[TriLUG] Choosing the right pipe

[Mike Johnson]

Jeff Bollinger [jeff01 at email.unc.edu] wrote:
 
> Say I've got two different NICs, each connecting to a different network.
> ~ If I want to SSH into network A (a private network) how do I tell SSH
> to run through eth0 (or the first NIC)?

You set a route for it.

An example:
I'd like to reach 192.168.3.0/24 through the gateway 192.168.1.1 that's
reachable through eth1 (and, presumably, eth1 has a 192.168.1.0/24
address).

Here's my starting table:
# /sbin/route -n
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
192.168.0.0     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         192.168.0.254   0.0.0.0         UG    0      0        0 eth0


So, to do what I want:
/sbin/route add -net 192.168.3.0/24 gw 192.168.1.1 dev eth0

And I have:
# /sbin/route -n
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
192.168.3.0     192.168.1.1     255.255.255.0   UG    0      0        0 eth1
192.168.0.0     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         192.168.0.254   0.0.0.0         UG    0      0        0 eth0

And then if I ssh to 192.168.3.15, it'll go out eth1.

There's really nothing special about SSH.  It's all about getting the
routes.

Mike
-- 
"Would you like to take advantage of wiretap Wednesdays?" -- Fed on Sealab 2021

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