add file about example IPs

docs/contribution/example-networks.md

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+# Example networks for documentation
+
+## Background
+
+When writing documents you often need networks or IP addresses for examples. This page lists the networks which are explicitly mentioned in Internet Standards for this purpose.
+
+### IPv4 Example Networks
+
+#### Source: RFC5737
+
+The following networks are fully routable /24 networks (256 addresses), but set aside for documentation purposes:
+
+- 192.0.2.0/24
+- 198.51.100.0/24
+- 203.0.113.0/24
+
+#### Source: RFC1918
+
+The following networks are so-called private networks, they cannot be routed in the global BGP table but can be freely used in private networks:
+
+- 10.0.0.0/8 (10.0.0.0 - 10.255.255.255)
+- 172.16.0.0/12 (172.16.0.0 - 172.31.255.255)
+- 192.168.0.0/16 (192.168.0.0. - 192.168.255.255)
+
+### IPv6 Example Network
+
+#### Source: RFC3849
+
+The following network block is fully routable, but set aside for documentation purposes:
+
+- 2001:db8::/32
+
+### Autonomous System Numbers
+
+#### Source: RFC5398
+
+The following AS numbers are set aside for documentation purposes:
+
+- 16-Bit numbers: 64496 - 64511
+- 32-Bit numbers: 65536 - 65551
+
+#### Source: RFC6996
+
+The following AS numbers are reserved for private use:
+
+- 16-Bit numbers: 64512 - 65534
+- 32-Bit numbers: 4200000000 - 4294967294
+
+### Domain Names
+
+#### Source: RFC2606
+
+The following domain names can be used for documentation:
+
+- ".example" (Top-Level Domain)
+- "example.com"
+- "example.net"
+- "example.org"