Introduction .............................................................................................................................................. 1

Products and software versions this note applies to ............................................................... 3

IGMP overview ......................................................................................................................................... 5

Queriers and Snoopers .................................................................................................................. 5

Messages ............................................................................................................................................. 6

Choosing group addresses ............................................................................................................. 7

IGMP snooping ......................................................................................................................................... 9

Example .............................................................................................................................................. 9

Explanation of IGMP snooping .................................................................................................... 11

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Page 1: Table Of Contents
How To | Managed Layer 3 Switches Introduction Allied Telesis routers and managed layer 3 switches use IGMP—Internet Group Management Protocol—to track which multicast groups their clients belong to. This enables them to send the correct multimedia streams to the correct destination.
Page 2 Multiple potential IGMP queriers ... 15 Example ... 15 Explanation of multiple potential IGMP queriers ... 17 IGMP proxy ... 21 Example ... 21 Explanation of IGMP proxy ... 23 Query solicitation (rapid recovery from topology changes) ... 26 How query solicitation works ... 26 Why convergence takes so long without query solicitation ...
Page 3: Products And Software Versions This Note Applies To
Switch 2 ... 109 Switch 3 ... 110 Products and software versions this note applies to IGMP is available on all the following Allied Telesis routers and managed layer 3 switches: AR400 series routers AR700 series routers AT-8600 series switches...
Page 4 The following table shows the software versions and products each feature is available on. IGMP feature Snooping Multiple potential queriers Proxy Filtering Filtering different message types Throttling Static IGMP Configurable counters and timers Snooping sub-features: Query Solicitation Fast Leave Controlling which addresses create All Groups entries Preventing All Groups entries Statically specifying router ports...
Page 5: Igmp Overview
IGMP overview Clients in an IP subnetwork use IGMP to indicate that they are interested in receiving a multicast. IGMP then ensures that routers and switches forward multicast packets out the appropriate ports to the interested clients. IGMP is very flexible, as the examples in this How To Note show, but the basic operation is simple.
Page 6: Messages
Querier’s group membership information stays up to date. The group address field for General Queries is set to 0.0.0.0. They are sent to a destination address of 224.0.0.1, and by default Allied Telesis routers and switches send them every 125 seconds.
Page 7: Choosing Group Addresses
Choosing group addresses This section describes things you need to be aware of when choosing addresses for your multicast groups. Reserved IP IP addresses in the range 224.0.0.0-239.255.255.255 are multicast addresses, but many addresses addresses in this range are reserved. Therefore, before choosing a multicast address, you should check its status in the “Internet Multicast Addresses”...
Page 8: Choosing Group Addresses
IGMP overview > Choosing group addresses Avoid x.0.0.y, x.0.1.y, x.128.0.y, and x.128.1.y It is particularly important to avoid using any address in the ranges x.0.0.y, x.128.0.y, x.0.1.y, or x.128.1.y (where x is 224-239 and y is 1-254). This is because x.0.0.y and x.128.0.y will map to the same multicast MAC address as 224.0.0.y. Similarly, x.0.1.y and x.128.1.y will map to the same multicast MAC address as 224.0.1.y.
Page 9: Igmp Snooping
In this example, we discuss IGMP snooping, the key to efficient multicast traffic flow in a layer 2 network. IGMP snooping is enabled by default on switch ports in Allied Telesis managed layer 3 switches and routers—it does not require any configuration.
Page 10: Igmp Snooping
Configure switch 1 Switch 1 is configured with IGMP, which makes it the IGMP Querier in this network. It is best practice to make the Querier the closest switch to the multicast source, and in this example switch 1 is closest. For more information about queriers see queriers"...
Page 11: Explanation Of Igmp Snooping
Explanation of This section steps through the events that occur in a typical use of multicasting in this network: to stream multicast packets for a group. IGMP The following figure shows the process by which IGMP tracks multicast clients and ensures learning that the correct clients receive the stream.
Page 12: Explanation Of Igmp Snooping
Using Show command output to investigate IGMP state No group In the first stage of the figure above, the multicast server is turned on and is streaming group 224.12.13.14 to the Querier, switch 1. Switch 1 knows about the group, but has nobody members interested in receiving it.
Page 13 This output now shows two entries, one for each of the following: group 224.12.13.14 and port 3, which shows that the client is attached to the Snooper through port 3 and is listening to group 224.12.13.14. The Snooper created this entry at stage 5 in the process Snooper forwards packets from 224.12.13.14 out port 3.
