Re: what does "::ffff" mean in netstat output?

Bennett Haselton <(E-Mail Removed)> wrote:
> When I run "netstat" on my machine I get some lines like:

> tcp 0 0 ::ffff:69.72.177.140:80 ::ffff:<remote ip
> address> TIME_WAIT

> I've read through the netstat man page, and several pages of Google
> hits for "netstat output", and I can't find an answer to this: What
> does the "::ffff" mean in front of an IP address in the netstat
> output?

> Some lines list a connection and its state, with the "::ffff" in
> front of the source and destination IP, and some list connections
> without the "::ffff". I just want to know what the difference is
> between the lines that have it and the lines that don't.

::ffff is the IPv6 prefix for an IPv4 address mapped into IPv6 space
(something along those lines).

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Hello,

Rick Jones a écrit :
> Bennett Haselton <(E-Mail Removed)> wrote:
>> When I run "netstat" on my machine I get some lines like:
>
>> tcp 0 0 ::ffff:69.72.177.140:80 ::ffff:<remote ip
>> address> TIME_WAIT
>
> ::ffff is the IPv6 prefix for an IPv4 address mapped into IPv6 space
> (something along those lines).

And it means that it is an IPv6 socket that is used for IPv4
communication. Application and socket-wise, it is IPv6 but network and
packet-wise it is IPv4. This is allowed as a transition mechanism if
net.ipv6.bindv6only=0 and the application didn't set the socket option
IPV6_V6ONLY.

It seems that some recent OSes disable this option by default so that
IPv6 sockets can handle only real IPv6 communications.