Eigrp one way path selection

[feroz syed]

Hi,

I have two router directly connected via two fast-ethernet, R1 have two neighbor with R2 (192.168.100.2, 192.168.200.1) both path metric aslo same doing loadbalance, Now i want to select only one path to reach r2  without breaking the EIGRP neighbor adjacency(not allow to change metric values), waiting for your suggestion.

[Alexandr Alakin · Accepted solution]

Hi,

If you meant not to change the K-values only, then you can change the delay value of one of the interfaces: Setting a Preferred Route by Influencing EIGRP Metrics. Keep in mind that delay command accepts values in tens of microseconds (check it with sh int fa0/0 | i DLY command) and change it on interfaces facing each other (on both routers). In this case neighbourship will be kept, you just will change the metric (they will be different) and if you did not change the default variance, then load-balancing will not be happening.

Or you can disable load-balancing completely (for the whole EIGRP process and without changing any metric arguments) with maximum-paths 1 command at router configuration mode (but I would rather change the delay).

HTH
Alexandr

[feroz syed]

Thanks for your reply, so if i change the dealy in one interface router 1 can reach both 100.0 and 200.0 network using one interface even the second link directly connected to router 2 ?

[Alexandr Alakin]

Sure enough. BTW, I have updated my previous answer: if you want to disable load-balancing in both directions (for traffic going R1–>R2 and for traffic going R1<–R2, forward and backwards), then you will need to change delay on interfaces of each router facing each other (if fa0/0 of R1 is connected to fa0/0 of R2, then change delay on both fa0/0 interfaces).

HTH
Alexandr

[feroz syed]

i changed increase delay on both side but still second path exist on  topology table.

[Alexandr Alakin]

This is what EIGRP is know for – keeping "hot" backup paths (paths, whoose AD is lower then current FD). It means that as soon as current path is lost router will use the backup path immediately (no need to recalculate anything).

To check if load-balancing is actually happening issue sh ip route command. Now it should show only one next-hop address for the networks advertised by neighbouring router. Having multiple next-hop addresses means that load-balancing is happening.

HTH
Alexandr

[feroz syed]

        via 192.168.100.1 (156160/128256), FastEthernet1/0

        via 192.168.100.1 (2713600/128256), FastEthernet1/1

how to increase this 128256 value() so if we increase this will complete remove from topology table.

[Jon Marshall]

As Alexander has said, the topology table is not the routing table. You should only have one route in the routing table and that route will be used for forwarding the traffic.

Why would you want to remove the entry in the topology table ? It is there in case the first route fails ie. the fa1/0 or the other end go down so i would leave it in. Unless the first route fails it will not be used to forward traffic.

Jon

[feroz syed]

Its lab task, they said only one path is used between router 1 and 2 without breaking the eigrp neighbor adjacency aslo  not allowed to change the metrics.

[Jon Marshall · Accepted solution]

You can't make the interface passive because that will break the adjacency. If you can't change the metrics then you can use a distribute-list to filter the route. You can either use a distribute-list out filter on R2 to stop the route being sent or a distibute-liist in filter on R1 to stop the route being accepted. See this link for config details -

http://www.cisco.com/en/US/docs/ios/12_2/iproute/command/reference/1rfeigrp.html#wp1030091

Jon

[Alexandr Alakin]

Do you actually have the same IP on different interfaces of the router (facing fa1/0 and fa1/1 of current router)?

I presume you cannot change those values independently, since this is an advertised distance sent by 192.168.100.1 (how far this network is from the router 192.168.100.1).

Having multiple entries in topology table only means, that there is a loop-free backup path, which will be used in case the primary path fails. If you don't want to use second link for routing at all, then you can make the interface passive (oops, the task was to not break the neighbourship, but passive-interface will ):

How Does the Passive Interface Feature Work in EIGRP?

HTH
Alexandr