Page 14 Finally, look at the output of the command show igmpsnooping on the Querier. Even though switch 1 is the Querier for this network instead of a Snooper, this command shows that a client for group 224.12.13.14 is reached out port 49. Manager Switch 1>...
Page 15: Multiple Potential Igmp Queriers
Multiple potential IGMP queriers To find out more about IGMP, we next investigate what happens when more than one router or switch has an IGMP configuration. RFC 2236, Internet Group Management Protocol, Version 2, should have only one IGMP Querier. You may configure IGMP on more than router or switch, perhaps for redundancy, but the routers and switches have a pseudo election and the device with the lower IP becomes the operating IGMP Querier.
Page 16 Configure switch 1 Switch 1 is a potential IGMP Querier. It acts as a Snooper if it is not elected as the Querier. set system name="Switch 1" # VLAN general configuration create vlan=vlan100 vid=100 add vlan=100 port=1-52 # IP configuration enable ip add ip int=vlan100 ip=172.31.0.254 mask=255.255.255.0 enable ip igmp...
Page 17: Explanation Of Multiple Potential Igmp Queriers
Explanation of When there are no group members Switch 1 and switch 2 are both possible Queriers, and an election determines which switch becomes the actual Querier. We can see the results of the election by using the command show ip igmp on each switch. Manager Switch 1>...
Page 18 When a client joins a group Now imagine that Client 1 sends a Membership Report to switch 2 for the group 224.12.13.14. If we check the group membership for switch 2 by using the command show igmpsnooping, we see a group entry for 224.12.13.14. Manager Switch 2>...
Page 19 To see the difference between a switch acting as a Snooper and a switch acting as a Querier, compare the IGMP snooping table for switch 1 (above) with its IGMP table (below). They seem to contradict each other. The IGMP snooping table tells us that switch 1 is aware that it is receiving the group 224.12.13.14 and will send all groups (including this one) out port 49 towards the IGMP Querier, switch 2.
Page 20 Manager Switch 2> show igmpsnooping IGMP Snooping ------------------------------------------------------------------------ Status ... Enabled Disabled All-groups ports ... None Vlan Name (vlan id) ... default (1) Fast Leave ... Off Group List ... No group memberships. Vlan Name (vlan id) ... vlan100 (100) Fast Leave ...
Page 21: Igmp Proxy
VLAN. Note that the Proxy can only have one configured upstream VLAN. IGMP Proxy is available on all Allied Telesis routers and managed layer 3 switches except AT-9800 and SwitchBlade series. For AT-8948, AT-9900 and x900-48 series switches, it requires software version 2.8.1 or later.
Page 22 Configure switch 1 Switch 1—the closest switch to the multicast source—is an IGMP Querier. set system name="Switch 1" # Switching configuration disable switch port=50 link=disable # VLAN general configuration create vlan=vlan200 vid=200 add vlan=200 port=1-49 # IP configuration enable ip add ip int=vlan200 ip=172.31.1.254 mask=255.255.255.0 enable ip igmp enable ip igmp int=vlan200...
Page 23: Explanation Of Igmp Proxy
Explanation of When there are no group members The multicast server streams group 224.12.13.14 to switch 1 through port 1. IGMP snooping detects the stream, as you can see by using the command show igmpsnooping on switch 1. Manager Switch 1> show igmpsnooping IGMP Snooping ------------------------------------------------------------------------ Status ...
Page 24: Explanation Of Igmp Proxy
through vlan200. Output of the commands show ip igmp and show igmpsnooping show that switch 3 knows of a client interested in the group 224.12.13.14 through port 25. Manager Switch 3> show ip igmp IGMP Protocol ------------------------------------------------------------------------ Status ... Enabled Default Query Interval ...
Page 25 Switch 1 receives the proxied report from switch 3. Switch 1 notes that switch 3 is interested in the group 224.12.13.14 and sends the group multicast to switch 3 on port 49. Output of the command show igmpsnooping shows the membership that switch 1 is aware of. Manager Switch 1>...
Page 26: Query Solicitation (Rapid Recovery From Topology Changes)
Query Solicitation minimises loss of multicast data after a topology change. It is a built-in feature of Allied Telesis managed layer 3 switches since software versions 281-03 and 2.9.1 when running EPSR or spanning tree (STP, RSTP, or MSTP) for loop protection.
