neighbour send community both

[amit bhatnagar]

enabling mp-bgp in our enviroment on 6509 , have been recommended to use neighbour X.X.X.X send-community both

was trying to understand the difference between  send community both , extended , standard .

Thanks for helpenabling mp-bgp in our enviroment , have been recommended to use neighbour X.X.X.X send-community both
was trying to understand the difference between  send community both , extended , standard .
Thanks for help

[cadet alain · Accepted solution]

Hi,

standard communities are used for filtering and tagging in BGP

extended ones carry other infos like route-targets for MP-BGP and MPLS VPN

http://www.cisco.com/web/about/ac123/ac147/archived_issues/ipj_6-2/bgp_communities.html

Regards

Alain

Don't forget to rate helpful posts.

[Peter Paluch · Accepted solution]

Hi Amit,

Communities are arbitrary numeric values attached to advertised networks in BGP that may influence the best path selection algorithm, influence the scope into which a route may be further advertised, and they may carry additional attributes about the network that are not BGP standalone attributes but the application using BGP to carry routes can hide its own attributes into these community strings (such as original component EIGRP metrics of routes redistributed from EIGRP into BGP).

Originally, the community attribute was specified in RFC 1997 and was a 4B long integer value. However, after some time, it was discovered that a wider integer would be useful. Therefore, RFC 4360 defined new type of the community attribute that is called an extended community which is an 8B long integer comprising 2B-long type field, and 6B-long value. Retroactively, the former communities from RFC 1997 were renamed into standard communities.

Not all BGP implementations support communities. Therefore, the willingness of a router to send and receive communities of a selected type with a neighbor has to be explicitly configured and negotiated. The neighbor send-community causes just that - it tells your router to try to negotiate the use of appropriate community type with the particular neighbor.

If you are not using the communities, there is little gain in activating the capability of exchanging them with the neighbor. Then again, if you expect to start using them at some point in the future, it may be wise to activate them now, because adding them later will cause the BGP peering to flap.

You may want to check the following documents for more information about using the communities:

http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a00800c95bb.shtml#communityattribute

http://www.nanog.org/meetings/nanog40/presentations/BGPcommunities.pdf

http://www.cisco.com/web/about/ac123/ac147/archived_issues/ipj_6-2/bgp_communities.html

http://www.cisco.com/en/US/tech/tk365/technologies_configuration_example09186a00801475b2.shtml

Best regards,

Peter

[amit bhatnagar]

Thanks for help one more query
when I am enabling MP-BGP , I was reading couple of documents they say if you give command below .
address-family vpnv4
neighbor x.x.x.x activate

automattically for all VRF on that Layer 3 device "address-family ipv4 vrf vrf name " command is added in show running configration . like below

address-family ipv4 vrf VRF_1
address-family ipv4 vrf VRF_2

I was worred becuase I didnts wated all VRF to be communicating over MP-BGP

Thanks for help

[Peter Paluch]

Hello Amit,

when I am enabling MP-BGP , I was reading couple of documents they say if you give command below . 
address-family vpnv4
neighbor x.x.x.x activate
automattically  for all VRF on that Layer 3 device "address-family ipv4 vrf vrf name "  command is added in show running configration . like below
address-family ipv4 vrf VRF_1
address-family ipv4 vrf VRF_2
I was worred becuase I didnts wated all VRF to be communicating over MP-BGP

I am not sure about what exactly you do not want to happen. The mere existence of address-family ipv4 vrf vrf-name simply says that the BGP knows about the VRF, and is able to advertise its contents to another neighbor defined under the address-family vpnv4 section. This does not mean that the VRFs will be leaking one into another or something similar.

Perhaps you could describe a scenario you want to avoid.

Best regards,

Peter

[Alex17539]

"and is able to advertise its contents to another neighbor defined under the address-family vpnv4 section"

what is the command to advertise a specific VRF to another neighbor define under address family vpnv4?