How to configure Link failover between Eigrp and BGP protocol

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May 27th, 2009
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Hello GS,


I am facing difficulty in configuring auto-failover between eigrp and bgp protocols.


Please see my config and scenario below-

LocationA --Leased line2MB --> Location B

|

|

|

secondary link 1MB

| BGP configured

ISP Cloud

| BGP configured|

Location B


Primary link is configured with Eigrp Protocol and secondary link is configured with BGP protocol.


when one of the link fails, i need the secondary link to take the all subnets and reach the destination Location B.


Also can anyone give a direct where Eigrp is configured with a BGP for link redundancy.


here at both location A & location B i am using single router to connect both the links.


I need to implement this in my current organization by soon, appreciate your prompt response with high regards.


~Mirza.








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Giuseppe Larosa Wed, 05/27/2009 - 22:32
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Hello Mirza,

in BGP address-family ipv4 you have just setup the BGP connection.

You need network commands to specify what routes you want to advertise to the neighobor or all you get is just an established BGP session


use

network 10.121.0.0 mask 255.255.0.0

network 10.1.0.0 mask 255.255.0.0


be also aware that being this an eBGP session (the neighbor is in a different BGP AS number) by default eBGP is preferred over EIGRP.


if you want to have BGP as backup path you need under router bgp to use

distance bgp command


see


http://www.cisco.com/en/US/docs/ios/iproute/command/reference/irp_bgp2.html#wp1014500


distance bgp 110 200 200


in this way EIGRP routes are preferred over eBGP


you need to do this on both sides


Hope to help

Giuseppe


mirzaakberali Thu, 05/28/2009 - 02:31
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hello Giuseppe,


Can you tell me how to make BGP as priamry link ( active link) and Eigrp as backup link so eigrp should come up automatically with out manual changes.


appreciate your response.

Giuseppe Larosa Thu, 05/28/2009 - 02:41
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Hello Miza,


if you want eBGP as primary simply don't insert the distance bgp command.


Be aware that routing protocols are always running so EIGRP is running on secondary link also when BGP primary link is active.

Simply the router doesn't use the secondary link for traffic for the better Administrative distance of eBGP (20) in comparison to EIGRP (90)


Note:

if you want to build a solution with a backup link with DDR (I'm not sure) you can have a look in dialer watch.


Dialer watch triggers a call when monitored routes disappear from routing table.


see


http://www.cisco.com/en/US/docs/ios/dial/configuration/guide/dia_backup_dia_watch_ps6350_TSD_Products_Configuration_Guide_Chapter.html




Hope to help

Giuseppe


mirzaakberali Thu, 05/28/2009 - 05:33
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Hello Giuseppe,


Please help me to understand your above post!


1) For BGP link i am using 10.141.121.0/24 ip subnet.

2) For eigrp link i am using 10.14o.121.1/24 ip subnet.


3) now i have my internal network as 10.150.0.0/16 and 172.168.0.0/16 are my internal network ips.


how would i need to publish my internal LAN in BGP so all the traffic will go from BGP only and how wud traffic would start going from Eigrp when BGP link goes down.


You mean to say as E-bgp-20 is having lower AD it will be prefered and next will be eigrp -90.


can u plz suggest me with configuration for the above scenario.


scenario2 - incase if i want to send traffic from both the links for the above two /16 subnets at a time ..as a load balancing , will i be able to achive it?


scenario 3-


If i have to send some of the 10.150.0.0/16 traffic as example


10.150.1.0/23 via bgp link and 10.150.4.0/24 via e-igrp can i achive this.


Please give me full configuration of all the above scenarios ..if possible.


Thank you all your explanation.


Giuseppe Larosa Thu, 05/28/2009 - 06:38
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Hello Mirza,


to advertise internal networks in BGP you need to use the network command

be aware that BGP will look for an exact match in the routing table

if you insert

router bgp xx

network 10.150.0.0 mask 255.255.0.0


a 10.150.0.0/16 has to be present in the routing by any mean (EIGRP rather then static routes)


configure accordingly you can use route to null0 to create the aggregate if it is not present


same reasoning for net 172.168.0.0/16


the router will prefer BGP routes to EIGRP routes but it will use most specific route first.


scenario2:

BGP has no concept of metric as something to be recalculated at each hop, while EIGRP uses BW and delay.

In short this is not possible if you want to perform load balancing use EIGRP on both links and use modified distance bgp (other possible solutions exist)


scenario3:

because router uses most specific route first, AD is used when both BGP and EIGRP provide the same prefix/prefix len.


so to have traffic to 10.150.4.0/24 to use the EIGRP path :

10.105.4.0/24 has to be advertised only by EIGRP


BGP can advertise a less specific route like 10.150.0.0/16 or 10.150.4.0/23


Hope to help

Giuseppe


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