nanog mailing list archives
Re: Ethernet NAPs (was Re: Miami ...)
From: Leo Bicknell <bicknell () ufp org>
Date: Wed, 22 Aug 2001 20:36:32 -0400
On Wed, Aug 22, 2001 at 05:24:12PM -0700, Marc Slemko wrote:
If you don't, the behavior is simple. A 9k MTU GigE arps for a 1500 byte FastEthernet host. Life is good. The TCP handshake completes, life is good. TCP starts to send a packet, putting a 9k frame on the wire. Depending the switch, the switch either drops it as over MTU for the FastEthernet, or the FastEthernet card cuts it off at 1500 bytes, and counts it as an errored frame (typically with a jabber or two afterwards) and no data flows.Well, the reasoning "why" is a bit more complex than that... The TCP handshake will result in the FE host saying "hey, I can do a max 1460 byte mss". The other host with a larger MTU won't send larger packets than remote MSS + 40 bytes header over that TCP connection, end of story.
I was assuming the TCP connection was between two end stations, not to the device itself. Consider: host---GE---exchange router--GE--<fabric>--FE--exchange router---GE---host The two hosts talk, get MSS of 9k (ish), SYN, SYN+ACK, ACK are all small and pass, the first data packet tries to be 9k, and gets lost between the fabric and the exit (FE) router. Yes, if the host talked to the FE device itself MSS should prevent any issues (eg, for BGP sessions across the exchange). -- Leo Bicknell - bicknell () ufp org Systems Engineer - Internetworking Engineer - CCIE 3440 Read TMBG List - tmbg-list-request () tmbg org, www.tmbg.org
Current thread:
- Maimi Nap of the America's Vinny India (Aug 22)
- RE: Maimi Nap of the America's Daniel Golding (Aug 22)
- RE: Ethernet NAPs (was Re: Miami ...) RJ Atkinson (Aug 22)
- RE: Ethernet NAPs (was Re: Miami ...) Mikael Abrahamsson (Aug 22)
- RE: Ethernet NAPs (was Re: Miami ...) RJ Atkinson (Aug 22)
- Re: Ethernet NAPs (was Re: Miami ...) Leo Bicknell (Aug 22)
- Re: Ethernet NAPs (was Re: Miami ...) Marc Slemko (Aug 22)
- Re: Ethernet NAPs (was Re: Miami ...) Leo Bicknell (Aug 22)
- Re: Ethernet NAPs (was Re: Miami ...) Dan Hollis (Aug 22)
- Re: Ethernet NAPs (was Re: Miami ...) Miquel van Smoorenburg (Aug 23)
- Re: Ethernet NAPs (was Re: Miami ...) Mikael Abrahamsson (Aug 23)
- RE: Ethernet NAPs (was Re: Miami ...) RJ Atkinson (Aug 22)
- RE: Maimi Nap of the America's Daniel Golding (Aug 22)
- Re: Ethernet NAPs (was Re: Miami ...) RJ Atkinson (Aug 22)
- Re: Ethernet NAPs (was Re: Miami ...) Mikael Abrahamsson (Aug 22)
- Re: Ethernet NAPs RJ Atkinson (Aug 23)
- Re: Ethernet NAPs (was Re: Miami ...) John Kristoff (Aug 23)
- Re: Ethernet NAPs (was Re: Miami ...) Mikael Abrahamsson (Aug 23)
- Re: Ethernet NAPs (was Re: Miami ...) John Kristoff (Aug 23)
- Re: Ethernet NAPs (was Re: Miami ...) RJ Atkinson (Aug 23)