Foundry Configuration Guide for the FESX, FSX, and FWSX
16 - 22
© Foundry Networks, Inc.
December 2005
jumbo frame (and the frame does not have the DF bit set), the device fragments the frame into 1500-byte
fragments, even if the outbound port has a larger MTU. For example, if a port has an MTU setting of 8000
and receives an 8000-byte frame, then must forward the frame onto a port with an MTU of 4000, the device
does not fragment the 8000-byte frame into two 4000-byte frames. Instead, the device fragments the 8000-
byte frame into six fragments (five 1500-byte fragments and a final, smaller fragment.)
Globally Changing the Maximum Transmission Unit (MTU)
The Maximum Transmission Unit (MTU) is the maximum size an IP packet can be when encapsulated in a Layer 2
packet. If an IP packet is larger than the MTU allowed by the Layer 2 packet, the Layer 3 Switch fragments the IP
packet into multiple parts that will fit into the Layer 2 packets, and sends the parts of the fragmented IP packet
separately, in different Layer 2 packets. The device that receives the multiple fragments of the IP packet
reassembles the fragments into the original packet.
You can increase the MTU size to accommodate jumbo packet sizes up to 9216 bytes.
To globally enable jumbo support on all ports of an X-Series device, enter commands such as the following:
FESX424 Router(config)# jumbo
FESX424 Router(config)# write memory
FESX424 Router(config)# end
FESX424 Router# reload
Syntax:
[no] jumbo
The above commands configure the Foundry device to forward Ethernet frames that are up to 9216 bytes long.
NOTE:
You must save the configuration change and then reload the software to place the jumbo support into
effect.
Changing the Maximum Transmission Unit on an Individual Port
By default, the maximum Ethernet MTU sizes are as follows:
•
1500 bytes – The maximum for Ethernet II encapsulation
•
1492 bytes – The maximum for SNAP encapsulation
When jumbo mode is enabled, the maximum Ethernet MTU sizes are as follows:
•
9216 bytes – The maximum for Ethernet II encapsulation
•
9216 bytes – The maximum for SNAP encapsulation
NOTE:
If you set the MTU of a port to a value lower than the global MTU and from 576 – 1499, the port
fragments the packets. However, if the port’s MTU is exactly 1500 and this is larger than the global MTU, the port
drops the packets.
NOTE:
You must save the configuration change and then reload the software to place the jumbo support into
effect.
To change the MTU for interface 1/5 to 1000, enter the following commands:
FastIron SuperX Router(config)# int e 1/5
FastIron SuperX Router(config-if-1/5)# ip mtu 1000
FastIron SuperX Router(config-if-1/5)# write memory
FastIron SuperX Router(config-if-1/5)# end
FastIron SuperX Router# reload
Syntax:
[no] ip mtu <num>
Содержание FastIron Edge Switch X424
Страница 36: ...Foundry Configuration Guide for the FESX FSX and FWSX 2 12 Foundry Networks Inc December 2005...
Страница 56: ...Foundry Configuration Guide for the FESX FSX and FWSX 3 20 Foundry Networks Inc December 2005...
Страница 70: ...Foundry Configuration Guide for the FESX FSX and FWSX 4 14 Foundry Networks Inc December 2005...
Страница 198: ...Foundry Configuration Guide for the FESX FSX and FWSX 8 38 Foundry Networks Inc December 2005...
Страница 316: ...Foundry Configuration Guide for the FESX FSX and FWSX 12 26 Foundry Networks Inc December 2005...
Страница 334: ...Foundry Configuration Guide for the FESX FSX and FWSX 13 18 Foundry Networks Inc December 22 2005...
Страница 350: ...Foundry Configuration Guide for the FESX FSX and FWSX 15 12 Foundry Networks Inc December 2005...
Страница 458: ...Foundry Configuration Guide for the FESX FSX and FWSX 18 18 Foundry Networks Inc December 2005...
Страница 712: ...Foundry Configuration Guide for the FESX FSX and FWSX 22 32 Foundry Networks Inc December 2005...
Страница 760: ...Foundry Configuration Guide for the FESX FSX and FWSX A 34 Foundry Networks Inc December 2005...
Страница 796: ...Foundry Configuration Guide for the FESX FSX and FWSX C 18 Foundry Networks Inc December 2005...
Страница 820: ...Foundry Configuration Guide for the FESX FSX and FWSX E 10 Foundry Networks Inc December 2005...