====== Alternate address ======

Based on my experiments with [[prefix_delegation|IPv6 prefix delegation and subnetting]] I determined a prefix to delegate to Steve. Steve has asked for a /64 delegation like the one I would get from him. The prefix became 1011, derived in this manner: My LAN (0019) is actually subnet 0 in the first level (/56), subnet 1 in the next level (/60) and subnet 9 in the third level (/64). So the 1011 is subnet 10 (first level), 1 second level and again 1 third level. The initial 10 could also be interpreted as subnet 1 in a /52 allocation and subnet 0 in the /56 allocation giving a total of four possible subnet levels.


===== Steve's configuration using 2a06:4000:8073:1011::/64 =====
(basically excerpts from an email)


i) on the VPN router
    ip addr add dev br-lan 2a06:4000:8073:1011::2/64
    ip route add default from 2a06:4000:8073:1011::/64 dev tun2 metric 10    ===> for return traffic

ii) on Ictoan
    ip addr add br-lan 2a06:4000:8073:1011:202:12:89:12/64
    ip route add default from 2a06:4000:8073:1011::/64 via 2a06:4000:8073:1011::2  ===> for return traffic

a) on Vultrgate
    ip route add 2a06:4000:8073:1011::/64 via tun0
    ip route add 2001:44b8:5135:7c07::/64 dev wg0
    Add 2001:44b8:5135:7c07::/64 to Bent's peer "allowed-ips"

===== Bent's end 2001:44b8:5135:7c07::/64 =====

==== gate-rpi ====
The basic IP commands are:
      ip addr add dev eth0 2001:44b8:5135:7c07::44/64
      ip route add default from 2001:44b8:5135:7c07::/64 dev wg0  metric 10    ===> for return traffic
      ip -6 route add 2a06:4000:8073:1011::/64 dev wg0 
Two of the three commands are easily transferred to Networkd configurations files but the one with 'default from' isn't. The solution chosen was to write a systemd service file for this. The service file is listed further down. Here is the configuration file for eth0:
  #/etc/systemd/network/eth0.network
  [Match]
  Name=eth0
  
  [Network]
  Address=192.168.19.44/24
  DNS=192.168.19.5
  IPForward=yes
  Address=2a06:4000:8073:19::44/64
  Address=2001:44b8:5135:7c07::44/64
  IPv6AcceptRA=yes
and for the tunnel interface (wg0):
  #/etc/systemd/network/wg0.network
  [Match]
  Name=wg0
  
  [Network]
  Address=10.8.3.2/24
  IPForward=yes
  
  [Route]
  #Gateway=10.8.3.1
  Destination=2a06:4000:8073:1011::/6

==== Spot ====
Similarly the basic IP commands are: 
      ip addr add dev enp2s0 2001:44b8:5135:7c07::5/64
      ip route add default from 2001:44b8:5135:7c07::/64 via 2001:44b8:5135:7c07::44 metric 10  ==> return traffic
The 'default from' entry is again handled by a service file.
Configuration file for enp2s0:
  [Match]
  Name=enp2s0
  
  [Network]
  Address=192.168.19.5/24
  Gateway=192.168.19.254
  Address=2a06:4000:8073:19::5/64
  DHCP=no
  IPv6AcceptRA=yes
  
  [Address]
  Address=2001:44b8:5135:7c07::5/64
  PreferredLifetime=0
(the PreferredLifetime=0 is there to prevent usein this address as source address for outgoing connections
==== Service script ====

  #/etc/systemd/system/return-route.service
  [Unit]
  Description=Return route for IPv6 traffic
  After=network-online.target
  
  [Service]
  ExecStart=/usr/bin/ip -6 route add default from 2001:44b8:5135:7c07::/64 via 2a06:4000:8073:19::44 dev enp2s0 metric 10
  ExecStop=/usr/bin/ip -6 route del default from 2001:44b8:5135:7c07::/64 via 2a06:4000:8073:19::44 dev enp2s0 metric 10
  Type=oneshot
  RemainAfterExit=yes
  
  [Install]
  WantedBy=multi-user.target
This is the script from Spot. The one on gate-rpi is identical except for the interface name which is eth0 on gate-rpi. It doesn't have the 'via' part either.