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IGMP snooping
Old IGMP Snooping Functionality
iMG/RG Software Reference Manual (IGMP)
3-14
Host B sends an unsolicited IGMP Membership report.
The Gateway intercepts the IGMP membership report sent by Host B.
As a multicast entry for this group already exists, the Gateway simply adds the port to the already existing
entry for that multicast group. It also adds another Timeout timer specific for this port to the multicast group.
If another host joins another multicast group or the same multicast group, the same procedures described in
the first and second scenarios are performed, respectively. A new Group entry will be added whenever a new
group has been joined.
Note:
In order to maintain group membership, the multicast router sends IGMP queries periodically. This query
is intercepted and forwarded to all ports on the switch. All hosts that are members of the group will
answer that query. The IGMP protocol was designed in such a way that only one member of any group
on any VLAN would have to respond to any given query. But, because the reports are intercepted, the
hosts do not see each other's reports, and thus, all hosts send a report (instead of one per group). These
reports are then forwarded to the router; one report per group from among all received responses.
3.1.3.2.2 Leaving a multicast group
When a host wants to leave group it sends an IGMP Leave message specific for the group it wants to leave.
The IGMP Leave message is captured and if no other devices are known to be joined to that multicast group on
that port - then the multicast stream is removed from that port. If no other ports have hosts joined to the
same multicast group, then the leave messages is forwarded to the multicast router. In this way the multicast
traffic the router is asked to stop sending the multicast stream.
If more than one port has hosts that have joined the multicast group, then the host that sent the IGMP Leave
message is removed from the multicast membership record without forwarding the leave message to the multi-
cast router.
•
Time-out interval expiring
When the Time-out Interval expires, the Residential Gateway removes that entry from the multicast member-
ship records and that multicast stream from the associated port - if it is the last entry registered against that
port.
3.1.3.3 Proxy Operation Mode
Proxy mode is the default operational mode for the old IGMP snooping mode. It's possible to force the IGMP
snooping to work in proxy mode via the igmp snooping set mode proxy command.
The Gateway responds to the IGMP Group Specific Query from the Multicast Router based on it's internal
multicast records - replying with an IGMP Membership report for each multicast stream that the hosts that it is
managing are subscribed to.
It also periodically sends IGMP Group Specific Query messages to all ports that are not known multicast router
ports - in order to understand which multicast streams are subscribed to on which ports. The frequency with
which this happens is based upon the Query interval that is configured on the device.
Page 277 / 998
Old IGMP Snooping Functionality
IGMP snooping
3-15
iMG/RG Software Reference Manual (IGMP)
Upon receiving an IGMP Leave message, the system can either process it immediately - as described above (This
is known as FastLeave) - or if configured to do so - send an IGMP Group Specific Query to the port where the
IGMP Leave message was received from. The Leave Time value is used in the query message to request a fast
response from other hosts that may be present on the same Ethernet segment. This can be used to ensure that
when one host asks for a multicast stream to be stopped - it does not adversely impact another host on the
same port that is subscribed to that multicast stream.
If no answer is received to the IGMP Group Specific Query and if no other ports have hosts joined to the same
multicast group, then an IGMP leave messages is sent to the multicast router. In this way the multicast traffic the
router is asked to stop sending any multicast data for that particular group.
The IGMP leave message forwarded by the Gateway will have as source MAC address the Gateway's MAC
address and will have as source IP address the ipaddress of the ip interface associated with the VLAN that is
associated with the IGMP service.
3.1.3.4
IP source address masking – Secondary IP Interface
If the Interface associated with the VLAN that the IGMP module is associated with does not have an IP address,
it is possible to refer, as source IP address for upstream IGMP signalling messages, the IP address of any other
existing IP interface. This interface is not required to be attached to the VLAN where IGMP snooping has been
enabled.
3.1.3.5
IGMP snooping security
This feature allows the iBG/iMG/RG to limit accepted IGMP signalling to that from designated STB identified by
their MAC addresses. These MAC addresses will be learned automatically by the software up to a configured
number and saved in a non volatile memory. They are specifically named in the configuration. with the maximum
number of STB MAC addresses supported being 10.
