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

Multiple BGP Sessions


We have our OWN AS numbers published via our ISP and Our comp. is merging with another who has their own AS. How do we get both running on the same Gateway, if not what do we need to accompolish this task.

Thanks in advance,


Re: Multiple BGP Sessions


I'd prefer running the BGP on 2 separate routers each with one of the ASNs, but if you don't have this choice, then please check the below feature:

Configuring the BGP Local-AS Feature


Mohammed Mahmoud.

Hall of Fame Super Gold

Re: Multiple BGP Sessions


If two companies are merging and each has its own AS number, in the long term they should consolidate and use a single AS number. Details of how to do this would depend somewhat on how the companies plan to consolidate their internal networks. Is there a plan for how the internal networks will be integrated with each other? Knowing this might help in giving advice about what to do with BGP and the AS numbers.



Re: Multiple BGP Sessions

HI Subramania, [Pls Rate all Informative POST]

In my prior experience with an other company, i have experienced the same Situation of MERGER.

If the Management Add's more pressure for Offices connectivity means, then establish a Link between the AS - AS and run the E - BGP to access the Application. Like running with an Service Provider for an Internet VPN Link.

Later divide the Offices into regions like, APAC, EMEA, NorthAmerica Country regions. The Major contributor in that regions in-terms of Business Results, Employee Strength, Traffic Load Analysis, Number of Offices, etc., will play a Prime Role and all other offices in that regions (may be already in the same AS or in the new AS of the merged company) will run on an Major Contributor AS. Similarly for Other regions also.

In the above case, make sure the to Study about IGP running within both the Companies Infra... If its OSPF means the Area / Route Consolidation & new IP Segment Allocation (for new Offices coming from other AS's) are to be done as Initial part of Migration and as well as routing to reach their own Former Application / Servers. This involves more study on the new office Network.

As told by RICK, the two companies has to come for an understanding to consolidate the IT INFRA.... by the way the SINGLE AS POLICY can be accompalished.

Hope I am Informative.

Pls Rate all Informative POST

Best Regards,

Guru Prasad R

New Member

Re: Multiple BGP Sessions

Hi All,

Thanks for your Inputs.

Post Merger, they still want to continue with their own AS and use as more like a Transit. In that case

1. can we just do a ebgp peering with them

2. ask our ISP to allow them through us.

Thanks in advance


Re: Multiple BGP Sessions

HI Sundar, [Pls Rate if HELPS]

Once Option is to, go with the same ISP's for both the AS's Connectivity for the better results in-terms of Latency and Others (easy Routing Changes, etc.,)

Ask the ISP to advertise the both AS's IP Prefixes on Local Gateway's of them. The ISP can share the Prefix's to each Other AS's using the Community Attribute & Prefix List.

Before all, create the E-BGP Connectivity betweeen the both Offices.

Talk to your ISP & provide your requirement, it should work.

Hope I am Informative.

Pls Rate if HELPS

Best Regards,

Guru Prasad R

CreatePlease to create content