Sharing DHCP address with attached device?

[Mike Donovan]

Hello, forum noob but networking non-noob here, I'm trying to do something unusual, and haven't found any discussion about this anywhere, maybe I just haven't found the right Google Foo yet....

I'm trying to replicate on a Linux-based router a behavior I've seen elsewhere, such as in cable modems: I need to get a single DHCP address from the WAN side, offer/pass that same address to the single attached client device, and mostly just act as a bridge, except that I also need to have the router use that DHCP-issued address to phone home for management. Also, the client device should be able to talk to the router using some fixed IP (like 192.168.100.1) for local troubleshooting. Any traffic coming from the outside which isn't a response to a request from the router itself should go straight through to the client device, except maybe for one reserved management port.

The client device phones its own home for management, and tells what IP it got, so it can get called back; otherwise I'd just use NAT and be done.

I'm pretty sure I can do most of this with ebtables, but I haven't figured out the proper incantations yet. The WAN side has a single hardware-linked reserved DHCP address, which I can't do anything about. My Plan B is straight bridging (with MAC fix-up) but I'd lose too much management functionality that way.

 

[Greg72]

https://docs.oracle.com/cd/E24191_01/common/tutorials/common_transparent_proxy.html

 

[Mike Donovan]

https://docs.oracle.com/cd/E24191_01/common/tutorials/common_transparent_proxy.html

Thanks, but that's for Oracle's own GUI-based product, I need to do it with generic Linux, using iptables/ebtables. Do you know of a more detailed explanation of what that product does at a lower level?

Edit: Spotted mention of the TPROXY kernel module in those docs, now exploring a new rabbit hole, but still hoping for help....

 

[Greg72]

It is regarding what you are asking for. You are wanting a transparent Proxy and it tells youwhat you need to start within the very first paragraph. Here, since web searches are so hard. https://wiki.squid-cache.org/Features/Tproxy4

 

[Mike Donovan]

I did find that page before. As I stated above, this is for a device which needs remote management, not for a local user browsing the web. (Besides, Squid wouldn't even fit on that little router.)

What I'm looking for is a series of iptables/ebtables/dnsmasq commands to set up the needed behavior, not a description of a large product with parts of the solution I need buried inside it.

 

[Greg72]

Not going to happen unless you are running a proper Router with pfsense, etc running on Linux.