For the power redundancy question, I believe this link will help:
http://www.cisco.com/univercd/cc/td/doc/product/lan/cat2950/12122ea2/2955hig/hginstal.htm
Also can any body tell me what IGMP snooping do? do I need to configure it? also the command (I need global command as well as port/interface based command)?
>>Layer 2 switches can use IGMP snooping to constrain the flooding of multicast traffic by dynamically configuring Layer 2 interfaces so that multicast traffic is forwarded to only those interfaces associated with IP multicast devices. As the name implies, IGMP snooping requires the LAN switch to snoop on the IGMP transmissions between the host and the router and to keep track of multicast groups and member ports. When the switch receives an IGMP report from a host for a particular multicast group, the switch adds the host port number to the forwarding table entry; when it receives an IGMP Leave Group message from a host, it removes the host port from the table entry. It also periodically deletes entries if it does not receive IGMP membership reports from the multicast clients.
The multicast router sends out periodic IGMP general queries to all VLANs. When IGMP snooping is enabled, the switch responds to the router queries with only one join request per MAC multicast group, and the switch creates one entry per VLAN in the Layer 2 forwarding table for each MAC group from which it receives an IGMP join request. All hosts interested in this multicast traffic send join requests and are added to the forwarding table entry.
IGMP Snooping is by default Enabled globally and per VLAN. If for some reason it is not enabled, "ip igmp snooping" at the config mode to enable it.
There is nothing else to configure.
http://www.cisco.com/univercd/cc/td/doc/product/lan/cat2950/12122ea5/2950scg/swigmp.htm#wp1020034
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