Re: Linux routing question
- From: Unruh <unruh-spam@xxxxxxxxxxxxxx>
- Date: 29 Mar 2006 20:49:59 GMT
Dave Hammond <iceman@xxxxxxxxxx> writes:
Good morning,
I have a linux routing question to ask. I am working on a linux server,
slackware 10.2 w/2.6.16 kernel, that has 2 ethernet cards in it. This
server is used for network monitoring of a LAN with mrtg and nagios. The
first NIC, eth0, is connected to a switch in the DMZ and has a public
routable IP address to the internet. The second NIC, eth1, is connected to
the internal network switches and has a private 10.x.x.x address to the
local LAN. The default route as of right now points to the internet
gateway router which is what I want. I have a network route set up on the
linux server to the 10.0.0.0 subnet for eth1 to talk to devices in the
private network. So as of right now I can ping and talk to everything I
need to.
Now, here is the wrinkle, this server does device failure notifications via
e-mail to specific persons. If the primary internet connection fails,
obviously, the notifications will not make it anywhere. I have learned
that there is a second internet connection available at a remote office. I
can contact that remote office network through the internal lan routing
with ping and my question is, how can I make this linux server routing
automatically fail-over to use that secondary internet connection if the
primary connection fails?
I am working on this server from 400 miles away where it is physically
located and would prefer to not have to call them to reset it 10,000 times
when I dink the routing table trying to figure it out.
Here is a copy of my current routing table as of right now, I have replaced
any public IP address info with XXX.XXX.XXX.XXX for obvious reasons.
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
localnet * 255.255.255.240 U 0 0 0 eth0
10.1.2.0 * 255.255.255.0 U 0 0 0 eth1
10.0.0.0 10.1.2.254 255.0.0.0 UG 0 0 0 eth1
loopback * 255.0.0.0 U 0 0 0 lo
default XXX.XXX.XXX.XXX 0.0.0.0 UG 1 0 0 eth0
Well, the first thing you do is to insert a specif route which points only
to your machine that you log on which.
route add -host 111.222.333.444 gw XXX.XXX.XXX.XXX eth0
This makes sure that even if the default goes down, the system still knows
how to get packets to your machne 400 miles with IP address 111.222.333.444
Now you can play with the default route.
Have a script which pings or tries to contact an external site every 5 min.
If it fails, the script does
route del default eth0
route add default gw 10.1.2.55 eth1
(where 10.1.2.55 is the internal machine which has external connectivity.
You never told us what its IP was so I made one up)
Alternatively if you do not want a default route, but just have that
internal machine act as a mail relay, set it up to accept mail relay stuff
from you, set up postfile to use it as a mail relay for as long as the
network is borked. Every 5 min check to see if the external connection
works and reset the mail relay.
.
- References:
- Linux routing question
- From: Dave Hammond
- Linux routing question
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