After deploying a new mail server/internet gateway (behind a firewall) I found a similar problem with packets being stopped by our firewall. After performing an nslookup on the "offending" IP address I found it belonged to our ISP. On querying them about this odd behavior the explanation given (and other evidence seems to bear this out) was that our mail server was performing DNS lookups for the delivery of mail and on behalf of our internal network as it was configured as a forwarder because it was behind a firewall. The IP address in question was merely replying to DNS queries which had been forwarded to it by our ISPs' primary DNS server and as the firewall would only allow DNS replies through from certain IP addresses it was stopping any others. The incrementing of the source ports you are seeing is due to the fact that when the DNS reply is not acknowledged by the target system it tries again on the next available port. It is only usually a minor inconvenience (although the other day one server filled my firewall log 4 times and I was alerted to possible port scans a number of times during the day). If it bothers you too much try filtering the logs to remove the offending entries or you can allow all port 53 traffic in (unless like me you suffer from paranoid delusions that everyone on the internet is out to get you). -----Original Message----- From: Ronald Belchez [mailto:meukoneat_private] Sent: 04 June 2003 22:14 To: incidentsat_private Subject: strange traffic on UDP port 53 Hi All, We don't have a firewall and is just relying on Access-list on our border router. After i applied the new access-list I am continously receiving the logs showed below. The destination IP is our mail server (not running any DNS service) while the source IP (unsolicited and using source port with some sort of incremental patterm, the denied packets logs is also continuous now for about 4 days) I am not aware of any trojan or worm using the below. I already tried searching google but cannot find the explanation or something that might help me understand the below.... Please advise. --logs starts here--- denied udp XX7.Y3.71.242(54067) -> XX3.Y1.246.66(53), 1 packet denied udp XX7.Y3.71.242(54070) -> XX3.Y1.246.66(53), 1 packet denied udp XX7.Y3.71.242(53967) -> XX3.Y1.246.66(53), 2 packets denied udp XX7.Y3.71.242(53972) -> XX3.Y1.246.66(53), 2 packets denied udp XX7.Y3.71.242(53979) -> XX3.Y1.246.66(53), 2 packets denied udp XX7.Y3.71.242(53989) -> XX3.Y1.246.66(53), 2 packets denied udp XX7.Y3.71.242(54003) -> XX3.Y1.246.66(53), 2 packets denied udp XX7.Y3.71.242(53982) -> XX3.Y1.246.66(53), 34 packets denied udp XX7.Y3.71.242(54009) -> XX3.Y1.246.66(53), 2 packets denied udp XX7.Y3.71.242(54027) -> XX3.Y1.246.66(53), 2 packets denied udp XX7.Y3.71.242(54035) -> XX3.Y1.246.66(53), 2 packets denied udp XX7.Y3.71.242(54042) -> XX3.Y1.246.66(53), 2 packets ------------------------------------------------------------------------ ---- ------------------------------------------------------------------------ ---- ##################################################################################### Note: This message is for the named person's use only. It may contain confidential, proprietary or legally privileged information. No confidentiality or privilege is waived or lost by any mistransmission. If you receive this message in error, please immediately delete it and all copies of it from your system, destroy any hard copies of it and notify the sender. You must not, directly or indirectly, use, disclose, distribute, print, or copy any part of this message if you are not the intended recipient. Coen Holdings Ltd. and any of its subsidiaries each reserve the right to monitor all e-mail communications through its networks. Any views expressed in this message are those of the individual sender, except where the message states otherwise and the sender is authorized to state them to be the views of any such entity. Thank You. ##################################################################################### ---------------------------------------------------------------------------- ----------------------------------------------------------------------------
This archive was generated by hypermail 2b30 : Fri Jun 06 2003 - 09:09:12 PDT