Cisco Sg2008 Manual

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Cisco Small Business SG200 Series 8-port Smart Switch 131
 
Multicast
This chapter describes how to configure the multicast protocols that forward 
packets from one source to multiple destinations.
It contains the following topics:
•Multicast Properties
•Configuring MAC Group Addresses
•Configuring Group-to-Port
•Configuring IGMP Snooping
•Configuring MLD Snooping
•Configuring IGMP Multicast Router Interfaces
•Configuring MLD Multicast Router Interfaces
Multicast protocols deliver packets from one source to multiple receivers. They 
facilitate better bandwidth utilization and help to reduce the processing load on 
hosts and routers, making them ideal for use in applications such as video and 
audio conferencing, whiteboard tools, and stock distribution tickers.
The switch maintains a multicast forwarding table to make forwarding decisions 
for packets that arrive with a multicast destination MAC address. When multicasts 
are restricted only to specified ports, traffic is prevented from going to parts of the 
network where there are no receivers. When a packet enters the switch, the 
destination MAC address is combined with the VLAN ID and a search is performed 
in the multicast forwarding table. If no match is found, then the packet is either 
flooded to all ports in the VLAN or discarded, depending on the switch 
configuration. If a match is found, the packet is forwarded only to the ports that are 
members of that multicast group. 
						

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Multicast Properties
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Multicast entries can be learned by snooping (listening in on) the layer 3 protocols 
that manage multicast memberships:
•IPv4 multicast group addresses can be learned through the Internet Group 
Management protocol (IGMP).
•IPv6 multicast group addresses can be learned through the Multicast 
Listener Discovery (MLD) protocol. 
Interfaces with IGMP and MLD multicast routers for a specific VLAN can be either 
statically or dynamic configured. The multicast routers use IGMP and MLD to 
manage the membership of the multicast groups. A multicast router is also 
required in order for the switch to support IGMP/MLD snooping properly in a 
VLAN.
Multicast Properties
You can use the Multicast Proper ties page to specify how multicast packets are 
for warded within VL ANs . 
When you create a VLAN, a default multicast forwarding option is assigned. You 
can use the Global Multicast Mode setting to set all VLANs currently configured on 
the switch to a selected forwarding mode. The global setting does not create a 
default setting for VLANs created subsequently—it simply ensures that all existing 
VLANs are configured with the specified mode. You can also configure how the 
switch forwards multicast packets on an individual or per-VLAN basis. 
Configuring a Multicast Forwarding Mode on all VLANs
To configure all current VLANs with a particular multicast forwarding mode:
STEP 1Click Multicast > Properties in the navigation window.
STEP  2Select a Global Multicast Mode to apply to all VLANs. If a VLAN has been 
configured with a different mode, it is reset to the following mode:
•Forward Unregistered—If a packet is received from a VLAN with a 
multicast destination address and no ports in the VLAN are registered to 
receive multicast packets for that address, then the packet is flooded to all 
ports in the VLAN. The responsibility for accepting or dropping the packets 
belongs to the hosts. If a multicast packet is received and there are ports 
registered to receive it, the packet is sent only to the registered ports. 
						

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Configuring MAC Group Addresses
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•Forward All—All multicast packets received from a VLAN are flooded to all 
ports in the VLAN, regardless of port registrations to multicast addresses.
•Filter Unregistered—If a packet is received from a VLAN for a multicast 
destination address and no ports in the VLAN are registered to receive 
multicast packets for that address, then the packets are dropped.
STEP  3Click Apply. Your changes are saved to the Running Configuration.
Configuring Multicast Properties on an Individual VLAN
To configure a VLAN to have a different forwarding mode than the Global Multicast 
Mode setting:
STEP 1Select the VLAN from the VLAN ID menu and click Edit.
STEP  2Select the Multicast Mode as described in Configuring a Multicast Forwarding 
Mode on all VLANs.
STEP  3Click Apply and then click Close. Your changes are saved to the Running 
Configuration.
Configuring MAC Group Addresses
The MAC Group Address page enables you to view and configure associations 
between multicast group MAC address and VLANs on the switch. You can 
configure static associations or they can be learned dynamically through IGMP or 
MLD snooping. When a packet is received for a multicast group address that 
matches an entry in the MAC Group Address Table, the packet is sent only to ports 
that are members of the VLAN.
The switch supports up to 256 IPv4 and IPv6 MAC group address table entries, 
static and dynamic combined. A dynamic entry is aged out if no packets are 
received for the MAC group address for a configurable time (see the IGMP 
Snooping page to configure the IGMP Group Membership interval). 
						

