MTU / IP MTU / MPLS MTU / TAG-SWITCHING MTU

[enriquebs]

Could someone explain each command meaning and the differences between them?

Thanks a lot in advance

[attrgautam]

MTU is the header size + L2 header

IP MTU is the layer 3 header alone.

MPLS MTU= Tag-Switching mtu is the MTU needed along a LSP to carry through MPLS Lables imposed.

[enriquebs]

Thanks a lot for clarify it!

Regards,

[balajitvk]

Hi,

MTU = representing interface mtu for all packets.

IP MTU = To set the maximum transmission unit (MTU) size of IP packets sent on an interface,

MPLS MTU = To set the per-interface Multiprotocol Label Switching (MPLS) maximum transmission unit (MTU) for labeled packets,

For example, to transport an IPv4 packet of 1500 bytes from the edge through an MPLS core, you need an MPLS MTU of at least 1504 bytes. This value accounts for the single 4-byte label and avoids fragmentation. Use the following calculation to determine the MTU:

MPLS MTU = edge MTU + (label stack * 4 bytes)

Simillarly, Changing the interface MTU value (using the mtu interface configuration command) can affect the MPLS MTU of the interface. If the MPLS MTU value is the same as the interface MTU value (this is the default), and you change the interface MTU value, the MPLS MTU value will automatically be set to this new MTU as well. However, the reverse is not true; changing the MPLS MTU value has no effect on the interface MTU.

TAG-SWITCHING MTU same as mpls mtu,

Using the tag switching forms of the commands allows older software that supports tag switching commands, but not new MPLS commands, to successfully interpret interface configurations.

Rate if this will helps,

Rgs

[enriquebs]

OK another perfect explanation! one more thing, if I apply this commands on an interface basis are all of them inherits by the subinterfaces?

[balajitvk]

Hi,

Yes it will inherit automatically.

Note that subinterfaces support a value that is different from the main interface as long as the main interface's value is as large as, or larger than the largest subinterface MTU.

Hope this will hepls,

Rgs