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louis0001
Participant

MPLS MTU - should I set it?

Hi, we have an ISP provided private MPLS network. We've left the MTU on the CE MPLS interface as default ie 1500.

Reading around these forums, it seems that you can increase this to prevent fragmentation?

Should I do this or leave it at it's default? Everything seems to be working fine although if we can squeeze a little bit more performance out of it by avoiding fragmentation, the better.

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balaji.bandi
VIP Expert

best practice leave it as it is, you can tweak but it is monitoring practice to check every day..see anything impacting yes or no..so on..............dedicated job for engineer.

 

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lespejel
Participant

hello

as everything in life,  it depends; you should leave it, your question is for CE, and the MPLS MTU applies on the MPLS cloud; assuming your CE is using 1500 on customer side and MPLS on ISP side, the ISP side interface should accommodate extra bytes for MPLS header without your change.

Now, some devices support larger MTU like 9200, but if you want to go that way it's a change for the ISP, and then you should adjust your enterprise side accordingly to take advantage of the new MTU, which will be a non standard MTU on your side, but it works for some environments as data centers.

 

briefly, you don't have to change it.

 

https://www.cisco.com/c/en/us/td/docs/switches/datacenter/sw/nx-os/mpls/configuration/guide/mpls_cg/mp_l2vpn_atom.html

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Elvin Arias Soto
Cisco Employee

I recommend you to do an analysis on the customer's applications that you have, if you there is no gain on increasing MTU, then there is no value on changing it, but if your applications are sending baby giants and devices are doing fragmentation, then increasing MTU through the path up to the CE would be a a big gain.

As others mentioned, it really depends on each particular network.

Elvin
Virendra Pratap
Beginner

hi

you should increase MPLS MTU in MPLS cloud to reduce fragmentation . this will reduce packet travelling time in SP network hence throughput will increase.

Deniz AYDIN
Beginner

Whats the MTU supported by the ISP?

You may increase your MPLS MTU for MPLS packets to a value of (ISP MTU - number of labels you are using X 4) as expected. You may first need to change interface MTU.

 

But the mpls mtu command effects is different for some platforms;

https://www.cisco.com/c/en/us/td/docs/ios/12_2sb/feature/guide/newmtu.html

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