Page 27: How Query Solicitation Works
The following figure shows how Query Solicitation works when a port goes down. Initial state: Port on Switch 3 is blocking. Multicasts flow from server to client via Switches 1 and 4 1. Link to Switch 4 goes down. Switch 3 stops blocking and sends topology change (TC)
Page 28: Why Convergence Takes So Long Without Query Solicitation
Query solicitation (rapid recovery from topology changes) > Why convergence takes so long without query solicitation Why convergence takes so long without query solicitation This section illustrates IGMP convergence in a simple network that does not need STP because it has no switch loops. Query Solicitation is disabled by default in networks like this, because no switch is an STP root bridge or an EPSR master node.
Page 29: Why Convergence Takes So Long Without Query Solicitation
Query solicitation (rapid recovery from topology changes) > Why convergence takes so long without query solicitation Explanation from the perspective of switch 2, the snooper When link When the link is connected (all ports are up), the Snooper has entries for two ports: is up port 9, which is the Snooper’s connection to the client.
Page 30 Query solicitation (rapid recovery from topology changes) > Why convergence takes so long without query solicitation When we reconnect port 1 on the Snooper, the All Groups entry does not reappear. When link comes up Manager Switch 2> show igmpsnooping again IGMP Snooping ------------------------------------------------------------------------...
Page 31 Query solicitation (rapid recovery from topology changes) > Why convergence takes so long without query solicitation Explanation from the perspective of switch 1, the querier When the link is connected (all ports are up), the Querier has an entry for port 1, so it sends When link the group 224.12.13.14 out port 1.
Page 32 Query solicitation (rapid recovery from topology changes) > Why convergence takes so long without query solicitation When we reconnect port 1 on the Snooper, the port does not reappear because the When link comes up Querier has not yet received a Report over it. Therefore, the Querier does not start again forwarding the multicast stream out the port.
Page 33: Speeding Up Igmp Convergence In A Non-Looped Topology
Query solicitation (rapid recovery from topology changes) > Speeding up IGMP convergence in a non-looped topology Speeding up IGMP convergence in a non-looped topology The previous section described how it can take up to 125 seconds for multicasting to recover in a non-looped topology after a port comes back up.
Page 34 Query solicitation (rapid recovery from topology changes) > Enabling query solicitation on multiple switches in a looped topology Initial state: Port on switch 3 is blocking. Multicasts flow from server to client via switches 1 and 4 1. Link to switch 4 goes down.
Page 35: Igmp Filtering (Controlling Multicast Distribution)
IGMP filtering (controlling multicast distribution) IGMP filtering lets you control the distribution of multicast services on each switch port. Filtering is useful for subscription services when clients must be explicitly authorised to view a multicast stream. IGMP Filtering is available in Software Version 2.7.5 or later. Example This example uses the same network configuration as convenience, the diagram is reproduced below.
Page 36 Configure switch 1 Switch 1—the closest switch to the multicast source—is an IGMP Querier. The filter is configured on it, as shown in bold in the script below. Note that the order of entries in a filter is important. When IGMP tries to match a message to a filter, it performs a linear search of the filter to find a matching entry, starting with the lowest-numbered entry.
Page 37 Configure switch 2 Switch 2 is an IGMP Snooper. IGMP snooping is enabled by default and does not need any configuration. set system name="Switch 2" # STP general configuration enable stp=default set stp=default mode=rapid set stp port=2 edgeport=yes # VLAN general configuration create vlan=vlan100 vid=100 add vlan=100 port=1-26 Configure switch 3...
Page 38: Explanation Of Igmp Filtering (Controlling Multicast Distribution)
IGMP filtering (controlling multicast distribution) > Explanation of IGMP filtering (controlling multicast distribution) Explanation of distribution) Immediately after applying the filter, we check the group entries on switch 1 by using the command show ip igmp, and see that the switch still has an entry for the group we are filtering out.
Page 39 IGMP filtering (controlling multicast distribution) > Explanation of IGMP filtering (controlling multicast distribution) If we enter these commands again a few minutes later, we see that the filter has dropped packets and the group entry has expired and disappeared. Manager Switch 1> show igmp filter=1 IGMP Filters ------------------------------------------------------------------ Entry...
Page 40: Igmp Throttling (Limiting The Number Of Streams For Each Subscriber)
IGMP throttling (limiting the number of streams for each subscriber) IGMP throttling allows you to limit the number of streams that subscribers may access at a given time, for example, to protect from bandwidth oversubscription. When the number of multicast group memberships associated with a switch port reaches the configured limit, the port can either deny further Membership Reports, or replace an existing membership with the new group.
Page 41 Configure switch 1 Switch 1 is an IGMP Querier. Note that it has a filter configured on it, which is from the previous example. set system name="Switch 1" # STP general configuration enable stp=default set stp=default mode=rapid set stp=default port=1 edgeport=yes # VLAN general configuration create vlan=vlan100 vid=100 add vlan=100 port=1-52...
