Exchange ActiveSync Monitor fails with read:errno=104

Just in case anyone stumbles across this, we have it fixed now. Exchange 2013 has its own health monitor and the local loopback addresses (127.0.0.1 and ::1) need to be in the IP filter list for the ActiveSync pool. If not, Exchange won't be able to poll it and mark the pool down and then the F5 monitor goes down as well. Hamish was right on the money with the meaning of error 104 (log from Exchange):

Fields: date time c-ip c-port s-ip s-port cs-version cs-method cs-uri sc-status s-siteid s-reason s-queuename

2014-01-22 17:58:03 192.168.1.2 43567 192.168.1.22 443 HTTP/1.1 GET /Microsoft-Server-Activesync/healthcheck.htm - 1 Connection_Dropped MSExchangeSyncAppPool

2014-01-22 17:58:03 192.168.1.2 43587 192.168.1.22 443 HTTP/1.1 GET /Microsoft-Server-Activesync/healthcheck.htm - 1 Connection_Dropped MSExchangeSyncAppPool

2014-01-22 17:58:03 192.168.1.3 48812 192.168.1.22 443 HTTP/1.1 GET /Microsoft-Server-Activesync/healthcheck.htm - 1 Connection_Dropped MSExchangeSyncAppPool