The IPv4 maximum transmission unit (MTU) is the maximum length of an IPv4 packet that a Layer 2 frame can contain. IP MTU is supported only on Layer 3 interfaces such as VE port or router port.
If an IPv4 packet is larger than the MTU allowed by the frame, the device fragments the IP packet into multiple parts that fit into frames, and sends the parts of the fragmented IP packet in separate frames. The device that receives the multiple fragments of the IP packet reassembles these fragments into the original packet. The default IPv4 MTU is 1500 bytes for Ethernet II packets.
There are limitations on MTU. The following table lists the MTU Profile Counts for various devices.
| Platform | L3 MTU Profile Count | Description |
|---|---|---|
| SLX 9150/SLX 9250 | 8 | 1 Default MTU (1500), 7 user-defined profiles |
| SLX 9540/SLX 9640 | 3 | 1 Default MTU (1500), 2 user-defined profiles |
| SLX 9740 | 7 | 1 Default MTU (1500), 5 user-defined profiles, 1 GRE Tunnel (1476) |
%Error: Maximum limit of allowed different IP MTUs reached.
You can increase the MTU to reduce packet fragmentation. However, MTU cannot be higher than the maximum frame size, minus 18. For more information, see IPv4 MTU and Maximum Frame Size.
The device supports hardware forwarding for unicast jumbo packets that are received on a port that supports the frame's MTU size and are forwarded to another port that also supports the frame's MTU size.
Note
For multicast data traffic, frames are not fragmented and the IP MTU setting is ignored.