I set up a lab DHCP server with 20 minutes’ clients lease duration. I also run Wireshark at this server with capture filter on client IP address 10.11.11.2. We can see client does DHCPREQ and received DHCPACK every 50% of lease time duration which is every 10 minutes or 600 seconds.
DHCP capture
So the problem is NOT with the DHCP server at user home router. RAP renews at ½ DHCP duration, but still reboots every 20 minutes that correlates with DHCP duration.
We know that RAP is the VPN tunnel that requires two IP addresses, the interface IP address (interface br0) configures at user home router, and the tunnel IP address (tun0) configures at controller l2tp local IPSEC pool. I observe that every time RAP reboots, the interface br0 IP address does NOT change but the interface tun0 IP address changes.
(LAB) #show ap debug log ap-name TN-Test | include reboot
Sep 8 14:45:15 nanny[1855]: <303022> <WARN> |AP TN-Test@172.31.50.155 nanny| ^[reason AP rebooted Sun Sep 8 14:41:29 CDT 2019; Unable to get IP address using DHCP after 10 tries, total DHCP retry:10 ]
(LAB) #show ap debug system-status ap-name TN-Test
Output omit ...
…
ifconfig output for br0
-----------------------
br0 Link encap:Ethernet HWaddr
---------------------------------------------------------
inet addr:10.11.11.2 Bcast:10.11.11.255 Mask:255.255.255.0
inet6 addr: fe80::224c:3ff:fe0f:2ec/64 Scope:Link
UP BROADCAST RUNNING ALLMULTI MULTICAST MTU:1500 Metric:1
RX packets:3165 errors:0 dropped:13 overruns:0 frame:0
TX packets:793 errors:0 dropped:49 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:0 (0.0 B) TX bytes:0 (0.0 B)
Rx broadcast packet:2 Rx broadcast packet per second:0
Rx multicast packet:2155 Rx multicast packet per second:9
Tx broadcast packet:2 Tx broadcast packet per second:0
Tx multicast packet:47 Tx multicast packet per second:0
ifconfig output for tun0
------------------------
tun0 Link encap:UNSPEC HWaddr 00-00-00-00-00-00-00-00-00-00-00-00-00-00-00 -00
-------------------------------------------------------------------------------- -----
inet addr:172.31.50.155 P-t-P:172.31.50.155 Mask:255.255.255.255
UP POINTOPOINT RUNNING NOARP MULTICAST MTU:1300 Metric:1
RX packets:2130 errors:0 dropped:0 overruns:0 frame:0
TX packets:726 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:64
RX bytes:280476 (273.9 KiB) TX bytes:142961 (139.6 KiB)
I'll open TAC case and update with any resolution.