DELL EQUALOGIC - Cisco 3750 Switch MTU issue

[soofiahtesham]

Hello Everyone,

I am running a three stackable 3750 ( ws-c3750g-24t )switches together with version  12.2.  These swicthes are dedicated to our SAN devices

( Dell Equalogic). System MTU is set to 1500.

ISSUE :

---->  Off latetly we are seeing some performance issue on some of VM running on the blade server. However after mutlipe test Dell came back to us and suggested increasing the mtu size should be set to 9216 in size on vlan 204 ( which is dedicated for SAN devices on the network )

My Question :

-> What is the difference between the System MTU and VLAN MTU ?

-> Can I change the VLAN MTU  from current 1500 to  9216?

-> And finally, if the changes are made would it impact the communication between the other vlans ?

Please see the results from Show VLAN

VLAN Name                             Status    Ports
---- -------------------------------- --------- -------------------------------
1    default                          active    Gi3/0/3, Gi3/0/9, Gi3/0/10
                                                Gi3/0/11, Gi3/0/12, Gi3/0/21
                                                Gi3/0/22, Gi3/0/23
4    XXXX                            active   
100  XXX                              active   
109  XXXXXXXX                    active   
201  XXXXXXXX                    active   
202  XXXXXXXXX                         active   
203  XXXXXXXXX                     active   
204  SAN                              active    Gi1/0/1, Gi1/0/2, Gi1/0/3
                                                Gi1/0/4, Gi1/0/5, Gi1/0/6
                                                Gi1/0/7, Gi1/0/8, Gi1/0/9
                                                Gi1/0/10, Gi1/0/11, Gi1/0/12
                                                Gi1/0/13, Gi1/0/14, Gi1/0/16
                                                Gi1/0/17, Gi1/0/18, Gi1/0/19
                                                Gi1/0/21, Gi1/0/22, Gi1/0/23
                                                Gi2/0/1, Gi2/0/2, Gi2/0/3
                                                Gi2/0/4, Gi2/0/5, Gi2/0/6
                                                Gi2/0/7, Gi2/0/8, Gi2/0/9
                                                Gi2/0/10, Gi2/0/16, Gi2/0/17
VLAN Name                             Status    Ports
---- -------------------------------- --------- -------------------------------
                                                Gi2/0/18, Gi2/0/19, Gi2/0/21
                                                Gi2/0/22, Gi2/0/23, Gi3/0/1
                                                Gi3/0/2
208  ****XXXXXXXX***               active   
209  XXXXXXX                           active   
219  XXXXXX                        active   
220  XXXX                              active   
230  XXXXXX                  active   
263  VLAN0263                         active   
264  VLAN0264                         active   
300  VLAN0300                         active   
623  VLAN0623                         active   
1002 fddi-default                     act/unsup
1003 token-ring-default               act/unsup
1004 fddinet-default                  act/unsup
1005 trnet-default                    act/unsup

VLAN Type  SAID       MTU   Parent RingNo BridgeNo Stp  BrdgMode Trans1 Trans2
---- ----- ---------- ----- ------ ------ -------- ---- -------- ------ ------
1    enet  100001     1500  -      -      -        -    -        0      0  
VLAN Type  SAID       MTU   Parent RingNo BridgeNo Stp  BrdgMode Trans1 Trans2
---- ----- ---------- ----- ------ ------ -------- ---- -------- ------ ------
4    enet  100004     1500  -      -      -        -    -        0      0  
100  enet  100100     1500  -      -      -        -    -        0      0  
109  enet  100109     1500  -      -      -        -    -        0      0  
201  enet  100201     1500  -      -      -        -    -        0      0  
202  enet  100202     1500  -      -      -        -    -        0      0  
203  enet  100203     1500  -      -      -        -    -        0      0  
204  enet  100204     1500  -      -      -        -    -        0      0  
208  enet  100208     1500  -      -      -        -    -        0      0  
209  enet  100209     1500  -      -      -        -    -        0      0  
219  enet  100219     1500  -      -      -        -    -        0      0  
220  enet  100220     1500  -      -      -        -    -        0      0  
230  enet  100230     1500  -      -      -        -    -        0      0  
263  enet  100263     1500  -      -      -        -    -        0      0  
264  enet  100264     1500  -      -      -        -    -        0      0  
300  enet  100300     1500  -      -      -        -    -        0      0  
623  enet  100623     1500  -      -      -        -    -        0      0  
1002 fddi  101002     1500  -      -      -        -    -        0      0  
1003 tr    101003     1500  -      -      -        -    srb      0      0  
1004 fdnet 101004     1500  -      -      -        ieee -        0      0  
1005 trnet 101005     1500  -      -      -        ibm  -        0      0  
Remote SPAN VLANs
------------------------------------------------------------------------------

Primary Secondary Type              Ports
------- --------- ----------------- ------------------------------------------

Thanks For the Help!

Soofi

[Amit Aneja · Accepted solution]

Soofi,

-> What is the difference between the System MTU and VLAN MTU ?

You cannot change Vlan MTU on SVI. this is not supported. This is for physical L3 ports only.

Use the system mtu global configuration command on the switch stack or

on a standalone switch to set the maximum packet size or maximum

transmission unit (MTU) size for Gigabit Ethernet ports, for routed

ports, or for Fast Ethernet (10/100) ports.

Syntax:

system mtu {bytes | jumbo bytes | routingbytes}

      * bytes - Set the system MTU for ports that are set to 10 or 100

        Mb/s. The range is 1500 to 1998 bytes. This is the maximum MTU

        received at 10/100-Mb/s Ethernet switch ports.

      * jumbo bytes - Set the system jumbo MTU for Gigabit Ethernet

        ports operating at 1000 Mb/s or greater. The range is 1500 to

        9000 bytes. This is the maximum MTU received at the physical

        port for Gigabit Ethernet ports.

      * routing bytes - Set the maximum MTU for routed packets. You

        can also set the maximum MTU to be advertised by the routing

        protocols that support the configured MTU size. The range is

        1500 bytes to the system MTU value. The system routing MTU is

        the maximum MTU for routed packets and is also the maximum MTU

        that the switch advertises in routing updates for protocols

        such as OSPF.

When you use this command to change the system MTU or jumbo MTU size,

you must reset the switch before the new configuration takes

effect.The system mtu routing command does not require a switch reset

to take effect.

-> Can I change the VLAN MTU  from current 1500 to  9216?

http://www.cisco.com/en/US/products/hw/switches/ps700/products_configuration_example09186a008010edab.shtml#c3

It has to be system MTU, not Vlan MTU. 3750 switch doesn't support configuring MTU on per port basis.

Moreover, what SAN guys want you to do is to enable jumbo frames on the switch.

The only choice you have got is to run "system mtu jumbo 9000". 9000 is the max that this hardware can support. There are others like 4948, 6500 which support 9216.

-> And finally, if the changes are made would it impact the communication between the other vlans ?

No, it is just enabling the support for jumbo frames on the switch so that if a frame with this much size comes in, it is accepted & processed.

HTH,

Amit

Please rate if helpful

[soofiahtesham]

Amit Thanks for the response.

( so according to your response )

In this case 

-> My System MTU is set to 1500 and I can change it  to 1998 bytes ). Right ?

-> Also, Since My jumbo frame are already set to 9000  So cant beyond that .. Correct ?

Please see the result from the " Sh System MTU "

System MTU size is 1500 bytes

System Jumbo MTU size is 9000 bytes

Routing MTU size is 1500 bytes System MTU size is 1500 bytes

Regards,

Soofi