Dual NIC cards Traffic Flow

Unanswered Question
Dec 24th, 2009

Hi,


Recently i have added Second NIC to our servers, the IP Address and Vlans are different for both network,


The problem starts when we pluggin the second NIC the entire server goes down becomes unstable.


Can anyone please help for both NIC's to be up and running without any descripancy.



Thanks

Tabrez

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Reza Sharifi Sat, 12/26/2009 - 18:49

Hello Tabrez,


If you have 2 NICs, then you should do NIC teaming and both NICs should be in the same subnet.  This way you have NIC redundency.


HTH

Reza

Jon Marshall Mon, 12/28/2009 - 09:45

balbaletabrez wrote:


Hi,


Recently i have added Second NIC to our servers, the IP Address and Vlans are different for both network,


The problem starts when we pluggin the second NIC the entire server goes down becomes unstable.


Can anyone please help for both NIC's to be up and running without any descripancy.



Thanks

Tabrez


Tabrez


The issue is probably because you cannot use 2 default-routes on your server or rather if you have 2 default-routes you could see intermittent successful traffic. Solutions are -


1) As Reza said team the NICs together which would mean the 2 NICs would use the same IP/subnet mask


or


2)  If you want to have 2 NICs on 2 separate subnets choose one default-gateway for the server. If you then want traffic to go via the other NIC you need to add static routes to the server pointing to the other NICs default-gateway. An example might help -


NIC1 = 192.168.5.10/24   - defaullt-gateway = 192.168.5.1

NIC2 = 192.168.6.10/24  -  default-gateway = 192.168.6.1


lets say most traffic goes via 192.168.5.10 NIC1. So leave the default-gateway as 192.168.5.1


when you configure NIC2 do not fill in the default-gateway in the IP configuration.


Now lets say you want all traffic for 172.16.5.0/24 to go via NIC2 -


route add 172.16.5.0 mask 255.255.255.0  192.168.6.1    <--- note the route syntax will be dependant on the server OS


For every route you want to use NIC2 you will need a static route on the server.


Jon

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