10-24-2015 11:00 PM - edited 03-05-2019 02:35 AM
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-K91P-M), Version 12.2(33)SB10 software
Sorry, i am also unclear if we need to use send-community towards both iBGP and eBGP neighbors ??
Thanks and Best Regards
Sandeep
10-25-2015 04:03 AM
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
10-25-2015 05:01 AM
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
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