IPv6 "no route to host"

    • New

    If I do a telnet to my IPv4 address it works correctly:

    ~> telnet 152.53.2.222 80 
    Trying 152.53.2.222... 
    Connected to 152.53.2.222. 
    Escape character is '^]'.

    But if I telnet to the IPv6 address, I get “No route to host”:

    ~> telnet 2a0a:4cc0:0:1e95:e857:12ff:fecd:c075 80 
    Trying 2a0a:4cc0:0:1e95:e857:12ff:fecd:c075... 
    telnet: connect to address 2a0a:4cc0:0:1e95:e857:12ff:fecd:c075: No route to host

    Reverse DNS provides the correct hostname for the IPv6 address (evc-comsc.at).

    When I use this IPv6 address: 2a0a:4cc0:0:1e95:0:0:0:0, I get the same reverse DNS result and the same “No route to host” from telnet. A friend in Mexico tried it and told me: “From nowhere (US, MX or EU) can I reach anything in that entire /64”

    Does this mean that, even though I have an IPv6 address, it never gets used? What am I doing wrong, and how do I advertise that yes, people can use IPv6 to access the server?

    • New

    Is the address configured correctly on the interface? Does the telnet client accept IPv6 addresses in that format? Often they have to be put in brackets [] or can't be given directly as an argument.

    BTW: Telnet is a horrible security leak! You should never Never NEVER NEVER!!! expose a telnet server to the internet. Please make yourself familiar at least with the absolute basic knowledge about hosting a server. You obviously don't have a clue what you are doing.

    Edited 2 times, last by frank_m (August 3, 2026 at 8:06 PM).

    • New
    Quote from Zierleiste

    By publishing your AAAA-Record in DNS what you already did.

    Which OS are you running? What does ip addr or ifconfig or similar show?

    openSUSE Leap version 15.6

    I do not have ifconfig installed. ip addr gives this result (pretty sure you don’t need to see the output for the loopback device)

    2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP group default qlen 1000 
       link/ether ea:57:12:cd:c0:75 brd ff:ff:ff:ff:ff:ff 
       altname enp0s3 
       altname ens3 
       inet 152.53.2.222/22 brd 152.53.3.255 scope global eth0 
          valid_lft forever preferred_lft forever

    ip -6 addr gives only the loopback device.

    Edited once, last by jdeisenberg: added extra information using -6 option (August 3, 2026 at 8:35 PM).

    • New

    Traceroutes get very close to your host, likely to the last router before it, so it's probably some configuration problem on your end. Is your IPv6 address configured on the interface? Can you ping your gateway (fe80::1)? Is your host firewall configured to allow IPv6? Is the Netcup Firewall enabled? If the basic configuration looks OK, you can check with sudo tcpdump -i eth0 ip6 while you're trying to connect from the outside whether any IPv6 packets arrive at your host, even if the firewall then drops/rejects them.

    Edit after earlier reply: No IPv6 address, no IPv6 connectivity...

    Edited once, last by NaN (August 3, 2026 at 8:44 PM).

    • New

    Ja, Du musst die Netzwerkkonfiguration um IPv6 erweitern. Also die o. g. IPv6-Adresse dem Interface zuweisen (mit Präfixlänge 64), das IPv6-Gateway einrichten (meistens fe80::1, ich hatte aber auch schon eine andere Adresse) und IPv6-DNS-Server ergänzen. Die genaue Adresse des Gateways findest Du im SCP auf dem Netzwerkreiter ganz unten. Als DNS-Server kannst Du z. B. die netcup-Server 2a03:4000:0:1::e1e6 und 2a03:4000:8000::fce6 benutzen.

    Nach den Anpassungen solltest Du auch testen, ob die Einstellungen einen Reboot überstehen.

    Quote from jdeisenberg

    openSUSE Leap version 15.6

    Version 15.6 wird offenbar (seit 30.04.2026) nicht mehr unterstützt, weshalb Du auf eine neuere Version gehen solltest. Siehe https://de.opensuse.org/Produktlebensdauer

    [Suche] RS Piccolo gesucht

    • New

    jdeisenberg Did you use an official image from netcup or your own to install the operating system?

    Quote from jdeisenberg

    (pretty sure you don’t need to see the output for the loopback device)

    Yes, but it should show inet6 ::1 or something similar as loopback address for IPv6.

    As mentioned earlier, you need to add IPv6 to your network interface. Normally, this should be inherited from the settings in the SCP (that's why I'm asking for the image you used).

    • New
    Quote from Zierleiste

    jdeisenberg Did you use an official image from netcup or your own to install the operating system?

    Yes, but it should show inet6 ::1 or something similar as loopback address for IPv6.

    As mentioned earlier, you need to add IPv6 to your network interface. Normally, this should be inherited from the settings in the SCP (that's why I'm asking for the image you used).

