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

In message <4671C82D.2DEE5F08@earthlink.net>
Erblichs writes:
>  
> Danny McPherson, eta al,
>  
> 	Let me take a stab at this, but do your own investigation..
>  
> 	IMO, one item is due to the use of TCP by BGP. After one
> 	RTO timeout, most implimentations use a slow-start after
> 	idle. To preserve TCP's fast transmit and power of two
> 	mem allocation the stardard link's MTU is 1.5K, times four
> 	with a reduction to the closest power of two, thus 4K.
>  
> 	Oh, and the recieve window size is normally 4 x MTU which
> 	is then capped at 6K for slow-start.
>  
> 	Mitchell Erblich
> 	----------------

Not even close.

The BGP update size has nothing to do with the TCP socket buffer size
that you set with setsockopt SO_SNDBUF and SO_RCVBUF.

The BGP update size can be 4K and the socket buffer size can be 16KB
or 64KB (or larger with modern TCP).  Or it could be smaller but you
wouldn't want to do that.

And the MTU of concern then was FDDI or DS3/HSSI (4372? something >4KB).

Also the MTU and TCP MSS are not quite the same thing.

Curtis

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