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Configuring MAC Group Addresses
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Viewing the MAC Group Address Table
To view the MAC Group Address Table, click Multicast > MAC Group Address in 
the navigation window.
By default, all entries display in the table. You can use the VLAN ID and MAC Group 
Address filters to display only entries that match the specified values. The 
following fields display:
•Type—Indicates whether the entry is statically configured or dynamically 
learned.
•VLAN ID—VLAN ID to which multicast packets are forwarded when they 
match the specified multicast MAC address.
•MAC Group Address—Multicast group MAC address in hexadecimal format 
that is compared to an incoming packet destination MAC address.
Adding a Static MAC Group Address Table Entry
To add a static multicast MAC address and associate it with a VLAN:
STEP 1Click Add on the MAC Group Address page.
STEP  2Enter the parameters:
•VLAN ID—Select a VLAN from the list.
•Address Type—Select IPv4 to specify an address in 32-bit IPv4 notation 
(xxx.xxx.xxx.xxx), or select MAC to specify the address in a 6-byte 
hexadecimal format (xx.xx.xx.xx.xx.xx).
•MAC Group Address—Enter the address in the selected format. For an IPv4 
address, the least significant 23 bits are mapped to an Ethernet MAC 
address.
STEP  3Click Apply and then click Close. The entry appears in the MAC Group Address 
Table. 
						

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Configuring Group-to-Port
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Configuring MAC Address Group Port Membership
By default, packets destined to a multicast MAC address are flooded on all ports. 
Ports might become members of a particular MAC address group dynamically 
through the exchange of IGMP packets, or you can statically configure them as 
members. 
To view details and configure the port members of a multicast group address:
STEP 1Select an entry on the MAC Group Address page and click Details.
The page identifies the members of the multicast group address on every port. 
STEP  2Click Static to configure a port as a static member of the multicast MAC address. 
Or click None to remove the port as a static member of the MAC Multicast 
Address.
STEP  3Click Apply and then click Close. Your changes are saved to the Running 
Configuration.
Configuring Group-to-Port
The Group to Por t page enables you to configure associations between VLANs 
and multicast group MAC address on the switch. You can configure static 
associations or they can be learned dynamically through IGMP or MLD snooping. 
(see the IGMP Snooping page to configure the IGMP Group Membership interval) 
The results can be displayed in the MAC Group Address Table.
To configure Group to Port:
STEP 1Click Multicast > Group to Port in the navigation window.
STEP  2Use the VLAN ID and MAC Group Address filters to display entries that match the 
specified values:
•VLAN ID equals to—Select the VLAN ID to which multicast packets are 
forwarded when they match the specified multicast MAC address.
•MAC Group Address equals to—Select the group MAC address that is 
compared to an incoming packet destination MAC address.
STEP  3Select the Filter. 
						

