++blog ipv4 via ipv6
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Nico Schottelius
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title: How to route IPv4 via IPv6
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---
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pub_date: 2019-12-10
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---
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author: ungleich network
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---
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twitter_handle: ungleich
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---
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_hidden: yes
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---
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_discoverable: no
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---
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abstract:
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Bringing IPv4 into the IPv6 world
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---
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body:
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Imagine the following: you are running an IPv6 only network. And now
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someone asks you to pass IPv4 traffic through it, without tunneling
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it. Was sounds crazy at first, is actually quite feasible.
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## A short routing recap
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Routers have routing tables. The routing tables basically say
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"if you receive a packet for this host, send it to that router".
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The important thing about this process is that the information on
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where to send it to, is **not in the packet**.
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## How to send IPv4 packets via IPv6
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Because the next hop is not written into the IPv4 packet, the router
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is free to forward the packet via any method it thinks is the
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best. And if that happens to be IPv6 - well, it will forward the IPv4
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packet via an IPv6 neighbour.
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## A practical example!
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```
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[root@diamond ~]# ip -6 r
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::1 dev lo proto kernel metric 256 pref medium
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2a0a:e5c1:137::/48 dev wgungleich proto kernel metric 256 pref medium
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fe80::/64 dev wlp0s20f3 proto kernel metric 256 pref medium
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[root@diamond ~]# ip r
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default via 192.168.84.1 dev wlp0s20f3 proto dhcp src 192.168.84.7 metric 302
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192.168.84.0/22 dev wlp0s20f3 proto dhcp scope link src 192.168.84.7 metric 302
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[root@diamond ~]# ip route add 10.0.0.0/8 via inet6 2a0a:e5c1:137::22
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[root@diamond ~]# ip -6 route
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::1 dev lo proto kernel metric 256 pref medium
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2a0a:e5c1:137::/48 dev wgungleich proto kernel metric 256 pref medium
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fe80::/64 dev wlp0s20f3 proto kernel metric 256 pref medium
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[root@diamond ~]# ip r
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default via 192.168.84.1 dev wlp0s20f3 proto dhcp src 192.168.84.7 metric 302
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10.0.0.0/8 via inet6 2a0a:e5c1:137::22 dev wgungleich
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192.168.84.0/22 dev wlp0s20f3 proto dhcp scope link src 192.168.84.7 metric 302
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[root@diamond ~]#
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```
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## More in the cloud
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Actually, what happens behind the scenes is that the VM is running VNC
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(we are also experimenting with XRDP), so I have actually full access
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to a remote Linux desktop via browser and can even run applications
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like libreoffice, blender or gimp remotely.
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Because I think it's a cool thing to have, our team at ungleich added
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it as an offer to our [Black IPv6 Friday
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Crowdfunding](https://swiss-crowdfunder.com/campaigns/black-ipv6-friday?locale=en).
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Below you can actually see how it looks like:
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root@beebox ~ # route add 192.168.0.0/16 2a0a:e5c1:100::1
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add net 192.168.0.0/16: gateway 2a0a:e5c1:100::1
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root@beebox ~ # route -n get 192.168.1.2
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route to: 192.168.1.2
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destination: 192.168.0.0
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mask: 255.255.0.0
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gateway: 2a0a:e5c1:100::1
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interface: tun3
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if address: 2a0a:e5c1:11e::1
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priority: 8 (static)
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flags: <UP,GATEWAY,DONE,STATIC>
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use mtu expire
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2 0 0
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89
content/u/blog/how-to-route-ipv4-via-ipv6/contents.lr
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89
content/u/blog/how-to-route-ipv4-via-ipv6/contents.lr
Normal file
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@ -0,0 +1,89 @@
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title: How to route IPv4 via IPv6
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---
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pub_date: 2020-02-10
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---
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author: ungleich network
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---
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twitter_handle: ungleich
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---
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_hidden: no
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---
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_discoverable: yes
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---
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abstract:
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Bringing IPv4 into the IPv6 world
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---
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body:
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Imagine the following: you are running an IPv6 only network. And now
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someone asks you to pass IPv4 traffic through it, without tunneling
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it. Was sounds crazy at first, is actually quite feasible.
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## A short routing recap
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Routers have routing tables. The routing tables basically say
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"if you receive a packet for this host, send it to that router".
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The important thing about this process is that the information on
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where to send it to, is **not in the packet**.
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## How to send IPv4 packets via IPv6
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Because the next hop is not written into the IPv4 packet, the router
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is free to forward the packet via any method it thinks is the
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best. And if that happens to be IPv6 - well, it will forward the IPv4
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packet via an IPv6 neighbour.
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## A practical example!
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In the IPv6 only coworking network in the [Digital
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Chalet](/u/projects/digital-chalet/), I can add an IPv4 default route
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via the IPv6 router:
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```
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[root@diamond ~]# ip route add 0/0 nexthop via inet6 fe80::21b:21ff:febb:6934 dev wlp0s20f3
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[root@diamond ~]# ip r
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default via inet6 fe80::21b:21ff:febb:6934 dev wlp0s20f3
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[root@diamond ~]#
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```
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Now to be able to actually transmit IPv4 packets, I do need a source
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IPv4 address. In the current network I can use an address in the
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unused 10.0.8.0/22 network:
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```
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ip addr add 10.0.8.42/32 dev wlp0s20f3
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[root@diamond ~]# ip r
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default via inet6 fe80::21b:21ff:febb:6934 dev wlp0s20f3
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[root@diamond ~]# ip a sh dev wlp0s20f3
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2: wlp0s20f3: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default qlen 1000
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link/ether 24:ee:9a:54:c3:bf brd ff:ff:ff:ff:ff:ff
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inet 10.0.8.42/32 scope global wlp0s20f3
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valid_lft forever preferred_lft forever
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inet6 2a0a:e5c0:0:4:c6ea:b1a8:ec14:6f35/64 scope global dynamic mngtmpaddr noprefixroute
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valid_lft 86400sec preferred_lft 14400sec
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inet6 fe80::3b98:cb58:ed02:c25/64 scope link
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valid_lft forever preferred_lft forever
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[root@diamond ~]#
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```
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And I can indeed ping another IPv4 address, routed via IPv6!
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```
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[root@diamond ~]# ping -4 10.0.8.3
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PING 10.0.8.3 (10.0.8.3) 56(84) bytes of data.
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64 bytes from 10.0.8.3: icmp_seq=1 ttl=64 time=2.37 ms
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^C
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--- 10.0.8.3 ping statistics ---
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1 packets transmitted, 1 received, 0% packet loss, time 0ms
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rtt min/avg/max/mdev = 2.365/2.365/2.365/0.000 ms
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[root@diamond ~]#
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```
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## Do it yourself
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If you don't believe us that it is possible, you can test it yourself
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on IPv6 only VMs on [IPv6OnlyHosting.com](https://ipv6onlyhosting.com).
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