[Kea-users] missing Relay-reply encapsulation on UDP Leasequery

[Martin Volf]

Hello,

I would like to use the Kea DHCPv6 server in a Broadband Network Gateway 
(BNG) environment utilizing Cisco ASR routers.

Kea Version: 3.0.4
OS: Alpine Linux 3.23.5
Relay Agent / Requester: Cisco ASR 1002-HX (IOS XE)
Backend Database: memfile (persist: true, store-extended-info: true)

I have encountered an issue with the UDP Leasequery implementation that 
prevents the BNG from successfully querying and restoring subscriber 
sessions: the UDP Leasequery-reply is missing Relay-reply encapsulation.

When our BNG receives a data packet for an unknown subscriber IPv6 
prefix, it attempts a Data-Triggered Leasequery via UDP to restore the 
session. Since the Cisco ASR acts as a DHCP Relay Agent, it sends the 
Leasequery encapsulated within a Relay-forward message.

Kea correctly receives the Relay-forward message, processes the inner 
Leasequery, finds the active lease, but incorrectly replies directly 
with a bare Leasequery-reply sent to the Relay Agent's link address.

Because Kea omits the Relay-reply envelope, the Cisco ASR drops the 
packet as malformed and unexpected in the relay context. The router 
expects a Relay-reply structure to match its initial Relay-forward query.

Is it a missing feature in libdhcp_lease_query.so or a bug in our 
configuration?

Thank you for your assistance. Please let me know if you need more 
information.

Best regards,

Martin Volf