2 NIC's on same subnet = problems

From: Bryan Whitehead (driver@jpl.nasa.gov)
Date: Tue Apr 08 2003 - 19:30:35 EST


I'm having a problem with one NIC always answering for both.

(I'm using fake address for the email - 192.168.1 was subbed for JPL IP's)

First machine:
eth0 has 192.168.1.213 (name is box1)
eth1 has 192.168.1.192 (name is box1-gw)
Route table:
Destination Gateway Genmask Flags Metric Ref Use
Iface
192.168.1.192 0.0.0.0 255.255.255.255 UH 0 0 0 eth1
192.168.1.104 0.0.0.0 255.255.255.255 UH 0 0 0 eth1
192.168.1.0 0.0.0.0 255.255.255.0 U 0 0 0 eth0
127.0.0.0 0.0.0.0 255.0.0.0 U 0 0 0 lo
0.0.0.0 192.168.1.1 0.0.0.0 UG 0 0 0 eth0

On another box the same setup / different IP's.

eth0 has 192.168.1.192 (name is box2)
eth1 has 192.168.1.104 (name is box2-gw)
Route Table:
Destination Gateway Genmask Flags Metric Ref Use
Iface
192.168.1.192 0.0.0.0 255.255.255.255 UH 0 0 0 eth1
192.168.1.104 0.0.0.0 255.255.255.255 UH 0 0 0 eth1
192.168.1.0 0.0.0.0 255.255.255.0 U 0 0 0 eth0
127.0.0.0 0.0.0.0 255.0.0.0 U 0 0 0 lo
0.0.0.0 192.168.1.1 0.0.0.0 UG 0 0 0 eth0

One each box the eth0 nics are on the internet.
The eth1 nics are plugged into a switch they share that is "private".

The problem is when a box on the internet pings or tries to connect to
an IP that is supposed to be on the "private" side (eth1) I get
responses from the eth0.

Also, the idea was if one of these boxes desired to communicate with
each other they would communicate over the private network. We configure
NFS and other services to use the -gw name.

On box1:
ping box2-gw
the ping goes out thru eth0 and is accepted by box2's eth0 instead of
going over the private network.

Apparently on this setup (so I'm told by the Senior Sun/Solaris admin)
Solaris will not accept packets from one nic that is the ip of another.

Is there any idea's you all have? (I'd like to just use a different
subnet for the private side, but the subnet decision wasn't technical -
it was political... long story).

-- 
Bryan Whitehead
SysAdmin - JPL - Interferometry and Large Optical Systems
Phone: 818 354 2903
driver@jpl.nasa.gov

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