[c-nsp] DHCPv6-PD relay with static route insertion not working on 7609 when CE's DHCPv6 request goes through access platform's LDRA

[Frank Bulk]

Our 7609 running 12.2(33)SRE2 has been using DHCPv6-PD relay with static
router insertion (with an external DHCPv6 server) for over a year now and
it's worked quite well for customers on our access platform.  The 7609
snoops the DHCPv6 responses and builds the static route like it's supposed
to.

Sep 27 14:02:46.714 CDT: IPv6 DHCP: Received SOLICIT from
FE80::5ED9:98FF:FE64:6823 on Vlan10
Sep 27 14:02:46.714 CDT: IPv6 DHCP_RELAY: Relaying SOLICIT from
FE80::5ED9:98FF:FE64:6823 on Vlan10
Sep 27 14:02:46.714 CDT: IPv6 DHCP_RELAY: Packet forwarded to <stripped>
Sep 27 14:02:46.714 CDT: IPv6 DHCP: Sending RELAY-FORWARD to <stripped> on
Vlan3
Sep 27 14:02:46.714 CDT: IPv6 DHCP: Received RELAY-REPLY from <stripped> on
Vlan3
Sep 27 14:02:46.714 CDT: IPv6 DHCP_RELAY: Relaying RELAY-REPLY from
<stripped> on Vlan3
Sep 27 14:02:46.714 CDT: IPv6 DHCP_RELAY: Packet forwarded to
FE80::5ED9:98FF:FE64:6823 via Vlan10
Sep 27 14:02:46.714 CDT: IPv6 DHCP: Sending ADVERTISE to
FE80::5ED9:98FF:FE64:6823 on Vlan10
Sep 27 14:02:47.726 CDT: IPv6 DHCP: Received REQUEST from
FE80::5ED9:98FF:FE64:6823 on Vlan10
Sep 27 14:02:47.726 CDT: IPv6 DHCP_RELAY: Relaying REQUEST from
FE80::5ED9:98FF:FE64:6823 on Vlan10
Sep 27 14:02:47.726 CDT: IPv6 DHCP_RELAY: Packet forwarded to <stripped>
Sep 27 14:02:47.726 CDT: IPv6 DHCP: Sending RELAY-FORWARD to <stripped> on
Vlan3
Sep 27 14:02:47.726 CDT: IPv6 DHCP: Received RELAY-REPLY from <stripped> on
Vlan3
Sep 27 14:02:47.726 CDT: IPv6 DHCP_RELAY: Relaying RELAY-REPLY from
<stripped> on Vlan3
Sep 27 14:02:47.726 CDT: [DHCPv6 Relay]IPv6RT[default]: static, Route add
<stripped>:1000:F800::/56 [new 1/0]
Sep 27 14:02:47.726 CDT: [DHCPv6 Relay]IPv6RT[default]: static, Added path
FE80::5ED9:98FF:FE64:6823/Vlan10
Sep 27 14:02:47.726 CDT: IPv6 DHCP_RELAY: Route added:
<stripped>:1000:F800::/56 via FE80::5ED9:98FF:FE64:6823 dist 1 ia id
08646823 lifetime 43200
Sep 27 14:02:47.726 CDT: IPv6 DHCP_RELAY: Packet forwarded to
FE80::5ED9:98FF:FE64:6823 via Vlan10
Sep 27 14:02:47.726 CDT: IPv6 DHCP: Sending REPLY to
FE80::5ED9:98FF:FE64:6823 on Vlan10

Our access platform vendor has a new major release that we're testing on a
lab shelf that now adds LDRA support.  We noticed that we could receive a
IPv6 address and delegated prefix on our CE, but had no routability.  Using
the same Cisco debug commands that gave me the output above, I could see
that no static routes were being added.

I did some packet sniffing between the access platform and the 7609 and I
could see that the access platform's LDRA added an Interface-ID (option 18),
Remote Identifier (option 37), and of course the original DHCP request
(option 9).  Now the access platform's LDRA must not mangle it so badly
because our 7609 does relay it to the external DHCPv6 server and relays back
its response, but the 7609 is not inserting a static route.  Hence no
routability between CE and the 7609.

Has anyone run into this before, and if so, what needs to be done?  I tried
chasing down the "dhcp snoop trusted" route, but it seems to be IPv4 only.
Perhaps I ran into a limitation of this rendition code and it's addressed in
a future release, but my google-fu has not uncovered anything.  There's some
talk about DHCPv6 relay chaining support in 15.x, but it doesn't explicitly
say it's needed to get static route insertion working again.

Any assistance would be helpful.

Regards,

Frank