Re: [Idr] why has 4096 bytes limit on BGP messages size?
Curtis Villamizar <curtis@occnc.com> Fri, 15 June 2007 05:50 UTC
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To: Danny McPherson <danny@tcb.net>
From: Curtis Villamizar <curtis@occnc.com>
Subject: Re: [Idr] why has 4096 bytes limit on BGP messages size?
In-reply-to: Your message of "Thu, 14 Jun 2007 16:40:31 MDT." <75E42991-5683-422A-89AD-733A11CEF6EE@tcb.net>
Date: Fri, 15 Jun 2007 01:51:34 -0400
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Cc: idr List Routing <idr@ietf.org>, Pekka Savola <pekkas@netcore.fi>
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In message <75E42991-5683-422A-89AD-733A11CEF6EE@tcb.net> Danny McPherson writes: > > > On Jun 14, 2007, at 9:59 AM, Pekka Savola wrote: > > > > (The header fields already tell the length of the message, so > > allocating 4K buffer for each BGP message (when most messages are > > much smaller than 4K) is probably a waste in many cases.) > > Pekka, > Do you have some references to data supporting your comment here > regarding most messages being smaller than 4K? > > -danny I looked into exactly this more than a decade ago. Its not likely to have changed much. Most of the time you get an occasional BGP keepalive. This is uninteresting. What is interesting is when a transient occurs. You have to engineer for the stress conditions and this is it for a BGP implementation. At that time many peers sent a large number of prefixes with the same AS path. These got packed into multiple full BGP updates and a few partial updates. Then there were AS paths (and other attributes, but mostly AS path) that had a smaller number of prefixes. If the BGP sender is efficient then lots of small updates are packed into a single write. TCP will deliver this as a stream of TCP segments making use of the full MSS. On the receiving end one big read will pick up multiple BGP updates. The BGP adj-in RIB processing is done (which is very minimal) and a read is immediately reposted. This way the flow of BGP updates goes quickly. By the time the BGP adj-out processing happens most or all of the updates have been transferred. A possible slow step is getting the route changes jammed into the forwarding cards. This too has improved. So during a transient most of the reads are delivering either full BGP updates or multiple partially filled updates. If the read buffer is larger than 4KB this is even more efficient as multiple full BGP updates can be read in a single read. Curtis _______________________________________________ Idr mailing list Idr@ietf.org https://www1.ietf.org/mailman/listinfo/idr
- [Idr] why has 4096 bytes limit on BGP messages si… Fenggen Jia
- Re: [Idr] why has 4096 bytes limit on BGP message… Tony Li
- Re: Re: [Idr] why has 4096 bytes limit on BGP mes… Fenggen Jia
- Re: Re: [Idr] why has 4096 bytes limit on BGP mes… Jeffrey Haas
- Re: [Idr] why has 4096 bytes limit on BGP message… Enke Chen
- Re: [Idr] why has 4096 bytes limit on BGP message… Pekka Savola
- Re: Re: [Idr] why has 4096 bytes limit on BGP mes… Vishwas Manral
- Re: [Idr] why has 4096 bytes limit on BGP message… Erblichs
- Re: [Idr] why has 4096 bytes limit on BGP message… Danny McPherson
- Re: [Idr] why has 4096 bytes limit on BGP message… Danny McPherson
- Re: [Idr] why has 4096 bytes limit on BGP message… Erblichs
- Re: [Idr] why has 4096 bytes limit on BGP message… Curtis Villamizar
- Re: [Idr] why has 4096 bytes limit on BGP message… Curtis Villamizar
- Re: [Idr] why has 4096 bytes limit on BGP message… Curtis Villamizar
- Re: [Idr] why has 4096 bytes limit on BGP message… Pekka Savola
- Re: [Idr] why has 4096 bytes limit on BGP message… Curtis Villamizar
- Re: [Idr] why has 4096 bytes limit on BGP message… Curtis Villamizar
- RE: [Idr] why has 4096 bytes limit on BGP message… Susan Hares
- RE: [Idr] why has 4096 bytes limit on BGP message… Susan Hares
- Re: Re: Re: [Idr] why has 4096 bytes limit on BGP… Fenggen Jia
- Re: [Idr] why has 4096 bytes limit on BGP message… Tony Li
- Re: [Idr] why has 4096 bytes limit on BGP message… Curtis Villamizar
- Re: [Idr] why has 4096 bytes limit on BGP message… Vishwas Manral
- RE: [Idr] why has 4096 bytes limit on BGP message… Bhatia, Manav (Manav)