Month: January 2019

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SSL Everywhere? Maybe not cups

Last night I made the aggravating discovery that cups has gone SSL. The option to have cups protected by SSL is wonderful but I’m not sure that SSL by default is a good thing for printing services. I discovered this because printing from my Apple machines was failing with no log messages from my the Apple machines on my network. At first I thought this might be an IPv6 issue. Using tcpdump I quickly determined that cups on my Mac was not only using IPv6 but that it was using the semi-random “private/temporary” address of my cups server. But continued debugging showed that IPv6 wasn’t the issue, and the private/temporary address wasn’t it either. Disabling Encryption with the:

DefaultEncryption Never

Did the trick. This is clearly not safe. What would be best would be cutting a certificate for my cups server. That’s problematic because two years from now when the certificate expires, how long will it take me to figure out why printing stops working. Perhaps best would be to encrypt requests that need a password and allow cleartext communications for plain printing.

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Turn off arp change noise on FreeBSD

If you run a FreeBSD server on a machine with any Apple infrastructure, Airport, AppleTV, etc then you are probably used to seeing lots of messages like this:

...
+arp: 169.254.124.133 moved from --- somewhere --- to - somewhere else- on em0
+arp: 169.254.124.133 moved from - somewhere else- to --- somewhere --- on em0
...

This is the Bonjour Sleep Proxy service in action. A device that provides a sleep proxy attempts to make Bonjour services available on your network at all times by advertising  the proxy’s IP address  as  the service destination while the  true provider is sleeping. For example, if you have an older, non-networked shared printer connected to an iMac Desktop, the sleep proxy will advertise it’s own address as the destination for your share printer. If someone sends a print request to your printer, the sleep proxy intercepts the request, sends a wake up packet to your iMac, and then the printing can actually go on.

This activity looks a lot like an arp poisoning attack. If you want to check for that look at the mac address of the devices in question. You can look up the first three octets of the mac address at Google. Those are a manufacturer ID. If one or both of the devices is from Apple, it’s more likely that you have a Bonjour Sleep Proxy working on your network.

Over time these messages are disruptive on a FreeBSD server because they blow valid information out of the kernel’s dmesg buffer. You can still the kernel’s boot dmesg by groveling through sysctl if you have a disk drive that’s misbehaving, that information will be lost in a day or two.

To turn these messages off, do the following:

$ sudo su -
Password: 
# ## Fix this for this kernel boot session...
# sysctl -w net.link.ether.inet.log_arp_movements=0
net.link.ether.inet.log_arp_movements: 1 -> 0
# ## Fix this permanently.
# echo 'net.link.ether.inet.log_arp_movements=0' >> /etc/sysctl.conf
#