3

When I initially connect to my home network my windows PC is assigned an IPv6 address - however after a few minutes it loses this address! I seem to have similar behaviour on multiple hosts using both wireless and wired connections.

My router is an Asus RT-AC87U.

How could it be losing the IPv6 address? How can I mintor / diagnose this issue?

Update: Based on @grawity's suggestion below I ran wireshark on this. Sure enough I see a Router Solicitation message and a Router Advertisment message with a Router lifetime of 600 seconds. After 600 seconds my computer drops its Ipv6 address.

What is supposed to happen? Should my host send another Router Solicitation message? Or should the router periodically resend the Router Advertisment message?

Update 2:

  • RFC 4862 says that Router Adverticement messages should be sent periodically.
Community
  • 1
Matthew
  • 171
  • 1
  • 6
  • 1
    Using Wireshark (capture filter `icmp6` or display filter `icmpv6`), can you check how often you see a Router Advertisement, and whenever you see one what "ICMP→Router lifetime" & "ICMP→Prefix→Valid lifetime" does it show? – u1686_grawity Nov 19 '18 at 11:23
  • Have you tried Asuswrt-Merlin? – Michael Hampton Nov 19 '18 at 14:58
  • Go to [test-ipv6.com](https://test-ipv6.com/). If it says that your ipv6 ICMP is filtered, then see [this article](https://www.howtogeek.com/howto/windows-vista/allow-pings-icmp-echo-request-through-your-windows-vista-firewall/). If this helps let me know and I'll put up a detailed answer. – harrymc Nov 19 '18 at 21:24
  • @grawity - looks like you were right, the router advertisements are timing out. I've updated the question. – Matthew Nov 21 '18 at 08:06
  • @harrymc: That only tells one whether ICMP from WAN is filtered; it doesn't necessarily correspond to multicast ICMP within the LAN itself... – u1686_grawity Nov 21 '18 at 11:14

2 Answers2

2

Ok I think I figured this out:

My router has a flag that says Enable Router Advertisement. This was enabled - but by switching it to disabled (restarting) and then back to enabled (and restarting again) seems to have done something to the router and now wireshark shows it sending Router Advertisement messages every few seconds!

Matthew
  • 171
  • 1
  • 6
  • 1
    Every few seconds is way too often. (Drains Wi-Fi devices' battery, among other things.) Normally it should be every few minutes, with the "Router Lifetime" field being 2x-3x the interval. If you saw that "Router Lifetime" is 600s, expect the advertisements to be automatically sent every 200-300s (plus whenever a PC requests/solicits one). – u1686_grawity Nov 21 '18 at 11:17
2

FYI, I have an answer, for those of you that don't have a "RA switch flip", in your router (I use a Cisco RV340 at home, an SMB router), so it's got a bit "more depth" in the IPv6 area. I was really scratching my head over this, our Win10 machines were all losing their IPv6 gateways, at 50 minutes, give or take a few seconds, right after a whole slew of RA messages (monitored using Wireshark). Turns out, it was my Router Lifetime value, which had worked fine, at the default 50 minutes (3000 seconds), for at least 2 years (I suspect my ISP changed something on their side here). Changing to 5 minutes (300 seconds) fixed, this, completely, for 3 different (wired) machines, and one WiFi machine, I tested all of them for several hours, each.
This also greatly reduced the number of advertisement queries, in general, although I'm still not sure I understand why it had that effect (I'm still learning the nuts/bolts of IPv6, at least at-depth, the documentation isn't quite as "well developed" as IPv4, for obvious reasons). Anyway, hopefully this clarifies things, and helps the next users who find this entry.

peteg
  • 21
  • 2