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Alias Interfaces Timing Out

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7 replies

by taminato

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I have a linux RedHat 7.2 box acting as a router. This box has two NICs. NIC 1 is connected to the Internet with 3 IP addresses. The gateway IP from the ISP and two aliased routable IPs for two webservers. NIC 2 is connected to the internal network with 192.168.1.1 address. The problem is when there has not been traffic going through the physical NIC 1 going out to the Internet for a period of maybe a couple of hours the aliased IPs are completely inaccessible from the Internet. Hence noone can access the two websites unless someone within the 192.168.1.0 network is accessing the Internet or someone is pinging the router IP address from the Internet.

Has anyone experienced this before or know what the issue is?

Thanks.

7 replies

by ryan

Just to recap, you've got:

-On the external interface
One nic, using ip aliases to answer for 3 addresses. One that you're internal network looks like when it is going out the door (ipmasq), and two that have static routes to web servers on the 192.168.1 network.
What are you using to get this done? ipportfw? what tools? Just curious because there are a bunch of ways to get it done.
Regardless, it sounds like it was working at one time and has quit - right? If that's the case, what are you plugged into upstream? If a router, then you might want to ask someone to check the arp table on it. I've had issues in the past where I'm trying to set up a previously used IP on a new box and couldn't seem to get anywhere and it turned out to be that the next hop had an old mac addressed listed for this IP in its cache.
If what you're looking at isn't that involved, and you're just looking for a way to get web (tcp80) traffic to these two web servers...

Leave the threeaddresses on the external interface and go snag rinetd. http://www.suse.de/~grimmer/rinetd/rinetd.html
It is a very simple tcp port redirector. Very nice for simple tcp protocols.

-goat

by taminato

Goat, Nice try.

I'm using IPTABLES to accomplish the routing. It is the Alias Network Interfaces which I am asking about. It seems when there is no traffic through the primary Inet NIC (which is also aliases to two other IPs for webservers) theother two webservers are inaccessible.

by ryan

Ah, I think I got it. Wow, that's a nice one...

Okay, off the top of my head, I'm not sure. However, here's what I'd be digging into if it were on my network:

1. Double check IP configuration for all three IPs on the external interface. Make sure that subnetting is correctly set up for all of those. Bad subnetting information can be sneaky in its symptoms.

2. Check the upstream (read: Internet) router. I.E. the next hop up from the RedHat box. Is it having arp table "issues". Is there another machine on the external side anywhere that might be telling the world that it has the IP of one of your interfaces - sending out arp and it wins when you've been quite for some time?

3. Can you ping from any of the three IPs to another? You'll have to bust out ol 'man ping' to find out how to specify which interface to send packets out. More than likely "-I", but memory doesn't always serve me well.

4. Check power saving "features" in the BIOS. Turn those bad boys off, if you're running a server. Just my opinion.

That's about it 'off the top of my head'. I hope something in there helps. Would be interested in hearing more about this too.

-goat

by servermonkey

Did you turn off advanded power management in the bios and in the os? APM will screw with you in ways you never imagined.

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