Is it possible to set mtu size by vlan on 3750E?

[jawill47ec]

In support of a SAN setup, I would like to set a specific mtu size per vlan.  I don't see a mtu parm under the interface vlan sub-commands.  I am able to set the system mtu jumbo command which applies to all interfaces on the 3750E.  Upon doing this I see the following:

Vlan88 is up, line protocol is down
  Hardware is EtherSVI, address is 9caf.ca76.b4c1 (bia 90af.ca76.b4c1)
  MTU 1500 bytes, BW 1000000 Kbit, DLY 10 usec,

GigabitEthernet1/0/1 is down, line protocol is down (notconnect)
  Hardware is Gigabit Ethernet, address is 9caf.ca76.b481 (bia 90af.ca76.b481)
  MTU 9198 bytes, BW 10000 Kbit, DLY 1000 usec,

other info:

1#sh vlan mtu

VLAN    SVI_MTU    MinMTU(port)   MaxMTU(port)  MTU_Mismatch
----         -------------         -------------        ------------           ------------
1             1500                9198              9198               No

#sh system mtu

System MTU size is 1500 bytes
System Jumbo MTU size is 9198 bytes
Routing MTU size is 1500 bytes

My question is will the system mtu jumbo be inherited by the Vlan?  or is their a way to set it by Vlan?  (e.g. If the above port is part of the above vlan)

thanks

[Jon Marshall · Accepted solution]

jawill47ec wrote:
In support of a SAN setup, I would like to set a specific mtu size per vlan.  I don't see a mtu parm under the interface vlan sub-commands.  I am able to set the system mtu jumbo command which applies to all interfaces on the 3750E.  Upon doing this I see the following:
Vlan88 is up, line protocol is down
  Hardware is EtherSVI, address is 9caf.ca76.b4c1 (bia 90af.ca76.b4c1)
  MTU 1500 bytes, BW 1000000 Kbit, DLY 10 usec,
GigabitEthernet1/0/1 is down, line protocol is down (notconnect)
  Hardware is Gigabit Ethernet, address is 9caf.ca76.b481 (bia 90af.ca76.b481)
  MTU 9198 bytes, BW 10000 Kbit, DLY 1000 usec,
other info:
1#sh vlan mtu
VLAN    SVI_MTU    MinMTU(port)   MaxMTU(port)  MTU_Mismatch
----         -------------         -------------        ------------           ------------
1             1500                9198              9198               No
#sh system mtu
System MTU size is 1500 bytes
System Jumbo MTU size is 9198 bytes
Routing MTU size is 1500 bytes
My question is will the system mtu jumbo be inherited by the Vlan?  or is their a way to set it by Vlan?  (e.g. If the above port is part of the above vlan)
thanks

James

You can't set mtu on a per vlan basis on the 3750E only on a system wide basis. The vlan will not "inherit" the values as such. So when you set the mtu it applies globally to the switch.

Jon

[jawill47ec]

Jon,

Thanks for the reply.  A follow-up question.  Is the global max mtu 9198?  The reason I ask is in comparison to another vendor switch which this 3750E is replacing supported per interface mtu up to 9216.

thanks,

james

[Reza Sharifi · Accepted solution]

Hi James,

From a 3750-E config

For Layer-3 is 9000

Switch-B(config)#system mtu routing ?
  <1500-9000>  MTU size in bytes

Switch-B(config)#system mtu routing

For Layer-2 is 9198

Switch-B(config)#system mtu jumbo ?
  <1500-9198>  Jumbo MTU size in bytes

Switch-B(config)#system mtu jumbo

HTH

Reza