[cisco-bba] IOS upgrade kills Linksys

[Dennis Peng]

Do you have "ip adjust mtu" under the VPDN group? That will change the
MTU automatically, but having a lower MTU can cause problems for some
applications. I usually recommend customers to remove it if they are
having MTU issues.

Dennis

Krzysztof Adamski [k at adamski.org] wrote:
> I upgrade my LNS from 12.2(12f) to 12.2(15)T14, and now some LinkSys boxes
> are showing weird behaviour. The LNS is doing PPPoE aggregation.
>  All the normal web access is working, but a VPN access to an exchange
> server is not. The VPN software is running on a PC behind the LinkSys. The
> VPN packets are encapsulated in UDP.
>  Not all VPN is the problem just the exchange traffic. Snooping the
> traffic it appears that the exchange is sending a 18k size UDP packet that
> is being fragmented. The size of each fragment is 1492 bytes. For some
> strange reason the MTU on the virtual-interface is 1464, this is how my
> virtual-template looks:
> 
> interface Virtual-Template1
>  ip unnumbered FastEthernet1/0
>  no ip proxy-arp
>  mtu 1492
>  ip tcp adjust-mss 1300
>  no logging event link-status
>  peer default ip address pool ADSL
>  ppp authentication pap
> 
> I have tried ip mtu 1492, mtu 1500, mtu 1464, even changing the MTU on the
> LinkSys to 1464 nothing helped.
> 
> Any ideas what can be wrong?
> 
> K
> 
> 
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