SNAT?

SNAT?

[Svavar Örn Eysteinsson]

Hi everyone.
I’m very new to doing the SNAT thing.

The thing is, is there any way to SNAT a individual computer on my
internal network to a different public ip address?


This is my network 


{ INTERNET }
    |
    |
[--------|
[ ROUTER ]
[--------]
    |
    |
    |
x.x.x.98/24
    |
|--eth0----|
| Firewall |
|          |
|          -eth1-> 10.100.0.0/24 Internal Network
|----------|

All my internal network is masqueraded as the x.x.x.98/24 ip address. I
want to SNAT my internal IP address 10.100.0.200 to x.x.x.99/24 Is that
possible?

Isn't that right, that I need to do the "ip" command for the x.x.x.99
address on my firewall? 

I did "ip address add x.x.x.99 dev eth0

Could someone advice me on doing the SNAT thing with iptables. Any help
would be appreciated.

Best regards to all,

Svavar Orn
Reykjavik - Iceland

Re: SNAT?

[Antony Stone]

On Tuesday 29 October 2002 12:33 pm, Svavar Örn Eysteinsson wrote:

> Hi everyone.
> I?m very new to doing the SNAT thing.
>
> The thing is, is there any way to SNAT a individual computer on my
> internal network to a different public ip address?

Yes, you can SNAT anything you like to anything else you like.   So long as a 
packet goes through netfilter, you can SNAT it.

However, depending on what source address you give it, the replies may or may 
not get back again, which is a separate routing problem, nothing to do with 
netfilter.

Remember that if you send packets out through netfilter and NAT them, they 
will only get reverse-NATted if the replies come back through the same 
netfilter machine.

Antony.

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RE: SNAT?

[R. Sterenborg]

> The thing is, is there any way to SNAT a individual computer on my
> internal network to a different public ip address?

Sure.

> All my internal network is masqueraded as the x.x.x.98/24 ip
> address. I
> want to SNAT my internal IP address 10.100.0.200 to
> x.x.x.99/24 Is that
> possible?

Create the rules in this order :

# iptables -t nat -A POSTROUTING -s 10.100.0.200 -j SNAT --to-source
x.x.x.99
# iptables -t nat -A POSTROUTING -s 10.100.0.0/24 -j SNAT --to-source
x.x.x.98

# iptables -A FORWARD -s 10.100.0.200 -d x.x.x.99 -j ACCEPT
# iptables -A FORWARD -s 10.100.0.0/24 -d x.x.x.98 -j ACCEPT

When the first rule is matched, it is executed.
So your PC on 10.100.0.200 hits first its own rule so never hits the
subnet rule.
The other PC's don't hit the specific rule and match the subnet rule.
Of course the PC would have to have a static IP address, because
otherwise another PC could be 10.100.0.200...


Rob