged matrixes

Both cause large delay in convergence

Link state protocols problems

Each node must know topology of the whole net, on LSA loses can become a problem

Complex to calculate: High memory requirements High CPU use if frequent changes

Harder to configure and troubleshoot

The EIGRP Challenge Simple to implement like distance vector

Quick to converge like link state (By doing distributed calculations)

Use low bandwidth and low memory/CPU

Loop free

Classless

Main features (1) Reliable transport

Reliable multicast (proprietary), if no response go to unicast (up to 16)

Use Sequence numbers (send/receive)

Link discovery - Hello protocol with hold time 3 X hello time (5/60 sec)

Main features (2) Diffusing distributed algorithm (DUAL)

Modules to integrate with network layer protocols (IP, AppleTalk, IPX)

All updates are non-periodic, partial and bounded

‘DUAL’ - diffusing algorithm.

Mark your cost to a route ,the next hop (successor) and the lowest cost (Feasible Distance)

Keep any neighbor with lower distance as possible replacement (Feasible Successor)

Reassess successors on any update or change

‘DUAL’ (2) If successor still best - do nothing

(update neighbors)

If replacement exist in table the can be no loop so switch to it immediately and update

If no replacement change state to active and query all neighbors

‘Dual’ (3) Every neighbor will start own

calculation based on data in query

Any neighbor not answering in timeout makes route ‘stuck in active mode’, neighbor removed from table and response assumed INF

After all ‘reply’ recalculate

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Example 1 - Feasible successor

(All metrics are 1 hop)

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Example 2 - No feasible successor

(Not all metrics are 1 hop)

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Main advantages to DUAL Simple

Converges as fast as link state

Recovery from loss involves no traffic if viable successor

No routing loops are possible Prevents problems Does not restrict network diameter

Other interesting EIGRP points

Uses a sophisticated matrix of bandwidth, delay, load and reliability

Classless routing - carries the subnet mask

Allows CIDR (VLSM and route aggregation)

Can be authenticated by MD5

Some last notes on EIGRP Proprietary to Cisco

On new neighbor discovery - form initial adjacency and pass whole route table

Questions ?

Extra data for questions EIGRP data structures:

link state table of neighbors list of neighbor route costs for all

neighbors EIGRP sequencing Active (waiting for reply) and passive

states explained Init with passive / 0 to self INF to all Drop passive neig with INF cost

More data Router in active does not issue

updates or update structures until passive for that route

Answer either ‘no path’ or feasible successor for neighbor, only when all arrive change

The 4 active states ???

Link state advantages Send only link changes not the resulting

route changes (smaller updates)

Propagates update before recalculation - faster convergence times.

Not prone to routing loops under normal circumstances

Routing loops in distance vec.

An error or fail increases matrix for router

Paths to routers who are in loop (learned from himself for example) look better then ‘real’ paths

Stabilizes when all network learns of failure (potentially very lengthy)

EIGRP packet types All under protocol number 88 Hello (5 sec multicast / 60 sec

unicast) ACK Update Query / Reply Request - not implemented

EIGRP HEADER

Version Opcode Checksum

Flags

Sequence

Ack

AS number

TLVs

IP Internal TLV

Type = 0x0102 Length

Next Hop

Bandwidth

MTU Hop CountReliability Load Reserved

DestinationPrefix len

Delay

Reserved External ID Flags

IP External TLV

Type LengthNext Hop

Bandwidth

MTU Hop CountReliability Load Reserved

DestinationPrefix len

Originating router

Originating AS

Arbitrary tag

Delay

External protocol metric

Reserved External ID Flags