Large BGP Communities

Milestone: Large BGP Communities Beacon Prefixes

Large BGP Communities has reached another milestone in its adoption today. Two beacon prefixes with Large BGP Communities are announced to the Internet routing table via BGP, allowing network operators to verify that they are receiving the community.

The following prefixes are announced with AS path 2914_15562$:

The NLNOG RING looking glass is running the latest version of BIRD which understands the Large BGP Communities path attribute. Since Large BGP Communities is an optional transitive BGP path attribute, all of the looking glass’ peers should announce it in theory. However, we observed that not all IPv6 peers propagate the Large BGP Community. This has been tracked down to a Cisco IOS bug which is triggered when send-community is not configured.

Implementations that support Large BGP Communities will show it natively. Relevant commands that allow you to see if you have received the attribute for some of the other implementations are below.

Cisco IOS: show ip bgp path-attribute unknown shows all prefixes with unknown path attributes. Here is an example from the Route Views project.

route-views>sh ip bgp
BGP routing table entry for, version 98399100
Paths: (39 available, best #30, table default)
   Not advertised to any peer
   Refresh Epoch 1
701 2914 15562 from (
      Origin IGP, localpref 100, valid, external
      unknown transitive attribute: flag 0xE0 type 0x1E length 0xC
       value 0000 3CCA 0000 0001 0000 0001
      rx pathid: 0, tx pathid: 0

Cisco IOS-XR:

RP/0/RSP0/CPU0:Router#show bgp ipv6 unicast 2001:67c:208c::/48 unknown-attributes
BGP routing table entry for 2001:67c:208c::/48
Community: 2914:370 2914:1206 2914:2203 2914:3200
Unknown attributes have size 15
Raw value:
e0 1e 0c 00 00 3c ca 00 00 00 01 00 00 00 01

Juniper Junos OS:

user@JunOS-re6> show route 2001:67c:208c::/48 detail
2001:67c:208c::/48 (1 entry, 1 announced)
    AS path: 15562 I
    Unrecognized Attributes: 15 bytes
    Attr flags e0 code 1e: 00 00 3c ca 00 00 00 01 00 00 00 01


ballerup-edge1#show bgp vpnv4 unicast vrf internet detail
BGP routing table entry for
25w4d received from (, path-id 0
Origin i, nexthop, metric 100, localpref 100,weight 0,
rtpref 200, best, block best, selected,
   Community 174:21100 174:22010 60876:174
   Unknown attribute type 30 flag e0 len 12
   As path [174 2914 15562]
   As4 path
   Received label notag