[Openswan Users] ipsec0: MTU of 16260

[Graham Leggett]

Hi all,

I have been having problems with transfers over a VPN connection. ssh 
works fine, but any file transfers hang. Transfers of any size direct 
(not via the VPN) seem to work fine.

I notice this though:

ipsec0    Link encap:Point-to-Point Protocol
           inet addr:196.34.112.95  Mask:255.255.255.255
           UP RUNNING NOARP  MTU:16260  Metric:1
                             ^^^^^^^^^
           RX packets:4526 errors:0 dropped:24 overruns:0 frame:0
           TX packets:5277 errors:0 dropped:0 overruns:0 carrier:0
           collisions:0 txqueuelen:10
           RX bytes:386567 (377.5 Kb)  TX bytes:1616632 (1.5 Mb)

This MTU looks wrong.

The IPSEC tunnel is created over a PPP interface that looks like this:

ppp0      Link encap:Point-to-Point Protocol
           inet addr:196.34.112.95  P-t-P:66.18.87.50  Mask:255.255.255.255
           UP POINTOPOINT RUNNING NOARP MULTICAST  MTU:1466  Metric:1
                                                   ^^^^^^^^
           RX packets:24348 errors:0 dropped:0 overruns:0 frame:0
           TX packets:26810 errors:0 dropped:0 overruns:0 carrier:0
           collisions:0 txqueuelen:3
           RX bytes:21977268 (20.9 Mb)  TX bytes:3238323 (3.0 Mb)

Can anyone explain why my MTU on ipsec0 is so big?

VPN is via openswan v2.1.4 on both ends.

Regards,
Graham
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