Arris NVG599, Administrator'S Handbook

Page: 139 / 228

139
IP DNS Commands
set ip dns domain-name domain_name
Specifies the default domain name for your network. When an application needs to resolve a host name, it
appends the default domain name to the host name and asks the DNS server if it has an address for the fully
qualified host name.
set ip dns primary-address ip_address
Specifies the IP address of the primary DNS name server.
set ip dns secondary-address ip_address
Specifies the IP address of the secondary DNS name server. Enter 0.0.0.0 if your network does not have a
secondary DNS name server.
set ip dns proxy-enable [ on | off ]
Allows you to disable the default behavior of acting as a DNS proxy. The default is on .
IP IGMP Commands
Multicasting is a method for transmitting large amounts of information to many, but not all, computers over an
internet. One common use is to distribute real-time voice, video, and data services to the set of computers
which have joined a distributed conference. Other uses include updating the address books of mobile
computer users in the field, or sending out company newsletters to a distribution list.
Since a router should not be used as a passive forwarding device, NVG599 devices use a protocol for
forwarding multicasting: Internet Group Management Protocol (IGMP).
NVG599 devices support IGMP Version 1, Version 2, or Version 3.
IGMP “Snooping” is a feature of Ethernet Layer 2 switches that “listens in” on the IGMP conversation between
computers and multicast routers. Through this process, it builds a database of locations where the multicast
routers reside by noting IGMP general queries used in the querier selection process and by listening to other
router protocols.
From the host point of view, the snooping function listens at a port level for an IGMP report. The switch then
processes the IGMP report and starts forwarding the relevant multicast stream onto the host's port. When the
switch receives an IGMP leave message, it processes the leave message, and if appropriate, stops the multicast
stream to that particular port. Basically, customer IGMP messages although processed by the switch are also
sent to the multicast routers.
In order for IGMP snooping to function with IGMP Version 3, it must always track the full source filter state of
each host on each group, as was previously done with Version 2 only when fast leave support was enabled.
IGMP Version 3 supports source filtering, which is the ability for group memberships to incorporate source
address filtering. This ability allows source-specific multicast (SSM). By adding source filtering, a gateway that
proxies IGMP can more selectively join the specific multicast group for which there are interested LAN
multicast receivers.
These features require no user configuration on the gateway.