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MPLS MTU problem of OSR's dot1q trunk link?

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

4 REPLIES
Community Member

Re: MPLS MTU problem of OSR's dot1q trunk link?

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?

Community Member

Re: MPLS MTU problem of OSR's dot1q trunk link?

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.

Bronze

Re: MPLS MTU problem of OSR's dot1q trunk link?

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.

Community Member

Re: MPLS MTU problem of OSR's dot1q trunk link?

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.

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