2020-02-10 15:09:49 +00:00
|
|
|
title: How to route IPv4 via IPv6
|
|
|
|
|
---
|
|
|
|
|
pub_date: 2020-02-10
|
|
|
|
|
---
|
|
|
|
|
author: ungleich network
|
|
|
|
|
---
|
|
|
|
|
twitter_handle: ungleich
|
|
|
|
|
---
|
|
|
|
|
_hidden: no
|
|
|
|
|
---
|
|
|
|
|
_discoverable: yes
|
|
|
|
|
---
|
|
|
|
|
abstract:
|
|
|
|
|
Bringing IPv4 into the IPv6 world
|
|
|
|
|
---
|
|
|
|
|
body:
|
|
|
|
|
|
|
|
|
|
Imagine the following: you are running an IPv6 only network. And now
|
|
|
|
|
someone asks you to pass IPv4 traffic through it, without tunneling
|
|
|
|
|
it. Was sounds crazy at first, is actually quite feasible.
|
|
|
|
|
|
|
|
|
|
## A short routing recap
|
|
|
|
|
|
|
|
|
|
Routers have routing tables. The routing tables basically say
|
|
|
|
|
"if you receive a packet for this host, send it to that router".
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
The important thing about this process is that the information on
|
|
|
|
|
where to send it to, is **not in the packet**.
|
|
|
|
|
|
|
|
|
|
## How to send IPv4 packets via IPv6
|
|
|
|
|
|
|
|
|
|
Because the next hop is not written into the IPv4 packet, the router
|
|
|
|
|
is free to forward the packet via any method it thinks is the
|
|
|
|
|
best. And if that happens to be IPv6 - well, it will forward the IPv4
|
|
|
|
|
packet via an IPv6 neighbour.
|
|
|
|
|
|
|
|
|
|
## A practical example!
|
|
|
|
|
|
|
|
|
|
In the IPv6 only coworking network in the [Digital
|
|
|
|
|
Chalet](/u/projects/digital-chalet/), I can add an IPv4 default route
|
|
|
|
|
via the IPv6 router:
|
|
|
|
|
|
|
|
|
|
```
|
|
|
|
|
[root@diamond ~]# ip route add 0/0 nexthop via inet6 fe80::21b:21ff:febb:6934 dev wlp0s20f3
|
|
|
|
|
[root@diamond ~]# ip r
|
|
|
|
|
default via inet6 fe80::21b:21ff:febb:6934 dev wlp0s20f3
|
|
|
|
|
[root@diamond ~]#
|
|
|
|
|
```
|
|
|
|
|
|
|
|
|
|
Now to be able to actually transmit IPv4 packets, I do need a source
|
|
|
|
|
IPv4 address. In the current network I can use an address in the
|
|
|
|
|
unused 10.0.8.0/22 network:
|
|
|
|
|
|
|
|
|
|
```
|
|
|
|
|
ip addr add 10.0.8.42/32 dev wlp0s20f3
|
|
|
|
|
[root@diamond ~]# ip r
|
|
|
|
|
default via inet6 fe80::21b:21ff:febb:6934 dev wlp0s20f3
|
|
|
|
|
[root@diamond ~]# ip a sh dev wlp0s20f3
|
|
|
|
|
2: wlp0s20f3: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default qlen 1000
|
|
|
|
|
link/ether 24:ee:9a:54:c3:bf brd ff:ff:ff:ff:ff:ff
|
|
|
|
|
inet 10.0.8.42/32 scope global wlp0s20f3
|
|
|
|
|
valid_lft forever preferred_lft forever
|
|
|
|
|
inet6 2a0a:e5c0:0:4:c6ea:b1a8:ec14:6f35/64 scope global dynamic mngtmpaddr noprefixroute
|
|
|
|
|
valid_lft 86400sec preferred_lft 14400sec
|
|
|
|
|
inet6 fe80::3b98:cb58:ed02:c25/64 scope link
|
|
|
|
|
valid_lft forever preferred_lft forever
|
|
|
|
|
[root@diamond ~]#
|
|
|
|
|
|
|
|
|
|
```
|
|
|
|
|
|
|
|
|
|
And I can indeed ping another IPv4 address, routed via IPv6!
|
|
|
|
|
|
|
|
|
|
```
|
|
|
|
|
[root@diamond ~]# ping -4 10.0.8.3
|
|
|
|
|
PING 10.0.8.3 (10.0.8.3) 56(84) bytes of data.
|
|
|
|
|
64 bytes from 10.0.8.3: icmp_seq=1 ttl=64 time=2.37 ms
|
|
|
|
|
^C
|
|
|
|
|
--- 10.0.8.3 ping statistics ---
|
|
|
|
|
1 packets transmitted, 1 received, 0% packet loss, time 0ms
|
|
|
|
|
rtt min/avg/max/mdev = 2.365/2.365/2.365/0.000 ms
|
|
|
|
|
[root@diamond ~]#
|
|
|
|
|
```
|
|
|
|
|
|
2020-02-10 15:22:55 +00:00
|
|
|
## Why?
|
|
|
|
|
|
|
|
|
|
Why would anyone want to do this? It's quite easy: with this you can
|
|
|
|
|
route an IPv4 address to an IPv6 only host. This enables IPv6 only
|
|
|
|
|
resources to create and send IPv4 packets, even if they don't have
|
|
|
|
|
IPv4 routes.
|
|
|
|
|
|
2020-02-10 15:09:49 +00:00
|
|
|
## Do it yourself
|
|
|
|
|
|
|
|
|
|
If you don't believe us that it is possible, you can test it yourself
|
|
|
|
|
on IPv6 only VMs on [IPv6OnlyHosting.com](https://ipv6onlyhosting.com).
|
