EIGRP load balancing when using HSRP on LAN

[kkaczmarski]

Hi 

I have a question about my topology. I have two routers  with EIGRP on both of them connected through 2 ISPs to other site. On those routers i have HSRP runing. Now my question is: HSRP is standby/active protocol so when one router act as active will it send data to other site only through one ISP??? will load balancing work on WAN side? will routers use both ISPs or just one- the one which is active in HSRP when sending data???

[sotiris_pafitis]

Hello, 

It should send from both ISPs if you have default routes one from the Active hsrp pointing to ISP1 and again from the Active hsrp pointing to the standby hsrp which in respect would have a default route to the second ISP. Have you tested and its not working ? 

[kkaczmarski]

i dont get it... two default routes on both routers? 

it looks like this   

 ISP1             ISP2

    |     EIGRP      |

RTR1---------RTR2

10.0.0.10      10.0.0.11

      |             |

         HSRP virtual gateway

          10.0.0.1

                |

              LAN

If let say RTR2 is the active router in hsrp then data will go through ISP2 or it can go through ISP1 too because of the EIGRP process?

Can u please explain a bit more about default routes cause i didnt get that...

[sotiris_pafitis]

Correct. You need though two default routes one from RT2 to ISP2 and one from RT2 to RTR1 you might need to use though the unequal load balancing feature of eigrp to do so using the variance command on the eigrp router configuration but first try without it.  

Hope that helps . 

[e.ciollaro]

Hi sotiris_pafitis, may be I didn't understand what you mean but if the idea is to configure one static on each router  (pointing it's ISP) and redistribute it in EGRIP, I disagree: is useless because the other router will prefer the static route due to its better administrative distance. Using EIGRP unequal load balancing is useless because  it balanced EIGRP path with different metric, not different Administrative distance. Isn't it ?

If you want to use static route simply configure two static route on each router: one though WAN interface and the other through the LAN.

For example:

R1#conf t
ip route 0.0.0.0 0.0.0.0 192.168.13.3
ip route 0.0.0.0 0.0.0.0 192.168.12.2

The result is:

R1#sh ip route 0.0.0.0
Routing entry for 0.0.0.0/0, supernet
  Known via "static", distance 1, metric 0, candidate default path
  Redistributing via eigrp 100
  Advertised by eigrp 100
  Routing Descriptor Blocks:
  * 192.168.13.3
      Route metric is 0, traffic share count is 1
    192.168.12.2
      Route metric is 0, traffic share count is 1

In any case I think static router is not a good choice: in case of a fault on ISP 1, WAN interface can remain up producing a routing blackhole. If possible it's better to have a dynamic routing protocol between router and ISP, receving the default route and changing delay on interf to have the same metric for both  the path 

Bye,

enrico

[sotiris_pafitis]

Dear Ciollaro,

If you check the threat carefully you will see that we are saying the same thing.

Thanks

[kkaczmarski]

ok so lets say i have two default routes on both routers but if one of them is hsrp active router let say RTR1 then data will go through ISP1 because first  default route points to ISP1 so there will be no load balancing... or am i wrong?

[sotiris_pafitis]

You will. hsrp cares only for the internal lan not the wan. WAN site works as no hsrp is running. The only way to do this is by adding to default routes on one the hsrp router 

[Richard Burts]

This discussion has focused on the two routers and default routes. Perhaps we should also consider the possibility that the routers might interact with the ISP in ways that can provide load sharing. Let us assume that RTR1 learns some particular routes from ISP1 and puts those routes into EIGRP so that they are advertised to RTR2. And let us assume that RTR2 learns some different particular routes from ISP2 and puts those routes into EIGRP so that they are advertised to RTR1. Now both routers know that some routes are unique to ISP1 and some routes are unique to ISP2. So it does not matter what HSRP is doing and some traffic will be forwarded to ISP1 and some traffic will be forwarded to ISP2 and you will have load sharing.

HTH

Rick

[e.ciollaro]

Hi Richard,

don't you think that could be hard to choose which routes have to be advertised by each ISP to have a good balancing ?

[Richard Burts]

It might be easy or it might be hard. The question in this thread was about whether there was a way to get load sharing when the routers were running EIGRP and using HSRP. I identified one of the possible ways to achieve this.

I worked with a customer who was connected to two ISPs (as is the scenario suggested in this thread). ISP 1 advertised their local routes and their connected customer routes. ISP 2 advertised their local routes and their connected cumtomer routes. There was very little overlap in these. The process was pretty easy and it did produce load sharing.

If you want to fine tune the sharing to improve the sharing you can always make the process more complex and difficult. But it does have to be either difficult or complex.

HTH

Rick