KB.15.15

Well-known or reserved multicast addresses excluded from IP multicast

filtering

Each multicast host group is identified by a single IP address in the range of 224.0.0.0 through

239.255.255.255. Specific groups of consecutive addresses in this range are termed "well-known"

addresses and are reserved for predefined host groups. IGMP does not filter these addresses, so

any packets the switch receives for such addresses are flooded out all ports assigned to the VLAN

on which they were received (except the port on which the packets entered the VLAN.)

Table 4 (page 35) lists the 32 well-known address groups (8192 total addresses) that IGMP does

not filter on.

Table 4 IP multicast address groups excluded from IGMP filtering

Groups of consecutive addresses in the range of

224.128.0.X to 239.128.0.X

Groups of consecutive addresses in the range of 224.0.0.X

to 239.0.0.X

232.128.0.x224.128.0.x232.0.0.x224.0.0.x

233.128.0.x225.128.0.x233.0.0.x225.0.0.x

234.128.0.x226.128.0.x234.0.0.x226.0.0.x

235.128.0.x227.128.0.x235.0.0.x227.0.0.x

236.128.0.x228.128.0.x236.0.0.x228.0.0.x

237.128.0.x229.128.0.x237.0.0.x229.0.0.x

238.128.0.x230.128.0.x238.0.0.x230.0.0.x

239.128.0.x231.128.0.x239.0.0.x231.0.0.x

X is any value from 0 to 255.

IP multicast filters

NOTE: This operation applies to the HP Series 5400zl switches, the Series 3500yl switches, the

switch 6200yl, the switch 8212zl, the Series 5300xl switches, as well as the 1600M, 2400M,

2424M, 4000M, and 8000M, but not to the Series 2500, 2650, Series 4100gl, Series 4200vl,

or 6108 switches (which do not have static traffic/security filters.)

IP multicast addresses occur in the range from 224.0.0.0 through 239.255.255.255 (which

corresponds to the ethernet multicast address range of 01005e-000000 through 01005e-7fffff.)

Where a switch has a static traffic/security filter configured with a "multicast" filter type and a

"multicast address" in this range, the switch will use the static filter unless IGMP learns of a multicast

group destination in this range. In this case, IGMP dynamically takes over the filtering function for

the multicast destination addresses for as long as the IGMP group is active. If the IGMP group

subsequently deactivates, the switch returns filtering control to the static filter.

Reserved addresses excluded from IP multicast (IGMP) filtering

Traffic to IP multicast groups in the IP address range of 224.0.0.0 to 224.0.0.255 will always be

flooded because addresses in this range are "well known" or "reserved" addresses. Thus, if IP

multicast is enabled, and there is an IP multicast group within the reserved address range, traffic

to that group will be flooded instead of filtered by the switch.

Multicast ARP support

To support IP multicasting, the multicast range of 01-00-5E-00-00-00 to 01-00-5E-7F-FF-FF is reserved

for Ethernet MAC addresses. The command ip arp-mcast-replies enables acceptance of

the MAC addresses in the IP multicast range.

Well-known or reserved multicast addresses excluded from IP multicast filtering 35