I have two questions regarding server networking, using Ethernet. They are as much theoretical questions as practical, and I appreciate advice both on existing software to do this, and whether it can be easily implemented but hasn't been.

Ok, 2 scenarios:

1) I have a network with a Gigabit-capable switch. Is there a way to use a server with two 10/100 cards, combine the bandwidth to the same switch, and have it effectively run 200 Mbps?

2) Failover - Server X is connected to two seperate switches on two seperate networks. The cards are eth0 and eth1 and they are both 10/100 Ethernet cards. Is there a way to configure it so that it uses eth0, but if eth0 goes down, it will (as absolutely quickly as possible) failover and use eth1?

Thanks.

1) yep, you'd use the bond module to combine them to an 802.3ad trunk.

2) you mean two seperate subnets or two connections to the same ip subnet? again the bond module can fail between two cards, but that'll abstract back to a bond0 interface, which will appear the same as the trunk option but with lower capacity. if you're wanting a non bonded approach, check linux-ha.org for a lot of useful information about heartbeat checks and such.

Chris -

My concept is this:

I want as much redundancy/fault tolerance as possible.

Is it possible to have two NIC's in one machine with the same IP?

i.e. in a simple example, I have a database program on a computer called CLIENT, and mySQL on SERVER.

I want to have one switch, called A, that is connected to eth0 in CLEINT (192.168.0.2) and eth0 in SERVER (192.168.0.3).

Then, I want a second switch, called B, that is connected to eth1 in CLIENT (also 192.168.0.2) and eth1 in SERVER (also 192.168.0.3).

The idea being, if Switch A blows up, loses power, gets run over by a spaceship, etc. CLIENT will still be able to connect to mySQL on 192.168.0.3, just going through a different set of NIC's, wires, and switch.

Does this make sense at all?

yes absolutely, so the bond module is definitely the direction to go in. this has a number of modes that change the way two (or more) nics are handled. if you're talking cisco switches, somethign like the 3750's then they do funky stacking where you can use two active nics on the server going to one port on each switch, and bond with a full 802.3ad trunk (mode 4 for bond module i think). here is one switch dies, nothign even fails over, you simply go from a 2gb (or 200mb) link down to a 1gb (or 100mb) link... that's just about as good as it gets really, but for a more basic implementation bond can manage the failover with an active/passive nic setup just fine. in fact, i think you can have an active/semi-active setup on the linux side where traffic will be pushed out of both nics but will only arp on one nic, so which two wholly seperate switches you still have nice resillient traffic flow over both switches, meaning you know they are working. if you run vlans you can even split vlans between switches further. neat stuff, but basically read the bond docs tofind the scenario that suits you best. at it's most default i think it's just a case of loading the module and it'll pick a safe a/p default and off you go.

Thanks. When I get the rest of the servers, I'll definitely look into it...

Your advice is very helpful.