Page 42 IGMP throttling (limiting the number of streams for each subscriber) > Example Configure switch 3 Switch 3 is also an IGMP Snooper. set system name="Switch 3" # STP general configuration enable stp=default set stp=default mode=rapid set stp port=3 edgeport=yes # VLAN general configuration create vlan=vlan100 vid=100 add vlan=100 port=1-26 Page 42 | AlliedWare™...
Page 43: Explanation Of Igmp Throttling (Limiting The Number Of Streams For Each Subscriber)
IGMP throttling (limiting the number of streams for each subscriber) > Explanation of IGMP throttling (limiting the number of streams Explanation of streams for each subscriber) In this example, switch 2’s configuration limits port 2 to six concurrent multicast groups. The port has a throttling action of replace, meaning that any additional group replaces the oldest group.
Page 44 IGMP throttling (limiting the number of streams for each subscriber) > Explanation of IGMP throttling (limiting the number of streams Next, the client joins three more groups (224.12.13.17-224.12.13.19). Output from the command show igmpsnooping still shows six memberships, but the oldest three groups have been dropped.
Page 45 IGMP throttling (limiting the number of streams for each subscriber) > Explanation of IGMP throttling (limiting the number of streams When switch 2 drops groups by throttling, it does not send a Leave message, because IGMP snooping cannot generate IGMP packets. Therefore, the Querier (switch 1) still believes that switch 2 is interested in the throttled groups, as output from the command show ip igmp on switch 1 shows.
Page 46 IGMP throttling (limiting the number of streams for each subscriber) > Explanation of IGMP throttling (limiting the number of streams Membership Report for that group. IGMP throttling cannot distinguish between different clients on the same port. For this reason, the limit is tied to the port, not to the client. When we deny groups instead of replacing them Finally, we will consider the effect of changing the IGMP throttle action to deny, by using the command below.
Page 47 IGMP throttling (limiting the number of streams for each subscriber) > Explanation of IGMP throttling (limiting the number of streams group. The following output for the command show igmpsnooping demonstrates this. Note that the timeout for the groups 224.12.13.11 and 224.12.13.12 has been reset. Manager Switch 2>...
Page 48: Static Igmp
Static IGMP and SLP, see How to configure IGMP snooping with unregistered multicast addresses such as Service Location Protocol (SLP) in the Static IGMP is available on all the Allied Telesis managed layer 3 switches listed on Example In this example, we will start by setting an IGMP static entry for the group 224.12.13.14 to go to port 5 on switch 1 (part of vlan100).
Page 49 Configure switch 1 Switch 1 is an IGMP Querier and has the static IGMP entry. Static IGMP also requires you to: add an IP address to the interface to which you will attach the static entry enable IGMP enable the interface as an IGMP interface set system name="Switch 1"...
Page 50 Configure switch 3 Switch 3 is also an IGMP Snooper. Later in this example, we will add a static IGMP entry on this switch. "Modify switch 3 Configuration" on page 52 set system name="Switch 3" # STP general configuration enable stp=default set stp=default mode=rapid set stp port=3 edgeport=yes # VLAN general configuration...
Page 51: Explanation Of Static Igmp
Explanation of When the IGMP static entry is created on switch 1, entries immediately appear in the IGMP snooping table and the IGMP table. Manager Switch 1> show igmpsnooping IGMP Snooping ------------------------------------------------------------------------ Status ... Enabled Disabled All-groups ports ... None Vlan Name (vlan id) ...
Page 52: Explanation Of Static Igmp
When the group 224.12.13.14 starts streaming into switch 1, we can use the command show switch port=5 counter to watch the number of multicast packets sent on port 5 increase. This means that the link is up and the static IGMP entry is working. Manager Switch 1>...
Page 53 To see the effect that the new configuration has on switch 1, we can check the IGMP snooping and IGMP tables. The IGMP snooping table shows that switch 1 now has an All Groups entry because it is no longer the Querier. The IGMP table also shows that switch 1 is not the Querier.
Page 54 We can see the static entry on switch 3 by checking the IGMP snooping and IGMP tables. Manager Switch 3> show igmpsnooping IGMP Snooping ------------------------------------------------------------------------ Status ... Enabled Disabled All-groups ports ... None Vlan Name (vlan id) ... default (1) Fast Leave ...
Page 55 Modify switch 3 Configuration destroy ip igmp destination=224.12.13.14 int=vlan100 create ip igmp destination=224.12.13.14 int=vlan100 port=5,26 To see the new static entry, we use the commands show igmpsnooping and show ip igmp, and to see multicast packets streaming, we use the command show switch port=5,26 counter.
