[lug] networking question

[Orion Poplawski]

On 9/12/20 5:36 PM, David L. Willson wrote:
> This feels like a newbie question that should be obvious to me, but it's 
> not obvious to me, so I'll ask.
> 
> If I have a subnet behind my router, and I want to put *part* of that 
> subnet (a sub-subnet?) behind an interior router (sub-router?)... Can I 
> do that?
> 
> Example (the actual case in point):
> 
> I have 67.42.246.112/29. It routes through 67.42.246.126. I have control 
> of 67.42.246.126. It's not Linux, but it's not entirely brainless, either.
> 
> Is there a way for me to carve the upper or lower /28 (67.42.246.112/28 
> or 67.42.246.120/28) off into an interior subnet and put it behind an 
> actual Linux box?
> 
> Come to look at it, I guess it would have to be the lower half, or I'd 
> have to re-number my router. Not the end of the world, but no sense 
> adding pointless work, either.
> 
> I know I lose three addresses in the process for the new network, 
> router, and broadcast address, but is it *possible*? Does it work? If 
> so, could I get a hand setting it up?


You've got a couple issues here.  One being that the upper/lower 
sub-nets would be /30 not /28.

What's the goal here?

My first take would be to make it a private subnet behind the linux box 
(say something from 172.16.X.X) and have it do NAT.  Otherwise you need 
to do tricky things with virtual IPs, proxy ARPs as in:

https://tldp.org/HOWTO/Proxy-ARP-Subnet/how.html


-- 
Orion Poplawski
Manager of NWRA Technical Systems          720-772-5637
NWRA, Boulder/CoRA Office             FAX: 303-415-9702
3380 Mitchell Lane                       orion at nwra.com
Boulder, CO 80301                 https://www.nwra.com/

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