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From: "Carlos E. R." <robin_listas@es.invalid>
Newsgroups: comp.os.linux.misc
Subject: Re: Anybody Using IPv6?
Date: Tue, 20 May 2025 19:52:26 +0200
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On 2025-05-20 19:43, Marc Haber wrote:
> "Carlos E. R." <robin_listas@es.invalid> wrote:
>> Consider that, for instance, this laptop has an IPv6 address:
>>
>> cer@Isengard:~> ifconfig
>> eth0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
>>          inet 192.168.1.16  netmask 255.255.0.0  broadcast 192.168.255.255
>>          inet6 fc00::16  prefixlen 64  scopeid 0x0<global>
>>          inet6 fe80::4ecc:6aff:fe61:50a1  prefixlen 64  scopeid 0x20<link>
>>          ether 4c:cc:6a:61:50:a1  txqueuelen 1000  (Ethernet)
>> ...
> 
> This laptop has an IPv6 link local address.

I know. That one is automatic.

And also a given global address that I personally wrote.

> 
> Btw, the GNU/Linux world has been using iproute2 for two decades now.

I am aware.

> What does the IPv6 routing table of the system in question say?

I don't have a problem with the laptop currently. The problem was some 
years ago, on several computers.

cer@Isengard:~> ip route
default via 192.168.1.1 dev eth0
192.168.0.0/16 dev eth0 proto kernel scope link src 192.168.1.16
cer@Isengard:~>

> 
>> So applications thought that IPv6 was available.
> 
> Tries to use it, gets a host unreachable, SHOULD¹ try again with the
> next IP address associated with the target hostname, which might
> happen to be IPv4, tries to use it, connects successfully.
> 
> Different behavior is a bug.
> 
> ¹ in the RFC2119 sense

The gai change makes things go faster, by not trying IPv6 first.

-- 
Cheers,
        Carlos E.R.