MPLS MTU problem of OSR's dot1q trunk link?

[td.wu]

ge-wan ge-wan ge-wan

P1(OSR)-----P2(OSR)-----P3(OSR)-----P4(OSR)

|FE |FE | FE | FE

PE(36) PE PE PE

As the above figure,I have four OSR connected using

OSM-4GE-WAN's ge-wan interface,at each OSR I use one

L2 GE port connected two one of the 4 GE-WAN interface,

the L2 GE port use 802.1q trunk.

Each OSR use a FE link to connect PE router, the FE links

are access link of a vlan which was trunked by the L2 GE port

to the LE GE-WAN interface.

The GE-WAN subinterface and the L2 GE/FE interface are

all configured to pass jumbo frames.

Everything seems ok and after the VPN and all network run

normally for almost a month,packets bigger than 1500 bytes

can't pass through P1 or P2, and no events logged .

The case never happened to P3 and P4 .

The hardware and IOS version and mpls vpn configuration

are the same at the four OSR.

Who can give me some help or advice about that?

THANKS

mail:td.wu@163.com

[ipotts]

Would you please clarify what the MTU problem is that you have? It it IP MTU? Are there any firewalls that could be blocking dynamic MTU discovery?

[td.wu]

There is no firewall.The IP mtu is 1526 and the layer2 fastethernet mtu is 9216.Everything is ok for the mpls ,but after running for almost a month,there is a OSR can't allow the big packet pass through.

[romccallum]

Away from your issue here you have one which is even worse. P switching and MPLS on the OSM-GIG-WAN modules is not supported. You require the osm+ cards along with the sup720+ module. If you dont have this then you will run into endless problems with blackholing etc etc. I found this out the hard way also so you are not alone.

[td.wu]

But I do use the OSM-GIG-WAN as the P router,the cisco document hasn't said that OSM can't running as P in mpls vpn.If it's true as you said,I'll come into a nightmare.