[Xorp-users] Maximum number of interfaces

[Pavlin Radoslavov]

Ben Greear <greearb at candelatech.com> wrote:

> Adam Greenhalgh wrote:
> > No, I don't think so. But you could easily try the livecd for the 1.4
> > release with the same config file but on a floppy. The cvs version
> > does include a number of enhancements though so you might want to try
> > that.
> >   
> Try this:
> 
> echo 2000 > /proc/sys/net/ipv4/igmp_max_msf
> echo 2000 > /proc/sys/net/ipv4/igmp_max_memberships

The original question didn't specify the OS, so I should clarify
that the above commands are for Linux.

I believe that igmp_max_msf is the max. number of source filters (i.e.,
if you use source-specific multicast with IGMPv3) and is per
interface, hence it shouldn't have impact on the max. number of
interfaces.

The second limit however (igmp_max_memberships) is global (the
max. number of joined groups across all interfaces) and is the
primary reason that by default you can't start XORP on more than 10
interfaces. Its default value is 20, and the XORP multicast modules
will join 2-3 multicast groups per interface.

There are few more limiting factors that have impact on the
max. number of interfaces you can use. See the IGMP/MLD and PIM-SM
sections in the latest version of the XORP ERRATA document for
details:

http://xorpc.icir.org/cgi-bin/cvsweb.cgi/xorp/ERRATA

Regards,
Pavlin

P.S. I believe all *BSDs also have similar limits for the
max. number of joined multicast group. E.g., FreeBSD has
defined IP_MAX_MEMBERSHIPS (max. 20) per socket, but in the next
7.0 release it can be scaled dynamically (thanks to Bruce M. Simpson).