Dual NIC Cards

Sat Apr 15 01:47:55 UTC 2006

> -----Original Message-----
> From: redhat-install-list-bounces at redhat.com
> [mailto:redhat-install-list-bounces at redhat.com]On Behalf Of Rick Stevens
> Sent: Friday, April 14, 2006 10:18 AM
> To: Getting started with Red Hat Linux
> Subject: Re: Dual NIC Cards
>
>
> On Fri, 2006-04-14 at 11:02 -0700, Rick Stevens wrote:
> > On Thu, 2006-04-13 at 23:18 -0600, karlp at ourldsfamily.com 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!
>

So you only assign a gateway entry to ONE of the nic cards?
> >
> > 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 at vitalstream.com -
> > - 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 at vitalstream.com -
> - VitalStream, Inc.                       http://www.vitalstream.com -
> -                                                                    -
> -                 IGNORE that man behind the keyboard!               -
> -                                                - The Wizard of OS  -
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