Routing

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  • 1.  dhcpv6 relay and demux0

    Posted 08-23-2023 13:51

    I have an MX204 acting as a PPPoE BNG and I recently setup an eth sub-interface that is within a VRF and has a dhcp and dhcpv6 relay configuration.  This is functioning, however I noticed that the MX is creating a demux0 interface for the dhcpv6 subscriber when they come online.  I have other MX204s that are NOT PPPoE BNGs thus do not have "subscriber-management" enabled and they are not doing this.

    So my question is: is there anyway to force the MX to not create a demux0 interface for each dhcp subscriber and instead just share the underlying eth sub-if?

    The reason that this apparently matters is because v6 is not functioning correctly as a result.  I have router-advertisements enabled on the sub-interface for the v6 prefix and when the clients send an RS, the MX is not seeing them.  The "Solicits received" in "show ipv6 router-advertisements" is staying at 0.  I've done some troubleshooting and the issue seems to be the demux0 interface being created.  I believe those RS messages are arriving internally on the demux rather than the eth sub-interface itself.

    Every client on the eth sub-if is sharing a v4 /24 and a v6 /64 and the dhcp server is sending each client a PD.  For v4, I am using forward-only and for v6 I am tracking the binding so that the /56 PD route can be tracked and installed in the FIB.  I want the MX to act as a very basic DHCP helper relay and not do any demux logic.  The shaping and authentication is handled on a downstream fiber OLT.

    Again this config works completely fine with no demux0 being created in all  my other MX204s that do not have subscriber-management enabled, so I'm trying to figure out how to replicate that behavior on this MX which is currently acting as a PPPoE BNG on other interfaces.

    Here is the routing-instance configuration:

    instance-type vrf;
    routing-options {
        auto-export;
    }
    forwarding-options {
        dhcp-relay {
            dhcpv6 {
                group all {
                    active-server-group grp1;
                    interface et-0/0/0.200;
                }
                server-group {
                    grp1 {
                        <hidden>
                    }
                }
            }
            server-group {
                grp1 {
                    10.192.32.2;
                    10.192.32.6;
                }
            }
            group all {
                active-server-group grp1;
                overrides {
                    trust-option-82;
                }
                forward-only;
                interface et-0/0/0.200;
            }
        }
    }
    interface et-0/0/0.200;
    route-distinguisher <hidden>:702;
    vrf-import CGN-INET-2-IMPORT;
    vrf-export CGN-INET-2-EXPORT;
    vrf-table-label;