Reassembly function

LNS reassembly is implemented through a generic IPv4 reassembly function that can be shared across multiple ISAs in a nat-group. The same ISA can be independently part of an lns-group and a nat-group.

Traffic that needs to be reassembled is steered to the nat-group via filters. After the fragmented traffic is in the nat-group, it is reassembled and injected back within the same routing context to the lns-group for further L2TP processing.

The configuration steps, along with corresponding CLI syntax examples, are as follows:

  1. Configure two isa groups, a nat-group providing generic reassembly function and a lns-group providing the L2TP services. The ISAs can be shared amongst the groups, or they can be separated per each group:

    configure
    isa
        nat-group 1
            active-mda-limit 2
            mda 1/1
            mda 1/1
        lns-group 1
            mda 1/1
            mda 1/2

  2. Configure redirection of the L2TP traffic to the nat-group performing reassembly:

    configure
    filter
        ip-filter 10
            entry 5
                match 
                    dst-ip 10.10.10.10  - traffic classification criteria ; in this case LNS tunnel endpoint.
                action reassemble 
            default-action forward

  3. Apply ‛reassembly’ filter on the incoming L2TP traffic:

    configure
    router
        interface  from-lac 
            address 10.0.0.1/24
                port 2/2/2
                    ingress
                    filter ip 10

  4. Associate the reassembly context with the same service where LNS is configured:

    configure
    service
        vprn 10
            reassembly-group 1 
                l2tp
                    group "lns-vrf-10" create 
                    ppp
                    authentication-policy "lns"
                    proxy-authentication
                    proxy-lcp
                    tunnel "lns-test-tunnel" create
                    lns-group 1
                    no shutdown
                    
                subscriber-interface "int1" create
                    address 10.20.20.254/24
                    group-interface "lns-grp-10" lns create
                    sap-parameters
                    sub-sla-mgmt
                    sub-ident-policy "sub-ident"
                dhcp
                    server 192.168.1.1 
                    trusted
                    client-applications ppp
                    gi-address 10.20.20.1
Parent topic: LNS reassembly