Page 56 Manager Switch 3> show switch port=5,26 counter Switch Port Counters -------------------------------------------------------------------------- Port 5. Fast Ethernet MAC counters: Combined receive/transmit packets by size (octets) counters: 65 - 127 128 - 255 256 - 511 General Counters: Receive Octets Pkts FCSErrors MulticastPkts BroadcastPkts Port 26.
Page 57 When a static entry’s port goes down Finally, note that when the port attached to a static entry goes down, the static entry remains but no ports are attached to it. You can see this from the output of the commands show igmpsnooping and show ip igmp for switch 1 when port 5 has been disconnected.
Page 58: How Clients Leave Groups: Queries And Timers
How clients leave groups: queries and timers When a client leaves a group, the Snoopers and the Querier check which ports now have clients that belong to that group. They will stop forwarding the group’s traffic out any ports that are now unnecessary. In this section, we describe the process in detail. Overview of leave process The basic process when a client leaves a group is as follows: The client sends a Leave message to indicate that it no longer needs to receive that...
Page 59: Snooper Timer Values
The command show ip igmp displays the timer for the most recently updated port as the group’s Refresh Time. From Software Version 291-08, the command show igmpsnooping vlan={<vid>|all} detail displays the timers for each individual port. Snooper timer values As described in it may update a timer for ports that forward that group.
Page 60: Queriers And Snoopers
If packet loss or lag time is an issue in your network, we recommend increasing the Robustness Variable on the Snoopers and the Querier. On Allied Telesis Snoopers and Queriers, LMQC = Robustness Variable. For Snoopers, not all vendors make these counters the same. RFC 2236 requires that LMQC and Robustness Variable have the same value on Queriers, but the IGMP timer rules for IGMP Snoopers are less well-defined.
Page 61: Igmp Fast Leave
IGMP fast leave IGMP Fast Leave enhances your control over router or switch bandwidth. Enabling Fast Leave tells IGMP snooping to stop the transmission of a group multicast stream to a port as soon as it receives a Leave message on that port. No timeouts are observed. Ordinarily, when IGMP snooping sees a Leave message, it waits for a Membership Query message before setting the entry timeout to 2 seconds.
Page 62: Igmp Fast Leave
Configure switch 1 Switch 1 is an IGMP Querier. set system name="Switch 1" # STP general configuration enable stp=default set stp=default mode=rapid set stp=default port=1 edgeport=yes # VLAN general configuration create vlan=vlan100 vid=100 add vlan=100 port=1-52 # IP configuration enable ip add ip int=vlan100 ip=172.31.0.254 mask=255.255.255.0 enable ip igmp enable ip igmp int=vlan100...
Page 63: Explanation Of Igmp Fast Leave
Explanation of Imagine that client 2 on switch 3 sends a Membership Report to join the group 224.12.13.14. The Snooper, switch 3, adds this to its the IGMP snooping table. When the same client then sends a Leave message, the IGMP Querier responds with a Membership Query and waits for a configured time for a response.
Page 64: Explanation Of Igmp Fast Leave
When fast leave is disabled The IGMP Snooper sees the Membership Query from the Querier and accordingly sets its expiry time to match the Querier. Output of the command show igmpsnooping on switch 3 shows that the timeout for the group 224.12.13.14 has dropped to 2 seconds and that port 3 is still attached to the group.
Page 65 When you enable fast leave on switch 3 When Fast Leave is enabled on switch 3, but not on switch 1, an interesting chain of events occurs when the client sends a Leave message, as shown in the following diagram. Client 2 The result of this is that switch 3 adds the group back into its snooping table (with the same timeout as the IGMP Querier) but has no ports interested in receiving the group.
Page 66 When you set fast leave on all interfaces Fast leave is enabled on a per-interface basis, but if you do not specify an interface, it is enabled on all interfaces. In this example, that means that if no VLAN is specified when enabling Fast Leave, it is enabled on all VLANs (vlan1 and vlan100).
Page 67 Multiple host mode for fast leave The previous discussion assumes that only one client is attached to the port on the Snooper. Imagine instead a situation where multiple clients are attached to a single port on the snooping switch, as the following figure shows. In this situation, you need to use fast leave in multiple host mode.
Page 68 You can see the list of hosts for each port by entering the command show igmpsnooping and specifying the detail parameter: show igmpsnooping vlan={name|1..4094|all} [group={multicast-ip-address|allgroups}] detail The group parameter lets you display information for only one group or for only the All Groups port (the allgroups option).
