Security Basics mailing list archives
RE: What could this icmp mean?
From: "Pablo Moore" <pemoore () fedex com>
Date: Thu, 24 Feb 2005 16:12:47 -0600
It looks like 10.30.1.16 may have a default route to 10.30.1.254 if it can't find something. Your next hop from 10.30.0.1 should have been 10.30.1.1 to get to the 10.30.1.0 subnet. I have no idea why you're getting a bad checksum. It could be as simple as a faulty cable causing this, or as complex as the two routers fighting over half/full duplex mode. Also, if you have "do not fragment" turned on, you may be killing your VPN connection. Just my humble opinion. Paul Moore Security & Business Continuity FedEx Express Corporation -----Original Message----- From: Tomas [mailto:s.tomas () gmail com] Sent: Tuesday, February 22, 2005 7:11 AM To: security-basics () securityfocus com Subject: What could this icmp mean? Hello list, We have networks (10.30.0.0/24 and 10.30.1.0/24) connected trough VPN and one internet line. The gateways for VPN are 10.30.0.1 from one side and 10.30.1.1 from the other, and 10.30.1.254 for internet (for both networks). I've launched tcpdump today on my internet firewall's internal interface (10.30.1.254) and I found this: 10.30.1.254 > 10.30.1.16: icmp: redirect 10.30.0.4 to host 10.30.1.1 for 10.30.1.16.445 > 10.30.0.4.1959: [|tcp] (DF) (ttl 127, id 7691, bad cksum c76d! differs by 100) (ttl 255, id 23807) I'm a bit confused, what could this icmp mean? First of all, I'm sure that neither of these hosts (10.30.1.254, 10.30.1.16, 10.30.0.4) are sending any icmp requests (I'm not sure about 10.30.1.1; it's not in my control). And the second of all, why the checksum is bad?
Current thread:
- RE: What could this icmp mean? Pablo Moore (Feb 28)
- <Possible follow-ups>
- RE: What could this icmp mean? Andrew Shore (Feb 28)