It is possible to manually configure the allowed MAC
addresses - so that via a provisioning action - the security of the Video network is maintained.
3.1.3.6 Routed IGMP proxy
An alternative to Bridged IGMP snooping is routed IGMP.
This is a layer-3 feature that allows multicast traffic to be routed between multiple IP interfaces.
IGMP traffic is typically limited to the VLAN where it is received. If a host joins a multicast group but multicast
traffic is received on another VLAN to which the host is not connected, the multicast traffic will never reach the
host.
Routed IGMP overrides this limitation with the only constraint that multicast traffic must be received only on
one IP interface called the
upstream
interface.
In this case, when a host joins a multicast group, the IP interface attached to the transport (VLAN) where the
host is located, becomes a downstream interface. It will receive all the multicast traffic related to the group that
the host has joined.
Page 278 / 998
IGMP snooping
Functional Differences in Product Categories
iMG/RG Software Reference Manual (IGMP)
3-16
It is possible to statically define the upstream IP interface.
3.1.4
Functional Differences in Product Categories
There are two different implementations of IGMP that are encountered in these ATI Gateways. The original
implementation is configured using IGMP SNOOPING and IGMP PROXY commands. It is a separate applica-
tion that IGMP packets are sent to - and is not integrated with the Bridge - that is an integral part of the Packet
processing on the CPU. The newer implementation is configured using BRIDGE IGMPSNOOP and IGMP com-
mands.It is integrated into the CPU based Bridge - which supports VLAN segregation of traffic flows.
In addition the IGMP PROXY commands have been superseded by the IGMP commands that are now available
to manage Routed IGMP Proxy. The IGMP PROXY commands are retained in older devices for backward com-
patibility - but are not recommended.
1) Utilizes IGMP SNOOPING command set. IGMP Command set recommended in place of IGMP PROXY
command set.
2) Utilizes integrated BRIDGE IGMPSNOOP and the IGMP command set.
3.1.5
IGMP Snooping command reference
This section describes the commands available to enable, configure and manage the
IGMP snooping
feature.
TABLE 3-1
Functional Mapping for Bridge
Functions
Fiber
A
Fiber
B
Fiber
C
Fiber
D
Fiber
E
Modular
ADSL
A
ADSL
B
ADSL
C
Multicast router port discovery
1
2
1
2
2
2
1
2
2
Joining a Multicast Group
1
2
1
2
2
2
1
2
2
Leaving a multicast group
1
2
1
2
2
2
1
2
2
Multicast router port discovery
1
2
1
2
2
2
1
2
2
Proxy Operation Mode
1
2
1
2
2
2
1
2
2
IP source address masking – Secondary IP Interface
1
2
