Load Sharing between BGP and IGP

[OMAR CANDARAVE]

Hi experts,

I have a question, how can we perform a load sharing between BGP and IGP?

Lets say that we have a WAN link connected to the MPLS with BGP in siteA, and in the same way we have siteB (we a MPLS link). Apart of that we have a Point2Point link between siteA and siteB with EIGRP for example. What if we want to perform a load sharing between both circuits?

Currently the preferred link is the MPLS since AD of eBGP is 20 vs 90 of EIGRP.

Thanks in advance.

[Joseph W. Doherty]

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Posting

As I suspect you realize, the AD difference between BGP and your IGP is going to keep routing from seeing both as equal.  So, either you need to need to make ADs the same for both routing protocols or run the same routing protocol across both paths.

Another possible (?) solution might be PfR, with PIRO, might be able to dynamically load balance across two different routing protocols.  (I'm not sure whether PIRO would support this.)

[OMAR CANDARAVE]

Hi Joseph,  thanks for respond.

I tried to change the AD on BGP eq to 90 and it changed but no load sharing:

B       3.3.3.3 [90/0] via 172.168.100.2, 00:04:24
     4.0.0.0/32 is subnetted, 1 subnets
B       4.4.4.4 [90/0] via 172.168.100.2, 00:04:24

The routes have 90 as AD but the routing table only shows the BGP routes.

When turned off BGP:

D       3.3.3.3 [90/2297856] via 10.36.0.2, 00:00:02, Serial1/1
     4.0.0.0/32 is subnetted, 1 subnets
D       4.4.4.4 [90/2297856] via 10.36.0.2, 00:00:02, Serial1/1

:(

[Joseph W. Doherty]

Disclaimer

The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.

Liability Disclaimer

In no event shall Author be liable for any damages whatsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.

Posting

That result might be, although ADs were then equal, the metrics were not.

[Jose Jara]

Hello,

I think is not possible to do load sharing through two different routing protocols adjusting the AD and making it the same. IOS will select just one, with different criteria depending on the protocol.

I would go with the solution that Joseph suggested, using the same protocol. I would say that EIGRP over the Top fits perfectly here.

Hope this helps,

Jose.

[OMAR CANDARAVE]

Thanks Jose!

[Mario Grozdanovic]

Hi Omar,

Would you be able to draw a quick topology map for your setup? It sounds like something similar that we have running in our environment. There are a few ways you can accomplish this load balancing and we can explore the options together after we look at the topology map. 

-Mario

[OMAR CANDARAVE]

Hi Mario, thanks for respond.

Please find attached a topology that just did in GNS3,

Site A learns route 3.3.3.3 (for example) from site B via BGP (MPLS link) and also the same via EIGRP (Point2Point link between them).

I hope this can clarify my question. Thanks in advance.

[Mario Grozdanovic]

Thanks Omar,

If you can change the PPP link from EIGRP to BGP, you can use BGP Multipath Load Sharing (see below links) 

Official Cisco Doc: http://www.cisco.com/c/en/us/td/docs/ios/12_2sx/feature/guide/fsxeibmp.html

Supporting 3rd Party Doc: http://routerjockey.com/2010/10/14/bgp-tips-multipath-load-balancing/

If you can not change the PPP link protocol then you will need to consider PfRv2 (v3 runs on the latest, non-main stream IOS releases and is not widely supported) as Joseph W. Doherty suggested. 

Changing the AD of the routing protocols as you may know, is not best practice and you open yourself up for routing loops, especially with your topology. 

Check out this Cisco live PfR presentation to wet your appetite: https://www.ciscolive.com/online/connect/sessionDetail.ww?SESSION_ID=76585&backBtn=true

-Mario

[OMAR CANDARAVE]

Thanks Mario!