Jun 27

How does the MTU configuration work on a Cisco Catalyst 6500

Catalyst 6500 Jumbo frame MTU Configuration

The CAT6500 has to have the MTU set in a couple places for everything to work with Jumbo Frames.

1. Global setting needs to be added
# system jumbomtu <# in Bytes> –> This command sets the maximum MTU for the switch in bytes.

2. Physical Interface
# mtu <# in Bytes> –> If the packet is smaller then the number here, it can pass, otherwise it’s dropped and marked as a giant.

3. Switch Virtual Interface (SVI)
# mtu <# in Bytes> –> If a packet is routed off of the subnet, this command sets the maximum size for a packet. If the packet is larger then the MTU value the packet would be sent to the CPU to be fragmented.

Always read the configuration guide for your version of software and hardware. Jumbo frames are not supported on all CAT6500 line cards and the config may change a bit based on the version.

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