nanog mailing list archives
Re: OpenBGPd problems relating to misuse of RESERVED bits in BGP Attribute Flags field
From: PC <paul4004 () gmail com>
Date: Thu, 29 Nov 2012 14:21:14 -0700
If you hear anything more, I'd be interesting in knowing about it. I had a an upstream going up and down last night; reportedly their BGP process was core dumping due to a BGP attribute issue. I never found out what vendor it was though. Paul On Thu, Nov 29, 2012 at 12:33 PM, Michael Sinatra < michael () rancid berkeley edu> wrote:
Jeff and NANOG: We are currently dropping the bad attribute within our network (as293) and are working with the customer to determine the origin of the attribute (equipment, code rev, etc.). The bad attribute should not be leaking beyond our AS at all. If you're filtering routes from AS68, you should be able to resume accepting routes from that AS. michael On 11/29/12 12:44 AM, Jeff Wheeler wrote:I had two downstream BGP customers experience problem with an OpenBGPdbugtonight. Before diving into detail, I would like to link this mailinglistthread, because this is not a new issue and a patch is available: http://www.mail-archive.com/misc () openbsd org/msg115071.html For the following DFZ routes, I see wrong use of the fifth bit in the Attribute Flags field: Aggregator (7), length: 8, Flags [OT+8]: AS #68, origin 192.65.95.253 0x0000: 0000 0044 c041 5ffd Updated routes: 128.165.0.0/16 141.111.0.0/16 192.65.95.0/24 192.12.184.0/24 204.121.0.0/16 According to RFC 4271 page 17, "the low-order four bits of the Attribute Flags octet are unused. They MUST be zero when sent and MUST be ignored when received." I read "ignored" to mean, don't tear down the BGPsessionand print a cryptic error that the user probably will be unable to debug. The OpenBGPd guys clearly agree and have supplied a patch, so affected users should visit the above mailing list link, and install it. Here are my notes for this RFC page and a small diagram of the packet header, because surprisingly, there isn't one in the RFC already http://inconcepts.biz/~jsw/img/1121129aa-rfc4271pg17scan.jpg Sorryaboutthe poor quality of this, but it is past 3am here, and I know of several operators (besides my downstream customers) who are experiencing this problem right now. If I were someone who is broken by this right now, I would either patchmyOpenBGPd or ask your eBGP neighbors not to send you the above five routes (filtering it on your own OpenBGPd router probably won't help.) Thanks, I hope this is helpful
Current thread:
- OpenBGPd problems relating to misuse of RESERVED bits in BGP Attribute Flags field Jeff Wheeler (Nov 29)
- Re: OpenBGPd problems relating to misuse of RESERVED bits in BGP Attribute Flags field Michael Sinatra (Nov 29)
- Re: OpenBGPd problems relating to misuse of RESERVED bits in BGP Attribute Flags field Michael Sinatra (Nov 29)
- Re: OpenBGPd problems relating to misuse of RESERVED bits in BGP Attribute Flags field PC (Nov 29)
- Re: OpenBGPd problems relating to misuse of RESERVED bits in BGP Attribute Flags field Stuart Henderson (Nov 29)