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Configuring IGMP Snooping
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STEP  4Set the type to indicate whether the entry is statically configured or dynamically 
learned. Ports can become members of a particular MAC address group 
dynamically through the exchange of IGMP packets, or you can statically configure 
them as members. 
STEP  5Click Apply. Your changes are saved to the Running Configuration.
Configuring IGMP Snooping
Internet Group Management Protocol (IGMP) is a layer 3 Internet protocol that 
enables IPv4 networks to manage memberships to multicast groups. (IPv6 
multicast traffic is managed using the MLD protocol, as described in Configuring 
MLD Snooping.) IGMP communication occurs between IGMP routers and IGMP-
enabled hosts (clients). Although the switch does not initiate or reply to IGMP 
packets, it can be configured to listen to IGMP communication between routers 
and clients that are connected by the switch, and to make forwarding decisions 
that help to reduce unnecessary network traffic.This listening behavior is referred 
to as IGMP snooping. This is particularly beneficial for high-bandwidth multicast 
network traffic. 
Ordinarily, when the switch receives broadcast or multicast packets, the switch 
forwards a copy into each of the remaining network segments. This approach 
works well for broadcast packets that are intended to be processed by all 
connected nodes. For multicast packets, however, this approach could lead to less 
efficient use of network bandwidth, particularly when the packet is intended for 
only a small number of nodes; packets are flooded into network segments where 
no node has an interest in receiving the packet.
IGMP snooping enables the switch to intercept membership reports from IGMP 
clients and queries from routers. If the intercepted communications indicate that 
no IGMP clients exist on a link for a particular multicast destination address within 
a VLAN, then the switch does not send copies of those multicast packets to that 
network segment.
IGMP snooping can be enabled or disabled on each VLAN. When enabled on a 
VLAN, IGMP snooping is performed on all interfaces that are members of that 
VLAN.
Although IGMP is based on IP multicast addresses, the switch performs the actual 
multicast forwarding based on the equivalent MAC addresses. 
						

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Configuring IGMP Snooping
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To configure IGMP snooping:
STEP 1Click Multicast > IGMP Snooping in the navigation window.
STEP  2Select Enable for the IGMP Snooping Status.
STEP  3Click Add in the IGMP Snooping Table.
STEP  4For VLAN ID, select the VLAN that is to support IGMP snooping.
STEP  5Configure the following settings:
•IGMP Fast Leave—Select Enable to allow the switch to immediately remove 
a port (or LAG) from its multicast forwarding table when it receives an IGMP 
leave message for that multicast group. When enabled, the switch removes 
the port without first sending out general queries to the interface. Enable 
Fast Leave mode only on VLANs where only one host is connected to each 
port. This prevents the inadvertent dropping of the other hosts that are 
connected to the same port and remain interested in receiving multicast 
traffic directed to that group.
•IGMP Group Membership Interval—Specify the time in seconds that the 
switch waits for an IGMP membership report from a particular group on a 
particular interface before deleting the interface from the multicast 
forwarding database entry. Select Default to specify 260 seconds, or select 
User Defined and enter a value in the range 2 to 3600 seconds.
•IGMP Max Response Time—Specify the time in seconds that the switch 
waits for a reply after sending a query on an interface because it did not 
receive a report for a particular group in that interface. This value must be 
less than the IGMP Group Membership Interval value. Select Default to 
specify 10 seconds, or select User Defined and enter a value in the range 1 
to 25 seconds.
•IGMP MRouter Expiry Time—Specify the time in seconds that the switch 
waits for a query to be received on an dynamic mrouter interface before the 
interface is removed from the VLAN. A value of 0 indicates an infinite timeout; 
i.e., no expiration. Select Default to specify 0 seconds, or select User Defined 
and enter a value in the range 0 to 3600 seconds.
STEP  6Click Apply and then click Close. Your changes are saved to the Running 
Configuration.
The new VLAN entry appears in the IGMP Snooping Table. 
						

