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Old 12-01-2011, 05:33 AM   #1
ThomasRonshof
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2 network cards


Hi,

I have defined eth0 and eth1 with 2 different IP's.

If eth0 stops working, I would like to be able to use eth1 instead.

What's to do when eth0 breaks down ? I think something about moving default gateway from eth0 til eth1 ?

Regards
 
Old 12-01-2011, 06:21 AM   #2
kvmfix
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Hi...

While eth0 is active, do you still need eth1 to be active?
 
Old 12-01-2011, 06:24 AM   #3
ThomasRonshof
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Yes, because I use them for virtualization. eth0 is bridged as br0 and eth1 as br1. I have several guests using br0 and br1 at the same time.
 
Old 12-01-2011, 06:31 AM   #4
kvmfix
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Are both nic are in same network?

Can you reach eth0 and eth1 from other devices?
 
Old 12-01-2011, 06:39 AM   #5
ThomasRonshof
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Jep, eth0 is 192.168.10.40, eth1 is 192.168.10.45,

GW: 192.168.10.1

I can ssh in to both IP's from another host.
If I unplug eth1, I can still ssh to eth0.
If I unplug eth0 alone, I can't ssh to eth1 ! I think it's because of the GW and sshd is listening on eth0 ??
 
Old 12-01-2011, 07:26 AM   #6
aazkan
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Hi,

Unless configured to listen on a defined ip , sshd will listen to any/all.

Code:
netstat -antpd|grep :22
shows where sshd runs on.

It is possible to have 2 default gateway (sort off). You will need the iproute2 utility to add modify the routing table. Search through the forum, you'll probably find some leads here.
 
Old 12-01-2011, 08:00 AM   #7
ThomasRonshof
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Well, I don't need 2 gw's, only 1.

When eth0 dies, I want to change def.gw from eth0 to eth1.

Isn't that possible, maybe with the route command ?
 
Old 12-01-2011, 08:52 AM   #8
aazkan
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Sorry i misunderstood your question, thought you wanted a dual gateway
Of course, you can change your def gw to eth1.
 
Old 12-02-2011, 03:10 AM   #9
ThomasRonshof
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Ok,,, but how ?
 
Old 12-02-2011, 03:35 AM   #10
enno_onne
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I'm also still learning unix here, but I hope this may work and help you out. If not, I am sorry and please let me know.

first, you need to see what is the original routing table by giving this command
Code:
netstat -rn
it will show you something like this
Code:
Routing Table: IPv4
  Destination           Gateway           Flags  Ref     Use     Interface 
-------------------- -------------------- ----- ----- ---------- --------- 
default              192.168.137.1        UG        9       3021 e1000g0   
127.0.0.1            127.0.0.1            UH        2        244 lo0       
192.168.137.0        192.168.137.41       U         3        495 e1000g0   

Routing Table: IPv6
  Destination/Mask            Gateway                   Flags Ref   Use    If   
--------------------------- --------------------------- ----- --- ------- ----- 
::1                         ::1                         UH      2      12 lo0   
fe80::/10                   fe80::203:1dff:fe0a:981c    U       3       0 e1000g0 
default                     fe80::b8cf:cb3a:d1ee:7554   UG      2       0 e1000g0
remember this IP routing tables.

Then you need to run this code
Code:
route add 192.168.10.0 192.168.10.45
--------------------- !!!!!! ------------------------
If it doesn't work then you need to do the reversal and when you re run the netstat -rn, it should be the same
Code:
route remove 192.168.10.0 192.168.10.45
--------------------- !!!!!! ------------------------

Good luck

Last edited by enno_onne; 12-02-2011 at 03:36 AM.
 
Old 12-02-2011, 05:30 AM   #11
ThomasRonshof
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Well, tried:

route del default
route add default gw eth1

But can't still ssh to 192.168.10.45 from the outside ?
 
Old 12-02-2011, 06:52 AM   #12
ThomasRonshof
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Works now. Must do a ifconfig eth0 down also :-)
 
  


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