route change and MTU

[Mike Tancsa]

This sort of seems like a bug, but not sure

If I had 2 interfaces, one tun1, pppoe with an MTU of 1492, and one 
ethernet, a normal MTU of 1500.

if the default route was via tun1, and I did a
route change default <ip of gateway on the ethernet>

the MTU stays at 1492

e.g. on my RELENG_7 box

0[cage]# route add 1.1.1.1/30 64.7.157.1
add net 1.1.1.1: gateway 64.7.157.1
0[cage]# route get 1.1.1.1
    route to: 1.1.1.1
destination: 1.1.1.0
        mask: 255.255.255.252
     gateway: dslborder1.sentex.ca
   interface: tun0
       flags: <UP,GATEWAY,DONE,STATIC>
  recvpipe  sendpipe  ssthresh  rtt,msec    rttvar  hopcount      mtu 
     expire
        0         0         0         0         0         0      1492 
         0

This is correct. The MTU on the PPPoE interface is 1492

0[cage]# route change 1.1.1.1/30  192.168.0.3
change net 1.1.1.1: gateway 192.168.0.3
0[cage]# route get 1.1.1.1
    route to: 1.1.1.1
destination: 1.1.1.0
        mask: 255.255.255.252
     gateway: 192.168.0.3
   interface: bge0
       flags: <UP,GATEWAY,DONE,STATIC>
  recvpipe  sendpipe  ssthresh  rtt,msec    rttvar  hopcount      mtu 
     expire
        0         0         0         0         0         0      1492 
         0
0[cage]# ifconfig bge0
bge0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu 1500
         options=9b<RXCSUM,TXCSUM,VLAN_MTU,VLAN_HWTAGGING,VLAN_HWCSUM>
         ether 00:10:18:14:15:43
         inet 192.168.0.12 netmask 0xffffff00 broadcast 192.168.0.255
         media: Ethernet autoselect (100baseTX <full-duplex>)
         status: active
0[cage]#

The MTU should be 1500 after the route change no ?

         ---Mike



--------------------------------------------------------------------
Mike Tancsa,                                      tel +1 519 651 3400
Sentex Communications,                            mike at sentex.net
Providing Internet since 1994                    www.sentex.net
Cambridge, Ontario Canada                         www.sentex.net/mike