VulnTech Static IPv6 on PCs, testing and troubleshooting

Static IPv6 on a PC

OS	Address	Default gateway
Windows	netsh interface ipv6 add address "Ethernet" 2001:db8:acad:10::10/64	netsh interface ipv6 add route ::/0 "Ethernet" fe80::1
Linux	sudo ip -6 addr add 2001:db8:acad:20::10/64 dev eth0	sudo ip -6 route add default via fe80::1
macOS	System Settings (or networksetup)	System Settings

A static address is added next to any SLAAC address: an IPv6 interface happily has several.

In NetLab

▶ PC2
student@PC2:~$ sudo ip -6 addr add 2001:db8:acad:20::10/64 dev eth0
student@PC2:~$ ip -6 addr show
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    inet6 ::1/128 scope host noprefixroute 
       valid_lft forever preferred_lft forever
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000
    inet6 2001:db8:acad:20::10/64 scope global 
       valid_lft forever preferred_lft forever
    inet6 2001:db8:acad:20:21a:f2ff:fe3a:a4ee/64 scope global dynamic mngtmpaddr 
       valid_lft 2591998sec preferred_lft 604798sec
    inet6 fe80::21a:f2ff:fe3a:a4ee/64 scope link 
       valid_lft forever preferred_lft forever
▶ PC1
NetLab Windows-style command prompt. Type help to see the commands.
C:\Users\student>ping 2001:db8:acad:20::10

Pinging 2001:db8:acad:20::10 with 32 bytes of data:
Reply from 2001:db8:acad:20::10: time<1ms
Reply from 2001:db8:acad:20::10: time<1ms
Reply from 2001:db8:acad:20::10: time<1ms
Reply from 2001:db8:acad:20::10: time<1ms

Ping statistics for 2001:db8:acad:20::10:
    Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
    Minimum = 0ms, Maximum = 0ms, Average = 0ms
C:\Users\student>tracert 2001:db8:acad:20::10

Tracing route to 2001:db8:acad:20::10 over a maximum of 30 hops

  1   <1 ms    <1 ms    <1 ms  2001:db8:acad:10::1
  2    2 ms     2 ms     2 ms  2001:db8:acad:20::10

Trace complete.

When it doesn't work

In this network the router has addresses but nobody turned on ipv6 unicast-routing. Look at what the PC has:

In NetLab

▶ PC1
NetLab Windows-style command prompt. Type help to see the commands.
C:\Users\student>ipconfig

Windows IP Configuration


Ethernet adapter Ethernet:

   Connection-specific DNS Suffix  . : 
   Link-local IPv6 Address . . . . . : fe80::11db:99de:fbce:36d1%12
   Default Gateway . . . . . . . . . : 
C:\Users\student>ping 2001:db8:acad:10::1

Pinging 2001:db8:acad:10::1 with 32 bytes of data:
PING: transmit failed. General failure. 
PING: transmit failed. General failure. 
PING: transmit failed. General failure. 
PING: transmit failed. General failure. 

Ping statistics for 2001:db8:acad:10::1:
    Packets: Sent = 4, Received = 0, Lost = 4 (100% loss),

Only a link-local address and no gateway: no RA ever came. The PC can't even reach the router's global address, because it has no route to it.

Symptom	Check
PC has only an fe80:: address	ipv6 unicast-routing on the router; the router's interface is up and has a /64
PC has an address but no gateway	The RA: again ipv6 unicast-routing
Can reach the gateway, not beyond	The far side: its prefix, its gateway, the router's routes
Static address doesn't work	The prefix must match the router's /64 on that LAN; the gateway must be the router's link-local (or global) address on that LAN

Tip: show ipv6 interface brief on the router and ipconfig / ip -6 addr on the PC answer most IPv6 questions in seconds.

Static IPv6 on a PC

When it doesn't work

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