Dual WAN with EIGRP to one provider and BGP to another.

Unanswered Question

Hello All !! Hope everyone is doing well !!

I have dual routers and WAN circuits at all locations and I am in the process of migrating one of the WAN circuits to a new WAN provider. Currently I am running EIGRP with a single AS to both existing WAN providers, and I'll be running BGP with the new WAN provider, so when the migration completes I'll be running EIGRP with one provider and BGP with another provider. Has anyone running in this mode before ? Any issues ?

I am thinking on the router that connects to the new WAN provider, I'll have to run both routing processes (EIGRP/BGP) and redistribute EIGRP into BGP and apply distribute-list to help filter routes where needed. Do I need to do two-way redistribution here ?

I am trying to learn BGP as I go, any inputs/suggestions is highly apprecited.

Thank you so much in advance !!!

Danny

I have this problem too.
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Anonymous (not verified) Mon, 04/27/2009 - 16:49

Laurent Aubert Mon, 04/27/2009 - 16:57

Hi Danny,

What is your routing policy ? are you in nominal/backup or load-sharing mode ?

You have two types of BGP updates: eBGP and iBGP. "e" is for external meaning you received an update from a peer which is outside of your BGP AS. "i" is for internal meaning you received an update from an internal peer belonging to your BGP AS.

Administrative distance (AD) of eBGP routes is 20 and 200 for iBGP so if on one site the gateway is your BGP router (primary path), by default it will choose its eBGP routes to reach the other sites (AD of 20 versus 90).

To achieve full redundancy, you need two-way redistribution between BGP and EIGRP so your EIGRP routers will be aware of a backup path via your 2nd WAN provider.

By default external EIGRP routes have an AD of 170 so they will never be chosen if you have an internal route available (AD of 90)

Can you tell us if it will be eBGP or iBGP connection and also if it will be the primary or secondary path ?

Here are some links to learn BGP:

http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a00800c95bb.shtml

http://www.cisco.com/en/US/tech/tk365/tk80/tsd_technology_support_sub-protocol_home.html

HTH

Laurent.

Hello Laurent !!! I appreciate your response !!!

At the moment I am not doing any special routing at all with the existing set up with EIGRP to both providers, I just let EIGRP dynamically figure out its own path but once I am done with the migration I am looking at Performance routing to load-sharing between the two provider and I am also looking into switching my other WAN provider from EIGRP to BGP as well but until then I'll running EIGRP and BGP.

For this migration I'll doing iBGP with the new WAN provider.

Thanks again Lauren !!! I really appreciate your help !!!

Danny.

Laurent Aubert Tue, 04/28/2009 - 05:22

My pleasure ;-)

If you go with iBGP, it means by default your EIGRP link will always be preferred so you will be in a nominal/backup mode.

Laurent.

Marwan ALshawi Tue, 04/28/2009 - 05:31

becareful that BGP by default will not redistribute IBGP learned rotue into IGP shuch EIGRP

if u want this function u need to add the follwing command under you bgp

bgp redistribute-internal

for load balanceing it is depend first on ur internal netowrk router

if have all internal network EIGRP and only one link to ISP as BGP you could play with AD as mentioned in other posts

and make sure u take in to consideration defualt facors that effect EIGRP loadbalncing dely and bandwidth of the link

good luck

Marwan ALshawi Tue, 04/28/2009 - 14:31

hi Danny

to be more practical

even thorugh after you configure routing correctly and you will see in your routing table tow entries for specific destinations

but actually this will not load balnce it will be one prefered route and other one willtake over after this used one aged out

you can see it after you get to entries

lets sau u see network 100.1.1.0 from both providers

do show ip route 100.1.1.0

u will this route learned from tow routers but one source has star beside it which means this is the used one

u can do actul load balnceing either by using fastswitching capabilities such as CEF

or u could use a loadbalancer

but use CEF after you get routing loadbalnceing

good luck

Laurent Aubert Wed, 04/29/2009 - 05:12

Hi Danny,

Actually, it makes more sense.

To be able to implement load-sharing, we need more information regarding your site topology: Are your two routers (EIGRP and BGP) the default-gateway of your host or do you have other routers behind ?

If those two are your gateway, the one which is HSRP Master need to add routes learned from its WAN and routes learned from the standby router.

1- HSRP Master is running EIGRP on the WAN

In this case, you need to adjust EIGRP external AD to 90 via the distance eigrp command so redistributed BGP routes will be taken into account. I think you may have to play with variance as well because the metric will be different

http://www.cisco.com/en/US/docs/ios/iproute/command/reference/irp_eig2.html#wp1014686

Your HSRP standby router running both BGP and EIGRP will prefer by default its eBGP routes so nothing to change after the mutual-redistribution is done.

2- HSRP Master is running BGP and EIGRP

Not possible as you can't install two identical routes learned from two different routing protocols even if the AD is the same for both protocols.

Solution is to move to the first case.

If you have another router behind, apply solution 1 to this router.

HTH

Laurent.

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