Re: Two NIC's connected to same subnet: routing question
From: Henry Su (henrysu_at_nttmcl.com)
Date: 02/18/05
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- In reply to: Jon Noack: "Re: Two NIC's connected to same subnet: routing question"
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Date: Thu, 17 Feb 2005 20:16:42 -0800 (PST) To: Jon Noack <noackjr@alumni.rice.edu>
On Thu, 17 Feb 2005, Jon Noack wrote:
> Henry Su wrote:
> > You can configure both NIC as /32. You also need proxy arp installed and
> > listen on both NIC. Then the traffic should be able to follow between two
> > NICs. Since Proxy ARP always answers its MAC to clients, so the clients can
> > always send traffic to em1 or em0. Based on client's mac entry in the ARP
> > table, client to client traffic is easily transferred. Other traffic should
> > be able to direct to default gateway.
>
> I gave this a shot and failed miserably. Admittedly, I know
> little-to-nothing about arp, so hopefully it's obvious why I failed.
>
> I have this in my /etc/rc.conf:
> network_interfaces="fxp0 fxp1 lo0"
> ifconfig_fxp0="inet 10.0.0.4 netmask 255.255.255.255 link0"
> ifconfig_fxp1="inet 10.0.0.5 netmask 255.255.255.255 link0"
> defaultrouter="10.0.0.1"
>
> Created an arp table file called /etc/arp.table (built-in dual fxps so
> the macs are actually consecutive):
> 10.0.0.4 00:01:02:03:04:06 pub
> 10.0.0.5 00:01:02:03:04:05 pub
>
> And had this in /etc/rc.local:
> /usr/sbin/arp -f /etc/arp.table
>
This is because you do not need these 2 entries in it, fxp0, fxp1 are
two interfaces in your machine, so their mac is of course known by the
system. You need a proxy arp server to listen on fxp0, and fxp2.
> On boot I ended up with the following error message and a blank arp table:
> set: proxy entry exists for non 802 device
>
> Do I need to add in some static routes to make this work? What am I
> missing?
>
> Would this make it possible to have each adapter/IP use a different
> gateway? I ask because I have 2 T1s and I'm curious if a single machine
> could utilize both. It's an SMP box so I was thinking of running 2
> peered instances of Squid on separate IP addresses with each IP address
> using one of the T1s as the gateway. That way I could force my power
> users through one connection and everyone else through the other while
> still gaining the benefit of caching everything for everyone. It's
> probably needlessly complicated, but it sounds fun... ;-)
>
> Jon
>
> > -----Original Message-----
> > From: owner-freebsd-net@freebsd.org
> > [mailto:owner-freebsd-net@freebsd.org]On Behalf Of Xin LI
> > Sent: Tuesday, February 01, 2005 10:12 AM
> > To: freebsd-net@freebsd.org
> > Subject: Two NIC's connected to same subnet: routing question
> >
> >
> > Dear folks,
> >
> > I think I got confused with the routing problem we will have when at
> > least two NIC's are connected into the same subnet.
> >
> > The scenario:
> > em0: 192.168.0.1/24
> > em1: 192.168.0.2/24
> >
> > We can't simply configure like this, since 192.168.0.0/24 network route
> > exists as soon as either em0 or em1 is up. A workaround for this is
> > that we assign 192.168.0.2/32 for em1, but that has another issue that
> > all traffics will go through em0 for "outgoing", say, outside the
> > current network.
> >
> > A google of the issue has indicated that the "Move ARP out of routing
> > table" work done last April should have resolved this, as "With this
> > change it is possible to have more than one interface in the same IP
> > subnet and layer 2 broadcast domain.". However, what I have found from
> > our mailing list archive says only to assign /32 IP address, or remove
> > routing item from route table, which is essentially identical to the /32
> > solution.
> >
> > So is there any way to utilize the both NIC's? I think I have been
> > confused :-(
> >
> > Cheers,
> > --
> > Xin LI <delphij delphij net> http://www.delphij.net/
>
>
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- Previous message: Robert Watson: "Re: solisten() question: why do we check for completed connections?"
- In reply to: Jon Noack: "Re: Two NIC's connected to same subnet: routing question"
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