Thu May 08, 2014 1:25 am
Hi, I came upon this exact problem, it ended up being the upstream DHCP server. Upon a DHCP "renew" request, the upstream server was returning the assigned IP address only, the server did not return additional information such as subnet mask etc.
This ended up being a known bug in Cisco's DHCP proxy service on there ASR9K running ios-xr4.3.4
As the DHCPACK was not "correct" according to the Mikrotik, the router would go through a full rebind, which causes the interface to completely loose its current IP address etc, which then causes routes to dis-appear which then causes TCP connections to die (due to the router sending icml unreachable messages...)
I tried a Cisco 887 instead of the Mikrotik, when I was experiencing this problem, this is the log entry i was getting:
*Apr 14 00:26:33.732: DHCP: Lease Seconds: 600
*Apr 14 00:26:33.732: DHCP: Server ID Option: 203.94.52.1
*Apr 14 00:26:33.732: DHCP: ack received without mandatory subnet mask.
Please contact the DHCP server administrator to upgrade the DHCP server.
*Apr 14 00:26:44.720: DHCP: Client socket is closed
*Apr 14 00:28:25.720: DHCP: Client socket is opened
I also found that cheap modems did not have any issue.
I would try and capture the DHCPACK pkt, and confirm that all the fields are correct.
cheers