AlliedWare OS How To | Configure IGMP Snooping with Unregistered

AlliedWareTM OS
How To | Configure IGMP Snooping with Unregistered
Multicast Addresses such as Service Location
Protocol (SLP)
Introduction
IGMP snooping enables the switch to forward
multicast traffic intelligently, instead of flooding all
ports in the VLAN. With IGMP snooping, the switch
listens to IGMP membership reports, queries and leave
messages to identify the switch ports that are
members of multicast groups. Multicast traffic will only
be forwarded to ports identified as members of the
specific multicast group or groups.
IGMP snooping is performed at Layer 2 on VLAN
interfaces automatically. By default, the switch will only
forward traffic out those ports with multicast
listeners, therefore it will not act as a simple hub and
flood all multicast traffic out all ports.
Multicast is sometimes used to learn, or to advertise
to users, services available on their network through
Directory Agents (DAs) or directly with Service
Agents (SAs) using Service Location Protocol (SLP).
User Agents (UAs) and SAs send multicast requests
(224.0.1.35), to locate DAs on the network. UAs and
SAs learn of DAs via periodic multicast
(239.255.255.253) advertisements. There is no need
for IGMP-joins to these addresses with SLP.
List of terms:
Directory Agent (DA)
A process which collects
information from Service Agents
to provide a single repository of
service information in order to
centralise it for efficient access by
User Agents.
Service Agent (SA)
Advertises the location and
attributes on behalf of services.
User Agent (UA)
A process working on the user’s
behalf to acquire service
attributes and configuration. The
User Agent retrieves service
information from the Service
Agents or Directory Agents.
As these addresses are not within the reserved multicast range (i.e. multicast IP addresses,
x.0.0.x), IGMP snooping will snoop this traffic and not forward it to all ports within the
VLAN unless the switch receives an IGMP-join for this group, or you statically add an IGMP
entry for these addresses into the IGMP table.
If you want to advertise or learn services via multicast and you still want to have IGMP
snooping enabled to snoop other multicast traffic so it's not switched/flooded through your
network then you need to configure static IGMP entries on the switch.
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Configuration example
The following figure shows a server allowing two PCs access to Service Location Protocol
addresses 224.0.1.22 and 224.0.1.35 by adding static IGMP entries to its table.
Server
1000BASE-X GBIC
PORT ACTIVITY
GBI C
LI NK / FUL L DUP ACT
L/ A
BAS E-T
100 0M
L/ A
LI NK / HAL F DUP ACT
G BI C
13
ENABL ED
DIS ABL ED
10BASE-T / 100BASE-TX / 1000BASE-T
14
16
1
2
3
4
5
224.0.1.22
6
7
8
9
10
11
12
ACT
HAL F DUP
COL
1
2
3
4
7
8
9
1 0 11 12
5
Multi-Layer Gigabit Switch
RS-232
TERMINAL PORT
STATUS
6
ASY N0
L/ A
FAUL T
D/ C
L/ A
15
AT-9812T
ACT
1 0 /1 0 0M
FUL L DUP
D/ C
FAUL T
1 3 14
L/ A
G BI C
L/ A
G BI C
RPS
PW R
D/ C
1 5 16
RES ET
224.0.1.35
IGMP1.eps
You have to have an IP interface associated with the VLAN that you are enabling IP IGMP on
before you configure IP IGMP.
1. Associate an IP interface with VLAN1
add ip int=vlan1 ip=x.x.x.x
2. Enable IGMP on the switch
enable ip igmp
3. Enable IGMP on VLAN1
This must be done before the static IGMP association is created.
enable ip igmp interface=vlan1
4. Create the static IGMP association
The multicast data for the group specified by the destination parameter will be forwarded over
the ports specified by the port parameter. If the port parameter is not entered, the association
will default to all ports belonging to the interface.
create ip igmp destination=224.0.1.22 interface=vlan1
create ip igmp destination=224.0.1.35 interface=vlan1
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