ip of my computer

bluesky · Apprentice Joined: 14 Aug 2002 Posts: 230 Location: USA

My computer is used both as router+gateway and both as server. I have dsl with dynamic ip. The computer has 2 NICs: eth0 is set to receive the dynamic ip through dhcpcd and eth1 is set as gateway. My question is:

Should I use the eth1 gateway address as the computer ip or should I create another ip (in /etc/hosts)? It seemed that both way will work and I have searched the web for this point but haven't found anything clear.

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bluesky

"free as the wind"

Lemma · Posted: Fri Jan 24, 2003 4:12 pm Post subject:

I'm not sure if I have gotten this right but as I can see the answer is that the computer will have not one but two addresses; one that is your "official", that is the one that you use when "talking" with computers outside your net, and one that you will use when acting as a part of your own network. Eth0 -> 130.238.*.* (if you are a part of the Uppsala University ;-)

) and eth1 -> 192.168.0.1 or similar as the local gateway.
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Sven Vermeulen · Posted: Fri Jan 24, 2003 4:57 pm Post subject:

You should set up your clients with gateway the eth1-ip (the static one). If you fill in the dynamic one, the internet sharing wont work anymore if the dynamic IP is changed (actually it shouldn't work in the first place since the dynamic IP isn't in your subnet).

bluesky · Apprentice Joined: 14 Aug 2002 Posts: 230 Location: USA

1. I completely agree that we can't use the dynamci ip as the computer ip address.

2. In case if I have ONLY one network to connect to then in this case I can use the ip of the gateway as the computer ip address. I also agree with this since it will work.

3. However, when I have more than one network to connect to. Let's say 2 networks then the computer will have eth1 and eth2. In this case, which ip address you will choose for the computer? :wink:

Have you follow my argument? I believe that in thsi case, I should create another ip address for the computer rather than select the ip of either eth1 or eth2?
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bluesky

"free as the wind"

Matje · Posted: Fri Jan 24, 2003 11:04 pm Post subject:

I'm presuming you use a DHCP server to distribute ip's to your clients, if not, you can just setup the computers on eth2 to use the ip of eth2 as gateway. In your dhcp.conf each of the subnets your pc is on needs to be defined, so you just define 192.168.0.x (eth1) and give it the option default-gateway 192.168.0.1, and then you define 192.168.1.x (eth2) and give it the option default gateway 192.168.1.1. I'm not sure about the option-name, as I'm not around a gw right now and am too lazy to ssh to one :-)

And about which IP to choose for your pc, I can't really follow that argument... Each and every one of your ip's points to your machine. In fact, in /etc/hosts you don't need to add an external IP, 127.0.0.1 does just fine:

Matje · Posted: Fri Jan 24, 2003 11:08 pm Post subject:

And yes, you can also add all of your IP's to that like so:

bluesky · Apprentice Joined: 14 Aug 2002 Posts: 230 Location: USA

>And about which IP to choose for your pc, I can't really follow that argument.

If you read my original post, you know that it is used as a router AND a server. A server needs an ip address. Of course, you can use either eth1's ip or eth2's ip as its ip address.

Anyway, thanks for all the interests.

:wink:

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bluesky

"free as the wind"

Naan Yaar · Bodhisattva Joined: 27 Jun 2002 Posts: 1549

An IP address is not associated with the computer but the interface. So, for a box that is a gateway, there is no "computer's ip". It has two (or more) interfaces with one address on each interface. You can also do IP aliasing to bind multiple addresses to the same interface. In fact, even without being a gateway, you have two IP addresses, the one associated with the network card and the loopback (127.0.0.1).

You may want to read the Network Administrators Guide, esp. this section.

Sven Vermeulen · Posted: Sat Jan 25, 2003 9:05 am Post subject:

I have a computer here that provides internetsharing et al, with 5 network devices (eth0-eth3, ppp0). ppp0 is the interface connected to the internet...