> Am 05.02.2023 um 18:30 schrieb Dan Ritter: > > (...) > > RJ45 is a physical connector with 8 pairs of twisted wires. The > > twisted pairs carry the same signal but with the polarity > > reversed, + on one is - on the other. Together with the > > twisting, that makes the signal being carried resistant to > > interference. Ethernet is a low level protocol often carried by > > RJ45-connected twisted pair cables. > > > > Bridging extends a network segment. Routing makes decisions > > about where IP packets should go. > > > > The router that connects to the internet for you is probably > > doing several jobs: > > > > - it is bridging from a long-haul network like xDSL, DOCSIS > > (cable modem), or fiber, to your local ethernet > That is correct, DOCSIS in my case. > > > > - it is acquiring an IP address from the provider and using it > > as your public address > > > > - it is probably using network address translation (NAT) to > > allow multiple internal addresses to masquerade as the single > > public address > > > > - it is probably providing those internal addresses via DHCP > I can confirm all of the above. And i'd have to add, that matters got > more complicated with dozens of VM's running on the host, and atm 5 > networks serving different purposes, which would really need some > unwinding to happen for progress to be even possible. I am afraid, > that i did create all this mess over time due to my understanding > being so poor... > > > > It would be reasonably cheap to put an ethernet switch between > > the router and your existing host and new backup host. In the > > US, an 8 port ethernet switch is $28: > > https://www.newegg.com/netgear-gs308-300pas-8-x-rj45/p/N82E16833222029?Item=N82E16833222029 > > > > and you would need at least two more ethernet cables, which are > > also cheap. > > > > $7.50 for preterminated 25 foot cable > > https://www.newegg.com/yellow-belkin-25-ft-accessories-cable-management/p/N82E16812107315?Item=9SIB897JGS5925 > > > > I presume that there are similar companies in Germany which will > > sell you basically the same things. > > > > You unplug the host from the router, plug the router into the > > switch, and the two hosts into the switch. No configuration > > changes, most likely. Everything is likely to work. > > > > --- > > If you insist on plugging your second host directly into your first, > > you can do that instead: > > > > - configure an ethernet interface on both sides with an RFC1918 > > network address > > > > - plug them into each other > > > > - you can now ping each from the other > > > > - now you configure routing and NAT masquerading on your primary > > host to hide the secondary host behind it > > > > I don't recommend this. Buy a switch and some cables.
I would second that recommendation. Get it all working and then play with the network afterwards if you must. > > -dsr- > > > > I believe, this would work, because i had someone lend me a switch for > some time and it just worked (somehow). > For some reason, i am still interested to get bridge-utils to work, > and i am taking your hint, to use static ip configuration as a > starting point. The difficulty in that case: the backup-server does > not have any OS at this point, which makes it necessary to switch > keyboard and monitor several times in the process, and my handicap > forces me to ask someone for physical help in order to do that. > Very inconvenient to say the least. :-( You don't say what you've done, but I presume you're following https://wiki.debian.org/BridgeNetworkConnections What steps have you taken? Regarding your computer without an OS, can you not load a Live system from CD or DVD or USB stick? None should require Internet access to start up and be usable.