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Multi homing PC - Multiple default gateways

Hi Guys

If I was to have a PC with 3 NIC's, e.g. 192.168.1.x , .2.x, .3.x can I have different gateways for each connection, the idea being if one connection goes down another one can take over.

PC isnt built yet but will be either XP Pro or Win 7 Pro.

Thanks
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Corp_Jones
Asked:
Corp_Jones
4 Solutions
 
KlinkeyeCommented:
Yes... but the second and third routes should be given higher metric values
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Kruno DžoićSystem EngineerCommented:
f you are NOT going to send specific traffic [by IP/network] to another
gateway that you ALWAYS want to use that gateway then do not configure via
route command.

If you simply want to specify two default gateways then use the network
adapter properties instead but realize that if the operating system changes
to a different default gateway it will continue using that gateway until it
is no longer available and not automatically switch back to the other
gateway that you may have listed first [principal] when it becomes available
again. There are internet routers [Sonicwall with enhanced OS for example]
that can use multiple gateways where it will only use an alternate gateway
if the primary gateway is not up and then switch back to the primary when it
is up again.

Your operating system will know that the currently used default gateway is
not online when it does not get a response from it when trying to send
traffic to it.

The link below explains how the metric works.

http://support.microsoft.com/kb/299540

copy/paste: http://www.eggheadcafe.com/microsoft/Windows-XP-Network-Web/31006130/multiple-gateways.aspx
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FideliusCommented:
Hello,

Yes it is possible by manually creating additional default routes with higher metric.

For example:
> route add 0.0.0.0 mask 0.0.0.0 192.168.2.1 metric 70
> route add 0.0.0.0 mask 0.0.0.0 192.168.3.1 metric 90
> route print
...
===========================================================================
Active Routes:
Network Destination        Netmask          Gateway         Interface          Metric
          0.0.0.0               0.0.0.0            192.168.1.1    192.168.1.10       20
          0.0.0.0               0.0.0.0            192.168.2.1    192.168.2.10       70
          0.0.0.0               0.0.0.0            192.168.3.1    192.168.3.10       90
...

Regards!


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Corp_JonesAuthor Commented:
Thanks guys sounds good, it looks like I can just let each nic get a gateway via DHCP and it will handle it automatically, no need to add default routes via command line as I dont mind which gateway the PC uses as they all go out to the internet, does that sound correct?
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FideliusCommented:
One important thing, I'm not sure you are aware of.
If you are doing this for case internet connection between one router and respective provider goes down, it will not work. This works only if local LAN connection goes down, between PC and router, not between router and ISP.

Explanation: Windows will switch default route only if PC ethernet interface goes down. From Windows perspective, if link to ISP goes down, it won't be noticed, as local LAN link stays up. All Internet IP traffic will be sent to same router, despite router lost it's Internet connection.

Regards!
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Corp_JonesAuthor Commented:
Thanks Fidelius I thought that was the case, i've had same problem with dual wan drayteks unless you change some settings.

The PC's role is more to provide access to all the separate networks from one location, e.g. administer multiple routers etc so should be ok
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