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Date: Fri, 14 Feb 1997 09:23:52 -0800 (PST)
From: "Tom Mueller" <trm@i-planet.com>
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Subject: misc/2733: TUNMTU limits MRU in tun device even if mtu set
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>Number:         2733
>Category:       misc
>Synopsis:       TUNMTU limits MRU in tun device even if mtu set
>Confidential:   no
>Severity:       non-critical
>Priority:       medium
>Responsible:    freebsd-bugs
>State:          open
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Fri Feb 14 09:20:01 PST 1997
>Last-Modified:
>Originator:     "Tom Mueller"
>Organization:
i-Planet, Inc.
>Release:        FreeBSD 2.1-STABLE i386
>Environment:

2.1 kernel built with the tun driver (if_tun.c)

>Description:

The TUNMTU variable in if_tun.h is used to initialize the value of
if_mtu in the tun driver and to limit the size of incoming packets
in the tunwrite function.  The TUNSIFINFO ioctl can be used to 
set the value of if_mtu to something different from TUNMTU, but
TUNMTU is still used to limit the size of incoming packets.

It seems that the tunwrite function should use if_mtu to limit
incoming packet size rather than TUNMTU.

>How-To-Repeat:

This problem can be seen using the user level ppp program (iij-ppp)
when the mru is set to greater than the value of TUNMTU.

>Fix:
	
Change TUNMTU to ifp->if_mtu in the tunwrite function.

>Audit-Trail:
>Unformatted: