Dual NIC Cards 2006-04-14 - By Rick Stevens
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On Fri, 2006-04-14 at 11:02 -0700, Rick Stevens wrote:
> On Thu, 2006-04-13 at 23:18 -0600, karlp@(protected) wrote:
> > On Thu, April 13, 2006 10:41 pm, Bret Stern said:
> > >
> > > I have dual network cards in a new box
> > > i'm putting together. Fedora 4
> >
> > Me, too.
>
> I have machines with up to 6.
>
> > > Both cards are set to activate on boot, but
> > > only one starts on boot. The other will start
> > > manually.
> >
> > Mine both start on boot.
> >
> > >
> > > One card has a static ip.
> > > One card gets assigned an ip address (dhcp)
> >
> > I assigned static IPs to both. That may be why one of yours doesn't start.
> > Is the one that starts the static or DHCP assigned nic?
> >
> > >
> > > Can both cards have the same hostname?
> > > (go ahead have fun with that question)
> >
> > They have to have the same hostname. I don't see an option in the gui setup
> > to give a different hostname for each card.
>
> Ah, fertile ground for misunderstandings. You must keep in mind that
> there are differences between hostnames, nodenames and FQDNs (fully
> qualified domain names).
>
> A machine can only have one hostname (as displayed by "hostname" or
> "uname -n"), and is the true hostname. By default, it's "localhost" or
> the FQDN "localhost.localdomain".
>
> A machine _may_ have a nodename under NIS/NIS+ and is set and displayed
> by the "domainname" command. Unless you run NIS/NIS+, you needn't worry
> about this, and if you do run it, 95 times out of 100 you'll set it to
> be the same as the hostname.
>
> Now, each IP address on the machine _may_ have a FQDN associated with
> it, but it's not required. Each FQDN can have a number of DNS aliases
> associated with it (called CNAMEs in DNS parlance).
>
> Confused yet?
>
> > > I've heard you can only have a gateway address
> > > on one nic card. Is this correct?
> >
> > Yes, it's correct.
>
> Uhm, this must be clarified. There is only one _default_ gateway, and
> that is the "route of last resort". In other words, if you try to send
> traffic to a node that is not on a network directly connected to one of
> your NICs (as determined by the IP address/netmask combination) AND you
> don't have a route forcing traffic for the remote node's network through
> one of your NICs, THEN the traffic goes out the default gateway. If you
> do have a route for the network, it goes out the NIC that has that
> route.
>
> As an example, assume a machine with two NICs. eth0 has an IP of
> 192.168.0.2. eth1 has an IP of 10.0.0.2. The default gateway is
> 192.168.0.1 (obviously on eth1).
DOH! That should read "(obviously on eth0)." That's what happens when
your boss is talking to you while you compose responses!
>
> Now, let's say you try to ping 10.24.1.1. The traffic will go out eth0,
> since the default gateway (actually, the default route) is on eth0.
> However, you really want any traffic for 10.0.0.0/8 to go out on eth1.
> You set up a static route:
>
> route add -net 10.0.0.0 netmask 255.0.0.0 dev eth1
>
> Now, any traffic for the 10.0.0.0/8 network will go out eth1. You
> can repeat that for as many networks (or hosts, if the netmask is /32)
> as you wish on each NIC (well, up to some practical limit).
>
> -- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- --
> - Rick Stevens, Senior Systems Engineer rstevens@(protected) -
> - VitalStream, Inc. http://www.vitalstream.com -
> - -
> - If this is the first day of the rest of my life... -
> - I'm in BIG trouble! -
> -- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- --
>
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-- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- --
- Rick Stevens, Senior Systems Engineer rstevens@(protected) -
- VitalStream, Inc. http://www.vitalstream.com -
- -
- IGNORE that man behind the keyboard! -
- - The Wizard of OS -
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