VLAN MTU size on the SG500x

[sg500user]

I need to change the MTU size on a specific VLAN on the Cisco SG500x.  However, I don't see an option to adjust the mtu size under the VLAN interface.  How else can this be accomplished?

switchcd71c1(config)#int vlan 100
switchcd71c1(config-if)#
  bridge               Bridge configuration commands
  do                   execute an EXEC-level command
  dot1x                dot1x protocol
  end                  Exit from configure mode
  exit                 Exit from current context
  help                 Description of the interactive help system
  ip                   Global IP configuration commands
  ipv6                 IPv6 commands
  name                 set vlan name
  no                   Negate command
  private-vlan         private VLAN command
  service-acl          Apply an ACL to particular interface.
  shutdown             Shutdown the selected interface
  snmp                 SNMP
  sntp                 Global Simple Network Time Protocol (SNTP)
                       configuration subcommands
  vrrp                 Define VRRP feature

[mdobiac]

Hello sg500user,

I am sorry you are experiencing this issue. Unfortunately the SG500x and the series does not have the option to adjust MTU by VLAN or by port.  By default it is 1512 and the only option you have to increase the size is to enable Jumbo Frames.  Though I caution you before enabling Jumbo Frames globally as it may be more harmful than helpful.

Hope this helps.

Michael D.

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[sg500user]

Is enabling jumbo frames only a global command? Can it at least be set at the physical port level?

[sg500user]

it looks like I do have the option to enable "port jumbo-frame" under a VLAN or physical interface

switchcd71c1(config)#interface gigabitethernet1/16
switchcd71c1(config-if)#port jumbo-frame

However, once I configure it the port jumbo-frame shows up in the global config and not under the interface I configured it for.   

I don't want to have this applied to every port.  Can you confirm if that is an option?  Or why do I have the option of configuring it under an interface if its really a global setting?

[mdobiac]

Hello sg500user,

The command port jumbo-frame actually enables the jumbo frames globally on the device.

From the CLI guide:  The following example enables jumbo frames on the device.
switchxxxxxx(config)# port jumbo-frame

From the admin guide:  Port Settings The Port Settings page displays the global and per port setting of all the ports. This page enables you to select and configure the desired ports from the Edit Port Settings page. To configure port settings:

STEP 1 Click Port Management > Port Settings.

STEP 2 Select Jumbo Frames to support packets of up to 10 Kb in size. If Jumbo Frames is not enabled (default), the system supports packet size up to 2,000 bytes. For jumbo frames to take effect, the device must be rebooted after the feature is enabled.

STEP 3 Click Apply to update the global setting. Jumbo frames configuration changes take effect only after the Running Configuration is explicitly saved to the Startup Configuration File using the Copy/ Save Configuration page, and the device is rebooted.

Link to the Admin guide:  http://www.cisco.com/c/dam/en/us/td/docs/switches/lan/csbms/Sx500/administration_guide/500_Series_Admin_Guide.pdf

Jumbo frames are strictly a global command on the switch and it can only be enabled or disabled.

Hope this helps,

Michael D.

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[sg500user]

That's disappointing to hear.  I have my uplink port from this switch go directly to the ISP's switch. They will not configure jumbo frames on their side.

1. I assume there is no way to exclude a port to have jumbo frames on?

2. Is there a roadmap to be able to have jumbo frame at the port or VLAN level instead of the entire switch? 

[mdobiac]

Hello sg500 user,

To answer your questions:  1.  unfortunately no it is strictly global, and for question 2. I have not heard of them making changes to this at this time in regards to Jumbo frames.

If you want you can and have an entitled switch you can open a case for a feature request.  The number to call will be 1-866-606-1866.

Hope this helps,

Michael D.

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[sg500user]

Just for my understanding, in which scenario would one be able to even use jumbo frames at every port? Wouldn't every single device connected into it be required to also be configured with jumbo frames?

[mdobiac]

Hello sg500user,

This document can explain more information in regards to Jumbo Frames:  http://www.smallnetbuilder.com/lanwan/lanwan-features/30201-need-to-know-jumbo-frames-in-small-networks.

But as long as you have all you devices that can support Jumbo frames and on a full Gigabit network you can enable jumbo frames globally.

Hope this helps,

Michael D.

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[sg500user]

That is my exact issue. I have DRAC ports which are only 100 mbps connections. I assume jumbo frames would prevent those ports from working?

[mdobiac]

Hello sg500user,

If it accepts the traffic it would be fragmented which will degrade throughput and then only until the interface can no longer handle the ingress/egress traffic.

Regards,

Michael D.

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