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17 May 2026
@raitobezarius:matrix.orgraitobezariusyeah, I'm not super familiar with PCP16:08:58
@emilazy:matrix.orgemily If the PCP-controlled device is stateless (that is, it does not establish any per-flow state, and simply rewrites the address and/or port in a purely algorithmic fashion, including no rewriting), the PCP server simply returns an answer indicating the external IP address and port yielded by this stateless algorithmic translation. This allows the PCP client to learn its external IP address and port as seen by remote peers. Examples of stateless translators include stateless NAT64, 1:1 NAT44, and NPTv6 [RFC6296], all of which modify addresses but not port numbers, and pure firewalls, which modify neither the address nor the port. 16:09:07
@emilazy:matrix.orgemilylooks like it does envision there might be 6/4 mapping in there!16:09:15
@raitobezarius:matrix.orgraitobezariusthe only way I achieved these things were static allocations via SIIT-DC or MAP-T16:09:20
@emilazy:matrix.orgemilymy thinking is that if you have PCP hooked up to the NAT64, then you can also have shim UPnP/NAT-PMP servers that take normal v4 port-forwarding requests, translate them to PCP NAT64 requests, and then translate back16:10:42
@emilazy:matrix.orgemilyso if you have kernel v4→v6 translation automatic port forwarding "just works" (maybe)16:11:08
@emilazy:matrix.orgemily"When the address field holds an IPv4 address, an IPv4-mapped IPv6 address [RFC4291] is used (::ffff:0:0/96). This has the first 80 bits set to zero and the next 16 set to one"16:11:52
@emilazy:matrix.orgemilyokay yeah, so you can totally mix 6/4 with PCP16:12:00
@emilazy:matrix.orgemilyfun!16:12:06
@emilazy:matrix.orgemilyI wonder if you can get Linux to automatically make PCP requests for sockets listening on public IPs 😅16:13:33
18 May 2026
@matthewcroughan:defenestrate.itmatthewcroughan Anyone wanna help debug my tailscale? I can't use magicdns on d233902 13:47:16
@matthewcroughan:defenestrate.itmatthewcroughanand I've bumped a few times, no real changes13:47:22
@matthewcroughan:defenestrate.itmatthewcroughan IPs can still be pinged at all times, if I restart tailscaled then magicdns works again 13:47:52
@matthewcroughan:defenestrate.itmatthewcroughanThen after some time, a few minutes, magicdns stops working13:49:18
@matthewcroughan:defenestrate.itmatthewcroughan 
resolvectl
Global
           Protocols: +LLMNR +mDNS -DNSOverTLS DNSSEC=no/unsupported
    resolv.conf mode: stub
  Current DNS Server: 1.1.1.1#cloudflare-dns.com
Fallback DNS Servers: 1.1.1.1#cloudflare-dns.com 8.8.8.8#dns.google 9.9.9.9#dns.quad9.net 1.0.0.1#cloudflare-dns.com 8.8.4.4#dns.google 149.112.112.112#dns.quad9.net 2606:4700:4700::1111#cloudflare-dns.com 2001:4860:4860::8888#dns.google 2620:fe::fe#dns.quad9.net 2606:4700:4700::1001#cloudflare-dns.com 2001:4860:4860::8844#dns.google 2620:fe::9#dns.quad9.net

Link 50 (enp199s0f4u1u4)
    Current Scopes: DNS LLMNR/IPv4 LLMNR/IPv6
         Protocols: +DefaultRoute +LLMNR -mDNS -DNSOverTLS DNSSEC=no/unsupported
Current DNS Server: 192.168.5.1
       DNS Servers: 192.168.5.1
     Default Route: yes

Link 49 (tailscale0)
    Current Scopes: DNS
         Protocols: -DefaultRoute -LLMNR -mDNS -DNSOverTLS DNSSEC=no/unsupported
Current DNS Server: 199.247.155.53
       DNS Servers: 199.247.155.53 2620:111:8007::53
        DNS Domain: tail91ecf.ts.net ~ts.net
     Default Route: no

Link 2 (enp196s0)
    Current Scopes: none
         Protocols: -DefaultRoute +LLMNR -mDNS -DNSOverTLS DNSSEC=no/unsupported
     Default Route: no

