Subject: kern/17151: IPv4 over fddi uses wrong MTU (4470, not 4352)
To: None <>
From: None <>
List: netbsd-bugs
Date: 06/03/2002 10:43:01
>Number:         17151
>Category:       kern
>Synopsis:       IPv4 over fddi uses wrong MTU (4470, not 4352)
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sun Jun 02 19:10:01 PDT 2002
>Originator:     Jun-ichiro itojun Hagino
>Release:        NetBSD 1.6A
System: NetBSD 1.6A NetBSD 1.6A (STARFRUIT) #25: Fri May 31 13:26:12 JST 2002 i386
Architecture: i386
Machine: i386
	RFC1390 says that IPv4 MTU for FDDI link is 4352 (FDDIIPMTU).

	sys/net/if_fddisubr.c sets if_mtu to FDDIMTU, which is 4470.
	in sys/netinet/ip_output.c and other places, we grab mtu values
	from ifp->if_mtu.  therefore, ip_output() uses 4470 as MTU, not 4352.

	for cloning routes (like directly-connected subnet routes),
	and cloned routes (like ARP-generated routes) arp_rtrequest() has
	special handling and there should be no problem.
	however, non-cloning routes (like default route) has the problem.
	code inspection