Cisco Support Community
cancel
Showing results for 
Search instead for 
Did you mean: 
Community Member

solution for prefix-splitting in eBGP

Dear All,

I am looking forward to split a prefix for downlink traffic. Let me just put my thoughts in more specific case.

1. Running eBGP with 3-ISPs (Multihoming).

2. Advertised 192.168.0.0/22 on three ISPs as per PBR.

Requirement:

1. I want to force the uplink via ISP-1.

2. I want to force the downlink traffic 6 class C networks via ISP2.

3. I want to force the downlink traffic for rest of 2 Class-C network via ISP-3.

please suggest the workaround with e-BGP.

3 REPLIES
Silver

Re: solution for prefix-splitting in eBGP

Hello,

1. It can be achieved by either raise the weight and local preference for the ISP1 neighbor therefore favoring for outbound traffic.

2-3. You have to advertise the longer prefixes separately (C's) and use as prepending (longer the AS path therefore make less favorable) for the particular prefixes. For the rest you can either advertise the /22 block without prepending or the individual C's without prepending.

If your upstream ISP's are using more sophisticated routing policy based on communities you can also use that.

Hope it helps

Krisztian

Re: solution for prefix-splitting in eBGP

Hi,

bellow are the suggestions:

1- setting a highest weight for a specific neighbor under the bgp neibor command would enforce all your upstream traffic.

2- to force the downlink, you either set the AS prpending option or the MED value, u can specify a route-map after the neighbors command & match certain prefixes then use the prepending option or manipulating the MED value.

Regards,

Mohamed Sobair

Silver

Re: solution for prefix-splitting in eBGP

Hi Mohamed,

As long as MED is not advertised after your peer's AS it will not influence the reverse path.

Krisztian

104
Views
0
Helpful
3
Replies
CreatePlease to create content