Link 5 (wlan0)
    Current Scopes: DNS LLMNR/IPv4 LLMNR/IPv6
         Protocols: +DefaultRoute +LLMNR -mDNS -DNSOverTLS DNSSEC=no/unsupported
Current DNS Server: 192.168.5.1
       DNS Servers: 192.168.5.1
     Default Route: yes
13:50:39
@matthewcroughan:defenestrate.itmatthewcroughanthis is what it looks like when magicdns is not working13:51:08
@matthewcroughan:defenestrate.itmatthewcroughan

Then, if I restart tailscaled:

user: matthew nixcfg on  master [$✘»!+?⇡] 
❯ sudo systemctl restart tailscaled
[sudo] password for matthew: 

user: matthew nixcfg on  master [$✘»!+?⇡] took 2s 
❯ resolvectl
Global
           Protocols: +LLMNR +mDNS -DNSOverTLS DNSSEC=no/unsupported
    resolv.conf mode: stub
  Current DNS Server: 1.1.1.1#cloudflare-dns.com
Fallback DNS Servers: 1.1.1.1#cloudflare-dns.com 8.8.8.8#dns.google 9.9.9.9#dns.quad9.net 1.0.0.1#cloudflare-dns.com 8.8.4.4#dns.google 149.112.112.112#dns.quad9.net 2606:4700:4700::1111#cloudflare-dns.com 2001:4860:4860::8888#dns.google 2620:fe::fe#dns.quad9.net 2606:4700:4700::1001#cloudflare-dns.com 2001:4860:4860::8844#dns.google 2620:fe::9#dns.quad9.net

Link 50 (enp199s0f4u1u4)
    Current Scopes: DNS LLMNR/IPv4 LLMNR/IPv6
         Protocols: +DefaultRoute +LLMNR -mDNS -DNSOverTLS DNSSEC=no/unsupported
Current DNS Server: 192.168.5.1
       DNS Servers: 192.168.5.1
     Default Route: yes

Link 51 (tailscale0)
    Current Scopes: DNS
         Protocols: -DefaultRoute -LLMNR -mDNS -DNSOverTLS DNSSEC=no/unsupported
Current DNS Server: 100.100.100.100
       DNS Servers: 100.100.100.100 fd7a:115c:a1e0::53
        DNS Domain: tail91ecf.ts.net ~0.e.1.a.c.5.1.1.a.7.d.f.ip6.arpa ~100.100.in-addr.arpa ~101.100.in-addr.arpa ~102.100.in-addr.arpa ~103.100.in-addr.arpa ~104.100.in-addr.arpa ~105.100.in-addr.arpa ~106.100.in-addr.arpa ~107.100.in-addr.arpa ~108.100.in-addr.arpa ~109.100.in-addr.arpa ~110.100.in-addr.arpa ~111.100.in-addr.arpa ~112.100.in-addr.arpa ~113.100.in-addr.arpa
                    ~114.100.in-addr.arpa ~115.100.in-addr.arpa ~116.100.in-addr.arpa ~117.100.in-addr.arpa ~118.100.in-addr.arpa ~119.100.in-addr.arpa ~120.100.in-addr.arpa ~121.100.in-addr.arpa ~122.100.in-addr.arpa ~123.100.in-addr.arpa ~124.100.in-addr.arpa ~125.100.in-addr.arpa ~126.100.in-addr.arpa ~127.100.in-addr.arpa ~64.100.in-addr.arpa ~65.100.in-addr.arpa
                    ~66.100.in-addr.arpa ~67.100.in-addr.arpa ~68.100.in-addr.arpa ~69.100.in-addr.arpa ~70.100.in-addr.arpa ~71.100.in-addr.arpa ~72.100.in-addr.arpa ~73.100.in-addr.arpa ~74.100.in-addr.arpa ~75.100.in-addr.arpa ~76.100.in-addr.arpa ~77.100.in-addr.arpa ~78.100.in-addr.arpa ~79.100.in-addr.arpa ~80.100.in-addr.arpa ~81.100.in-addr.arpa ~82.100.in-addr.arpa
                    ~83.100.in-addr.arpa ~84.100.in-addr.arpa ~85.100.in-addr.arpa ~86.100.in-addr.arpa ~87.100.in-addr.arpa ~88.100.in-addr.arpa ~89.100.in-addr.arpa ~90.100.in-addr.arpa ~91.100.in-addr.arpa ~92.100.in-addr.arpa ~93.100.in-addr.arpa ~94.100.in-addr.arpa ~95.100.in-addr.arpa ~96.100.in-addr.arpa ~97.100.in-addr.arpa ~98.100.in-addr.arpa ~99.100.in-addr.arpa
                    ~ts.net
     Default Route: no

