Download - 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