PIM-DM (Dense Mode) on the 5300xl Switches
Operating Notes
Flow Capacity. The routing switch provides an ample multicast environ-
ment, supporting 1022 multicast flows in hardware across a maximum of 64
VLANs. (A flow comprises a unicast source address and a multicast group
address, regardless of the number of active hosts belonging to the multicast
group at any given time.) While the typical multicast environment should not
normally exceed 1022 flows, the routing switch can support up to 978 addi-
tional flows in software, depending on available system resources. (Because
the switch processes flows in hardware much faster than in software, you may
notice slower processing times for flows occurring in software.) Also, while
the routing switch can support up to 2,000 flows, the total demand on system
resources from the combined use of more than 1,022 simultaneous flows, a
high number of VLANs supporting multicast routing, and/or other, resource-
intensive features can oversubscribe memory resources, which reduces the
number of flows the routing switch can support in software. That is, the switch
does not route flows in software that oversubscribe current memory
resources. If the routing switch regularly exceeds the hardware limit of 1022
flows and begins routing flows in software, you may want to move some hosts
that create multicast demand to another routing switch, or reduce the number
of VLANs on the routing switch by moving some VLANs to another routing
switch. Note that the routing switch generates a log message if it either routes
a flow in software or drops a flow intended for software routing because
memory is oversubscribed. (Refer to
“Messages Related to PIM Operation” on
page 5-37.)
IGMP Traffic High-Priority Disabled. Enabling IP multicast routing to
support PIM-DM operation has the effect of disabling IGMP traffic high-
priority, if configured. (Refer to
“Configuring IGMP Traffic Priority” on page 4-
10.)
ACLs and PIM. The switch allows ACL filtering on unicast addresses, but
not on multicast addresses. Also, an ACL does not take effect on a flow if the
flow began before the ACL was configured.
When To Enable IGMP on a VLAN. When PIM is enabled on a VLAN, it is
not necessary to also enable IGMP unless there may be Joins occurring on
that VLAN. But if IGMP is enabled on a VLAN, you must also enable PIM if you
want that VLAN to participate in multicast routing.
IP Address Removed. If you remove the IP address for a VLAN, the switch
automatically removes the PIM configuration for that VLAN.
5-35
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