Help needed for configuring BGP Multihoming

[neonjacob1234567890]

Hi,

I need to configure BGP multihoming with two ISP using only one Router(L3 Switch with BGP). We have our own AS Number and a /24 IP Pool. We need to configure it as normal failover, we don't want to load balance between the two ISP links. We need ISP A to be the primary link through which all (IN & OUT) the traffics would pass through normally, and the ISP B  link would be used only if ISP A link fails.

ISP A should start handling the traffic again, as soon as the ISP A link becomes active.

Here is a Diagram of the Scenario :

Please help

[paul driver]

Hello

Humm - I dont know at this present why peer-groups wont allow that, But peer-policys do!

Below are two other examples:

Without peer-groups
router bgp 123456
 bgp router-id 192.168.3.1
 no bgp fast-external-fallover
 bgp log-neighbor-changes
 neighbor 192.168.1.1 remote-as 111111
 neighbor 192.168.1.1 description "ISP1 Peering"
 neighbor 192.168.2.1 remote-as 222222
 neighbor 192.168.1.1 description "ISP2 Peering"

 address-family ipv4
 neighbor 192.168.1.1 activate
 neighbor 192.168.1.1 weight 40000
 neighbor 192.168.1.1 soft-reconfiguration inbound  <-------Why do you wish for this to be enabled
 neighbor 192.168.1.1 route-map ISP-IN in
 neighbor 192.168.1.1 filter-list 10 out

 neighbor 192.168.2.1 activate
 neighbor 192.168.2.1 weight 30000
 neighbor 192.168.2.1 soft-reconfiguration inbound<--------Why do you wish for this to be enabled
 neighbor 192.168.2.1 route-map ISP-IN in
 neighbor 192.168.2.1 route-map AS-Prpend out
 neighbor 192.168.2.1 filter-list 10 out
 maximum-paths 2


With peer-policys 
router bgp 123456
 template peer-policy generic
  route-map ISP1-IN in
  filter-list 10 out
  soft-reconfiguration inbound
 exit-peer-policy

 bgp log-neighbor-changes
 neighbor 192.168.1.1 remote-as 111111
 neighbor 192.168.1.1 description "ISP1 Peering
 neighbor 192.168.2.1 remote-as 222222
 neighbor 192.168.2.1 description "ISP2 Peering

 address-family ipv4
  neighbor 192.168.1.1 activate
  neighbor 192.168.1.1 inherit peer-policy generic
  neighbor 192.168.1.1 weight 40000
  neighbor 192.168.2.1 activate
  neighbor 192.168.2.1 inherit peer-policy generic
  neighbor 192.168.2.1 weight 30000
  neighbor 192.168.2.1 route-map AS-Prpend out <------------------ the router seems to take this no problem
  maximum-paths 2

res
Paul

[neonjacob1234567890]

Hello,

Thanks for all the help. Do I need the following lines too along with the above configurations?

=========

ip as-path access-list 10 permit ^$    <----- Advertised ONLY local routes

route-map AS-Prpend  <-- Prepend all local routes with local ASN to least prefferd ISP
set as-path prepend 999 999 999

ip prefix-list ISP1-IN permit 0.0.0.0/0  
route-map ISP-IN permit 10 <-----------Allow only a  received Default from both ISP's
match ip address prefix-list ISP1-IN

=============

Regards

[paul driver]

Hello

Yes you do

[neonjacob1234567890]

Hi,

One last thing, I'm a bit confused about these: 

==============

--------------
neighbor 192.168.1.1 route-map ISP-IN in
neighbor 192.168.2.1 route-map ISP-IN in
----
or
----
route-map ISP1-IN in
--------------

&

----
ip as-path access-list 10 permit ^$
route-map AS-Prpend
set as-path prepend 999 999 999
ip prefix-list ISP1-IN permit 0.0.0.0/0  
route-map ISP-IN permit 10
match ip address prefix-list ISP1-IN

----

==============

While testing Without peer-groups, I found that the path to default route advertised by the INTERNET/CLOUD router (in GNS3 simulation) is actually taken through ISP1 (primary/prefered) router (desired) as you said, but the path taken by CLOUD router to reach network advertised by OUR router is via ISP2 (backup) router (not desired), with the above configuration.

Also, when the link between OUR Router and ISP2 Router goes down, the CLOUD router cannot see network advertised by OUR Router.

:( 

Pls help!!!!

[paul driver]

Hello

Apologies it naming convertion is a bit confusing so just to clarify:

The prefix-list ISP1-IN is part of the route-map ISP-IN

So its this route-map ISP-IN what needs to be applied to the bgp peering

neighbor 192.168.1.1 route-map ISP-IN in
neighbor 192.168.2.1 route-map ISP-IN in

So just leave it as it is and it should be fine

res
Paul