CenturyLink PPPoE and 6rd on an OpenBSD router

!README.md

Replacing the CenturyLink provided ethernet router with OpenBSD

Unfortunately CenturyLink provisions their fiber to the home with a PPPoE authentication over vlan 201, this makes replacing the router more difficult than it should be. I also had to call CenturyLink support to get the password for the PPPoE connection.

cnmac0 is the egress interface on my EdgeRouter Lite.

You also need to add match on pppoe0 scrub (max-mss 1452) to your pf.conf because otherwise many things don't work. (Thanks Bryan) Specifically, 40 less than the mtu on pppoe0.

If you're doing ipsec over this link, you also need to scrub the enc0 max-mss to 64 smaller than the max-mss on the pppoe interface. match on enc0 scrub (max-mss 1428).

Overall it ends up being fairly forward, the PPPoE config is copied directly from the man page with the minor change that CenturyLink uses chap instead of pap.

The IPv6 setup was based on these resources from some DuckDuckGo.com searches

• http://internethelp.centurylink.com/internethelp/modem-q1000-ipv6rd.html
• http://undeadly.org/cgi?action=article&sid=20130828151241
• https://forum.openwrt.org/viewtopic.php?id=37516
• https://www.reddit.com/r/ipv6/comments/15u4hi/6rd_centurylinkqwest/

6rd.sh

#!/bin/ksh
# http://internethelp.centurylink.com/internethelp/modem-q1000-ipv6rd.html
# http://undeadly.org/cgi?action=article&sid=20130828151241
# https://forum.openwrt.org/viewtopic.php?id=37516
# https://www.reddit.com/r/ipv6/comments/15u4hi/6rd_centurylinkqwest/
# https://gist.github.com/afresh1/791343380b4410687d51fdd94f20bd42

# Put this in root's crontab with -s:
# * * * * * -ns /usr/local/sbin/6rd.sh

PATH=/usr/bin:/usr/sbin:/bin:/sbin

if=gif0
publicif=pppoe0
set -A int_ifs -- vlan40 vlan41

search_domain=home.hewus.com

# CenturyLink
rdprefix=2602
rdmask=24
v4dest=205.171.2.64

v4ip=''
while [ -z "$v4ip" -o "$v4ip" = "0.0.0.0" ]; do
  v4ip=$( ifconfig $publicif |
    sed -ne 's/[[:space:]]*inet[[:space:]]\([^[:space:]]*\).*/\1/p' )
  sleep 1
done

if [ "$v4ip" = "0.0.0.0" ]; then
  echo "No IP on $publicif" >&2
  exit 1
fi

v6ip=$( ifconfig $if |
    sed -ne "s/[[:space:]]*inet6[[:space:]]\($rdprefix[^[:space:]]*\).*prefixlen[[:space:]]*\([[:digit:]]*\)/\1\/\2/p" )

v6format="$rdprefix:%x:%x%02x:%x"
v6prefix=$( printf ${v6format}      $( echo $v4ip   | tr '.' ' ' ) )
v6dest=$(   printf ${v6format}00::1 $( echo $v4dest | tr '.' ' ' ) )

# The prefix I get to use is the rdmask + the 32 bits of the v4 address
# Some OS's only seem to accept a /64 (linux, macos)
v6external=${v6prefix}00::1/$rdmask

# We're already configured, don't try again
[ "$v6ip" = "$v6external" ] && exit

# Lose 20 bytes for the 6rd tunnel
mtu="$( ifconfig "$publicif" | sed -ne 's/.* mtu \([0-9]*\)$/\1/p' )"
#mtu=$(( mtu - 20 )) # trying a smaller mtu
# testing shows that to make it internally, we need a _way_ smaller MTU
#mtu=1232

# add "include: /var/unbound/etc/6rd.conf" to the end of unbound.conf
exec 5>/var/unbound/etc/6rd.conf
exec 6>/etc/rad.conf

#exec 5>/tmp/6rd.conf
#exec 6>/tmp/rad.conf
#route() { true; }
#ifconfig() { true; }
#rcctl() { true; }

ifconfig $if mtu    $mtu
ifconfig $if tunnel $v4ip $v4dest

# reset any old v6 addresses
route -qn delete -inet6 default
ifconfig $if           -inet6

cat <<-EOL >&5
	server:
	    # I have this already configured, you might have to uncomment
	    #local-zone: "$search_domain." static
	    local-data: "$( hostname ). IN AAAA ${v6external%/*}"
EOL

cat <<-EOL >&6
	mtu $mtu
	dns { search $search_domain }

EOL

ifconfig carp 2>/dev/null | grep -q "status: backup" &&
    echo "router preference low" >&6

integer i=0
for iif in "${int_ifs[@]}"; do
	ifconfig $iif   -inet6
	i=$(( i + 1 ))

	# wow this is ugly
	typeset -Z5 -i16 ih=$i
	v6=${v6prefix}${ih%16#*}${ih#*16#}::1/$(( rdmask + 32 + 8 ))

	echo "$iif $v6" >&2
	ifconfig "$iif" inet6 $v6

	cat <<-EOL >&5
	    interface: ${v6%/*}
	    access-control: $v6 allow
	    local-data: "ns$i.$search_domain. IN AAAA ${v6%/*}"

	EOL

	cat <<-EOL >&6
		interface $iif { dns { nameserver ${v6%/*} } }
	EOL
done

5>&-
6>&-

echo "$if $v6external" >&2
ifconfig $if   inet6 $v6external
route -qn add -inet6 default $v6dest

rcctl reload rad
rcctl start  rad
rcctl restart unbound # reload didn't seem to listen on new interfaces

hostname.pppoe0

# mtu is 8 less than vlan201
# or the seeming max of 1492 that CenturyLink allows 
inet 0.0.0.0 255.255.255.255 NONE mtu 1492 \
        pppoedev vlan201 authproto chap \
        authname '[email protected]' authkey 'mypassword' up
dest 0.0.0.1
!/sbin/route add default -ifp \$if 0.0.0.1
!/usr/local/sbin/6rd.sh

hostname.vlan201

# the parent interface needs to be able to hold this, but commonly can
# you may need to set mtu 1518 or something on cnmac0
mtu 1500
vnetid 201 parent cnmac0
up

I've used tpmr(4) to snoop the traffic between the ISP router and their service to figure out what's going on before, like what VLANs are in use, pppoe or not, or pppoe creds.