Intro

This guide introduces a minimal CoreRAD configuration which can be used to provide IPv6-enabled hosts with a default route and IPv6 addresses via Stateless Address Autoconfiguration (SLAAC).

This guide will assumes a Linux-based router with the following configuration:

a LAN-facing network interface named eth0
IPv6 addresses from one or more /64 subnets configured on eth0, via static assignment, DHCPv6 prefix delegation, or another mechanism
IPv6 forwarding enabled for eth0

$ ip -6 addr show dev eth0
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP group default qlen 1000
    inet6 fd9e:1a04:f01d::1/64 scope global
       valid_lft forever preferred_lft forever
    inet6 2600:6c4a:787f:d100::1/64 scope global dynamic noprefixroute
       valid_lft 537884sec preferred_lft 537884sec
    inet6 fe80::20d:b9ff:fe53:eacd/64 scope link
       valid_lft forever preferred_lft forever

$ cat /proc/sys/net/ipv6/conf/eth0/forwarding
0
$ echo 1 | sudo tee /proc/sys/net/ipv6/conf/eth0/forwarding
1

Create a minimal corerad.toml configuration file with the following contents.

# Advertise an IPv6 default route on eth0.
[[interfaces]]
name = "eth0"
advertise = true

  # Advertise an on-link, autonomous prefix for all /64 addresses on eth0. This
  # also enables stateless address autoconfiguration (SLAAC) for clients.
  [[interfaces.prefix]]

  # Serve route information for IPv6 routes destined to the loopback interface.
  [[interfaces.route]]

  # Inform clients of a recursive DNS server running on this interface.
  [[interfaces.rdnss]]

# Optional: enable Prometheus metrics.
[debug]
address = "localhost:9430"
prometheus = true

As of January 2022, CoreRAD packages are available for:

For other Linux distributions or operating systems, download and build the latest CoreRAD release from source. A Go 1.18+ compiler is required.

$ go build ./cmd/corerad/
$ ./corerad -h
CoreRAD v1.1.0 (2022-03-19)
flags:
  -c string
        path to configuration file (default "corerad.toml")
  -init
        write out a minimal configuration file to "corerad.toml" and exit

Ensure the CoreRAD binary has the Linux capabilities CAP_NET_ADMIN and CAP_NET_RAW to appropriately manage network interfaces and handle raw ICMPv6 NDP traffic:

$ sudo setcap cap_net_raw,cap_net_admin+ep ./corerad

Finally, start CoreRAD with the configuration file:

$ ./corerad -c ./corerad.toml
CoreRAD v1.1.0 (2022-01-31) starting with configuration file "corerad.toml"
starting HTTP debug listener on "localhost:9430": prometheus: true, pprof: false
eth0: "prefix": ::/64 [2600:6c4a:787f:d100::/64, fd9e:1a04:f01d::/64] [on-link, autonomous], preferred: 4h0m0s, valid: 24h0m0s
eth0: "route": ::/0 [fd9e:1a04:f01d::/48], preference: Medium, lifetime: 24h0m0s
eth0: "rdnss": servers: [:: [fd9e:1a04:f01d::1]], lifetime: 20m0s
eth0: "lla": source link-layer address: 00:0d:b9:53:ea:cd
eth0: initialized, advertising from fe80::20d:b9ff:fe53:eacd%eth0

Client machines on the router’s LAN should now have an IPv6 default route and one or more IPv6 addresses per advertised prefix, generated via SLAAC:

client $ ip -6 route show dev eth0
2600:6c4a:787f:d100::/64 proto ra metric 101 pref medium
fd9e:1a04:f01d::/64 proto ra metric 101 pref medium
fd9e:1a04:f01d::/48 via fe80::20d:b9ff:fe53:eacd dev wlp170s0 proto ra metric 600 pref medium
fe80::/64 proto kernel metric 101 pref medium
default via fe80::20d:b9ff:fe53:eacd proto ra metric 20101 pref medium

client $ ip -6 addr show dev eth0
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP group default qlen 1000
    inet6 2600:6c4a:787f:d100:e446:69ee:4970:114e/64 scope global temporary dynamic
       valid_lft 86011sec preferred_lft 14011sec
    inet6 2600:6c4a:787f:d100:6d9:f5ff:fe7e:1c47/64 scope global dynamic mngtmpaddr noprefixroute
       valid_lft 86011sec preferred_lft 14011sec
    inet6 fd9e:1a04:f01d:0:e446:69ee:4970:114e/64 scope global temporary dynamic
       valid_lft 86011sec preferred_lft 14011sec
    inet6 fd9e:1a04:f01d:0:6d9:f5ff:fe7e:1c47/64 scope global dynamic mngtmpaddr noprefixroute
       valid_lft 86011sec preferred_lft 14011sec
    inet6 fe80::6d9:f5ff:fe7e:1c47/64 scope link noprefixroute
       valid_lft forever preferred_lft forever

Optionally, check out CoreRAD’s Prometheus metrics output:

$ curl -s localhost:9430/metrics | grep corerad_advertiser_prefix_autonomous
# HELP corerad_advertiser_prefix_autonomous Indicates whether or not the Autonomous Address Autoconfiguration (SLAAC) flag is enabled for a given advertised prefix.
# TYPE corerad_advertiser_prefix_autonomous gauge
corerad_advertiser_prefix_autonomous{interface="eth0",prefix="2600:6c4a:787f:d100::/64"} 1
corerad_advertiser_prefix_autonomous{interface="eth0",prefix="fd9e:1a04:f01d::/64"} 1

From here, you may wish to read through the Operation guide to learn how to run CoreRAD under systemd supervision, and how to monitor upstream network traffic.