Re: [Anima] GRASP DULL, IPv6 LL scope and multicast and BSD sockets API

Michael Richardson <mcr+ietf@sandelman.ca> Wed, 07 April 2021 14:57 UTC

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From: Michael Richardson <mcr+ietf@sandelman.ca>
To: Brian E Carpenter <brian.e.carpenter@gmail.com>
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Date: Wed, 07 Apr 2021 10:57:00 -0400
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Subject: Re: [Anima] GRASP DULL, IPv6 LL scope and multicast and BSD sockets API
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Brian E Carpenter <brian.e.carpenter@gmail.com> wrote:
    > 2. At startup, I create a socket for multicast sending for each interface in that list.
    > Details are in the function '_try_mcsock', including setting SO_REUSEADDR, 1,
    > IPV6_MULTICAST_LOOP, 0 and IPV6_MULTICAST_HOPS, 1.

I don't think I've set MULTICAST_LOOP, so I will investigate that.

    > 4. To listen for multicasts, I have a thread that listens to a single socket
    > with SO_REUSEADDR, 1 that is bound to GRASP_LISTEN_PORT and explicitly joins
    > ALL_GRASP_NEIGHBORS_6 on each interface. I don't understand my own code (magic
    > borrowed from stackoverflow) but it's just after 'class
    > _mclisten(threading.Thread)'

So it joins ALL_GRASP_NEIGHBOURS multiple times.
I didn't think I could do that.  That would be better.

    > I hope that helps. This is code I wrote years ago now, and I'm not proud
    > of it; in fact I'm frightened to touch it. A few remarks in line below:

Yes, it does help.

--
Michael Richardson <mcr+IETF@sandelman.ca>   . o O ( IPv6 IøT consulting )
           Sandelman Software Works Inc, Ottawa and Worldwide