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Configuring MLD Snooping
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STEP  7Ensure that an IGMP Mrouter interface has been configured for this VLAN (or all 
VLANs). See Configuring IGMP Multicast Router Interfaces.
Configuring MLD Snooping
MLD is a protocol used by IPv6 multicast routers to discover the presence of 
multicast listeners (nodes wishing to receive IPv6 multicast packets) on its 
directly-attached links and to discover which multicast packets are of interest to 
neighboring nodes. MLD is derived from IGMP, which performs a similar function 
for IPv4 multicast traffic (see Configuring IGMP Snooping).
When MLD snooping is enabled, the switch selectively forwards IPv6 multicast 
packets to a list of ports that want to receive the data instead of flooding the 
packets to all ports in the VLAN. This list is constructed by snooping IPv6 multicast 
control packets.
NOTEThe switch supports MLD snooping of MLD version 1 and version 2 packets. The 
switch can be configured to perform MLD snooping and IGMP snooping 
simultaneously.
MLD snooping can be enabled or disabled separately on each VLAN. Although 
MLD is based on IPv6 addresses, the switch performs the actual multicast 
forwarding based on the equivalent MAC addresses. 
To enable and configure MLD snooping:
STEP 1Click Multicast > MLD Snooping in the navigation window.
The MLD Snooping Table lists each VLAN on which this feature is enabled.
STEP  2Select Enable for the MLD Snooping Status.
STEP  3Click Add in the MLD Snooping Table. 
						

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Configuring MLD Snooping
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STEP  4For VLAN ID, select the VLAN that is to support MLD snooping.
STEP  5Enter the parameters:
•MLD Fast Leave Mode—Select Enable to allow the switch to immediately 
remove a port (or LAG) from its multicast forwarding table when it receives 
an MLD leave message for that multicast group. When enabled, the switch 
removes the port without first sending out MAC-based general queries to 
the interface. Enable Fast Leave mode only on VLANs in which only one host 
is connected to each port. This prevents the inadvertent dropping of the 
other hosts that are connected to the same port and remain interested in 
receiving multicast traffic directed to that group.
•MLD Group Membership Interval—Specify the time in seconds that the 
switch waits for an MLD membership report from a particular group on a 
particular interface before deleting the interface from the multicast 
forwarding database entry. Select Default to specify 260 seconds, or select 
User Defined and enter a value in the range 2 to 3600 seconds. 
•MLD Max Response Time—Specify the time in seconds that the switch 
waits for a reply after sending a query on an interface because it did not 
receive a report for a particular group in that interface. This value must be 
less than the MLD Group Membership Interval value. Select Default to 
specify 10 seconds, or select User Defined and enter a value in the range 1 
to 65 seconds. 
•MLD Mrouter Expiry Time—Specify the time in seconds that the switch 
waits for a query to be received on an interface before the interface is 
removed from the list of interfaces with an MLD multicast router attached. A 
value of 0 indicates an infinite timeout; i.e., no expiration. Select Default to 
specify 0 seconds, or select User Defined and enter a value in the range 0 to 
3600 seconds.
STEP  6Click Apply and then click Close.
The new VLAN entry appears in the MLD Snooping Table.
STEP  7Ensure that an MLD Mrouter interface has been configured for this VLAN. See 
Configuring MLD Multicast Router Interfaces. 
						

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Configuring IGMP Multicast Router Interfaces
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Configuring IGMP Multicast Router Interfaces
An IGMP router must exist to manage the IGMP clients in a VLAN. For each VLAN 
that supports IGMP snooping, the switch must be statically configured with or 
must dynamically learn one or more interfaces where there is an IGMP router. An 
interface that has an IGMP router is known a IGMP Multicast router Interface. A 
VLAN that is IGMP snooping-enabled must have one or more IGMP multicast 
router interfaces. An IGMP multicast router can serve one or more VLANs.
To enable a switch port or LAG as an IGMP Mrouter interface and to configure 
related settings:
STEP 1Click Multicast > IGMP Mrouter in the navigation window
By default, the IGMP MRouter Table lists each switch port. To show LAGs, select 
LAG from the Interface Type list.
STEP  2Select the port or LAG that you want to configure and click Edit.
STEP  3Select Enable for the Mode.
STEP  4To specify the VLANs that use this interface as the IGMP Mrouter interface, move 
the VLAN to the Selected list, as described below.
•To select a VLAN: Click a VLAN in the Available list, and then click the right-
arrow button to move it to the Selected list. 
•To remove a VLAN: Click a VLAN in the Selected list, and then click the left-
arrow button to move it to the Available list. 
STEP  5Click Apply and then click Close.
In the IGMP Mrouter Table, the interface displays Enable in the Mode column and 
lists the selected VLANs.