Date: Sat, 29 Jun 2024 17:17:18 -0700 From: Craig Leres <leres@freebsd.org> To: freebsd-stable@freebsd.org Subject: FreeBSD 14.x localhost source address Message-ID: <086405e2-8fc2-4463-b8bb-d6c652745ae1@freebsd.org>
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When I upgraded ~10 systems from 13.3 to 14.1 recently, 90%+ of my
breakage was due to the localhost source address changing from 127.0.0.1
to 127.0.0.2. This was on two of my systems.
My lo0 config is standard:
mote 20 % ifconfig lo0
lo0: flags=1008049<UP,LOOPBACK,RUNNING,MULTICAST,LOWER_UP> metric 0
mtu 16384
options=680003<RXCSUM,TXCSUM,LINKSTATE,RXCSUM_IPV6,TXCSUM_IPV6>
inet 127.0.0.1 netmask 0xff000000
inet6 ::1 prefixlen 128
inet6 fe80::1%lo0 prefixlen 64 scopeid 0x2
groups: lo
nd6 options=21<PERFORMNUD,AUTO_LINKLOCAL>
What's different on the two problematic systems is that they are
authoritative nameservers. Following best practices, I use the (bind)
server for authoritative queries and unbound for recursive resolver
duties. The way I did this was to configure unbound to listen on
127.0.0.2 and then change /etc/resolv.conf to use "nameserver
127.0.0.2". (Which reminds me of another 14.X breakage -- unbound is no
longer able to provide me with authoritative sshfp records!)
For 14.1 at least, this has the side effect that the source address for
anything in the 127.0.0.0/8 domain becomes 127.0.0.2 instead of 127.0.0.1.
Given a host that has unbound listening on 127.0.0.2:
mote 133 # lsof -np `cat /usr/local/etc/unbound/unbound.pid` |
fgrep domain
unbound 39496 unbound 3u IPv4 0xfffff8001ee56000 0
UDP 127.0.0.2:domain->*:*
unbound 39496 unbound 4u IPv4 0xfffff80037c2ea80 0
TCP 127.0.0.2:domain->*:* (LISTEN)
you can see this with the iperf3 port. Start the server side with:
iperf3 -s 127.0.0.1
and connect using:
iperf3 -c 127.0.0.1
The server session will report:
Accepted connection from 127.0.0.2, port 37306
I believe my configuration is far enough off the well-traveled path that
I'm the first to notice this. But there are definitely some programs
(e.g. sendmail/opendkim which appears to sign messages from 127.0.0.1
but not from 127.0.0.2!) that are hardwired to know about 127.0.0.1 and
deal with it specially/differently...
Craig
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