# Two NICs with same subnet



## elcopion (Aug 2, 2011)

Hello I can't work with two network connections *(same subnet)* simultaneously.

In linux it fix : enabling arp_filter but in FreeBSD how to fix it?


```
ETH1 : 200.121.12x.4 router 200.121.12x.1
ETH2 : 200.121.12x.8 router 200.121.12x.1
```

Error Log

```
arpresolve: can't allocate llinfo for 200.121.12x.1
```


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## Crest (Aug 2, 2011)

Their is no use in connecting 2 NICs to the same subnet if you don't use them for something more than having two addresses. Do you want to double the bandwidth? Look for the lagg(4) pseudo interface. Do you want two addresses from the same subnet? Define an alias on one of them. FreeBSD get's confused when it's attached to the same broadcast domain with more than one NIC because MAC addresses will jump interfaces based on which interface reacts the first to a ARP message.


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## elcopion (Aug 2, 2011)

Hi thanks for your response and your time.
I explain about my problem.

ETH0 -> CABLEMODEN-X1 (ISP YY) 
ETH1 -> CABLEMODEN-X2 (ISP YY)

X1 != X2
SAME ISP

Do you want to double the bandwidth?
Yes (loadbalance route)

But do not work together, only work one.

*Look for the lagg(4) pseudo interface*
How to ? please help me.

Thanks


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## wblock@ (Aug 2, 2011)

lagg(4) in post #2 is a link to the lagg device man page.  Click it, or use the man(1) command:
`% man lagg`


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## Crest (Aug 2, 2011)

Unless your ISP supports this setup (in which case they will document it and have you pay extra for it) you can't just "loadbalance". You can route different outgoing TCP connections though different interfaces. It looks like you have no idea of the protocols you mess with. The closest thing possible to what you might think you want is documented here . You can't just send out packets on uplinks to your ISP and expect the reply to find it's way back to you. That would require the ISP to announce your prefix or require you to establish a BGP session with your ISP and announce your prefix your self.


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## elcopion (Aug 2, 2011)

Yes I repair it .... LAGG!!! 

PFSENSE + LAGG (ROUN Robin) = double the bandwidth

Thanks :


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