RE: [Idr] why has 4096 bytes limit on BGP messages size?

Pekka:

Oops - I shouldn't type before my coffee in the morning. Please change
the question to the following information: 

What is the complexity of the BGP peering at your DFZ? Can you give an
overview of the type of updates this represents?  

Without that information, it is difficult to quantify your data point. 

Millions of routes in several virtual routers with RD tags may have a
different flow pattern of updates. 

Thanks,

-----Original Message-----
From: Susan Hares [mailto:skh@nexthop.com] 
Sent: Friday, June 15, 2007 10:53 AM
To: Pekka Savola; Danny McPherson
Cc: idr List Routing
Subject: RE: [Idr] why has 4096 bytes limit on BGP messages size?

Pekka:

What is the complexity of the BGP peering at your DFZ? Can you give an
overview of the type of updates this represents?  

Without that information, it is difficult to quantify your data point. 

Millions of routers in several virtual routers with RD tags may have a
different flow pattern of updates. 

Thanks,

Sue

-----Original Message-----
From: Pekka Savola [mailto:pekkas@netcore.fi] 
Sent: Friday, June 15, 2007 1:48 AM
To: Danny McPherson
Cc: idr List Routing
Subject: Re: [Idr] why has 4096 bytes limit on BGP messages size?

On Thu, 14 Jun 2007, Danny McPherson wrote:
> 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?

Yes.  I've sometimes taken debugs logs of BGP when a DFZ table flapped 
and looked at the packets.  Here's a plot of BGP Update size versus 
occurrences (in this about 10-15min trace, 87K BGP updates).  BGP 
Updates are sent by a Juniper T-series router.  The smallest is 26B, 
the largest 4095B.  Top 20 sizes (6995 through 1229 occurrences) are 
all between 58 and 95 bytes.

(Not sure if the small attachment gets on the list, but if not, I'll 
post it somewhere.)

-- 
Pekka Savola                 "You each name yourselves king, yet the
Netcore Oy                    kingdom bleeds."
Systems. Networks. Security. -- George R.R. Martin: A Clash of Kings

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