Date: Thu, 13 Apr 2006 07:48:55 +0100 (BST) From: Robert Watson <rwatson@FreeBSD.org> To: Bruce M Simpson <bms@spc.org> Cc: Stephen Clark <Stephen.Clark@seclark.us>, freebsd-stable@freebsd.org Subject: Re: IP_MAX_MEMBERSHIPS Message-ID: <20060413074608.Y443@fledge.watson.org> In-Reply-To: <20060413063604.GB94628@spc.org> References: <443DB8A5.1020006@seclark.us> <20060413063214.GA94628@spc.org> <20060413063604.GB94628@spc.org>
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On Thu, 13 Apr 2006, Bruce M Simpson wrote: > On Thu, Apr 13, 2006 at 07:32:14AM +0100, Bruce M Simpson wrote: >> On Wed, Apr 12, 2006 at 10:34:13PM -0400, Stephen Clark wrote: >>> Can anyone tell me why the maximum number of members in a multicast >>> group is set at >>> 20? >>> Are there issues with increasing this number? > > Ah. Your original question appears not to have been answered. My bad. > > I do not see a limit on the members of a multicast group on FreeBSD either > for individual sockets or for multicast forwarding based on my reading of > the source code. We have a bounded size array of possible memberships for each socket in the per-pcb multicast option structure. I don't know of any reason why changing this limit would break anything, although in the end testing is good. If the limit is raised too much, we face significant wasted kernel memory if it's not actually used, and could think about adding code to scale the array size up as needed, but it's not clear that's useful unless the maximum is increased significantly. A typical reason one might need more memberships is if one has a multicast service that needs to work on all available interfaces, and one has a lot of interfaces (i.e., lots of vlans). Robert N M Watson
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