Page 69: Configurable Igmp Timers And Counters
Configurable IGMP timers and counters This section looks at some of the timers and counters that control how often IGMP sends queries and how quickly entries time out. First, it gives background information in the following subsections: "Timer and counter relationships" on page 69 "Software versions"...
Page 70: Software Versions
Software versions Since software versions 281-03 and 2.9.1, IGMP automatically sets the Default Timeout Interval to the value from the formula in the section above. Therefore, if you change any of the Robustness Variable, the LMQC, the Default Query Interval, or the Query Response Interval, IGMP changes the Default Timeout Interval to match.
Page 71 Configure switch 1 Switch 1 is an IGMP Querier. set system name="Switch 1" # STP general configuration enable stp=default set stp=default mode=rapid set stp=default port=1 edgeport=yes # VLAN general configuration create vlan=vlan100 vid=100 add vlan=100 port=1-52 # IP configuration enable ip add ip int=vlan100 ip=172.31.0.254 mask=255.255.255.0 enable ip igmp enable ip igmp int=vlan100...
Page 72: Default Values
Default values Output of the command show ip igmp shows the values of the configurable IGMP settings. The following output shows the default values. Manager Switch 1> show ip igmp IGMP Protocol ------------------------------------------------------------------------ Status ... Enabled Default Query Interval ... 125 secs Default Timeout Interval ...
Page 73 Configurable IGMP timers and counters > Last Member Query Count and Last Member Query Interval Potential problems with changing these counters For most networks, the default LMQI and LMQC values work. You should only change them if you are aware of the likely effect on the network. In particular, note that: Changing the LMQC automatically changes the Robustness Variable.
Page 74 Configurable IGMP timers and counters > Last Member Query Count and Last Member Query Interval Similarly, if we change the LMQC from 2 to 3, the refresh time also changes. Manager Switch 1> set ip igmp lmqc=3 Info (1005003): Operation successful. Manager Switch 1>...
Page 75: Robustness Variable
Robustness Variable What this counter does The Robustness Variable (RV) allows you to tune for the expected packet loss on a subnet. If you expect a subnet to be lossy, you can increase the RV. IGMP is robust to packet loss of one packet less than the RV.
Page 76: Robustness Variable
Default Query Interval What this timer does To maintain an accurate picture of group membership, the Querier periodically sends General Queries to all its IGMP interfaces. The Default Query Interval is the gap between General Queries. Note that General Queries are quite different from Specific Queries, which the Querier sends to a group address when it receives a Leave message for that group.
Page 77: Query Response Interval
Query Response Interval What this timer does The Query Response Interval determines the longest time clients can take to reply to a General Query. The Querier inserts the Query Response Interval into General Query messages. Clients randomly choose a time between 0 and the Query Response Interval at which to respond to a General Query.
Page 78: Default Timeout Interval
Default Timeout Interval The Default Timeout Interval is referred to as the Group Membership Interval in What this timer does The Default Timeout Interval specifies the length of time before the router or switch deletes a group from its multicast group database after the router or switch last receives a Membership Report for that group.
Page 79 Defaults First, the following output shows the default settings. Manager Switch 1> show ip igmp IGMP Protocol ------------------------------------------------------------------------ Status ... Enabled Default Query Interval ... 125 secs Default Timeout Interval ... 260 secs Last Member Query Interval ... 10 (1/10secs) Last Member Query Count ...
Page 80 Increase Next, change the Query Response Interval to 200 tenths of a second. Query Manager Switch 1> set ip igmp queryresponseinterval=200 Response Interval Info (1005003): Operation successful. Manager Switch 1> show ip igmp IGMP Protocol ------------------------------------------------------------------------ Status ... Enabled Default Query Interval ... 130 secs Default Timeout Interval ...
Page 81 Override To support existing configurations and for maximum flexibility, you can manually override the Default Default Timeout Interval. We do not recommend this. Timeout Manager Switch 1> set ip igmp timeout=180 Interval Warning (2005430): The Default Timeout Interval is below the default safe value of (Default Query Interval * Robustness ) + (Query Response Interval / 10).
Page 82 Earlier With software versions earlier than 281-03 and 2.9.1, you need to manually calculate and software change the Default Timeout Interval if you change any of the Robustness Variable, the versions LMQC, the Default Query Interval, or the Query Response Interval. Simply use the formula Default Timeout Interval = (Robustness Variable * Default Query Interval) + one Query Response Interval in seconds...
