>Number:         16761
>Category:       kern
>Synopsis:       gre(4) interfaces work with a larger mtu
>Confidential:   no
>Severity:       non-critical
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sat May 11 11:19:00 PDT 2002
>Closed-Date:
>Last-Modified:
>Originator:     Jasper Wallace
>Release:        NetBSD 1.5ZC
>Organization:
	none whatsoever.
>Environment:
System: NetBSD spagetti 1.5ZC NetBSD 1.5ZC (SPAGETTI) #0: Fri Apr 26 02:31:12 UTC 2002 jasper@spagetti:/usr/src/sys/arch/i386/compile/SPAGETTI i386
Architecture: i386
Machine: i386
>Description:
	When trying to use ospf over gre a tunnel to a cisco router i
noticed that the two machines where failing to sync beacause the mtu used at
either end of the link was different.

	The cisco was using 1476, where as NetBSD uses 1450.

	Unfortunatly there dosn't appear to be a way to change the mtu under
Cisco IOS, fortunatly NetBSD comes with source code.

	I've been running with the larger MTU on both -current and
1.5.3_whatever for a few weeks now without any problems.

>How-To-Repeat:

	Create a gre tunnel between a router running cisco IOS and one
running NetBSD and try to run OSPF over the tunnel.

look at the log messages complaining about "MTU missmatches".

>Fix:
Index: if_gre.c
===================================================================
RCS file: /cvsroot/syssrc/sys/net/if_gre.c,v
retrieving revision 1.26
diff -u -r1.26 if_gre.c
--- if_gre.c	2002/02/24 17:22:20	1.26
+++ if_gre.c	2002/05/11 17:44:11
@@ -107,7 +107,7 @@
  * before changing if state to up to find the
  * correct value
  */
-#define GREMTU 1450
+#define GREMTU 1476
 #define LINK_MASK (IFF_LINK0|IFF_LINK1|IFF_LINK2)
 
 struct gre_softc_head gre_softc_list;


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