How do you check MTU Size??

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  • Updated 5 months ago
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We are currently using an SCG200, and we are using the Default Tunnel Profile, upon checking the manual it is configured as MTU AUTO or we can manually configure it between 850-1500. Our client is asking if we have a way to check the MTU size? 
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Clifford Ray Seno

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Posted 5 months ago

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Ankush, Employee

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SCG allows maximum 1500 MTU and that basically sets the MTU on AP as 1440. You can check this from AP CLI with command “get mtu gre”.
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Clifford Ray Seno

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Hi Ankush, we are only getting 1392 when we issued the get mtu gre, what does this mean?
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Ankush, Employee

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Hi Clifford,

The MTU is negotiated between the two end points and it depends upon the path MTU. AP sends ICMP packet to the vDP every 10 minutes to discover the PMTU and if any fragmentation needed for the ICMP packet, AP reduces the gre MTU from 1440 to 1392.
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Clifford Ray Seno

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Hi Ankush,

Thanks. What is the composition  of the 60 bytes that was subtracted, 20 bytes  IP + 16 bytes Ruckus GRE(this are just assumption on my end). We want to know so we could explain to customer the 1440. 
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Ankush, Employee

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Hi Clifford,

The calculation will be Eth + IP + UDP + Ruckus GRE : 14+20+8+16 =58 . This negotiates MTU to no more than 1440.

Regards,
-Ankush




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Clifford Ray Seno

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Got it. Thank you very much.