kern/184389: libalias fails to adjust MTU from jails

[Monkey]

>Number:         184389
>Category:       kern
>Synopsis:       libalias fails to adjust MTU from jails
>Confidential:   no
>Severity:       non-critical
>Priority:       medium
>Responsible:    freebsd-bugs
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Sat Nov 30 10:00:00 UTC 2013
>Closed-Date:
>Last-Modified:
>Originator:     Monkey
>Release:        FreeBSD 9.2-RELEASE-p2 amd64
>Organization:
MonkeyBrains.net
>Environment:
System: FreeBSD papadum 9.2-RELEASE-p2 FreeBSD 9.2-RELEASE-p2 #0: Sat Nov 30 00:46:30 PST 2013 monkey at papadum:/usr/obj/usr/src/sys/GENERIC amd64


	ipfw_nat, libalias
>Description:
	MTU size is not properly discovered from packets generated from jails.  libalias and/or ipfw_nat
	need to communicate with the network stack to determine MTU.
>How-To-Repeat:
	Set up ipfw_nat to nat packets generated from a jail.
	Send those packets to a second FreeBSD box that has a GRE tunnel to third machine.
	Attempt to ssh or scp a file larger than 1500 bytes from the jail to the third machine -- it hangs.
	If you SSH from the host (outside of the jail), the ssh connects.
	If you quickly log into the jail, it will briefly work (OS remembers MTU size for that path).
>Fix:
	Set the MTU to 1476 on the interface connecting computer A to computer B.

>Release-Note:
>Audit-Trail:
>Unformatted: