On Thu 04 Feb 2021 at 23:03:17 (+0000), Mark Fletcher wrote: > First apologies for the off-topic post, but I know this community is > full of experts on this topic and my ask in the end is a simple one:
Disclaimer: I'm no expert. > Can anyone point me at a reasonably accessible guide to the details of > how IP networks work, in particular the communications that occur > between router devices that are designed to support home networks? I'm > computer science trained but from many years ago and if I ever learned > these specific details I have forgotten them, but I feel equipped to > understand them. I'm after a certain amount of detail and would prefer > to avoid adverts or advice of the "just buy our product, plug it in and > your problems will all be solved" type. I think this gives a good practical introduction: https://homenetworkgeek.com/what-is-the-wan-port-on-my-router-for/ > The background to my request is this: > > A while ago I moved house (and countries) and since arriving in the new > house I have been using a WiFi router provided by my broadband provider, > somewhat reluctantly, but without a really serious alternative since the > router also contains the ISP's modem. In the old place I used a > store-bought router+WiFi device of very typical type (Buffalo brand, > although I don't expect that to be relevant) plugged into the (cable) > modem. (Presumably it's still legal to run.) > My kids have been complaining recently about the quality of the WiFi and > so I thought I'd fire up the old router from the old house and see if > it's any better. I experimentally fired it up without plugging it into > anything and the old WiFi networks came up, I could connect to them, and > got an IP address in the range I used to use at the old house (which is > different from what I use now, for arbitrary reasons). > > I powered the router down again, plugged its WAN port into one of the > LAN ports of the ISP-supplied router, and brought it back up. It came up > but seems to have automatically subordinated itself to the ISP-supplied > router and is now offering up IP addresses in the range supplied by the > ISP's router... It seems like it has automatically taken a subordinate > role to the ISP's router. It is still offering up the old network names > with the old password but when I connect I get an IP address in the > range used by the ISP's router (said address works fine). If that really is the WAN port that you connected, that does seem rather surprising, as if it has automatically turned itself into a bridge. I have a similar hardware configuration (to what you intended) here, as it happens. A primary modem/router's LAN port is connected to the secondary router's WAN port. We use the secondary router's LAN ports and WiFi for many of the devices in the house, so the primary router is basically ignored, ie the box is treated exactly like the modem it replaced. The secondary router gets its external IP address via DHCP (there's no login required), and it assigns IP addresses, that I chose, to all the devices by their MAC. You mentioned "old network names" and "old password". I assume here you mean the WiFi SSID and WPA2 password. That's a separate issue, and has nothing to do with IP addresses and hostnames. (BTW while you're experimenting, you probably want to keep using different SSID and passwords on the two routers, so that it's easy to choose the specific one you connect to. Later on, you can set them all the same so that you can move devices around transparently.) > I don't think I expected it to do that, certainly not automatically, and > before I decide if I am happy with this outcome or not I want to > understand in detail what just happened and why, so I can understand its > implications. Just as one example, I want to understand what the > implications are for the store-bought router's firewall -- has it just > been bypassed? and so on. Your description, as Stefan said, sounds as if you connected two LAN ports together, which I imagine is what you really want. In that case, you'd want the store-bought router to leave DHCP and IP addresses to the ISP's router to handle, rather like you described. I have a similar hardware configuration (to what I think you really want) here, as it happens. A secondary router's LAN port is connected to a tertiary¹ router's LAN port (via a very long cable), and that router serves more devices by wire and WiFi. Now, I turned off DHCP in the tertiary router, but I haven't actually tested what would happen if you didn't. (I don't remember whether its old list of reserved addresses for DHCP got deleted, or whether it has just hidden them all.) So with the SSIDs and passwords set to the same values, I can move a device around the house and it just uses whichever signal from the secondary and tertiary routers is the stronger. This might be what you want. > Hence the request for a pointer to some good > documentation. Book, website, whatever you think would be most helpful, > I would much appreciate any pointers. The reference above contains other links that are probably helpful. ¹ Background, if you got this far: the tertiary router was once my primary router, but the WAN port died. Its replacement, the secondary router, was once connected to my modem, but the modem fried (literally). The current primary router/modem is a temporary hire. Cheers, David.
