[c-nsp] IGMP differences between c3560 & c4948

[vince anton]

Hi

ive been doing some work in the lab with igmp and pim on 3560 and 4948 and
they seemed to behave differently.  i'd like to see if anyone on the list
has had similar experiences or if im getting something wrong, or hitting any
bugs.


On the C3560, with default config, i believe igmp snooping is enabled by
default.  A multicast source floods all traffic to all ports in the vlan,
until I configure 'ip igmp snooping querier' at which point the flooding
stops.  I would have expected igmp snooping to figure out that no receiver
requested traffic, so no flooding should never occur at all ?

If I remove 'ip igmp snooping querier', and configure 'ip pim sparse-mode'
on an SVI in that vlan, again I would expect the 3560 to stop the flooding,
but the flooding goes on an on, which i dont expect.

On the 4948, flooding again does occurs with default config with igmp
snooping enabled by default, but different to the c3560 both 'ip igmp
snooping querier' and/or 'ip pim sparse-mode' take care of controlling that.

am i getting it wrong, or is it indeed by design that the boxes behave
differently ?

any pointers to bugs or other gotchas would be nice, thanks.


Thanks,

anton