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    IPv6: Which way to go?
    Contributed by sees on Tuesday, October 16 @ 02:31:41 BST

    I'm the Debian maintainer and recently the upstream maintainer of a
    package called psmisc. Inside this package is a program called fuser.
    fuser is a useful tool that can tell you what programs have a certain
    file open, they can also tell you what programs have a certain network
    port open.

    And this leads to my problem, I received a bug report (#115672) saying
    that fuser -n tcp 22 does not work, and for me it doesn't too. This is
    because for some people this program (sshd) uses an IPv6 socket, not
    an IPv4 one.

    alp: See inside for further details on the issue, and a few pointers on IPv6 with Debian.

    I know how to fix this, but it then leads to the question, which way is
    the correct way? There are three possibilities:

    • Combine IPv6 and IPv4 sockets together -n tcp finds both IPv4 and
      IPv6 sockets but you cannot distinguish between the two.

    • Make a new namespace for IPv6, this means -n tcp 22 fails but -n tcp6 22 will find sshd, -n tcp6 80 wont find apache.
    • Combine them and also have separate flags, perhaps tcp6 and tcp4.
    • Is there another way?

    I have to be very careful about the -n tcp flag, as this is an existing
    one so I don't want to change it current behaviour too much. I'm asking
    what would people expect this program to do, not how it is done (I got
    that pretty much worked out). This change will effect all users of
    psmisc, not just Debian ones.

    For the technically inclined, the bug is due to the inode of the socket
    not being found in /proc/net/tcp as it lives in /proc/net/tcp6 The
    flags will just determine if i combine or select these two files in
    different ways.

    alp: Debian is making much progress in the area of IPv6 support. The Debian IPv6 working group has a comprehensive list of packages that currently support, or are dedicated to the management of IPv6 hosts, and the
    debian-ipv6 mailing list is also reassuringly active.
    There's a concise guide on getting a Debian box onto an IPv6 network as well as a more comprehensive and general IPv6-HOWTO.

    Perhaps one of the most visible signs of IPv6 support for the average Debian user is /etc/hosts -- in testing/unstable it comes complete with the standard IPv6 host entries (localhost, loopback, multicast etc). Debian really shines in areas like this where the bulk of interest is academic and not (yet) commercial. We will undoubtedly have an edge over competitors as more IPv6 nodes come online.

    Related Links

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  • "IPv6: Which way to go?" | Login/Create Account | 12 comments

    The comments are owned by the poster. We aren't responsible for their content.

    Anyone tried an IPv6-only network? (Score: 0, Interesting)
    by Anonymous on Tuesday, October 16 @ 04:17:51 BST

    Has anyone tried running an IPv6-only network? Any suggestions?

    [ Reply ]

    Re: Anyone tried an IPv6-only network? (Score: 1)
    by Anonymous on Thursday, October 18 @ 07:10:02 BST

    Do you mean a network that only uses IPv6 and there is no IPv4 at all? It would be very interesting to see how this went and what would break. I run a dual-stack network, meaning that the ethernet has both IPv6 and IPv4 packets floating through it.

    Running an IPv6 only kernel would also be very interesting, I would expect that lots of programs would be in trouble.

    For example, when I was fixing fuser I basically run over the "load the socket table file" code twice. In the old code, you load /proc/net/tcp the new code you load that and /proc/net/tcp

    But now you cannot assume that /proc/net/tcp will definitely be there. I would suspect there are a lot of other programs that make this sort of assumption too and think that no IPv4 facility means no network.

    [ Reply ]

    least surprises: option 3 (Score: 5, Insighful)
    by Anonymous on Tuesday, October 16 @ 05:55:57 BST

    for -n tcp select both IPv4 and IPv6 sockets

    for -n tcp4 select ONLY IPv4

    for -n tcp6 select ONLY IPv6

    That way old behavior is correct, plus the new behavior is what is expected ('tcp' refers to all kinds of tcp) and options exist for being more specific should the need arise.

