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EIGRP on Cat3750

chloi
Level 1
Level 1

For EIGRP equal path loadbalancing, when i do a traceroute from one switch to another, there are some kind of loop happen. is this normal when we configure equal path loadbalancing?

This is my setup:

172.16.168.1---------C1---172.16.78.2---------172.16.78.1---C2

C1---172.16.78.6---------172.16.78.5---C2

C2 Config:

router eigrp 7008

passive-interface default

no passive-interface FastEthernet1/0/23

no passive-interface FastEthernet1/0/24

network 172.16.78.0 0.0.0.3

network 172.16.78.4 0.0.0.3

no auto-summary

C1 Config:

router eigrp 7008

passive-interface default

no passive-interface FastEthernet1/0/23

no passive-interface FastEthernet1/0/24

network 172.16.78.0 0.0.0.3

network 172.16.78.4 0.0.0.3

network 172.16.168.0 0.0.0.255

no auto-summary

---------------------------------------------------------------------------------

C2 traceroute to C1:

Type escape sequence to abort.

Tracing the route to 172.16.168.1

1 172.16.78.6 0 msec

172.16.78.2 0 msec

172.16.78.6 0 msec

c2#traceroute 172.16.168.1

Type escape sequence to abort.

Tracing the route to 172.16.168.1

1 172.16.78.2 0 msec

172.16.78.6 0 msec

172.16.78.2 0 msec

2 Replies 2

ruwhite
Level 7
Level 7

This isn't a loop, it's normal traceroute functioning, or it should be. This is the result of trace packets being sent through different available paths. Note that the source is the local router, and, AFAIK, all locally sourced packets are still "process switched," so per packet load sharing would be the norm in this situation, rather than per flow or source/destination pair.

:-)

Russ.W

If you are a router, and you have two route's, for the same exact destination network, and the metrics are the same for both routes, you (as a router) can load balance across either path to the destination network.  This is "equal cost (metric) load balancing".
If you are the same router, and are running EIGRP, and have 2 route's advertised to you, but one has a cost of 222, and the other route (to that same network) has a cost (metric) of 400, your router will only use the best (lowest cost) route.    If you use the variance command set to 2, then both of the routes may be used, but they are not equal paths.   That is why it is called "unequal cost (metric) path load balancing".    EIGRP will send more traffic over the better path, and will send less traffic over the worse path proportionally.

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