Hi all,
Some time ago I encountered an issue where APs could not establish capwap tunnel with the AC after upgrade to V2R7 and remain in an idle state, in V2R6 the APs were in a normal state.
So I wanted to share with you all the cases I encountered hoping that it might help if you have a similar situation.
In this topology, the DHCP server was not in the same network as the APS so option 43 was needed to send the IP of the AC when giving the APs IP address.
While checking the configuration on AC and the DHCP server we noticed a miss-match between capwap source configured on AC and option 43 IP configured on the DHCP server.
On AC:
#
capwap source ip-address 172.20.227.254
#
On DHCP server(Linux):
subnet 172.20.224.128 netmask 255.255.255.128
range 172.20.224.129 172.20.224.251;
option routers 172.20.224.254;
option subnet-mask 255.255.255.128;
option serverip 03:0E:31:37:32:2E:32:30:2E:32:35:35:2E:31:30:39;
dhcp serveroption 43 [ sub-option sub-code ] { asciiascii-string | hex hex-string | ip-address ip-address &<1-8> }
If you convert from Hex to ASCII 31:37:32:2E:32:30:2E:32:35:35:2E:31:30:39 you will get the IP address 172.20.255.109, not the capwap source configured on AC but the IP configured as VRRP IP for a VLAN if.
For the conversion tool, you can check the following link: https://www.rapidtables.com/convert/number/ascii-hex-bin-dec-converter.html
The reason it worked before the upgrade is that in software version V2R6 and bellow in order for an AP to establish capwap tunnel with AC it was needed for the option 43 IP to be any IP found on the AC, so when the AP made the request for capwap tunnel to the AC, the AC would recognize that its a capwap request on one of his IPs and reply to the AP with the correct capwap IP.
In software version V2R7 and above if the AC receives a request for capwap tunnel establishment from a different IP then the configured capwap source the AC will drop the packet and as a result, the APs will not be able to establish the capwap tunnel and remain in idle state.
In order to solve this issue we changed the Linux DHCP server configuration like below:
option serverip 03:0E:31:37:32:2E:32:30:2E:32:32:37:2E:32:35:34;
31:37:32:2E:32:30:2E:32:32:37:2E:32:35:34 in decimal is 172.20.227.254.
I hope you've enjoyed reading this case.
