MySQL connection via auxiliary network card

sneakyimp

I'm dealing with two dedicated servers hosted at liquidweb. The basic idea is that one machine might not be enough to handle the traffic at launch so we have a second machine to shoulder the MySQL duties -- it seemed a natural way to divy up computation burdens.

The support staff at LW tells me that each machine has three network cards
1) Public-facing NIC through which all public visitors are served
2) NIC on LAN so that liquidweb can access the machine locally for maintenance and support
3) Third NIC so that the two machines can speak to each other rapidly on their own private network. Apparently the two machines are connected via crossover cable.

It's my understanding that machine 1 has IP of 192.168.0.1 on this third card and machine 2 has IP of 192.168.0.2 on its third card. For some reason, these machines cannot speak to each other using ping, telnet, ssh, http, or MySQL.

I've contacted tech support about this issue but was wondering how I might be sure that the MySQL traffic transits the third network card on each machine. I'm guessing that it's just a matter of using the third card's IP addresses but want to be sure. Is there any way to specify a NIC when connecting via MySQL ?

bradgrafelman

The way you'd specify a NIC is simply by specifying the target IP address.

Presumably, the 2nd and 3rd NIC's are on separate subnets, meaning that when your server attempts to locate 192.168.0.2, it's route table forces the connection to be made on the 3rd NIC.

dalecosp

What does netstat -nr give you, particularly in regard to the 192.168.0 network?

Firewall on/off, unknown?

I assume you've verified that these IP addresses are indeed set on the interfaces.

dalecosp

Also, if you have shell access, ping could help you (I'm assuming Linux/Unix? It might also in Windows, but I use ping less there and it doesn't seem as featureful as the 'Nix version).

If you have firewall issues on your machine (machine 1), you will get a "permission denied" reply. You might get "no route to host", which would indicate problems in the routing tables.

Like I said, with shell access, a competent 'Nix admin should be able to test firewall, interface settings, and routing tables within a few minutes; I'm not saying it has to be one of these problems, but they're top suspects based on your description of the issue.

dalecosp

And, sorry to keep jumping in here ... I suppose it's possible that MySQL on box 2 isn't actually listening on the right interface. Might be worth a look. If you can get into box 2, something like netstat -anf inet might be worth looking at.