show iap table long should show the BID, if you have configured a distributed DHCP server on the IAP.
BID can be seen in the following logs:
IAP#show log vpn-tunnel
controller:
(Controller) #show logging level verbose
(Controller) (config) #logging level debugging system process iapmgr
After debugging remove via, (Controller) (config) #no logging level debugging system process iapmgr
to check logs on controller:
(Controller) #show log system 500 | include IAP <- use include to avoid chatty kernel level logs
Jan 25 12:37:50 :342006: <DBUG> |IAP manager Pro| papi_rcv_cb, Recvd auth Message
Jan 25 12:37:50 :342005: <DBUG> |IAP manager Pro| handle_iap_up:109 !!!new IAP branch up with inner IP 172.16.1.101
Jan 25 12:37:50 :342005: <DBUG> |IAP manager Pro| handle_auth_msg:729 tip ac100165
Jan 25 12:37:55 :342005: <DBUG> |IAP manager Pro| rx_raw_message:624 MASTER received reg-req, going to process itself
Jan 25 12:37:55 :342005: <DBUG> |IAP manager Pro| register_iap_bid:313 switch_role is 2
Jan 25 12:37:55 :342005: <DBUG> |IAP manager Pro| register_iap_bid:349 Jan 25 12:37:55 :342005: <DBUG> |IAP manager Pro| register_iap_bid:381 Received from IAP - key='8339f2a0015feed8e090cbb79f3a7ae9204eed130c095af3ec'; ip='172.16.1.101'; mac_addr='aca31ec2d596'; subnet_count='0'; back_up='no';trusted_branch=no
Adding in inrIPandBrnchID ip 172.16.1.101 brkey 8339f2a0015feed8e090cbb79f3a7ae9204eed130c095af3ec
Jan 25 12:37:55 :342005: <DBUG> |IAP manager Pro| handle_iap_dpp_branch_add: new branch 8339f2a0015feed8e090cbb79f3a7ae9204eed130c095af3ec/172.16.1.101
Jan 25 12:37:55 :342005: <DBUG> |IAP manager Pro| handle_iap_dpp_branch_add: added branch 8339f2a0015feed8e090cbb79f3a7ae9204eed130c095af3ec
however out of curiosity. why are you going for distributed L2. The same aim can be fulfilled via CL2 and DL3. Do you really want the same subnet/layer 2 domain, on all the sites?