Network Router User Manual

Chapter 8: IP Routing Configuration Guide
80 SmartSwitch Router User Reference Manual
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.
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.3.1-8 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
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