Allied Telesis AR400 manual Igmp overview, Queriers and Snoopers, AlliedWare OS How To Note Igmp

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IGMP overview > Queriers and Snoopers

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. When a client wants to start receiving a multicast—which is also called joining a multicast group—the client sends an IGMP Membership Report message. When a router or switch is running IGMP and receives a Report message, it starts forwarding traffic for the relevant multicast group to the client.

IGMP periodically polls clients by sending General Query messages, to check that the clients still belong to their multicast groups.

To leave a group, a client sends an IGMP Leave message to indicate that it no longer needs to receive the group traffic.

Note that IGMP does not exchange multicast routing information between subnets. The multicast routing protocols PIM and DVMRP do this.

Queriers and Snoopers

It is neither necessary nor desirable for every router or switch in an IP subnetwork to coordinate multicast traffic flows. Instead, a single router or switch does this and is called the Querier or the Designated Router. The Querier generates Query messages to check group membership, and processes Membership Reports and Leave messages.

However, other routers and switches in the network need to know whether to send multicasts out each of their ports. They find out this information by becoming Snoopers. Each Snooper checks IGMP messages before forwarding them to and from the Querier, and uses the information in the messages to determine which ports to send multicasts out of.

IGMP terms:

Multicast or Multicast stream

A flow of information—usually video or audio—that can go from one source to many destination clients.

Group

A multicast stream that clients can join. Groups have IP addresses in the 224.0.0.0/4 network.

Group member

A client that belongs to a particular multicast group.

IGMP Querier or Designated Router

A device in a subnetwork that is the coordinator for all multicast streams and IGMP membership information.

Each subnetwork has only one Querier (see "Multiple potential IGMP queriers" on page 15). The Querier generates Membership Query messages to check which clients are group members, and processes Membership Reports and Leave messages.

IGMP Snooper

A device that spies on IGMP messages to create flow efficiencies by ensuring that multicast data streams are only sent to interested ports. A Snooper can decide on the best path to send multicast packets at Layer 2 but it cannot alter those packets or generate its own IGMP messages.

IGMP Proxy

A device that passes membership reports upstream and multicast streams and queries downstream. The proxy acts on behalf of clients and servers by altering packets.

