[c-nsp] Should the AS # listed under the BGP AGGREGATOR attribute be the same as the AS # used to bring up a bgp session in a multiple VRF/AS router? Or the global routing table AS #?

[P C]

I have a prefix I announce (Let's say 1.1.1.0/24) via a VRF-lite
instance on a Cisco 7200 router.  I announce this prefix with the
aggregate-address command, which causes the aggregator attribute to be
added.  The router when adding this attribute is using the global
routing table's autonomous system number (a private AS) which is
defined under "router bgp xxx" and not the per-VRF bgp identifier
assigned with the" local AS replace-as" command.


The result is something like this when you query the other side: (note
the private AS # under "aggregated by"):

show ip bgp 1.1.1.0
BGP routing table entry for 1.1.1.0/24, version
...
  Not advertised to any peer
  1 2 3 (aggregated by 65000 10.0.0.1), (received & used)

Of course this seems mostly informational, I know I could just drop
sending the community, and it doesn't appear to cause any harm, but I
rather it have the real AS #.

Sample configuration:


router bgp 65000
<neighbor x.x.x.x remote-as 65001>
 address-family ipv4 vrf vrfa
   <neighbor x.x.x.x remote-as 2>
   neighbor x.x.x.x local-as 3 no-prepend replace-as
   network 1.1.1.0 mask 255.255.255.128
   aggregate-address 1.1.1.0 255.255.255.0 summary-only.


Do you feel it should be leaking out the global/private AS like this?
I looked at RFC4271, and although it's not entirely clear to me, I
believe this value should be the identifier used to bring up the BGP
session with the peer.  However I suppose "Should" means optional in
RFC-sense?

This particular item also seems to have changed in RFC4271 compared to
previous BGP RFCs.


 g) AGGREGATOR (Type Code 7)

            AGGREGATOR is an optional transitive attribute of length 6.
            The attribute contains the last AS number that formed the
            aggregate route (encoded as 2 octets), followed by the IP
            address of the BGP speaker that formed the aggregate route
            (encoded as 4 octets).  This SHOULD be the same address as
            the one used for the BGP Identifier of the speaker.

            Usage of this attribute is defined in 5.1.7.

BGP Identifier
      A 4-octet unsigned integer that indicates the BGP Identifier of
      the sender of BGP messages.  A given BGP speaker sets the value of
      its BGP Identifier to an IP address assigned to that BGP speaker.
      The value of the BGP Identifier is determined upon startup and is
      the same for every local interface and BGP peer.