Category Archives: networking

arch linux, gateways, ipv6, linux, networking, raspberry pi, raspbian, systemd, ubuntu, vpn

Network Configuration and Services

I have written a lot of drivel previously about the various aspects of managing network service, as I’ve tried to figure out the improvements that have been made in linux networking over the last 30 years. I don’t read the kernel threads, and don’t know what’s happening a lot of the time, and haven’t been good about being attentive to release notes, so I get behind and then have to catch up. Previous efforts to catch up have usually been in a hurry when something was busted, and weren’t comprehensive.

This time I have tried to be a bit more comprehensive, so I could settle on the set of solutions and tools I am going to use on the 20 or so different boxes where I have to set this stuff up. A few of them actually need something special, but not most of them. Still, things have to be consistent, and I need to know what I’m doing – at least better than I previously did.

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cloud, networking, postfix, security

Switching Mail Sending to Amazon

This is another aide-memoire about changes in mail on Tarragon.

Some weeks back a change in one of the website contact pages was done and the captcha code was inadvertantly omitted. There followed a period of massive junk email directed at the owner of the site, on her google gmail account. Google decided to cut off tarragon’s ip address.

Although the problem is fixed, google has not relented. And this is the same kind of issue I have had in the past with microsoft. Although I have never been a source of spam, the big mail outfits are quick to ban the ip address of any small personal smtp server, and it takes a lot of effort to convince them to release the ban. I am tired of it. Despite my quixotic desire to run my own mail server as a symbolic cry against the erosion of personal services on the internet, I am tired of fighting, and I think it is time to stop.

Continue reading Switching Mail Sending to Amazon →
arch linux, ipv6, linux, networking, systemd, ubuntu

Using IWD instead of wpa_supplicant

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I always feel like I am a few years behind. Here is another example. Here at nearly the end of 2021 I have learned about IWD (iNet Wireless Daemon), which is a replacement for wpa_supplicant.

This is just to record a few facts about experiences over the last couple of days, subsequent to receiving and setting up a new frame.work laptop. I install Arch on this laptop, and initially followed what I had previously done in the earlier post: Switching to systemd-networkd.

One of the problems described in that post is that if one follows what it says, a side-effect is the loss of any very good “graphical” way to switch a laptop from one SSID to another. I detail there how I used a downloaded package called wpa_gui to do that, but while it is a good step forward, it is a bit clunky. Maybe I’m not using it exactly right… I mean no disrespect to its authors, and am glad it exists; but I went looking for something else. And I discovered the IWD package.

When I downloaded and installed IWD, in ignorance, I managed to completely eliminate my wireless device and spent a good deal of time recovering. Following are some things I learned. But there are two different changes in my environment going on here, and while they are related I’m not claiming that one requires the other. One of the changes is the substitution of IWD for wpa_supplicant as the party responsible for interacting with wireless radios, selecting one, authenticating to it, and making it available as a device. The second change is that I have begun to use NetworkManager again, in conjunction with systemd-networkd.

IWD is a systemd service, as is wpa_supplicant, NetworkManager, and systemd-networkd, and it is possible to create a great deal of confusion when all of these bits are installed on the same system. If one desires to have more confusion, one has only to do all this on an ubuntu system, where the presence of Canonical’s netplan software adds another order of magnitude increase in complexity, and additional opportunities for foot target practice.

One of the big opportunities for confusion arises when IWD renames network devices. If one has “.network” files (for steering systemd-networkd) which rely upon matches on the device names, surprise! the device names (like wlp11S0) get changed to (e.g.) wlan0 by IWD.

I probably don’t understand all this well enough to attempt to explain it, and will probably only look foolish if I try, so instead I will just detail where I ended up on two of my laptops.

I have enabled the services IWD, systemd-networkd and NetworkManager. In /etc/NetworkManager/NetworkManager.conf I have a [device] section containing the setting “wifi.backend=iwd” which instructs NetworkManager to rely on IWD rather than wpa_supplicant, and prevents NetworkManager from trying to start a wpa_supplicant. I have removed the local service file /etc/systemd/system/wpa_supplicant/wpa_supplicant@wlp11s0 (which I had described in my previous blog post), and have stopped and disabled (and even masked) the associated wpa_supplicant@wlp11s0 service as well as the plain wpa_supplicant service. Update, March, 2022, I was trying to switch some things around on a Debian 11 box, and was unable to get a wireless connection until after reading some stuff in upstream on NetworkManager I found a suggestion that I add: iwd-config-path=auto in the [main] section of /etc/NetworkManager/NetworkManager.conf (same file where I put in the backend spec). Until I did this it was unable to connect to anything.

