no-export community with summary address using attribute map- won't it advertise the prefix to direct eBGP neighbor ??

[Sandeep Verma]

Hi everyone,

I am trying to change the attribute of a summary route using attribute map. The attribute of the summary gets modified but the prefix is not being advertised to direct eBGP neighbor.

route-map abc permit 10

set community no-export

router bgp 1

aggregate address 10.0.0.0 255.0.0.0 summary-only attribute-map abc

I am using (C7300-K91​P-M), Version 12.2(33)SB​10 software

Sorry, i am also unclear if we need to use send-community towards both iBGP and eBGP neighbors ??

Thanks and Best Regards

Sandeep

[Rolf Fischer]

Sandeep

as you know, "no-export" means "do not advertise this prefix to eBGP neighbors".

I'm not a BGP expert but I think it depends on the order. When you generate an aggregate locally with an attribute-map that sets the no-export community attribute, the local router won't advertise this aggregate to eBGP neighbors (simply following the above-mentioned rule).

If you want to advertise the aggregate with no-export community set to an eBGP peer, you could do something like this:

ip prefix-list 10/8 permit 10.0.0.0/8
!
route-map SET_NOEXPORT permit 10
 match ip address prefix-list 10/8
 set community no-export
!
router bgp 1
 aggregate-address 10.0.0.0 255.0.0.0 summary-only
 neighbor <eBGP-Peer> send-community
 neighbor <eBGP-Peer> route-map SET_NOEXPORT out
!

The difference is that the no-export community now is not assigned to the aggregate in the local BGP table, but will be set in the update to <eBGP-Peer>.

Whether or not use the send-community command for iBGP peers as well depends on what exactly you want to achieve.

HTH

Rolf

[paul driver]

Hello

Following on from Rolfs post:

Notice he has added an important command which is the send community   This is required, As by default bgp will not advertise any communities until this is specified

FYI-

No-export wont advertised outside the AS it being advertised into
No-Advertise - The neighbor you advertise this to wont advertise to any its neighbors (internal/external AS)

access-list permit 1 10.0.0.0 0.255.255.255

route-map NOAVERT
match ip address 1
set community no-advertise

router bgp 1
neighbor x.x.x.x send-community
neighbor x.x.x.x route-map NOAVERT

res

Paul