Cisco Support Community
cancel
Showing results for 
Search instead for 
Did you mean: 
Community Member

MTU on FE/GigE trunk ports

Is setting the 'mpls mtu' sufficient for increasing the MTU size for tagged packets or do I need to modify the MTU on the master interface also ? We are using trunking (dot1q) as well.

Also, once I've set the mpls MTU, will I need to go to all the ethernet switches and configure jumbo frame support ?

What the max MTU size I should set ?

Thanks for any help.

= K

1 ACCEPTED SOLUTION

Accepted Solutions
Cisco Employee

Re: MTU on FE/GigE trunk ports

Because of the penultimate hop popping behavior the IGP lable would most likely be an implicit null (unless you change the default behavior) leaving you with only your service label (assuming that you are doing MPLS VPN).

Harold Ritter
Sr. Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México
Paseo de la Reforma 222
Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México
3 REPLIES
Cisco Employee

Re: MTU on FE/GigE trunk ports

From the router perspective, setting the "mpls mtu" is all you need.

You need to make sure the switch is configured to support baby giants. The following URL can help you with that task.

http://www.cisco.com/en/US/products/hw/switches/ps700/products_configuration_example09186a008010edab.shtml

Tha maximum MTU you should set is dependent on what type of MPLS application you are running (number of labels involved). It is safe though to set it to 1524, which would basically allow you to hold 6 labels (more than you really need bu won't hurt).

Hope this helps,

Harold Ritter
Sr. Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México
Paseo de la Reforma 222
Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México
Community Member

Re: MTU on FE/GigE trunk ports

Thanks for the note.

Now it turns out that I've got an issue with my Cat4000 switches not being able to support baby-giants. Argh.

I may be able to use the suggested work-around by enabling trunking to allow for an extra 4 bytes. (1 label)

If all my MPLS tag-switched interfaces are in the same subnet, it's likely 1 label is all I'm going to need right ?

= K

Cisco Employee

Re: MTU on FE/GigE trunk ports

Because of the penultimate hop popping behavior the IGP lable would most likely be an implicit null (unless you change the default behavior) leaving you with only your service label (assuming that you are doing MPLS VPN).

Harold Ritter
Sr. Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México
Paseo de la Reforma 222
Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México
249
Views
0
Helpful
3
Replies
CreatePlease to create content