Reassembly

Reassembly of L2oGRE over IPv4 transport is supported through a generic reassembly function that requires a vISA. Filters redirect fragmented traffic, as it enters the VSR node, to a vISA. After the traffic is reassembled in the vISA, it is re-inserted into the vFP where normal processing continues, as if the non-fragmented traffic had originally entered the node.

Perform the steps in Table 1 to configure reassembly for L2oGRE.

Table 1. Configuration Steps for L2oGRE Reassembly
Step	Example CLI	Comments
1. Create a NAT-group that contains MS-ISAs	`configure isa nat-group 1` `mda 1/1`	The reassembly function is performed in a NAT group that contains a vISA.
2. Reference a reassembly-group that is used for traffic in the base routing context	`configure router` `reassembly-group 1`	The reassembly-group that is used for traffic in the base routing context is identified. Upon reassembly, traffic is re-inserted in the same base routing context. The reassembly-group id corresponds to the nat-group id (in this case, the ID is 1).
3. Identify and direct fragmented traffic to the reassembly function	`configure filter ip-filter <id>` `default-action forward` `entry <id> create` `match protocol gre` `fragment true` `exit` `action reassemble` `exit`	Fragmented GRE traffic is identified using a filter and is then redirected to the reassembly function. This filter must be applied to all ingress interfaces on which GRE traffic is expected to arrive.