ipv4 mtu (BNG)
To set the maximum transmission unit (MTU) size of IPv4 packets sent on an interface, use the ipv4 mtu command in an appropriate configuration mode. To restore the default MTU size, use the no form of this command.
ipv4 mtu bytes
Syntax Description
bytes |
MTU in bytes. Range is 68 to 65535 bytes for IPv4 packets. The maximum MTU size that can be set on an interface depends on the interface medium. |
Command Default
If no MTU size is configured for IPv4 packets sent on an interface, the interface derives the MTU from the Layer 2 MTU.
Command Modes
Interface configuration (for releases prior to R4.2.0)
Dynamic template configuration (for releases R4.2.0 onward)
Command History
Release |
Modification |
---|---|
Release 3.7.2 |
This command was introduced. |
Release 4.2.0 |
This command was supported in the dynamic template configuration mode for BNG. |
Usage Guidelines
The router punts the packets that needs fragmentation; whereas the software path drops the subscriber traffic that needs fragmentation.
The maximum MTU size that can be set on an interface depends on the interface medium. If the Layer 2 MTU is smaller than the Layer 3 MTU, the Cisco IOS XR software uses the Layer 2 MTU value for the Layer 3 MTU. Conversely, if the Layer 3 MTU is smaller than the Layer 2 MTU, the software uses Layer 3 MTU value. In other words the Cisco IOS XR software uses the lower of the two values for the MTU.
All devices on a physical medium must have the same protocol MTU to operate.
For releases R4.2.0 onward, to enter the dynamic template configuration mode, run the dynamic-template command in the Global Configuration mode.
Note |
Changing the MTU value (with the mtu interface configuration command) can affect the IPv4 MTU value. If the current IPv4 MTU value is the same as the MTU value, and you change the MTU value, the IPv4 MTU value will be modified automatically to match the new MTU. However, the reverse is not true; changing the IPv4 MTU value has no effect on the value for the mtu command. |
Task ID
Task ID |
Operations |
---|---|
ipv4 |
read, write |
network |
read, write |
config-services |
read, write |
Examples
For releases prior to R4.2.0, this example shows how to set the maximum IPv4 packet size for GigabitEthernet interface 0/1/1/0 to 300 bytes:
RP/0/RSP0/CPU0:router(config)# interface gigabitethernet 0/1/1/0
RP/0/RSP0/CPU0:router(config-if)# ipv4 mtu 300
For releases R4.2.0 onward, this example shows how to set the maximum IPv4 packet size to 300 bytes in dynamic template configuration mode:
RP/0/RSP0/CPU0:router# configure
RP/0/RSP0/CPU0:router(config)# dynamic-template type ppp p1
RP/0/RSP0/CPU0:router(config-dynamic-template-type)# ipv4 mtu 300