Re:[isp-bgp] BGP AS path

[vdadlaney@...]

Hi,

I believe this is a feature in MPLS based VPN's MBGP where the customer is connected to the Service Provider Router and requires using the same AS at each site.  I don't think this feature is available in normal BGP v4. Please correct me if I am wrong. Thx


Including an example from cisco's documentation on why this command is used.

"
Usage Guidelines 
In a hub and spoke configuration, a PE router readvertises all prefixes containing duplicate autonomous system numbers. Use the neighbor allowas-in command to configure two VRFs on each PE router to receive and readvertise prefixes: 

1. One VRF receives prefixes with ASNs from all PE routers and then advertises them to neighboring PE routers. 

2. The other VRF receives prefixes with ASNs from the CE router and readvertises them to all PE routers in the hub and spoke configuration. 

You control the number of times an ASN is advertised by specifying a number from 1 to 10. 

Examples 
In the following example, the PE router with ASN 100 is configured to allow prefixes from the VRF address family VPN IPv4 vrf1. The neighboring PE router with the IP address 192.168.255.255 is set to be readvertised to other PE routers with the same ASN 6 times: 

router bgp 100 
 address-family ipv4 vrf vrf1
 neighbor 192.168.255.255 allowas-in 6
"

The above was taken from 

http://www.cisco.com/en/US/products/sw/iosswrel/ps1830/products_feature_guide09186a0080087b1f.html#wp1045854

HTH

Regards,

Vikram


> > Subject: RE: BGP AS path
> > From: "Paul Stewart" <pstewart@...group.net>
> > Date: Wed, 3 Aug 2005 09:16:47 -0400
> > X-Message-Number: 1
> > 
> > Why would you want to permit your own AS in the path?=20
> > 
> 
> Yes Why? I had a look at the bgp conditional advertisement docs
> Mustafa mentioned earlier at cisco.com and there was no requirement
> for such a feature.
> 
> Rgrds
> 




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