    [ Reply ]

    Re: least surprises: option 3 (Score: 0)
    by Anonymous on Tuesday, October 16 @ 14:20:08 BST

    I concur with this assessment.


    [ Reply ]

    Re: least surprises: option 3 (Score: 1)
    by Anonymous on Tuesday, October 16 @ 16:56:34 BST

    >>what would people expect this program to do

    I agree with the 3 options, only thing is:

    i would expect a seperate option e.g:

    --ipv6-only -n tcp

    and/or maybe -6 and -4 for short.

    (Not sure about udp, but if that gives similar problems, a seperate option would be very handy)

    [ Reply ]

    [OFFTOPIC] anonymous! (Score: 0, Offtopic)
    by Anonymous on Tuesday, October 16 @ 17:04:53 BST

    hrm, dunno why this became anonymous.

    I'm logged in but, got some weird error after pressing the OK! button.

    Could be konqueror (have to use that, cause galeon is broken at the moment in sid) or the crappy php nuke code 😉

    This message is just a test to see if it works now. It should not be by anonymous now.

    [ Reply ]

    Re: [OFFTOPIC] anonymous! (Score: 0, Offtopic)
    by drone0709 on Tuesday, October 16 @ 17:21:02 BST
    (User Info)

    Lala, this is also me (drone0709) testing - probably our broken php-nukle code 🙁

    [ Reply ]

    Re: [OFFTOPIC] anonymous! (Score: 0, Offtopic)
    by jor ( on Tuesday, October 16 @ 18:15:01 BST
    (User Info)

    And this is me, the original poster, again now using links 🙂

    [ Reply ]

    Re: [OFFTOPIC] anonymous! (Score: 0, Offtopic)
    by jor ( on Tuesday, October 16 @ 18:18:42 BST
    (User Info)

    Me (the orginal poster) again, now with links

    [ Reply ]

    this is good. (Score: 1)
    by captainlarry (org.spack@larry) on Tuesday, October 16 @ 19:00:29 BST
    (User Info)

    i like this idea. by default it finds everything so you don't have to struggle to find out what's changed, and if you need more granularity it's a simple, and fairly obvious, option change.

    i prefer "-n tcp6" or "-n tcp4" to the other suggestion of a seperate option.


    [ Reply ]

    Re: IPv6: Which way to go? (Score: 1)
    by caf on Wednesday, October 17 @ 10:37:20 BST
    (User Info)

    I think I prefer:

    -n tcp4 = ipv4 tcp

    -n tcp6 = ipv6 tcp

    -n tcp = both

    On another note, while you're at it could you add support for the other sockets that have something like a "port" and a similar file in /proc/net? I'm thinking "raw" and "unix" at the moment, eg:

    fuser -n unix @00000002

    Sound plausible?

    - caf.

    [ Reply ]

    We got two bugs. (Score: 1)
    by seeS (csmall@d.o) on Wednesday, October 17 @ 13:42:35 BST
    (User Info)

    Just to make life more interesting, there are actually two bugs in psmisc 20.1 This is why some people find fuser no longer works for them even if they are not using IPv6.

    There is a real IPv6 related bug, psmisc 20.2 has that fix so you can use -4 and -6 flags (these are the same as for, say ssh which is why i used them) to select IPv4 or IPv6 only namespaces. By default it will look in both. Thankyou for everyone for the comments.

    The second bug happens in kernel 2.4.12. fuser made some assumptions about the proc files that, until 2.4.12, were true. Someone kindly gave me a patch and that is also in 20.2 Essentially fuser thought sockets used st_dev of 0, but they don't now.

    So where is psmisc 20.2? It's currently sitting in the sourceforge CVS I will be checking it tomorrow (my time) and putting a new package up as well, assuming testing is ok.

    If you want to download the CVS version and test it, that would be good. I know the patches work for me but they migth not work for you.

    For those that are interested, the next psmisc will have IPv6 address selection and internationalisation.

    [ Reply ]

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