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Contents Introduction ContentsHow clients leave groups queries and timers Query solicitation rapid recovery from topology changesConfigurable Igmp timers and counters Example of bad choices for timer valuesProducts and software versions this note applies to 4 AlliedWare OS How To Note Igmp Igmp feature Software versions ProductsQueriers and Snoopers 5 AlliedWare OS How To Note IgmpIgmp overview Messages 6 AlliedWare OS How To Note IgmpChoosing group addresses 7 AlliedWare OS How To Note IgmpIP address, binary MAC address, hexAvoid x.0.0.y, x.0.1.y, x.128.0.y, and x.128.1.y 8 AlliedWare OS How To Note IgmpExample 9 AlliedWare OS How To Note IgmpIgmp snooping 10 AlliedWare OS How To Note Igmp Configure switchExplanation of Igmp snooping 11 AlliedWare OS How To Note IgmpGroup List Entry timeout 136 secs Ports None Using Show command output to investigate Igmp stateGroup List Entry timeout 257 Secs Ports All Groups 235 12 AlliedWare OS How To Note IgmpGroup Last Adv 13 AlliedWare OS How To Note Igmp14 AlliedWare OS How To Note Igmp When a client leaves a groupGroup List Entry timeout 247 secs Ports Multiple potential Igmp queriers 15 AlliedWare OS How To Note Igmp16 AlliedWare OS How To Note Igmp 17 AlliedWare OS How To Note Igmp When there are no group membersOther Querier timeout .. secs Group List Entry timeout 225 secs Ports When a client joins a groupAll Groups Entry timeout Secs Ports 18 AlliedWare OS How To Note IgmpGroup List Last Adv 19 AlliedWare OS How To Note IgmpGroup List 20 AlliedWare OS How To Note Igmp Igmp proxy 21 AlliedWare OS How To Note Igmp22 AlliedWare OS How To Note Igmp Switch 3 is an Igmp ProxyAll Groups Entry timeout 145 Secs Ports Group List Entry timeout 122 secs Ports None23 AlliedWare OS How To Note Igmp Explanation of Igmp proxy24 AlliedWare OS How To Note Igmp Group Entry timeout Secs Ports25 AlliedWare OS How To Note Igmp Group Entry timeout 182 secs PortsHow query solicitation works Query solicitation rapid recovery from topology changes26 AlliedWare OS How To Note Igmp Initial state 27 AlliedWare OS How To Note IgmpExample Why convergence takes so long without query solicitation28 AlliedWare OS How To Note Igmp 29 AlliedWare OS How To Note Igmp Explanation from the perspective of switch 2, the snooper30 AlliedWare OS How To Note Igmp All Groups Entry timeout 236 secs PortsGroup Entry timeout 18 secs Ports Explanation from the perspective of switch 1, the querier31 AlliedWare OS How To Note Igmp Shows this entry32 AlliedWare OS How To Note Igmp Group Entry timeout 115 secs PortsSpeeding up Igmp convergence in a non-looped topology 33 AlliedWare OS How To Note IgmpSwitch 1 sends GQ 34 AlliedWare OS How To Note IgmpIgmp filtering controlling multicast distribution 35 AlliedWare OS How To Note Igmp36 AlliedWare OS How To Note Igmp Types commandSet switch port=1 igmpfilter=1 37 AlliedWare OS How To Note Igmp Switch 3 is also an Igmp SnooperReceived Passed Dropped 38 AlliedWare OS How To Note IgmpNo group memberships 39 AlliedWare OS How To Note Igmp40 AlliedWare OS How To Note Igmp 41 AlliedWare OS How To Note Igmp 42 AlliedWare OS How To Note Igmp 43 AlliedWare OS How To Note Igmp 44 AlliedWare OS How To Note Igmp 45 AlliedWare OS How To Note Igmp 46 AlliedWare OS How To Note Igmp When we deny groups instead of replacing themModify switch 2 Configuration 47 AlliedWare OS How To Note Igmp Group 224.12.13.11 Entry timeout 255 secs Ports 224.12.13.12Static Igmp 48 AlliedWare OS How To Note Igmp49 AlliedWare OS How To Note Igmp Switch 2 is an Igmp Snooper50 AlliedWare OS How To Note Igmp Explanation of Static Igmp Group Entry timeout Infinity Ports51 AlliedWare OS How To Note Igmp Modify switch 3 Configuration When we add a static entry on another switch52 AlliedWare OS How To Note Igmp MulticastPkts 67582653 AlliedWare OS How To Note Igmp All Groups Entry timeout 247 secs Ports54 AlliedWare OS How To Note Igmp 55 AlliedWare OS How To Note Igmp Group Entry timeout Infinity Ports 5,26MulticastPkts 14756 56 AlliedWare OS How To Note IgmpMulticastPkts 36350 57 AlliedWare OS How To Note Igmp When a static entry’s port goes downGroup Entry timeout Infinity Ports None Querier timer values How clients leave groups queries and timers58 AlliedWare OS How To Note Igmp Overview of leave process59 AlliedWare OS How To Note Igmp Snooper timer values60 AlliedWare OS How To Note Igmp Comparing the Querier and Snooper timersConsequences for high-loss and high-lag networks Describes the new behaviourIgmp fast leave 61 AlliedWare OS How To Note Igmp62 AlliedWare OS How To Note Igmp