Linux - SecurityThis forum is for all security related questions.
Questions, tips, system compromises, firewalls, etc. are all included here.
Notices
Welcome to LinuxQuestions.org, a friendly and active Linux Community.
You are currently viewing LQ as a guest. By joining our community you will have the ability to post topics, receive our newsletter, use the advanced search, subscribe to threads and access many other special features. Registration is quick, simple and absolutely free. Join our community today!
Note that registered members see fewer ads, and ContentLink is completely disabled once you log in.
If you have any problems with the registration process or your account login, please contact us. If you need to reset your password, click here.
Having a problem logging in? Please visit this page to clear all LQ-related cookies.
Get a virtual cloud desktop with the Linux distro that you want in less than five minutes with Shells! With over 10 pre-installed distros to choose from, the worry-free installation life is here! Whether you are a digital nomad or just looking for flexibility, Shells can put your Linux machine on the device that you want to use.
Exclusive for LQ members, get up to 45% off per month. Click here for more info.
A few days ago my server suddenly went offline out of the blue, after over a year of uptime. RHEL 4. I could get the ISP to ping it from the switch, but from outside the subnet ping requests were being ignored. The machine was up and running, and when I got to the console I noticed a few "Neighbour table overflow" entries on the console.
After a few hours of struggling, I eventually found that the default route in the routing table was incorrectly set to the IP of the server and not the IP of the gateway. So all packets to the subnet were getting out, but no others. My /etc/sysconfig/network file had an incorrectly set GATEWAY setting, which must have been there since I installed over a year ago (the date of the file pretty much confirms this), and I must have adjusted the routing tables by hand.
I can only think that for some reason the routing tables where suddenly reloaded, and the incorrect gateway was loaded from the /etc/sysconfig/network file. Does anyone know why this might have happened?
I think it's pretty unlikely that I've been hacked (although always possible). The firewall is configured well, very few ports open, and there seem to be no other signs of a hack - I would have expected more than a routing table change / reload in that case.
What could cause the reload? IPTables throwing a wobbly? TCP stack? Kernel? Malicious packets, ICMP or otherwise?
Yeah, good idea, but the machine is in a data centre and had been up for over a year...
The interesting this is that if I hadn't incorrectly configured the /etc/sysconfig/network file, I would never have known that the routing tables were reloaded - OK, to be accurate, I'm *assuming* they were reloaded, as that's not recorded in the logs AFAIK... It's the only explanation I have for why the default route was suddenly incorrect.
LinuxQuestions.org is looking for people interested in writing
Editorials, Articles, Reviews, and more. If you'd like to contribute
content, let us know.