Outbound Traffic Manage via eBGP

[dc-csa-blr]

Dear Experts,

Herewith attached diagram(with proposed req)

We are using multihomed eBGP in single Router from multiple ISPs bandwidth for internet.

We have our own IP Address , at present our oubound traffic going throug ISP 1 , when ISP-1 b/w goes down then it will autometic traffic going throug ISP-2 bydefault.

But our required when ISP-1 B/W goes down our all outbound traffic will going throug ISP-3 inplace of ISP-2.

How can i achieve this as per our requirement.

Thanks in ADV.

[mfurnival · Accepted solution]

Just to clarify - do you mean when the link on ISP1 goes down? It is just that you said "when ISP-1 b/w goes down" which could be interpreted differently.

It would be helpful if you could share your existing configs but the solution that springs to mind is to use local preference on the BGP learned routes with ISP1 routes having a higher local preference than ISP3.

[paul driver · Accepted solution]

Hello

Another option is to specify weight - with again giving  the higher vaule to the most preferred path.

Local pref on a single router is a possibility but as I understand it, It would usually be best utilised with ibgp peering-

res

Paul

Please don't forget to rate any posts that have been helpful.

Thanks.

[Akash Agrawal · Accepted solution]

Hi dc-csa-blr,

Outbound traffic can be controlled via Local Pefeence attribute. If you dont want to alter local prefeence, you have single internet gateway and it is egde router you can use weight attribute also.

LP and Weight -- Higher is better.

By default local preference is 100.

You can set

ISP-1 : LP103

ISP-3 : LP102

ISP-2 : LP101

Or

ISP-1 : weight 103

ISP-3 : weight 102

ISP-2 : weight 101

By default if all attributes are same, tie breaker is BGP router-id and router prefesr the route that comes from the BGP router with the lowest router ID. So possibly router-id of ISP-1 is lowest then for ISP-2 and then ISP-3, which is deciding route preference in your case.

Regards,

Akash

[dc-csa-blr]

Dear Experts,

Thank you all.

Just for confirm

like this

router bgp 12345

nei 1.1.1.1 weight 103 (ISP-1)

nei 3.3.3.3 weight 102 (ISP-3)

nei 2.2.2.2 weight 101 (ISP-2)

[mfurnival · Accepted solution]

Yes - that will do it. Ignore my comments about Local Preference - for some reason I thought you had 3 routers on site which is why I recommended LP. Weight is a better option if you have a single router.

You can do the configuration as you have written above or write a route-map statement to apply weight to the routes learned from each peer.

[paul driver]

Hello

I would set the weight higher than 32768 (default weight value) maybe starting at 50000

neighbor (isp1) weight 50000

neighbor (isp3) weight 45000

res

Paul

Please don't forget to rate any posts that have been helpful.

Thanks.

[Akash Agrawal]

Hi Paul,

any specific reason for setting weight higher than 32768 (default weight value) ? Normally you never originate the same prefix on your router that you are receiving from upstream ISP.

Regards,

Akash

[paul driver]

Hello Akash,

This weight value is generated by local routes which have a admin weight of 32768 - the weights I have specified for routes advertised from the ebgp peers are only for clarity.

res

Paul

Please don't forget to rate any posts that have been helpful.

Thanks.

[dc-csa-blr]

Dear Team,

I have configured for outbound traffic manage via eBGP but it is not work when i shut bgp nei of ISP-1 then again outbound traffic going through ISP-2 intead of ISP-3 after change of weight of all eBGP neigh.

router bgp 12345

nei 1.1.1.1 weight 103 (ISP-1)

nei 3.3.3.3 weight 102 (ISP-3)

nei 2.2.2.2 weight 101 (ISP-2)

Edit: I found that when i show ip bgp that indicate weight 0 of ISP-3 not change when i already it change but why it not change and also in ISP-1 and ISP-2 weight it changed and indicate 103 and 101.

Pl hlep to achieve this.

Cheers!!!

Message was edited by: CSA-BLR DC