Subject: [Idr] FW: Large BGP Communities beacon in the wild

From: Job Snijders <[email-masked]>
Date: Tue, 11 Oct 2016 17:29:50 +0200

This message was posted to various operational mailing lists.

TL;DR - there are now two beacons carrying a Large BGP Community in the
DFZ. On IPv4 we observe full coverage from the NLNOG RING LG - on IPv6
not so much.

Kind regards,

Job

----- Forwarded message from Job Snijders <[email-masked]> -----

Date: Tue, 11 Oct 2016 17:01:56 +0200
From: Job Snijders <[email-masked]>
To: [email-masked], [email-masked], Jared Mauch <[email-masked]>
Subject: [routing-wg] Large BGP Communities beacon in the wild

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@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@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

----- End forwarded message -----

---

From: Job Snijders <[email-masked]>
Date: Tue, 11 Oct 2016 20:51:29 +0200

> DFZ. On IPv4 we observe full coverage from the NLNOG RING LG - on IPv6

We tracked down the IPv6 discrepency: All the looking glass peers that
don't propagate the Large Community to the Looking Glass are Cisco IOS
boxes.

These IOS boxes won't send attribute 30 (and possibly other unknown
attributes) over IPv6 BGP sessions which are _not_ configured with
'send-community'.

Kind regards,

Job

---

From: Job Snijders <[email-masked]>
Date: Thu, 13 Oct 2016 12:08:22 +0200

Hi all,

Can anyone from Huawei help debug an issue?

It appears that some Huawei routers (at least NE40E with VRP 8.100) are
entirely ignoring route announcements which have a Large BGP Community
path attribute attached.

For testing, pingable beacon IPs: 192.147.168.255 / 2001:67c:208c::1

Not propagating an unknown optional transitive path attribute is one
thing, but outright dropping the entire route is a whole other level :)

Kind regards,

Job

On Tue, Oct 11, 2016 at 05:29:50PM +0200, Job Snijders wrote:
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