In /etc/systemd/network I have a .network file for 09_<laptop>_wireless.network containing the networkd description, same as before, except that the [match] now says “name=wl*” instead of the previous “name=wlp*” (because of IWD changing the name from wlp11s0 to wlan0).

Finally, one of these laptops is still ubuntu, so one gets the additional joy of netplan. There, in the /etc/netplan directory I went back to a yaml file which names the “renderer” as NetworkManager instead of systemd-networkd. My current, perhaps flawed understanding of this setting in netplan is that when netplan runs at boot time it uses the (collected and merged) yaml files to build at boot time the files for either systemd-networkd (in /run/systemd/network/), or for NetworkManager (in /run/NetworkManager/). These generated files will then get combined with similar files from /lib and from /etc (the latter having greatest priority, the former having least, and /run in the middle).

Going back to NetworkManager has one downside for me, the thing which drove me earlier to abandon NetworkManager in favor of systemd-networkd, and that is the specification of the IPv6 DUID to be used when soliciting an IPv6 address from DHCPv6. I can’t find information about how to stipulate the DUID to be used (for example in this nm_connection documentation). What I have done is develop better tools to figure out what NetworkManager decided to send, so I can arrange for the DHCPDv6 server to assign a static address to that DUID.

backup, gateways, linux, networking, openssh, raspberry pi, security, virtualization

Protecting ssh

I have a dozen or so boxes, mostly little raspberry pis, out in people’s houses which let me do backups for them, and attach to their networks. I’ve documented this before in “Gateway pi”, “Memory on the Gateway Pi”, and “Timemachine on Gateway pi” for example.

Connection between these boxes and my house is with SSH, and I use openssh certificates as described in “Using openssh certificates” and “Re-signing Openssh Certificates”. However, there has always been a little nagging problem, which is that these boxes must (re-)establish their connection to me automatically upon reboot, without user intervention. This means that the private keys that accompany the certificates cannot be encrypted, for that would require human intervention.

So there is a risk. Those raspberry pis have upon them a certificate and a private key which would enable access to boxes in my house. Not completely unrestricted access, and not root access, but nevertheless.

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linux, networking, openssh, security

Detecting SSH Brute Force

It always annoys me when I see the log filling up with ssh attacks. It isn’t really a worry, these are password guessing and since passwords aren’t permitted they will never work.

I’ve been meaning for a long time to investigate the tools available in iptables with the “recent” module to detect them and block them. Today I finally did it.

There is a little script in /root called sshdrop, which contains the iptables rules. It is parameterized, but currently set for reacting to more than 2 syn in 20 seconds, and sends rejects with tcp-reset.

I also downloaded a little python script to inspect the /proc/net/xt-recent/DEFAULT and decode it a bit, which lets me see how many attackers, and how recently. The script is invoked with ipt_recents -txt.

Seems to be working well.

boot issues, networking, video, vnc, Windows

Headless Windows 10

The oldest physical box in the house, a 12 years old Core2 Quad in an old case was my Windows 10 box, nutmeg, which I don’t use very much except to test out various things under Windows. I don’t do much with Windows any more, yet it was attached to one of the three monitors on my desk – using up 1/3 of my total screen real estate; and it was generating heat and fan noise, and its presence offended me. I decided it needed to move to the basement, alongside Cinnamon and Rosemary who are already down there in a rack — banished to the basement because they have a lot of disk drives, and so generate a lot of heat and noise.

I bought another rack mount chassis, and moved nutmeg’s innards to it. This proved annoyingly difficult because various old bits of hardware decided this was a good time to give up the ghost – I lost two old disk drives that decided to stop functioning. But eventually got everything up and running.

The idea was that I would manage the box, on the relatively few occasions I needed to do so, just as I do both Cinnamon and Rosemary, with a VNC connection. So after it was up and running on my work table, I pulled the monitor, keyboard and mouse and rebooted. But attempting to connect with VNC failed. For the record, this was TightVNC.

I eventually found that VNC would work if and only if I had a monitor attached. Furthermore, if I had a monitor attached and established a VNC viewer to nutmeg, if I then unplugged the monitor the VNC viewer would immediately freeze. WTF?