Page 83: Timer And Counter Relationships
Example of bad choices for timer values It is generally unwise to change any of the default IGMP settings unless you have advanced knowledge of how IGMP works. As most of the timers and counters are related. This means setting timers can cause problems unless you understand the potential impact on the IGMP process.
Page 84: Problem 1: Last Member Query Interval Too Short
Problem 1: Last Member Query Interval too short The Last Member Query Interval was set to 5, using the command: set ip igmp lmqi=5 This value is incredibly low—actually 5 tenths of a second (half a second). A Last Member Query Count of 2 (the default), gives your clients 1 second to get their Report back to the Querier before the Snooper and Querier stop sending the data stream.
Page 85 Example of bad choices for timer values > Problem 3: Default Timeout Interval too short Note that the Query Response Interval is specified in 1/10 second units on the command line and in output of show ip igmp, but in units of seconds in the above formula. In this example, the Query Response Interval was set with queryresponseinterval=5, so is 0.5 seconds.
Page 86: Stopping Snoopers From Snooping Non-Igmp Messages
Switch 2: Snooper Router We used an AR410 router, but the router configuration works on any AR400 or AR700 series router. Each example in this section modifies the following base configuration. Page 86 | AlliedWare™ OS How To Note: IGMP Stopping snoopers from snooping non-IGMP messages >...
Page 87 Configure switch 1 Switch 1 is an IGMP Querier. set system name="Switch 1" # STP general configuration enable stp=default set stp=default mode=rapid set stp=default port=1 edgeport=yes # VLAN general configuration create vlan=vlan100 vid=100 add vlan=100 port=1-52 # IP configuration enable ip add ip int=vlan100 ip=172.31.0.254 mask=255.255.255.0 enable ip igmp enable ip igmp int=vlan100...
Page 88: Configure The Router
Configure the router The router uses OSPF. set system name=Router # VLAN general configuration create vlan=vlan100 vid=100 add vlan=100 port=1-4 # IP configuration enable ip set ip autonomous=65000 add ip int=vlan100 ip=172.31.0.1 mask=255.255.255.0 add ip int=eth0 ip=10.0.0.1 # OSPF configuration set ospf routerid=172.31.0.1 add ospf area=0.0.0.1 add ospf range=172.31.0.0 area=0.0.0.1 mask=255.255.255.0...
Page 89 Manager Switch 3> show igmpsnooping IGMP Snooping ------------------------------------------------------------------------ Status ... Enabled Disabled All-groups ports ... None Vlan Name (vlan id) ... default (1) Fast Leave ... Off Group List ... No group memberships. Vlan Name (vlan id) ... vlan100 (100) Fast Leave ...
Page 90: Preventing An All Groups Entry For A Port
Stopping snoopers from snooping non-IGMP messages > Preventing an All Groups entry for a port Preventing an All Groups entry for a port This section stops port 24 from being in switch 2’s All Groups entry, then adds it back again. Disabling All Groups entry for a port You can avoid the All Groups entries shown above by simply disabling the All Groups entry for the port that switch 2 uses to connect to the router.
Page 91: Preventing An All Groups Entry For A Port
Stopping snoopers from snooping non-IGMP messages > Preventing an All Groups entry for a port Enabling All Groups entry again To further explore the system we will next reverse the process and follow switch 2 while group entries time out and the switch starts transmitting traffic for the group 224.12.13.14 to the router again.
Page 92 Stopping snoopers from snooping non-IGMP messages > Preventing an All Groups entry for a port 4. Display port 24’s packet counters, which show that only a few multicast packets have been transmitted on the port. Manager Switch 2> show switch port=24 counter Switch Port Counters ------------------------------------------------------------------------ Port 24.
Page 93 Stopping snoopers from snooping non-IGMP messages > Preventing an All Groups entry for a port 6. Enable IGMP debugging. Manager Switch 2> enable ip igmp debug Info (1005003): Operation successful. 7. Observe the debugging output, which shows that the group 224.12.13.14 was deleted when its timer expired, then was immediately added in again.
Page 94 Stopping snoopers from snooping non-IGMP messages > Preventing an All Groups entry for a port 9. Display port 24’s packet counters, which show that many multicast packets have been transmitted on the port. Manager Switch 2> show switch port=24 counter Switch Port Counters ------------------------------------------------------------------------ Port 24.
Page 95: Controlling Which Addresses Create All Groups Entries
Stopping snoopers from snooping non-IGMP messages > Controlling which addresses create All Groups entries Controlling which addresses create All Groups entries The router or switch adds a port to its All Groups list when it determines that the port has a router attached to it.