1
2
2
2
1
2
2
IGMP snooping security
1
2
1
2
2
2
1
2
2
Routed IGMP proxy
1
2
1
2
2
2
1
2
2
Page 279 / 998
IGMP Snooping command reference
IGMP snooping
3-17
iMG/RG Software Reference Manual (IGMP)
3.1.5.1
IGMP snooping CLI commands
The table below lists the
IGMP snooping
commands provided by the CLI:
TABLE 3-2
Bridge
IGMP Snooping Commands
Functions
Fiber
A
Fiber
B
Fiber
C
Fiber
D
Fiber
E
Modular
ADSL
A
ADSL
B
ADSL
C
BRIDGE ADD IGMPSNOOP MCASTROUTERINTF
X
X
X
X
X
X
BRIDGE ADD IGMPSNOOP SECURITY
X
X
X
X
X
X
BRIDGE DELETE IGMPSNOOP MCASTROUTERINTF
X
X
X
X
X
X
BRIDGE DELETE IGMPSNOOP SECURITY
X
X
X
X
X
X
BRIDGE LIST IGMPSNOOP GROUPINFO
X
X
X
X
X
X
BRIDGE LIST IGMPSNOOP INTERFACESTATS
X
X
X
X
X
X
BRIDGE LIST IGMPSNOOP STATIC MCASTROUTERINTFS
X
X
X
X
X
X
BRIDGE LIST IGMPSNOOP SECURITY
X
X
X
X
X
X
BRIDGE SET IGMPSNOOP
X
X
X
X
X
X
BRIDGE SET IGMPSNOOP DEFAULTFASTLEAVE
X
X
X
X
X
X
BRIDGE SET IGMPSNOOP LASTMBERQUERYINTVL
X
X
X
X
X
X
BRIDGE SET IGMPSNOOP MCASTROUTERTIMEOUT
X
X
X
X
X
X
BRIDGE SET IGMPSNOOP MODE
X
X
X
X
X
X
BRIDGE SET IGMPSNOOP NETINTERFACE
X
X
X
X
X
X
BRIDGE SET IGMPSNOOP QUERYINTVL
X
X
X
X
X
X
BRIDGE SET IGMPSNOOP QUERYRESPONSEINTVL
X
X
X
X
X
X
BRIDGE SET IGMPSNOOP ROBUSTNESSVAR
X
X
X
X
X
X
BRIDGE SET IGMPSNOOP SECURITY
X
X
X
X
X
X
BRIDGE SET IGMPSNOOP AUTOLEARNING
X
X
X
X
X
X
BRIDGE SET IGMPSNOOP SECURITY MAXMACNUMBER
X
X
X
X
X
X
BRIDGE SET IGMPSNOOP VLAN
X
X
X
X
X
X
BRIDGE SET IGMPSNOOP V1TIMER
X
X
X
X
X
X
Page 280 / 998
IGMP snooping
IGMP Snooping command reference
iMG/RG Software Reference Manual (IGMP)
3-18
IGMP SET FORWARDALL
X
X
X
X
X
X
X
X
X
IGMP SET LASTMBERQUERYINTVL
X
X
X
X
X
X
X
X
X
IGMP SET QUERYINTVL
X
X
X
X
X
X
X
X
X
IGMP SET QUERYRESPONSEINTVL
X
X
X
X
X
X
X
X
X
IGMP SET ROBUSTNESS
X
X
X
X
X
X
X
X
X
IGMP SET UPSTREAMINTERFACE
X
X
X
X
X
X
X
X
X
IGMP SHOW FORWARDALL
X
X
X
X
X
X
X
X
X
IGMP SHOW STATUS
X
X
X
X
X
X
X
X
X
IGMP SHOW TIMERCONFIGURATION
X
X
X
X
X
X
X
X
X
IGMP SHOW UPSTREAMINTERFACE
X
X
X
X
X
X
X
X
X
IGMP SNOOPING DISABLE
X
X
X
IGMP SNOOPING ENABLE
X
X
X
IGMP SNOOPING SET SECONDARY-NETINTERFACE
X
X
X
IGMP SNOOPING SET MODE
X
X
X
IGMP SNOOPING SET LEAVETIME
X
X
X
IGMP SNOOPING SET TIMEOUT
X
X
X
IGMP SNOOPING SHOW
X
X
X
IGMP SNOOPING SECURITY
X
X
X
IGMP SNOOPING SECURITY SET MAXMACNUMBER
X
X
X
IGMP SNOOPING SECURITY LEARNING
X
X
X
IGMP SNOOPING SECURITY ADD
X
X
X
IGMP SNOOPING SECURITY DELETE
X
X
X
IGMP SNOOPING SECURITY SHOW
X
X
X
IGMP PROXY SET UPSTREAMINTERFACE
X
X
IGMP PROXY SHOW UPSTREAMINTERFACE
X
X
IGMP PROXY SHOW STATUS
X
X
TABLE 3-2
Bridge
IGMP Snooping Commands
(Continued)
Functions
Fiber
A
Fiber
B
Fiber
C
Fiber
D
Fiber
E
Modular
ADSL
A
ADSL
B
ADSL
C

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