maximum segment size

<networking> (MSS) The maximum amount of {TCP} data that a {node} can send in one {segment}. This should be the size of the receiver's reassembly buffer to try to avoid {fragmentation}.

The equivalent at the {physical layer} is "{Maximum Transmission Unit}".

(1998-03-06) (thx dict)

advmss allows you to change the advertised MSS that your host offers to the peer. TCP has all kinds of weird options like this.

...

But there are unfortunately many networks that don't play nice with this.

Interesting. An example, and why? Sorry, I'm in ultra-inquisitive mode.

Well, it relies on a packet with a Don't Fragment bit set having an ICMP packet returned by some router or the destination along the route. NAT often breaks this, and many people just block outbound/inbound ICMP. IDSen don't like PMTU generally, because it involves several "large" ICMP packets, that often get flagged as DoS attempts. (Why is ftp.sunet.se DoSing me?!)

Some load balancers (I forget the brand) send out dummy packets on port 53 (dns) to assess the round trip time to a client so it can determine a server most topologically close to the client. IDSen don't like this either. :)

PS. Anyone fancy GIVING me £3000 so I can go back to university? Anyone? Anyone? oh. Oh well!

hehe, <aol sed=s,back ,,> me too! </aol>