Page 96 Stopping snoopers from snooping non-IGMP messages > Controlling which addresses create All Groups entries Configuring switch 2 The example below shows how to tailor the list of router addresses on switch 2. In summary, you do this by using the commands: set igmpsnooping routermode=ip delete igmpsnooping routeraddress=224.0.0.5 The example removes 224.0.0.5 because it is the address for OSPF messages, as the table...
Page 97 Stopping snoopers from snooping non-IGMP messages > Controlling which addresses create All Groups entries Manager Switch 2> show igmpsnooping IGMP Snooping ------------------------------------------------------------------------ Status ... Enabled Disabled All-groups ports ... None Vlan Name (vlan id) ... default (1) Fast Leave ... Off Group List ...
Page 98 Stopping snoopers from snooping non-IGMP messages > Controlling which addresses create All Groups entries Configuring switches 1 and 3 The output of the command show igmpsnooping, above, shows that switch 2 is still receiving the multicast group 224.12.13.14 even though it has no ports interested in receiving it.
Page 99 Stopping snoopers from snooping non-IGMP messages > Controlling which addresses create All Groups entries Manager Switch 2> show igmpsnooping routeraddress IGMP Snooping Router Address ---------------------------------------------------------------------- IGMP Snooping Router Mode ... ip Router Address List -------------------------------------------------------- 224.0.0.1 224.0.0.2 ---------------------------------------------------------------------- Returning to the default list To return to the default list, change the router mode to default.
Page 100 Stopping snoopers from snooping non-IGMP messages > Controlling which addresses create All Groups entries Using the other routermode options As described earlier, routermode=multicastrouter is just a shortcut for the two IP addresses for DVMRP and PIM. Manager Switch 2> set igmpsnooping routermode=multicastrouter Info (1005282): IGMPSnooping Routermode successfully updated.
Page 101: Statically Specifying That A Port Is A Router Port
Statically specifying that a port is a router port Since software versions 281-04 and 291-04, you can statically configure particular ports as multicast router ports. This feature is useful in some unusual network configurations in which the learning process cannot identify all router ports. You could also use it creatively in special circumstances, when a Querier is unnecessary.
Page 102: Statically Specifying That A Port Is A Router Port
3. Statically add port 6 as a router port attached to VLAN 1. Manager Rapier 48i> add igmpsnooping vlan=1 routerport=6 snooped group 224.0.0.2 added Adding port 6 for group 224.0.0.2 on default Info (1005003): Operation successful. Manager Rapier 48i> show igmpsnooping IGMP Snooping ------------------------------------------------------------------------ Status ...
Page 103: Igmp Debugging
IGMP debugging In this section, we shall examine the debugging messages that the router or switch outputs when certain events occur while debugging is enabled. To enable debugging, use the command: enable ip igmp debug Example This example uses the same network configuration as convenience, the diagram is reproduced below.
Page 104: Igmp Debugging
A client leaves a group Client 2 sends a Leave message for group 224.12.13.14. Switch 1 sees the Leave message on vlan100 (port 49). The port is in a state of “deferred deletion” because of the Last Member Query process (see page 72).
Page 105 A port entry times out Client 2 sends a Membership Report for group 224.12.13.14. Switch 1 sees the report on vlan100 (port 49) and adds an entry. The entry eventually expires. Manager Switch 1> IGMP Snoop(48): Report -> snooped group 224.12.13.14 added Adding port 49 for group 224.12.13.14 on vlan100 IGMP Rx(48): Report ->...
Page 106 This example also shows what debugging output looks like when the Snooper receives a General Query. The Querier sends the General Query to the destination address 224.0.0.1 (the IGMP Query address) and the Snooper tells us that it has added the “router” port to its All Groups list.
Page 107 Output for show ip igmp changes When IGMP debugging is enabled, the command show ip igmp gives more information about static IGMP associations, as shown in bold in the following output. See Static IGMP" on page 51 IGMP Protocol ------------------------------------------------------------------------ Status ...
Page 108: Appendix: Stp State
Appendix: STP state In most of the examples in this document, the switches are configured in a loop and are all in the same VLAN. To prevent packets from looping the network, STP is configured. The STP state on each switch is given in the following output screens. Switch 1 Note that port 50 on switch 1 is in a discarding state.
Page 109 Switch 2 Manager Switch 2> show stp=default port=25-26 STP Port Information ------------------------------------------------------------------------ STP ... default STP Status ... ON Port ... 25 RSTP Port Role ... Root State ... Forwarding Point To Point ... Yes (Auto) Port Priority ... 128 Port Identifier ...
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Allied Telesis AR400 Series How To Configure

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