MTUnIPMTU

[ncnaveen_arasu]

Hi Team,

What is the diddrence between MTU and IP MTU

PFA, in that MTU can be configured to

<1500-9216>  MTU size in bytes

IP MTU can be configured to

  <68-1500>  MTU (bytes)

and even for sub interface i could not able to change the MTU alone without changing MTU for physical interface.

% Interface GigabitEthernet0/0/3.6 does not support user settable mtu.

So please explain how ca we fix this.

Thanks & Regards,

Naveen

[Joseph W. Doherty]

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Posting

MTU applies to the physical interface.

IP MTU applies to IP packets.

It's possible you could have IP and something like (Novell's) IPX using the same interface and you might want to restrict the size of IP packets but not IPX packets.

[Jan Hrnko]

Hi Naveen,

MTU

Each interface (based on technology) have its minimum and maximum supported size of PDU(protocol data unit), for example:

Ethernet  - 1500B

Token Ring - 4464B

ATM - 4470B

FDDI - 4352B

IP MTU

Sets the maximum size of IP packet.

and even for sub interface i could not able to change the MTU alone without changing MTU for physical interface.
% Interface GigabitEthernet0/0/3.6 does not support user settable mtu.

Setting MTU is possible only on the physical interface, then it applies to all subinterfaces. After all, this makes sense.

Best regards,

Jan

[ncnaveen_arasu]

HI Jan,

Thanks for your reply,

If MTU is 1500 bytes and if IP MTU is 1600 bytes, How it works.

[Jan Hrnko]

Hi Naveen,

If MTU is 1500 bytes and if IP MTU is 1600 bytes, How it works.

If this is the case, IP packet must be fragmented before sent by such interface. They need to be "cut" to more pieces of 1500B or less to make it over that link.

And even MTU of an Ethernet can be set to 1600 bytes right ?

Maximum ethernet MTU is 1500B.

If your interface supports giant frames or jumbo frames the payload can be as big as 9000B. But standard ethernet MTU is only 1500B.

Best regards,

Jan

[ncnaveen_arasu]

And even MTU of an Ethernet can be set to 1600 bytes right ?