netdev - Re: Proxy arp for non-overlapping subnets on an interface without assigning IP aliases

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Date:   Sat, 29 Jun 2019 19:39:06 +0530
From:   Aks Kak <akskak2012@...il.com>
To:     netdev <netdev@...r.kernel.org>
Subject: Re: Proxy arp for non-overlapping subnets on an interface without
 assigning IP aliases

Ignore previous one or consider /27 as /25 at two places in previous mail:
***************************************************************************************
I have a linux box with 2 interfaces with following IPs
eno1 : 10.1.1.0/24
eno2 : 192.168.2.0/25

I want to use network 10.3.3.0/25 as virtual IPs for 192.168.2.0/25
i.e. I will be doing DNAT using NETMAP target of IPTABLES.

DNAT and NETMAP, etc. is not the issue.

For my requirement to work, main thing is who (or how) will give arp
replies for 10.3.3.0/25 !!!
I have 2 ways of achieving this:
1. Create all 126 IPs 10.3.3.1 - 10.3.3.126 as alias IPs on eno1. I
want to avoid it.
2. Use proxy arp for entire subnet 10.3.3.0/25 on eno1 but this
require having atleast one IP from this subnet to be created as IP
alias on eno1, say 10.3.3.1/25. However, my concern is that this
10.3.3.1, as it has been assigned to eno1,may be used by mistake to
listen for any service, etc. or ping, etc. which otherwise I would
have to control using iptables rule set. I totally want to avoid it.

So, my query is how to do proxy arp for 10.3.3.0/25 on eno1 without
assigning 10.3.3.1/25 to eno1???

On Sat, Jun 29, 2019 at 7:34 PM Aks Kak <akskak2012@...il.com> wrote:
>
> I have a linux box with 2 interfaces with following IPs
> eno1 : 10.1.1.0/24
> eno2 : 192.168.2.0/27
>
> I want to use network 10.3.3.0/25 as virtual IPs for 192.168.2.0/25
> i.e. I will be doing DNAT using NETMAP target of IPTABLES.
>
> DNAT and NETMAP, etc. is not the issue.
>
> For my requirement to work, main thing is who (or how) will give arp
> replies for 10.3.3.0/27 !!!
> I have 2 ways of achieving this:
> 1. Create all 126 IPs 10.3.3.1 - 10.3.3.126 as alias IPs on eno1. I
> want to avoid it.
> 2. Use proxy arp for entire subnet 10.3.3.0/25 on eno1 but this
> require having atleast one IP from this subnet to be created as IP
> alias on eno1, say 10.3.3.1/25. However, my concern is that this
> 10.3.3.1, as it has been assigned to eno1,may be used by mistake to
> listen for any service, etc. or ping, etc. which otherwise I would
> have to control using iptables rule set. I totally want to avoid it.
>
> So, my query is how to do proxy arp for 10.3.3.0/25 on eno1 without
> assigning 10.3.3.1/25 to eno1???