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New Member

mpls on gre

Hi All,

We happened to observe that when we enable tag in our backbone, the gre customers face issues with respect to browsing. It becomes very inconsistent. We have made mtu as 1500. What could be the issue. Will it be related to IOS.

(hope this is the right forum for this conversation)

New Member

Re: mpls on gre

Hi.GRE adds some more overhead, I don't know how much. Even without GRE, you should set your MTU to at least 1504 or 1508 (if you are using MPLS VPNs) because each tag, sorry... label, takes 4 bytes. Try to increase the MTU size on you LAN segments if your LAN switches/interfaces support MTUs higher than 1500. WAN links shouldn't be a problem.

Hope this helps.


Cisco Employee

Re: mpls on gre

if you interfaces does not support mtu higher than 1500, try reducing the mtu in the GRE.

Use relying on path mtu discovery will then be ok.

Others would still use a mtu of 1500.

You can also change the DF bits value to enable fragmentation for packet entering the tunnel.

Inside a route-map use the following command :

set ip df

To change the DF-bit value in the IP header, use the set ip df route-map

configuration command. To instruct the router to leave the DF-bit value

alone, use the no form of this command.

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