Chapter 8: IP Routing Configuration Guide80 SmartSwitch Router User Reference ManualConfiguring Jumbo FramesCertain SSR line cards support jumbo frames (frames larger than the standard Ethernetframe size of 1518 bytes). See Appendix A for more information about features supportedon 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 portset mtu command. You can also set the MTU at the IP interface level; if you set the MTU atthe IP interface level, the MTU size must be less than the size configured for each port inthe interface. Note that the interface MTU only determines the size of the packets that areforwarded in software.In the following example, the ports gi.3.1 through gi.3.8 are configured with an MTU sizeof 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.If you do not set the MTU at the interface level, the actual MTU of the interface is thelowest MTU configured for a port in the interface. In the following example, port gi.3.1 isconfigured with an MTU size of 50022 octets while ports gi.3.2-8 are configured with anMTU size of 65535 octets. The interface MTU will be 50000 octets (50022 octets minus 22octets of link layer overhead).ssr(config)# port set gi.3.1-8 mtu 65535ssr(config)# vlan create JUMBO1 ipssr(config)# vlan add ports gi.3.1-4 to JUMBO1ssr(config)# interface create ip int3 mtu 50000 address-mask 10.20.3.42/24vlan JUMBO1ssr(config)# port set gi.3.1 mtu 50022ssr(config)# port set gi.3.2-8 mtu 65535ssr(config)# vlan create JUMBO1 ipssr(config)# vlan add ports gi.3.1-4 to JUMBO1ssr(config)# interface create ip int3 address-mask 10.20.3.42/24 vlan JUMBO1
