Large BGP Communities beacon in the wild

Job Snijders job at ntt.net
Tue Oct 11 15:01:56 UTC 2016


Dear all,

Large BGP Communities are a novel way to signal information between
networks. An example of a Large BGP Communities is: 2914:4056024901:80.

Large BGP Communities are composed of three 4-octet integers, separated
by something like a colon. This is easy to remember and accommodates
advanced routing policies in relation to 4-Byte ASNs. It is the tool that has
been missing since 4-octet ASNs were introduced.

IANA has made an Early Allocation of the value 30 (LARGE_COMMUNITY) in
the "BGP Path Attributes" registry under the "Border Gateway Protocol
(BGP) Parameters" group.

The draft can be read here: https://tools.ietf.org/html/draft-ietf-idr-large-community

Additional information about Large BGP Communities can be found here:
http://largebgpcommunities.net/

Starting today (2016.10.11), the following two BGP beacons are available
to the general public, with AS_PATH 2914_15562$

    Both these prefixes have a Large BGP Community attached:

    2001:67c:208c::/48
    192.147.168.0/24

    Large BGP Community - 15562:1:1

The NLNOG RING BGP Looking Glass is running the latest version of BIRD
which understands the Large BGP Community Path Attribute.

IPv4 LG: http://lg.ring.nlnog.net/prefix_detail/lg01/ipv4?q=192.147.168.0/24
IPv6 LG: http://lg.ring.nlnog.net/prefix_detail/lg01/ipv6?q=2001:67c:208c::/48

In theory, since this is an optional transitive BGP Path Attribute, all
the Looking Glass' peers should boomerang the Large Community back to
the LG.  However we currently observe that 50 out of 75 peers propagate
the Large BGP Community to the LG.

Relevant Router commands to see if you receive the attribute, or whether
one of intermediate networks has stripped the attribute from the route:
    
    IOS: show ip bgp path-attribute unknown 
        shows all prefixes with unknown path attributes.

	IOS #2 - like on route views:
		route-views>sh ip bgp 192.147.168.0
		 BGP routing table entry for 192.147.168.0/24, version 98399100
		 Paths: (39 available, best #30, table default)
		   Not advertised to any peer
		   Refresh Epoch 1
		   701 2914 15562
			 137.39.3.55 from 137.39.3.55 (137.39.3.55)
			   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
		 
    IOS-XR: (you must look at specific prefixes)
        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 
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
        
    JunOS:
        user at 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
                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

A note about router Configurations:
    
Ensure you are not fitlering the path attributes, eg:

JunOS:
    [edit protocols bgp]
    user at junos# delete drop-path-attributes 30

XR:
    configure
    router bgp YourASN
        attribute-filter group ReallyBadIdea ! avoid creating bogons
        no attribute 30 
      !
    !

Contact persons: myself or Jared Mauch or NTT NOC. BGP Session
identifier 83.231.213.230 / 2001:728:0:5000::a92 AS 15562.

Kind regards,

Job


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