1500 packet size in Ethernet over MPLS over GRE without fragement

[driss JABBAR]

Hello

our customer need to pass a 1500 packet size  with df set between  2 site connected via Ethernet over MPLS over GRE

i configured  the interface connecting the ASRs between them r with the max MTU value but it doesn't work.

[blau grana]

Hello driss,

Ask your customer what is the max MTU which will pass the link, with that information we can deduce where can be problem.

Best Regards

Please rate helpful posts and close solved questions

[driss JABBAR]

The Max MTU size can pass throught the SP L2L solution is 1476

[Alessio Andreoli · Accepted solution]

Hi driss,
Remember that IOS XR and regular IOS have a different way to compute the mtu. Make sure that the mtu value matches between the ends. Having said this, you should also consider how the p routers are set. However, common sp design is to filter a too big packet on the ingress PE routers. Honestly, 1500 bytes of payload without the layer two info with the df bit set is quite a challenge. Can't your customer reduce it to 1450 for example? You would have some margin for the layer 2+GRE info and MPLS encapsulation you need.


Alessio

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[driss JABBAR]

Hi Alessio

i agree with you about MTU at the SP side because  i tested the link using a ping with 1500 bit and df bit set without passing via ASRs and it doesn't pass,so i asked our customer to call SP in ordre to fix the MTU problem.

I monitored the behavior of the application with and without using the ASR and I found that there is a change in TCP sessions.

the first Image is a sniff when we used ASRs and the second is without ASRs