Without making this a long story, I found that the problem could be resolved by changing an option in Settings/Accounts/Sign-in options which is down at the bottom under Privacy, and reads “Use my sign-in info to automatically finish setting up my device after an update or restart.”

So my mental model of what is going on is that if that option is set, windows is attempting to “set up my device” and I suppose the device it is trying to “set up” must be the monitor. What I don’t exactly get is why the VNC viewer should freeze when an existing monitor is removed. I suppose that removal generates some event internally, and processes attached in some way as consumers must be killed or something. Not sure. I don’t need to understand it. I have very few cycles in my advanced age and am not planning to waste any of them trying to figure out Windows.

I was very pleased that after I did this, and was able to connect via VNC, I was able to set the resolution to various values up to 4K. And after rebooting and reattaching it even retained my display resolution setting.

networking, systemd

Waiting for system online with systemd

I had previously used the NetworkManager utility nm-online in my startup script as described in Waiting for networks, but now that I have moved to systemd-networkd that isn’t available anymore.

There is a fair amount of stuff on the net about the systemd service called systemd-networkd-wait-online.service. And indeed, that is a useful service, if one wants other services to wait for the network to be online. But somehow most of it seems to miss the point somehow, or at least one big point. I found various statements on the net that systemd doesn’t have the equivalent of nm-online. The only way in which that is true is if one means by it that systemd doesn’t have something as primitive. In truth what systemd has is much better, and much more powerful.

Continue reading Waiting for system online with systemd →
arch linux, ipv6, linux, networking, raspbian, systemd, ubuntu

Switching to systemd-networkd

Since moving to IPv6 I have had two recurrent problem: one with some conflict between systemd and the kernel over the /proc/sys/net/ipv6/conf/*/accept_ra, and the second with losing the static ipv6 address assignments on some boxes. I believe the former problem to have something to do with systemd wanting to have control of the sysctl variables, such as accept_ra.

The latter problem is due to the various bits of software that want to have a say in the control of the network. In part some of this is my own fault, as I do have these various bits installed – and if they weren’t installed they could not be causing trouble.

I installed NetworkManager in some places, even when it hadn’t been installed by default, because I wanted to be able to control things with the network applet in gnome. I installed dhclient even though it wasn’t installed, because I wanted better ability to see and control the dhcpv6 leases, particularly the DUID, and network manager made that difficult (and astonishingly, in some cases simply didn’t work).

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arch linux, gateways, ipv6, linux, mac, networking, openssh, postfix, raspberry pi, raspbian, security, ubuntu, vpn

IPv6 Re-implementation

This is a follow up to the activities in IPv6 implementation, which was published on March 2nd and revised up through March 19th, as new challenges were addressed. Since March 19th a great deal of what I wrote has been revised, as I have learned a lot more.

The main issue was that there remained a number of problems with the implementation of IPv6 in my residence.

  • The biggest was the question how to handle the delegated prefix, particularly in renumbering. Over the course of the last several months I have to note that Comcast has never changed my prefix, except early on, when I forced it to do so by changing my DUID. And I don’t think it likely that my prefix would change unless some great catastrophe befalls which results in my being down for a very extended period – like 30 days; or more likely there is some change in my service (a change in ISP, or perhaps fiber arriving in my area).
  • The first implementation required that I make patches to the code of my router. This meant that I would have to figure out how to carry those patches forward in the event of firmware updates from Ubiquiti, the maker of the Edgerouter-X that I am using.
  • The implementation was pretty fragile, with a lot of unrelated bits in different places. In particular there was a lot of hand-waving in trying to assign and maintain a separate network for the virtual machines on one of the interior boxes.
Continue reading IPv6 Re-implementation →
arch linux, boot issues, gateways, linux, networking, raspberry pi, raspbian, ubuntu

Waiting for networks

I was revising some things in my startup scripts. I have a sort of generalized startup script in all the boxes in my constellation, which is capable of doing 8 or 10 different things that various of the boxes need to do at startup.

For example, the various gateway boxes need to open up (auto)ssh connections to my house with reverse tunnels so I can reach them. On some boxes I want them to open a vncserver so I can get a graphical environment up. On some others they may need to mount some filesystems, with smb or nfs. On some of them I want them to figure out where their router is, in case I want to open up their router in a browser. On some I need them to establish the keychain.

Continue reading Waiting for networks →