MTU commands flavors

nightdreamer0

Hello all, i would like your help in understanding the differenet types of MTUs in IOS CLI. I have searched a lot but found nowhere a straight answer.

#mtu

This is the mtu for the physical interface,correct? Does this mean that all L2 overhead is excluded? E.g for non-tagged ethernet we have 14 bytes for header + 24 bytes for others = 38 bytes/packet total overhead. So is this value maximum 1500, having as a result  1538 bytes totally transmitted?

#ip mtu

Does this include IP header (20 bytes)?

#mpls mtu

I dont know what this includes

Any help is very welcome!

davidrothera

Rather than writing out basically the same information:

http://thenetworksherpa.com/ospf-master-the-mtu-madness/

David

On Monday, 25 February 2013 at 13:41, nightdreamer0 wrote:

Hello all, i would like your help in understanding the differenet types of MTUs in IOS CLI. I have searched a lot but found nowhere a straight answer.

#mtu

This is the mtu for the physical interface,correct? Does this mean that all L2 overhead is excluded? E.g for non-tagged ethernet we have 14 bytes for header + 24 bytes for others = 38 bytes/packet total overhead. So is this value maximum 1500, having as a result  1538 bytes totally transmitted?

#ip mtu

Does this include IP header (20 bytes)?

#mpls mtu

I dont know what this includes

Any help is very welcome!

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nightdreamer0

Thanks for the link. So if i understood correctly, the mtu command excludes all L2 overhead.For ethernet is 1500 bytes/packet. Do you know what will be the final length for a non-tagged frame? Here says that it is 1538

http://sd.wareonearth.com/~phil/net/overhead/

ip mtu is the maximum ip packet size allowed (this includes ip header). Beyond that,we will have fragmentation. Correct?

Still, not sure how mpls mtu is correlated to the above

 

 

davidrothera

Usually 1514 as it doesn't count the FCS in the calculation.

-- 

David Rothera

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M: 07584060207

W: networkbroadcast.co.uk

On Monday, 25 February 2013 at 15:50, nightdreamer0 wrote:

Thanks for the link. So if i understood correctly, the mtu command excludes all L2 overhead.For ethernet is 1500 bytes/packet. Do you know what will be the final length for a non-tagged frame? Here says that it is 1538

http://sd.wareonearth.com/~phil/net/overhead/

ip mtu is the maximum ip packet size allowed (this includes ip header). Beyond that,we will have fragmentation. Correct?

Still, not sure how mpls mtu is correlated to the above

 

 

INE - The Industry Leader in CCIE Preparation

http://www.INE.com



Subscription information may be found at:

http://www.ieoc.com/forums/ForumSubscriptions.aspx