Wrong IPv6 interface ID given to modem

folatt · 2017-12-23 10:00:37

Setup

Device: desktop
- Mobo: ASRock
- Distro: Arch Linux
- hostname: MyComputer
Modem
- Fritz!Box 7581

My modem is automatically entering the wrong ipv6 address for my main computer, resulting into odd behaviour like not being able to ping -6 my server computers' domain names.
The address it enters is 73a:34a1:5d16:a67f when it should be 5766:a840:f358:5b00.

https://i.stack.imgur.com/5qCcz.png

IP lookup

[me@MyComputer ~]$ ip -6 addr
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 state UNKNOWN qlen 1000
    inet6 ::1/128 scope host 
       valid_lft forever preferred_lft forever
2: enp5s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 state UP qlen 1000
    inet6 2001:983:8610:1:5766:a840:f358:5b00/64 scope global dynamic noprefixroute 
       valid_lft 6571sec preferred_lft 3492sec
    inet6 fe80::90d9:53e6:a878:801c/64 scope link noprefixroute 
       valid_lft forever preferred_lft forever

Network manager settings
https://i.stack.imgur.com/rpsrx.png

/etc/dhcpcd.conf

# A sample configuration for dhcpcd.
# See dhcpcd.conf(5) for details.

# Allow users of this group to interact with dhcpcd via the control socket.
#controlgroup wheel

# Inform the DHCP server of our hostname for DDNS.
hostname

# Use the hardware address of the interface for the Client ID.
#clientid
# or
# Use the same DUID + IAID as set in DHCPv6 for DHCPv4 ClientID as per RFC4361.
# Some non-RFC compliant DHCP servers do not reply with this set.
# In this case, comment out duid and enable clientid above.
duid

# Persist interface configuration when dhcpcd exits.
persistent

# Rapid commit support.
# Safe to enable by default because it requires the equivalent option set
# on the server to actually work.
option rapid_commit

# A list of options to request from the DHCP server.
option domain_name_servers, domain_name, domain_search, host_name
option classless_static_routes
# Most distributions have NTP support.
option ntp_servers
# Respect the network MTU. This is applied to DHCP routes.
option interface_mtu

# A ServerID is required by RFC2131.
require dhcp_server_identifier

# Generate Stable Private IPv6 Addresses instead of hardware based ones
slaac private
noipv4ll

Mod note: Converted images to urls -- V1del

Last edited by V1del (2017-12-26 16:15:11)

lo1 · 2017-12-24 13:52:58

I don't know if I'm getting it wrong, but I'm going to answer:

you posted your dhcpcd.conf, so the wrong address is given when requesting an ipv6 address through dhcpcd. What happens if you use a static IP instead? (please do that without NetworkManager if you still experience issues)
Also, I take it that the other nodes in your network are not affected by this? And why your DNS address is not the same of your gateway? If that's what you want, it's fine, I misread the addressess.

Are you sure there's not more than a dhcp server handling the request?

Anyway, post some logs (dmesg would be fine) to get started.

Last edited by lo1 (2017-12-24 13:54:08)

folatt · 2017-12-24 15:01:45

I'm not familiar with networking, so I just infodumped anything I could find.
Perhaps I should have said this in the beginning of my question.

lo1 wrote:

Also, I take it that the other nodes in your network are not affected by this?

They are. They just don't run Arch Linux.
I've been banned on this forum once before, because I asked too many questions about devices that were running either ArchBang, ArkOS or Parabola.
My two RPi servers are running Debian and their IPv6 interface IDs assigned by the modem are the local link adresses instead of
a randomly generated one that I'm experiencing on my Arch Linux desktop.

lo1 wrote:

What happens if you use a static IP instead?

I've never done this before, so I'm a bit hesistant to just put in random settings and numbers.

https://i.stack.imgur.com/QCw9o.png

Is this the right button? What am I supposed to put in here?
the IPv6 address of my modem for LAN prefix?
And for DNS server the DNS server addresses of my ISP?

https://i.stack.imgur.com/dN1Gp.png

https://i.stack.imgur.com/sc0dz.png

I'm also wondering whether this thread is still allowed within the Arch Linux forum.
This is proving to be more and more of a modem configuration problem then an Arch Linux one.

If I have correctly understand it from others,
Clients generate the subnet address based on a fixed MAC address or randomly generated every X hours.
And then they send/broadcost those addresses to the modem.

That should mean that I could find out how the subnet address is being generated on my Desktop computer
and reconfigure it to take the interface hardware address.

[Update]

I think I finally have at least part of my question answered.

First off I want to say that there's an IPv6 address on every interface and this address has two scopes, global and local link.
The global scope is the only important one in this case.

An IPv6 address also consists of a prefix and an interface hardware address.
The prefix and interface hardware address combined makes a EUI-64 address.

It's the interface hardware addresses that should be equal to the IPv6 Interface ID on the modem.

According to this site, I shouldn't do all this, because for DNS it's better to use static IPs, but I think that's of later concern if at all.

Anyway I found the IPv6 address generation configuration setting on my Desktop.

Networkmanager -> IPv6 Settings -> IPv6 addresss generation mode was set to "Stable privacy".
I set it to EUI64.

https://i.stack.imgur.com/E896M.png

Looking at the ips now, they finally match.

https://i.stack.imgur.com/ScIRJ.png

    [me@MyComputer ~]$ ip -6 addr
    1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 state UNKNOWN qlen 1000
        inet6 ::1/128 scope host 
           valid_lft forever preferred_lft forever
    2: enp5s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 state UP qlen 1000
        inet6 2001:983:8610:1:225:22ff:fede:b509/64 scope global dynamic noprefixroute 
           valid_lft 6676sec preferred_lft 3592sec
        inet6 fe80::225:22ff:fede:b509/64 scope link noprefixroute 
           valid_lft forever preferred_lft forever

I still get this though.

    [me@MyComputer ~]$ ping -6 guilder-test.eu.org
    guilder-test.eu.org: Name or service not known

Mod note: converted links to URLs, please try to do so in the future -- V1del

Last edited by V1del (2017-12-26 16:13:09)

lo1 · 2017-12-26 14:17:20

Glad you made it on your own

And for DNS server the DNS server addresses of my ISP?

The DNS server is and must be equal to your gateway, and unless you plan on setting up an enterprise-like network it should stay like this. Make sure that your rouer isn't using a different ip address to reply to DNS queries and check if /etc/resolv.conf lists that ipv6 address.

Last edited by lo1 (2017-12-26 14:17:50)

V1del · 2017-12-26 16:20:02

Please try to post images as urls instead of embedded , people on metered connections will thank you https://wiki.archlinux.org/index.php/Co … s_and_code

Lone_Wolf · 2017-12-28 16:57:14

Does pinging guilder-test.eu.org by it's ip address work ?

ping 2001:983:8610:1:2239:6fcb:6144:21d2

* ping now defaults to ipv6 if nothing is specififed, so the "-6" is not needed

If that ping works, what is the output of drill guilder-test.eu.org ?

(drill is in ldns package)

Arch Linux

#1 2017-12-23 10:00:37

Wrong IPv6 interface ID given to modem

#2 2017-12-24 13:52:58

Re: Wrong IPv6 interface ID given to modem

#3 2017-12-24 15:01:45

Re: Wrong IPv6 interface ID given to modem

#4 2017-12-26 14:17:20

Re: Wrong IPv6 interface ID given to modem

#5 2017-12-26 16:20:02

Re: Wrong IPv6 interface ID given to modem

#6 2017-12-28 16:57:14

Re: Wrong IPv6 interface ID given to modem

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