Problem with Path MTU Discovery

[Jeremie Le Hen]

Hi George,

sorry for the delay.

> > I set a gif(4)-based IPSec tunnel between my network and a friend's one.
> > This works pretty well, except that Path MTU Discovery doesn't work.
> > 
> > Quick draw:
> >           MTU: 1500       MTU:1280       MTU:1500
> >     Comp1 --------- Gate1 -------- Gate2 -----+-- Comp2
> >     RELENG_5        RELENG_4       RELENG_5   |   RELENG_5
> >                                               |
> >                                               +-- Comp3
> >                                                   RELENG_5
> 
> Can you look at the routing table for each of Comp1 and Comp2 and also
> use the -W flag to show the path MTU?  If there is something wonky in
> the routing table then TCP will not hear about the MTU change.

There doesn't seem to be strange MTUs in routing table (each host has
multiple jails, which explains why the routing table is somewhat large).

%%%
    comp1:root# netstat -rnWf inet
    Routing tables
    
    Internet:
    Destination        Gateway            Flags    Refs      Use    Mtu    Netif Expire
    default            192.168.1.1        UGS         0  3878073   1500      em0
    127.0.0.1          127.0.0.1          UH          0        4  16384      lo0
    192.168.1          link#3             UC          0        0   1500      em0
    192.168.1.1        00:09:5b:1a:48:94  UHLW        1   594449   1500      em0   1169
    192.168.1.25       00:04:23:89:e5:84  UHLW        0    20232   1500      lo0 =>
    192.168.1.25/32    link#3             UC          0        0   1500      em0
    192.168.1.53       00:04:23:89:e5:84  UHLW        0    24765   1500      lo0 =>
    192.168.1.53/32    link#3             UC          0        0   1500      em0
    192.168.1.178      00:c0:9f:94:39:8f  UHLW        0      275   1500      em0    316
    192.168.1.241/32   link#3             UC          0        0   1500      em0
    
    
    comp2:root# netstat -rnWf inet
    Routing tables
    
    Internet:
    Destination        Gateway            Flags    Refs      Use    Mtu    Netif Expire
    default            192.168.4.13       UGS         0    58623   1500      xl0
    127.0.0.1          127.0.0.1          UH          0     1244  16384      lo0
    192.168.4          link#1             UC          0        0   1500      xl0
    192.168.4.4        00:60:08:60:fe:10  UHLW        0       20   1500      lo0
    192.168.4.13       00:0a:5e:3d:40:cb  UHLW        1  1307764   1500      xl0   1012
    192.168.4.40       00:60:08:60:fe:10  UHLW        0     1255   1500      lo0 =>
    192.168.4.40/32    link#1             UC          0        0   1500      xl0
    192.168.4.49       00:60:08:60:fe:10  UHLW        0     2317   1500      lo0 =>
    192.168.4.49/32    link#1             UC          0        0   1500      xl0
    192.168.4.50       00:60:08:60:fe:10  UHLW        0     1220   1500      lo0 =>
    192.168.4.50/32    link#1             UC          0        0   1500      xl0
    192.168.4.51       00:60:08:60:fe:10  UHLW        0  4763999   1500      lo0 =>
    192.168.4.51/32    link#1             UC          0        0   1500      xl0
    192.168.4.52       00:60:08:60:fe:10  UHLW        0     1215   1500      lo0 =>
    192.168.4.52/32    link#1             UC          0        0   1500      xl0
    192.168.4.53       00:60:08:60:fe:10  UHLW        0    14393   1500      lo0 =>
    192.168.4.53/32    link#1             UC          0        0   1500      xl0
    192.168.4.54/32    link#1             UC          0        0   1500      xl0
    192.168.4.80       00:60:08:60:fe:10  UHLW        0    24577   1500      lo0 =>
    192.168.4.80/32    link#1             UC          0        0   1500      xl0
%%%

Thank you.
Regards,
-- 
Jeremie Le Hen
hen dot org >< ttz at chchile dot org >