Eigrp unequal cost per destination load balancing with

[kamlesh.sharma]

Hi All,

N1 and N2 are having 2-2 E1 links and a Fethernet crossconnect connectivity. all lan data should go from N1 (as VRRP primary ) but from N1 100 % of data should be devided like this 50 % data should go to N2 via Fethernet and 50 % should go to 2 E1 links.

Thanks in advance

Kamlesh

[amit-singh]

Hi Kamlesh,

In this case, the unequal cost path load-balancing is possible if all the 3 links satisfy the feasibility condition .i.e AD < RD. Untill and unless your all the links satisy this condition, load-balancing will not occur.

As I think this can be done by setting the metric of the advertised routes as such that it does the automatic traffic sharing on all the links.You can use prefix list at N2 for outgoing routes or at N1 for incoming routes. For example If your Metric is 100, the routes coming from FE to N1 should have metric 20 and all the routes coming from 2 E1's should have metric 100. As per the EIGRP share count goes it will divide Metric of the routes with the best metric, so in this case if you divide 100/20 , it will send 5 packets from FE and then 1 packet eack from the E1's and goes on.

May I am not able to make you understand the funda clearly.If not , pls check the EIGRP traffic share count process in EIGRP guide on Cisco.

May be some other can also give more info on this or any other mehtod to do that.

regards,

-amit singh

[kamlesh.sharma]

hi amit,

Thanks for your prompt help

According to your metric calculation it will be possible by changing delay on N2's E1 links to 1990

one thing where i am not sure is if you apply a prefixlist for incoming or outgoing update than router will do per-packet load balancing which we don't want.

please help

Kamlesh

[amit-singh]

Yes, the delay factor will help us in this case. Set the delay to a value that influence to our need.

regards,

-amit singh

[kamlesh.sharma]

Hi Amit,

Cisco prefer changing delay in place of bandwidth

other thing is related to per-destination load balancing.

VRRP is running in between N1 and N2 where N1 is master and getting all lan data to forward to LA1 and LA2. in case of N1's lan interface goes down than also N2 should load balance between it's E1's and Fastethernet.

thanks in advance.

Kamlesh

[tcordier]

Hi Kamlesh,

for unequal-cost load-balancing in EIGRP you do not necessarily need to manipulate the costs of the EIGRP routes. EIGRP provides a mechanism to automatically load-balance accross unequal-cost paths using the "variance" parameter. If, for instance, you have two routes to 10.0.0.0/8 in your EIGRP topology table, one with cost 4 and one with cost 6, you can add this command under the EIGRP process:

router eigrp xyz

network x.x.x.x

variance 2

The router will now equally load-balance traffic to 10.0.0.0/8 across the two routes. The router in fact multiplies the smallest cost (4) with the variance factor (2), and includes all routes which have a cost smaller than 8 (2*4) in its routing table. See for more details this link:

http://www.cisco.com/en/US/partner/tech/tk365/technologies_tech_note09186a008009437d.shtml

Regarding your question as to what happens when the LAN interface of N1 goes down: since N1 and N2 are EIGRP neighbors, the load-balancing on N2 will occur as desired, provided you have configured it also for unequal-cost load-balancing. This will of course only happen if N2 itself and its serial interfaces remain up.

HTH, Thomas

[kamlesh.sharma]

Hi tcordier,

Thanks for reply.

When i change delay from N2 E1 from 2000 to 1990 then N1 will load balance but for the same load balancing on N2 i can't configure delay on N1 E1 becos it will remove the load balancing from N1. What will be the best option i can't figure out should i play with bandwidth instead of delay.

Please help

Kamlesh

[tcordier]

Hi Kamlesh,

my suggestion was to use the option in EIGRP rather than to manipulate the metrics. I still think this is the better option. When you use a variance of 3 as suggested, each EIGRP router will include routes even when the metric is 3 times greater than the least cost route. Please see this link for more information:

http://www.cisco.com/en/US/partner/tech/tk365/technologies_tech_note09186a008009437d.shtml

Let me know if you need additonal information.

HTH, Thomas