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Change MTU on Cat4006


I have a Catalyst 4006 with a Sup2 engine, and a 6 port GigE card.

I need to change the default system MTU from 1500 to 1546 to resolve some MPLS over Ethernet issues i am having.

How do i do this?

On an IOS switch, i would use system mtu 1546, but how is this done in CatOS.

Thanks in advance



Re: Change MTU on Cat4006

Re: Change MTU on Cat4006

Catalyst 4000 Series

You can classify the Catalyst 4000 series switches into two groups in relation to jumbo or baby giant support:


Supervisor I (WS-X4012) and Supervisor 2 (WS-X4013)


Supervisor III (WS-X4014) and Supervisor IV (WS-X4515)

Supervisor I (WS-X4012) and Supervisor 2 (WS-X4013)

This group includes the WS-C2948G, WS-C2980G, and the WS-C4912G fixed-configuration switches also. Due to an ASIC limitation, there is no support for baby giants or jumbo.


As a workaround, you can enable a port for trunking in order to support baby giants. When you enable a port for 802.1q trunking, the switch automatically assumes that an extra four bytes of data are appended on, and increment the frame size of the L2 packet. Note that ISL encapsulation is not supported on these platforms.

Hence, for implementations that require exactly one tag to be carried (either 802.1q or MPLS, but not both), you can configure the port as a trunk port to force the switchport to accept an extra four bytes of data. If the port were to carry multiple VLANs for VLAN-ID tagging or 802.1p prioritization, configure the port as a 802.1q trunk. However, even if VLAN tagging is not necessary, but you want the increased four-byte support, you can configure the port as a 802.1q trunk. Change the Native VLAN to be the one desired to carry the traffic. When you do so, you can accommodate an extra four bytes of data.

No jumbo frame support on any Cat4000 based switch (which includes the 400x, switches) due to the limitation of the Cat4000 asic.

regarding the workaround above Up to a max 1522 bytes is supported on ports enabled for .1q. Anything above that will fail.

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Community Member

Re: Change MTU on Cat4006

What command is need to configure the GE ports on the SupII to support 1522 bytes??



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