User manual

Publication 1783-UM003D-EN-E - December 2009 35
Chapter 2
The switch supports IP multicast group-based bridging, rather than
MAC-addressed based groups. With multicast MAC address-based groups, if
an IP address being configured translates (aliases) to a previously configured
MAC address or to any reserved multicast MAC addresses (in the range
224.0.0.xxx), the command fails. Because the switch uses IP multicast groups,
there are no address aliasing issues.
The default number of multicast groups allowed in the switches is as follows:
• Stratix 8000 switch: 256
• Stratix 8300 switch: 1024
You can modify the number of multicast groups supported by using the
command line interface.
The IP multicast groups learned through IGMP snooping are dynamic. If you
specify group membership for a multicast group address statically, your setting
supersedes any automatic manipulation by IGMP snooping. Multicast group
membership lists can consist of both user-defined and IGMP
snooping-learned settings. Multicast IP addresses used by the EtherNet/IP
network for I/O traffic are learned by the switch.
IGMP implementation in the switch is IGMP V2. This version is
backward-compatible with switches using IGMP V1. The switch has a built in
querier function, and the global macro enables on IGMP Snooping and the
querier.
Spanning Tree Protocol
Spanning Tree Protocol (STP) is a Layer 2 link management protocol that
provides path redundancy while preventing loops in the network. For a Layer 2
Ethernet network to function properly, only one active path can exist between
any two stations. Multiple active paths among end stations cause loops in the
network. If a loop exists in the network, end stations might receive duplicate
messages. Switches might also learn end-station MAC addresses on multiple
Layer 2 interfaces. These conditions result in an unstable network.
Spanning-tree operation is transparent to end stations, which cannot detect
whether they are connected to a single LAN segment or a switched LAN of
multiple segments.