Large BGP Communities beacon in the wild

Job Snijders job at ntt.net
Thu Oct 27 06:19:46 UTC 2016


Dear Internet,

Through this beacon it was discovered that a vendor was squatting on BGP
Path Attribute value 30. And another vendor sat on 31.

So, a twisted turn of events, the Large BGP Communities effort has ended up
with BGP Path Attribute value 32 - very befitting if you look at the very
problem we're trying to solve :-)

The beacon has been updated to use the new IANA assigned value, nothing
else was changed. Hopefully we are in the clear this time around!

Please verify if you can see 192.147.168.0/24 and 2001:67c:208c::/48

Kind regards,

Job

On Tue, Oct 11, 2016 at 05:01:56PM +0200, Job Snijders wrote:
> 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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