Configuring MRRU on Multilink and Link Services Logical Interfaces
The maximum received reconstructed unit (MRRU) is similar to a maximum transmission unit (MTU), but applies only to multilink bundles; it is the maximum packet size that the multilink interface can process. By default, the MRRU is set to 1500 bytes; you can configure a different MRRU value if the peer equipment allows this. The MRRU accounts for the original payload, for example the Layer 3 protocol payload, but does not include the 2-byte PPP header or the additional MLPPP or MLFR header applied while the individual multilink packets are traversing separate links in the bundle.
To configure a different MRRU value, include the mrru statement:
You can include this statement at the following hierarchy levels:
- [edit interfaces interface-name unit logical-unit-number]
- [edit logical-systems logical-system-name interfaces interface-name unit logical-unit-number]
For link services interfaces, you also can configure a different MRRU at the physical interface level by including the mrru statement at the [edit interfaces ls-fpc/pic/port:channel mlfr-uni-nni-bundle-options] hierarchy level:
The MRRU size can range from 1500 through 4500 bytes.
 | Note: If you set the MRRU on a bundle to a value larger than the MTU of the individual links within it, you must enable a fragmentation threshold for that bundle. Set the threshold to a value no larger than the smallest MTU of any link included in the bundle. Determine the appropriate MTU size for the bundle by ensuring that the MTU size does not exceed the sum of the encapsulation overhead and the MTU sizes for the links in the bundle. |
You can configure separate family mtu values on the following protocol families under bundle interfaces: inet, inet6, iso, and mpls. If not configured, the default value of 1500 is used on all except for mpls configurations, in which the value 1488 is used.
| Note: The effective family MTU might be different from the MTU value specified for MLPPP configurations, because it is adjusted downward by the remote MRRU’s constraints. The remote MRRU configuration is not supported on M120 routers. |
