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Bug #6868

Interface MTU Setting not applied to all IPv6 routes

Added by Daryl Morse 11 months ago. Updated about 1 month ago.

Status:
Confirmed
Priority:
Normal
Assignee:
Category:
Interfaces
Target version:
Start date:
10/20/2016
Due date:
% Done:

0%

Affected version:
All
Affected Architecture:

Description

Running 2.3.2_1 using an HE/64 tunnel. Adjusting MTU to troubleshoot possible PMTUD problem. Found that setting for MTU in Interfaces / OPT1 only changes MTU for default route, but not for other gif0 routes. MTU of 1280 is applied to other routes.

default 2001:abc:c:1111::1 (MTU changed by OPT1 setting)
2001:abc:c:111::1 link#7 (MTU not changed)
fe80::%gif0/64 link#7 (MTU not changed)
ff01::%gif0/32 2001:abc:c:1111::2 (MTU not changed)
ff01::%gif0/32 2001:abc:c:1111::2 (MTU not changed)

Used command prompt route -6 change <route> -mtu 1480 to change MTU. After disabling OPT1 and enabling OPT1, MTU reset back to 1280.

History

#1 Updated by Jim Thompson 11 months ago

  • Assignee set to Jim Pingle

assigned to Pingle for analysis.

#2 Updated by Jim Pingle 11 months ago

  • Subject changed from MTU Setting in for OPT1 Interface not applied to all gif0 routes to Interface MTU Setting not applied to all IPv6 routes
  • Category set to Interfaces
  • Status changed from New to Confirmed
  • Assignee deleted (Jim Pingle)
  • Target version set to 2.4.0
  • Affected version set to All

I can reproduce the behavior on 2.3.x. If I adjust the MTU of an assigned interface, only the default and/or link route for IPv6 on the interface has its MTU adjusted, not others.

If I attempt the same thing on an IPv4 interface, the MTU for all routes is adjusted.

This does not appear to be specific to GIF, but to IPv6 in general. If I change the MTU on LAN, for example, the link route MTUs lower but none of the link-local routes do:

: netstat -rWn | grep vmx1
10.163.0.0/24      link#2             U             0   1350       vmx1
2001:470:xxxx:xxxx::/64           link#2                        U             0   1350     vmx1
fe80::%vmx1/64                    link#2                        U             0   1500     vmx1
fe80::20c:29ff:xxxx:42f6%vmx1     link#2                        UHS           0  16384      lo0
ff01::%vmx1/32                    fe80::20c:29ff:xxxx:42f6%vmx1 U             0   1500     vmx1
ff02::%vmx1/32                    fe80::20c:29ff:xxxx:42f6%vmx1 U             0   1500     vmx1

And the same on WAN (which doesn't have V6, but has multiple V4 routes):

default            xxx.xxx.xxx.161    UGS           4   1450       vmx0
xxx.xxx.xxx.160/28 link#1             U             6   1450       vmx0
xxx.xxx.253.14     xxx.xxx.xxx.161    UGHS         13   1450       vmx0
fe80::%vmx0/64                    link#1                        U             0   1500     vmx0
fe80::20c:29ff:xxxx:42ec%vmx0     link#1                        UHS           0  16384      lo0
ff01::%vmx0/32                    fe80::20c:29ff:xxxx:42ec%vmx0 U             0   1500     vmx0
ff02::%vmx0/32                    fe80::20c:29ff:xxxx:42ec%vmx0 U             0   1500     vmx0

We have had some issues setting MTU in the past (e.g. #4397, #5842, #2674), but none appear to exactly match this.

Attempting to reproduce the same issue on 2.4 has better but not perfect results. The link-local routes are updated with the correct MTU, but host and static routes are not.

If I manually set the MTU on an interface in stock FreeBSD 11, all link-local and static routes get an updated MTU.

#3 Updated by Jim Thompson 11 months ago

  • Assignee set to Luiz Souza

#4 Updated by Luiz Souza about 1 month ago

  • Target version changed from 2.4.0 to 2.4.1

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