This feature is supported only on the 7210 SAS-Mxp.
The 7210 SAS does not support native IP fragmentation for IP packets that exceed the configured MTU. However, in situations where IP fragmentation is necessary, the CPM can be configured to extract oversized IPv4 packets from the datapath, fragment them using the system CPU, and insert the fragmented packets back into the datapath.
Run the configure system ip allow-cpu-fragmentation command to enable IP fragmentation. See the 7210 SAS-Mxp, R6, R12, S, Sx, T Basic System Configuration Guide for more information about this command.
CPU-fragmented packets are subject to additional delay when compared to non-fragmented datapath forwarded packets.
IP fragmentation in the CPM CPU competes for CPU cycles as a low-priority task. The number of fragmentations at any given time is limited to ensure system performance.
Even when IP fragmentation is enabled, packets that exceed the configured MTU are dropped if the Do not Fragment (DF) bit is set in the IP header.
IP fragmentation on the 7210 SAS is supported in the following contexts:
network IP interface
IES including R-VPLS
On R-VPLS interfaces, the decision to fragment a packet is based on the egress port MTU and the fragment size is determined by the service MTU.