On Mon, 2007-04-16 at 10:32 +0100, Alex wrote: > Jared, > Max BGP message size is 4096 bytes anyway and I cannot possibly see how 9K > MTU can further increase tcp performance in case of iBGP in comparison with > MTU of 4470. > Rgds > Alex
It's sometimes foolish to run iBGP sessions with a TCP MSS > 536 bytes. This is the minimum allowed for IP networks, and there should never be a router transporting your iBGP session which cannot forward TCP segments conforming to this minimum MSS value. A topology change might happen and cause your iBGP session, which under nominal conditions is transported over a 4470 MTU path, to pass across a 1500 MTU link. Now your TCP stack is sending packets larger than the path MTU, which will either be fragmented or discarded. The minimum values are the safest ones for iBGP, in my opinion; and the benefit to using any larger TCP MSS for iBGP is poor given the CPU time your router spends in its TCP/IP stack vs other tasks like calculating routes. You could argue that converge time is improved if the iBGP TCP session is more efficient, but that benefit goes away the first time your operators page you at 4am to find out why an iBGP session flaps when a topology change favoring a lower-MTU core link happens. :-) -- Jeff S Wheeler <[EMAIL PROTECTED]> +1-212-981-0607 Sr Network Operator / Innovative Network Concepts _______________________________________________ juniper-nsp mailing list [email protected] https://puck.nether.net/mailman/listinfo/juniper-nsp
