[e2e] Question on MTU

David Borman david.borman at windriver.com
Thu Apr 21 12:58:05 PDT 2005

On Apr 21, 2005, at 11:28 AM, Joe Touch wrote:

> MSS usually refers to a transport protocol, e.g., TCP, and denotes the
> max payload size there too. It is also relative to the network (IPv4,
> IPv6) protocol _and_ link layer used.
> And just as link layer overhead sizes vary, so do network layer 
> overhead
> sizes (minimums of 20 for IPv4, 40 for IPv6 - larger if options are
> included, e.g., 48 for IPv6 with jumbogram option).

But the advertised MSS in the TCP MSS option should not be adjusted to 
reflect any options or intermediary headers, just the fixed IP and TCP 
header sizes; 40 bytes for IPv4/TCP, and 60 bytes for IPv6/TCP.  When 
the sender generates the packet, he is responsible for reducing the TCP 
data to allow room for any additional options or headers.

			-David Borman

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