Switch 1 is an Igmp QuerierExplanation of Igmp fast leave 63 AlliedWare OS How To Note IgmpGroup Entry timeout 2 secs Ports When fast leave is disabled64 AlliedWare OS How To Note Igmp Fast Leave OffIt is safe to ignore the group entry on switch When you enable fast leave on switchGroup Entry timeout Secs Ports None 65 AlliedWare OS How To Note Igmp66 AlliedWare OS How To Note Igmp When you set fast leave on all interfacesTo specify multiple mode, use the command Multiple host mode for fast leaveTo specify single mode, use either of the commands 67 AlliedWare OS How To Note Igmp68 AlliedWare OS How To Note Igmp 69 AlliedWare OS How To Note Igmp Configurable Igmp timers and countersTimer and counter relationships Each example modifies the following base configuration Initial configuration70 AlliedWare OS How To Note Igmp Software versions71 AlliedWare OS How To Note Igmp 72 AlliedWare OS How To Note Igmp Default valuesLast Member Query Count and Last Member Query Interval What these counters doHow to change these counters Potential problems with changing these counters73 AlliedWare OS How To Note Igmp Last Member Query Interval 255 10secsLast Member Query Count 74 AlliedWare OS How To Note IgmpHow to change this counter Potential problems with changing this counterRobustness Variable What this counter doesWhat this timer does Default Query IntervalPotential problems with changing this timer How to change this timerQuery Response Interval 100 10secs 77 AlliedWare OS How To Note IgmpQuery Response Interval 78 AlliedWare OS How To Note Igmp Default Timeout IntervalSynchronisation of timers 79 AlliedWare OS How To Note Igmp Default Timeout Interval = 2*130 + 100/10 = 270 secondsDefault Timeout Interval 280 Secs Default Timeout Interval = 2*125 + 100/10 = 260 seconds80 AlliedWare OS How To Note Igmp Query Response Interval 200 10secs81 AlliedWare OS How To Note Igmp Default Timeout Interval 180 Secs82 AlliedWare OS How To Note Igmp Default Query Interval 200 Secs Default Timeout Interval 410Imagine the following changes to the configuration Example of bad choices for timer valuesCommands to configure these settings are 83 AlliedWare OS How To Note IgmpProblem 2 Query Response Interval short Problem 1 Last Member Query Interval too shortProblem 3 Default Timeout Interval too short Last Member Query Interval was set to 5, using the command85 AlliedWare OS How To Note Igmp For more information, see Synchronisation of timers onStopping snoopers from snooping non-IGMP messages 86 AlliedWare OS How To Note Igmp87 AlliedWare OS How To Note Igmp 88 AlliedWare OS How To Note Igmp Configure the routerRouter uses Ospf Ports 24Ports 25 89 AlliedWare OS How To Note Igmp90 AlliedWare OS How To Note Igmp Disabled All-groups PortsPreventing an All Groups entry for a port Disabling All Groups entry for a portReset port 24’s packet counters Check the group entry timeout valuesEntry timeout 216 Secs Enabling All Groups entry againEntry timeout Secs Check the group entry timeout values again92 AlliedWare OS How To Note Igmp MulticastPkts93 AlliedWare OS How To Note Igmp Enable Igmp debuggingEntry timeout 259 Secs MulticastPkts 914 94 AlliedWare OS How To Note IgmpControlling which addresses create All Groups entries 95 AlliedWare OS How To Note Igmp224.0.0.5 Configuring switch96 AlliedWare OS How To Note Igmp 97 AlliedWare OS How To Note Igmp Adding other router addresses Configuring switches 198 AlliedWare OS How To Note Igmp 224.0.0.254 Returning to the default list99 AlliedWare OS How To Note Igmp 100 AlliedWare OS How To Note Igmp Using the other routermode optionsCheck the current Igmp snooping entries 101 AlliedWare OS How To Note IgmpStatically specifying that a port is a router port 102 AlliedWare OS How To Note Igmp To remove the static configuration, simply delete itStatically add port 6 as a router port attached to Vlan Stop port 6 from being a static router portClient joins a group 103 AlliedWare OS How To Note IgmpIgmp debugging 104 AlliedWare OS How To Note Igmp IgmpSnoopMembershipQuery setting timer at 2 secs for groupClient leaves a group Several minutes later the group entry times out105 AlliedWare OS How To Note Igmp Manager Switch 3 del vlan=100 port=5Port entry times out Snooped ports changePort in the All Groups list is unplugged 106 AlliedWare OS How To Note IgmpReport is filtered out Output for show ip igmp changes 107 AlliedWare OS How To Note Igmp108 AlliedWare OS How To Note Igmp SwitchAppendix STP state State Forwarding109 AlliedWare OS How To Note Igmp Manager Switch 3 show stp port=25-26
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