L2oGRE reassembly for IPv4 transport is supported through a generic reassembly function that requires an MS-ISA. As fragmented traffic enters an SR OS node, it is redirected to an MS-ISA via filters. When the traffic is reassembled in the MS-ISA, it is re-inserted into the forwarding complex where normal processing continues (as if the non-fragmented traffic originally entered the node).
Table: Configuring reassembly for GRE describes the configuration steps to support reassembly for GRE.
| Step | Example CLI | Comments |
|---|---|---|
Creation of a NAT-group that contains MS-ISAs |
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The reassembly function is performed in a NAT group that contains one or more MS-ISAs. |
Referencing a reassembly group that is used for traffic in the Base routing context |
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Identification of the reassembly group that is used for traffic in the Base routing context. Upon reassembly, traffic is re-inserted in the same (Base) routing context. Reassembly group ID corresponds to the NAT group ID (in this case 1). There can be multiple NAT groups (reassembly groups) configured in the system and this command identifies the reassembly group that is used in the Base routing context. |
Identifying and directing fragmented traffic to the reassembly function. |
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Fragmented GRE traffic is identified via a filter and redirected to the reassembly function. This filter must be applied to all ingress interfaces on which GRE traffic is expected to arrive. |