BGP configuration

Unanswered Question
Apr 20th, 2007
User Badges:

Here is one for you BGP experts...

We are designing a multihomed network that connects two routers to two different ISP?s. My two routes will be running HSRP for redundancy between them. I would like to implement BGP for my WAN routing protocol. We have our own private class C address space and will be advertising three supernets out of that space, 206.224.196.0/22, 206.224.200.0/21 and 206.224.208.0/20 to ISPA and ISPB.


We are currently using four on those networks 206.224.223.0/24, 206.224.222.0/24, 206.224.221.0/24 and 206.224.196.0/24. The problem we are having is that we would like to send everything coming from 206.224.222.0/24 out to ISPA and only use ISPB for that network when ISPA goes down. The other two networks will be handled dynamically by BGP.


  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 0 (0 ratings)
Loading.
mohammedrafiq Fri, 04/20/2007 - 06:45
User Badges:

Hi,

1-can u explain, if 206.224.222.0/24 go through ISPA, what of remaining subnets, R they will go to both ISP's and perform any load balancing ?

2-Which router will have higher priorty in HSRP,is higer priorty router in HSRP ,connected to ISPA or ISPB?


Regards,


wmurphyccla Fri, 04/20/2007 - 07:57
User Badges:

The remaining subnets will be controlled dynamically by BGP best route to ISPA or ISPB. RouterA is connected to both ISP?s. RouterB is only connected to ISPB. RouterA is the

walleyewiz Fri, 04/20/2007 - 10:00
User Badges:

If I understand what you are trying to accomplish correctly, you could to the following:


Setup HSRP for the subnet you want to send to ISPA to use priority on that router with interface tracking on the ISP connection.


For outbound advertisement to the ISP, you could do a conditional advertisement in BGP for the subnet. You would only advertise that subnet to ISP A--if ISP A is down you would then advertise to ISP B.


HTH.

royalblues Sat, 04/21/2007 - 10:45
User Badges:
  • Green, 3000 points or more

Friend,


You can use AS-path prepending to make sure the network has a better reachability via ISPA. To force your traffic via ISPA use PBR


A sample config


router bgp

network 206.242.196.0

network 206.224.223.0

network 206.224.222.0

neighbor remote-as

neighbor remove-private-AS

neighbor route-map ISPA-local-routes out


neighbor remote-as

neighbor remove-private-AS

neighbor route-map ISPB-local-routes out


route-map ISPA-local-routes permit 10

match ip address 1

set as-path prepend


route-map ISPA-local-routes permit 20

match ip address 2


route-map ISPB-local-routes permit 10

match ip address 2

set as-path prepend

!

route-map ISPB-local-routes permit 20

match ip address 1

!

access-list 1 permit 206.224.221.0 0.0.0.255

access-list 1 permit 206.224.223.0 0.0.0.255

access-list 1 permit 206.224.196.0 0.0.0.255

access-list 2 permit 206.224.222.0 0.0.0.255


int fa 0/0

Description " inside interface"

ip policy route-map ISP-Pref


route-map ISP-Pref permit 10

match ip address 2

set ip next-hop


HTH, rate if it does

Narayan

wmurphyccla Mon, 04/23/2007 - 05:32
User Badges:

Thanks...

Also, is there anyway to control source address routing in BGP coming from my inside network?? I only want packets coming from my 206.224.222.0/24 to be routed out ISPA unless the link goes down. I understand I can use a prefix-list and deny it going out ISPB, but if ISPA goes down I would have to manually remove the deny statement... I was hoping to make it more dynamic.

CSCO10899265 Sun, 04/22/2007 - 17:01
User Badges:

you could achieve this by advertising the ip address of your network with a higher mask. by default if there are 2 equal paths, BGP advertises the prefixes with the higher mask. if needed you may also consider using BGP attributes such as weight or Local preference to achieve this.


Actions

This Discussion