Media for Cisco 1700

Cisco 1700

I have a cisco 1700 running IOS 12.1(8). It is running as the gateway between us and our ISP They have given me the username/password for the

1700 and I am trying to setup a deny for port 6881 in and out. But everytime i set it up it cuts our DNS. I'm at a loss. I haven't used any cisco stuff in a long time and can't seem to find out what I'm doing wrong. the command I tried was this

router(config)#access-list 110 deny tcp any any eq 6881 router(config-if)#ip access-group 110 in

and at that point our net goes down. I get cut from the telnet session i'm in and I have to reset the router. any help? I also tried:

router(config)#access-list 110 deny tcp any #.#.#.# 0.0.0.0 eq 6881 (where the # is our IP) router(config-if)#ip access-group 110 in

Please can someone help me? We are getting a flood of 6881 syn packets from a huge number of sources. At first I thought it was BitTorrent but it has been continuing for 3 days now and I have checked every machine and we have no BT clients running.