Changing MTU size ....

[S891]

Hi,

I have VLAN X with MTU 9216 on Switch-A. I also have VLAN Y with MTU 9216 on Switch-B. But not their SVIs are MTU 9216.They are not communicating to each other on packet size of above 1500. This is because SVI VLAN X and SVI VLAN Y connect to each other  through SVI VLAN Z (Point-to-point Layer-3 connection between two switches).  Although SVI VLAN X and SVI VLAN Y communicate through SVI VLAN Z, this inter-link port is a trunk port carrying other VLANs but VLAN Z is a native vlan for which SVI VLAN Z is defined.             

In order to make it work.

1. Do I need to change SVI VLAN X and SVI VLAN Y to 9216?

2. Change MTU for VLAN Z and SVI VLAN Z to 9216?

3. DO I need to change MTU sizes for other VLANs that are on TRUNK port?

In simple, how many VLANs and SVI VLANs require MTU size change? What is command to verify it , I guess it should look like this ?

ABC#sh vlan mtu

VLAN    SVI_MTU    MinMTU(port)   MaxMTU(port)  MTU_Mismatch
----          ------------- -------------  ------------  ------------

X           9216           1500 (Te1/7 )       9216 (Te1/1 )     No

why there is diffent minMTU and MaxMTU port?

Thanks

[Alessio Andreoli]

Hi Fawad,

it is not enough generally to configure the new MTU size. You need to enable the jumbo-freame feature on your platform and i am afraid that is can be sometimes platform-specific. Check the documentation of your switches/routers and you will be let them communicate (if they can) on the MTU you desire. Remember that two different VLAN require some for of layer 3 switching (inter-vlan routing) or routing to be able to communicate.

One point more you should check is the encapsulation and the tag behaviour by enabling debug events.

Hope this helps

Alessio

[S891]

Hi Alessio,

Thanks for your input. I have 6509-E switches for the entire communication.

So beside enabling vlans and svis for mtu 9216 I need to enable jumbo frame feature as well. Isn't it same thing?

Also what will happen to the other vlans on trunk between switches?

If someone could give specific answer or link it would really help !

Fawad

[S891]

Hi,

I have been told this by our Support engineer,  can any of you please confirm ?

The default system MTU in 6500-E is 9216 bytes, hence you do not need to change it.  In this case we just need to change the MTU of all SVI and physical ports taking part of this communication. And you can veirfy this in show interface command. The line card specified does support Jumpo frames.

There are two type of modules for connection.

     WS-X6708-10GE

     VS-S720-10G  Supervisor Engine

So  I do not need to enable jumbo frame feature ??

Also what about other vlans on trunk port?

Tx

Fawad