Re: IGMP join/leave time variability

Alan Cox
2001-07-26T17:50:57Z

> >From this, I infer that there should be _no_ initial delay on sending
> the IGMP join. In fact, a quick peek at the source confirms this:
> (net/ipv4/igmp.c):
>
> #define IGMP_Initial_Report_Delay (1*HZ)
>
> /* IGMP_Initial_Report_Delay is not from IGMP specs!
> * IGMP specs require to report membership immediately after
> * joining a group, but we delay the first report by a
> * small interval. It seems more natural and still does not
> * contradict to specs provided this delay is small enough.
> */
>
> But this "small interval" is actually very noticeable in our application.

I suspect the small interval for the first one should be 1 not 1*HZ. That
would keep a little bit of jitter which is good to avoid the multicast
receive/join group problem

[Lots of clients all running an app listening for multicast packets, one
packet says 'do xyz on this group' and they all then send joins at the same
instant]

Alan