Link 2 (enp196s0)
    Current Scopes: none
         Protocols: -DefaultRoute +LLMNR -mDNS -DNSOverTLS DNSSEC=no/unsupported
     Default Route: no

Link 5 (wlan0)
    Current Scopes: DNS LLMNR/IPv4 LLMNR/IPv6
         Protocols: +DefaultRoute +LLMNR -mDNS -DNSOverTLS DNSSEC=no/unsupported
Current DNS Server: 192.168.5.1
       DNS Servers: 192.168.5.1
     Default Route: yes
13:51:30
@matthewcroughan:defenestrate.itmatthewcroughan You can see tailscale0 has tons more in it, including the correct dns server 100.100.100.100 13:51:50
@matthewcroughan:defenestrate.itmatthewcroughanthen after some time it reverts back to the broken state, which sees the DNS servers being wrong13:52:04
@matthewcroughan:defenestrate.itmatthewcroughanRedacted or Malformed Event13:53:43
@matthewcroughan:defenestrate.itmatthewcroughanRedacted or Malformed Event13:53:55
@matthewcroughan:defenestrate.itmatthewcroughanhttps://github.com/tailscale/tailscale/issues/1655813:56:00
@matthewcroughan:defenestrate.itmatthewcroughanYeah IDK then13:57:26
@matthewcroughan:defenestrate.itmatthewcroughanhow diagnose resolved, I can't use nslookup because resolved takes over13:57:42
@matthewcroughan:defenestrate.itmatthewcroughan 
May 18 15:09:03 p4 tailscaled[2394634]: LinkChange: major, rebinding: old: interfaces.State{defaultRoute=enp199s0f4u1u4 ifs={enp199s0f4u1u4:[192.168.5.133/24 /64 /64 llu6] wlan0:[192.168.5.176/24 /64 llu6]} v4=true v6=true} new: interfaces.State{defaultRoute=enp199s0f4u1u4 ifs={enp199s0f4u1u4:[192.168.5.133/24 /64 /64 llu6] tailscale0:[100.75.160.14/32 fd7a:115c:a1e0::fd01:a011/128 llu6] wlan0:[192.168.5.176/24 /64 llu6]} v4=true v6=true} diff: ips tailscale0: [fe80::a95c:c3ea:5f16:dbf4/64]->[100.75.160.14/32 fd7a:115c:a1e0::fd01:a011/128 fe80::a95c:c3ea:5f16:dbf4/64] rebind-reason=[ips-changed]
May 18 15:09:03 p4 tailscaled[2394634]: dns: Set: {DefaultResolvers:[] Routes:{ts.net.:[199.247.155.53 2620:111:8007::53]} SearchDomains:[tail91ecf.ts.net.] Hosts:30}
May 18 15:09:03 p4 tailscaled[2394634]: dns: Resolvercfg: {Routes:{} Hosts:30 LocalDomains:[]}
May 18 15:09:03 p4 tailscaled[2394634]: dns: OScfg: {Nameservers:[199.247.155.53 2620:111:8007::53] SearchDomains:[tail91ecf.ts.net.] MatchDomains:[ts.net.]}
May 18 15:09:03 p4 tailscaled[2394634]: wgengine: set DNS config again after major link change
May 18 15:09:03 p4 tailscaled[2394634]: router: portUpdate(port=41641, network=udp6)
May 18 15:09:03 p4 tailscaled[2394634]: router: portUpdate(port=41641, network=udp4)
May 18 15:09:03 p4 tailscaled[2394634]: Rebind; defIf="enp199s0f4u1u4", ips=[192.168.5.133/24 /64 /64 fe80::2e0:4cff:fe68:67/64]
May 18 15:09:03 p4 tailscaled[2394634]: magicsock: 1 active derp conns: derp-8=cr3m0s,wr1m0s
14:16:39
@matthewcroughan:defenestrate.itmatthewcroughanThis is what is logged when the failure begins14:16:57
@matthewcroughan:defenestrate.itmatthewcroughanCan't tell if client bug or bug in my router config14:17:44
@matthewcroughan:defenestrate.itmatthewcroughanLike hwy is there even a "major link change" ?14:20:13
@matthewcroughan:defenestrate.itmatthewcroughanI'm not changing anything14:20:17
@matthewcroughan:defenestrate.itmatthewcroughan* Like why is there even a "major link change" ?14:20:23

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