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Routing Question - Non-contiguous IP Blocks

 
 
Edumac
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      09-01-2005
Hi, I'm having a little trouble figuring out how to do this, or even if it
can be done.

When we originally got our t1 installed, we ordered 5 public IP addresses.
At the time, this seemed like enough, all we needed was smtp, www, and a
couple of other things.

Now it turns out we need more public ip addresses for ftp, more www, etc.

Our ISP could not expand our existing subnet. Instead, they offered us 5
more ip addresses in a non-contiguous subnet.

For example:

Original subnet: 62.43.171.2 through 62.43.171.6 (255.255.255.24

Additional subnet: 62.43.171.242 through 62.43.171.246 (255.255.255.24

The way I envision this working is to put a secondary ip address on my
router's outside interface:

Router#(conf-int): ip address 62.43.171.242 255.255.255.248 secondary.

But I'm not sure what the routing statement should be. Currently the
default is set to:

0.0.0.0 --> 62.43.171.1

If I add a route statement: 62.43.171.241 --> 62.43.171.242, will that work
to route traffic to/from this new subnet?

Thanks.


 
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Arnold Nipper
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      09-01-2005
On 01.09.2005 17:40 Edumac wrote

> Hi, I'm having a little trouble figuring out how to do this, or even if it
> can be done.
>
> When we originally got our t1 installed, we ordered 5 public IP addresses.
> At the time, this seemed like enough, all we needed was smtp, www, and a
> couple of other things.
>
> Now it turns out we need more public ip addresses for ftp, more www, etc.
>
> Our ISP could not expand our existing subnet. Instead, they offered us 5
> more ip addresses in a non-contiguous subnet.
>
> For example:
>
> Original subnet: 62.43.171.2 through 62.43.171.6 (255.255.255.24
>


actually the subnet is 62.43.171.0/29, 62.43.171.0-62.43.171.7

> Additional subnet: 62.43.171.242 through 62.43.171.246 (255.255.255.24
>


actually the subnet is 62.43.171.240/29, 62.43.171.240-62.43.171.247

> The way I envision this working is to put a secondary ip address on my
> router's outside interface:
>
> Router#(conf-int): ip address 62.43.171.242 255.255.255.248 secondary.
>
> But I'm not sure what the routing statement should be. Currently the
> default is set to:
>
> 0.0.0.0 --> 62.43.171.1
>
> If I add a route statement: 62.43.171.241 --> 62.43.171.242, will that work
> to route traffic to/from this new subnet?
>


That of course will work. But observe that traffic from network1 to
network2 always has to go via the router.

You could also set

ip route add 62.43.171.240/29 dev eth0

on network1 system and

ip route add 62.43.171.0/29 dev eth0
ip route add default via 62.43.171.2

on network2 system (given 62.43.171.2 is your router's primary LAN address).

That way traffic between network1 and network2 is directly exchanged.

Another option might be to get a /28 (or even /27) from your provider
and to return network1.

I would go for that option.


Arnold
--
Arnold Nipper, AN45
 
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