[OpenAFS] Today on "bad ideas": path MTU discovery for AFS via "aside" TCP?

Derrick Brashear shadow@gmail.com
Tue, 19 Jan 2010 12:44:16 -0500

(Deliberately copied to -info for admin take as well as -devel for
developer take)

Comments on using a TCP socket to discover the Path MTU to a
fileserver, e.g. when an Rx connection is made, a connection to a TCP
socket, presumably port TCP 7000, is made, and the discovered PMTU if
any is applied to Rx connections to that fileserver?

1) this would not block establishment of a connection
2) this *would* use extra bandwidth as the path MTU needs to be established
3) this would require any firewalls allow the TCP connection (if not, no change)
4) even if a value is established, there's no guarantee it's accurate
as routers could send UDP and TCP via different routes
5) routers may cheat and make the discovered value invalid anyway