[Kea-users] KEA bind issue

[Mayank Tiwari]

Hi,

  I have a kea kubernetes pod which we need to redeploy in few scenarios.
At rare times I have seen following issue:
2020-07-10 16:11:02.655 WARN  [kea-dhcp6.dhcpsrv/1]
DHCPSRV_OPEN_SOCKET_FAIL failed to open socket: Failed to open unicast
socket on  interface bond0, reason: Failed to bind socket 15 to
fec0:xxxx:yyy:3::17/port=547: Address not available
2020-07-10 16:11:02.668 INFO  [kea-dhcp6.dhcp6/1] DHCP6_STARTED Kea DHCPv6
server version 1.7.3 started

when this issue happens kea is running but since bind failed it will get
any incoming DHCP packets.

  The "Address not available" maps to binding error EADDRNOTAVAIL. This
particular connection is UDP. However, when I look for this error for TCP I
got following explanation in one place:


```
After connection close, Connections will go in TIME_WAIT state for some
time.

During this state if any new connections comes with same IP and PORT, if
SO_REUSEADDR is not provided during socket creation then socket bind() will
fail with error EADDRINUSE.

But even though after providing SO_REUSEADDR also sockect connect() may
fail with error EADDRNOTAVAIL if tcp timestamp is not enable on both side.

Solution: Please enable tcp timestamp on both side client and server.

echo 1 > /proc/sys/net/ipv4/tcp_timestamps
```

However this won't be applicable for us as our scenario is UDP.

  Please let me know if there are any inputs to handle this scenario in
kea. Some options I can think of and need to explore:
1. Introduce delay in bringing up kea with some value greater
than TIME_WAIT. However I need to explore on how to get value of TIME_WAIT
2. Explore tcp equivalent for UDP which if set in OS will ensure that this
scenario will not happen


  Please let me know your inputs from kea perspective which can solve this
problem.

Thanks and Regards,
Mayank
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