    Egads, it does not show anything for IPv6 as a loopback address!

    1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000 
       link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00 
       inet 127.0.0.1/8 scope host lo 
          valid_lft forever preferred_lft forever

    • New
    Quote from terence

    Gibt es in /etc/sysctl.conf Einträge mit …disable_ipv6 = 1?

    In /etc/sysctl.conf.d/70-yast.conf, ich habe net.ipv6.conf.all.disable_ipv6 = 1

    In /etc/sysctl.conf.d/50-IPv6.conf, sind alle gleich 0:

    net.ipv6.conf.default.accept_ra=0
    net.ipv6.conf.default.autoconf=0
    net.ipv6.conf.all.accept_ra=0
    net.ipv6.conf.all.autoconf=0
    net.ipv6.conf.eth0.accept_ra=0
    net.ipv6.conf.eth0.autoconf=0
    usw.

    Auch, es gibt keine IPv6 Adressen in /etc/hosts (ausgenommen „Special IP addresses“ ::1, fe00::0, ff00::0, ff02::1, ff02::2, und ff02::3)

    ::1 localhost ipv6-localhost ipv6-loopback

    fe00::0 ipv6-localnet

    ff00::0 ipv6-mcastprefix
    ff02::1 ipv6-allnodes
    ff02::2 ipv6-allrouters
    ff02::3 ipv6-allhosts

    In Antwort zu eine andere Frage, ja, ich benutze das openSUSE Leap 15.6 image von netcup. (Ich will nicht upgrade zu 16.0 versuchen; ich habe gelesen, dass es Netzwerk Problemen macht). Entschuldigen Sie bitte, mein Deutsch ist nur auf Niveau B1.

    • New
    Quote from jdeisenberg

    Entschuldigen Sie bitte, mein Deutsch ist nur auf Niveau B1.

    Alles gut!

    The file 50-IPv6.conf is for „hardening“ the IPv6 stack while 70-yast.conf looks like a configuration file written by yast. As far as I remember you should simply call yast and enable IPv6 in your server configuration (though I‘m using Red Hat Linux only since more than 10 years).

    • New
    Quote from Zierleiste

    Alles gut!

    The file 50-IPv6.conf is for „hardening“ the IPv6 stack while 70-yast.conf looks like a configuration file written by yast. As far as I remember you should simply call yast and enable IPv6 in your server configuration (though I‘m using Red Hat Linux only since more than 10 years).

    Yes, using yast worked. There is still some problem with netcup’s setup; a friend who knows a lot about networking tried doing a traceroute to the IPv6 address and it took a very, very long time to complete; it appears to get hung up at 2a0a:4cc0:80:4000::1, but that is a different problem entirely.

    Thanks everyone for all the advice!

    • New

    Yeah, it's not working here, yet.
    So did you successfully configure the interface and the gateway?
    And does the telnet command from your initial post work when you execute it on the server?
    Can you reach the internet via IPv6 from the server (does ping 2620:fe::9 work for example)?

    [Suche] RS Piccolo gesucht

    • New
    Quote from terence

    Yeah, it's not working here, yet.
    So did you successfully configure the interface and the gateway?
    And does the telnet command from your initial post work when you execute it on the server?
    Can you reach the internet via IPv6 from the server (does ping 2620:fe::9 work for example)?

    The interface and gateway seem to be OK. I cannot install telnet on the server (it is complaining about conflicting packages, and I do not want to tempt the fates). ping from the server does not work at all; gives Das Netzwerk ist nicht erreichbar

    The firewall is set to allow incoming and outgoing ping on ipv4 and ipv6

    Edited once, last by jdeisenberg: add detail about firewall settings (August 4, 2026 at 9:32 PM).

    • New
    Quote from terence

    Can you post the output of the following commands?
    ip -6 addr
    ip -6 route
    ip -6 neigh

    david@evc-comsc:~> ip -6 addr 
    1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 state UNKNOWN qlen 1000 
       inet6 ::1/128 scope host proto kernel_lo  
          valid_lft forever preferred_lft forever 
    2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 state UP qlen 1000 
       inet6 2a0a:4cc0:0:1e95:e857:12ff:fecd:c075/64 scope global  
          valid_lft forever preferred_lft forever 
       inet6 fe80::e857:12ff:fecd:c075/64 scope link proto kernel_ll  
          valid_lft forever preferred_lft forever 
    david@evc-comsc:~> ip -6 route 
    2a0a:4cc0:0:1e95::/64 dev eth0 proto kernel metric 256 pref medium 
    fe80::/64 dev eth0 proto kernel metric 256 pref medium 
    david@evc-comsc:~> ip -6 neigh 
    2a0a:4cc0:0:1000::1 dev eth0 lladdr 00:1c:73:00:00:99 router STALE  
    fe80::21c:73ff:fe00:99 dev eth0 lladdr 00:1c:73:00:00:99 router STALE