Cabletron Systems 9032578-05 manual Configuring Jumbo Frames

Chapter 8: IP Routing Configuration Guide

Configuring Jumbo Frames

Certain SSR line cards support jumbo frames (frames larger than the standard Ethernet frame size of 1518 bytes). See Appendix A for more information about features supported on line cards.

To transmit frames of up to 65535 octets, you increase the maximum transmission unit (MTU) size from the default of 1500. You must set the MTU at the port level with the port set mtu command. You can also set the MTU at the IP interface level; if you set the MTU at the IP interface level, the MTU size must be less than the size configured for each port in the interface. Note that the interface MTU only determines the size of the packets that are forwarded in software.

In the following example, the ports gi.3.1 through gi.3.8 are configured with an MTU size of 65535 octets. Ports gi.3.1 through gi.3.4 are configured to be part of the interface ‘int3,’ with an MTU size of 65000 octets.

ssr(config)# port set gi.3.1-8 mtu 65535 ssr(config)# vlan create JUMBO1 ip ssr(config)# vlan add ports gi.3.1-4 to JUMBO1

ssr(config)# interface create ip int3 mtu 50000 address-mask 10.20.3.42/24 vlan JUMBO1

If you do not set the MTU at the interface level, the actual MTU of the interface is the lowest MTU configured for a port in the interface. In the following example, port gi.3.1 is configured with an MTU size of 50022 octets while ports gi.3.2-8 are configured with an MTU size of 65535 octets. The interface MTU will be 50000 octets (50022 octets minus 22 octets of link layer overhead).

ssr(config)# port set gi.3.1 mtu 50022 ssr(config)# port set gi.3.2-8 mtu 65535 ssr(config)# vlan create JUMBO1 ip ssr(config)# vlan add ports gi.3.1-4 to JUMBO1

ssr(config)# interface create ip int3 address-mask 10.20.3.42/24 vlan JUMBO1

80 SmartSwitch Router User Reference Manual