Introduction
Contents
Example of bad choices for timer values
Query solicitation rapid recovery from topology changes
How clients leave groups queries and timers
Configurable Igmp timers and counters
Products and software versions this note applies to
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Igmp feature Software versions Products
Igmp overview
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Queriers and Snoopers
Messages
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MAC address, hex
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Choosing group addresses
IP address, binary
Avoid x.0.0.y, x.0.1.y, x.128.0.y, and x.128.1.y
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Igmp snooping
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Example
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Configure switch
Explanation of Igmp snooping
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Using Show command output to investigate Igmp state
Group List Entry timeout 136 secs Ports None
Group List Entry timeout 257 Secs Ports All Groups 235
Group Last Adv
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Group List Entry timeout 247 secs Ports
When a client leaves a group
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Multiple potential Igmp queriers
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Other Querier timeout .. secs
When there are no group members
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When a client joins a group
Group List Entry timeout 225 secs Ports
All Groups Entry timeout Secs Ports
Group List
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Group List Last Adv
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Igmp proxy
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Switch 3 is an Igmp Proxy
Explanation of Igmp proxy
Group List Entry timeout 122 secs Ports None
All Groups Entry timeout 145 Secs Ports
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Group Entry timeout Secs Ports
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Group Entry timeout 182 secs Ports
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Query solicitation rapid recovery from topology changes
How query solicitation works
Initial state
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Why convergence takes so long without query solicitation
Example
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Explanation from the perspective of switch 2, the snooper
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All Groups Entry timeout 236 secs Ports
Shows this entry
Explanation from the perspective of switch 1, the querier
Group Entry timeout 18 secs Ports
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Group Entry timeout 115 secs Ports
Speeding up Igmp convergence in a non-looped topology
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Switch 1 sends GQ
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Igmp filtering controlling multicast distribution
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Set switch port=1 igmpfilter=1
Types command
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Switch 3 is also an Igmp Snooper
Received Passed Dropped
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No group memberships
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Modify switch 2 Configuration
When we deny groups instead of replacing them
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Group 224.12.13.11 Entry timeout 255 secs Ports 224.12.13.12
Static Igmp
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Switch 2 is an Igmp Snooper
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Group Entry timeout Infinity Ports
Explanation of Static Igmp
MulticastPkts 675826
When we add a static entry on another switch
Modify switch 3 Configuration
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All Groups Entry timeout 247 secs Ports
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Group Entry timeout Infinity Ports 5,26
MulticastPkts 36350
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MulticastPkts 14756
Group Entry timeout Infinity Ports None
When a static entry’s port goes down
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Overview of leave process
How clients leave groups queries and timers
Querier timer values
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Snooper timer values
Describes the new behaviour
Comparing the Querier and Snooper timers
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Consequences for high-loss and high-lag networks
Igmp fast leave
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Switch 1 is an Igmp Querier
Explanation of Igmp fast leave
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Fast Leave Off
When fast leave is disabled
Group Entry timeout 2 secs Ports
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When you enable fast leave on switch
It is safe to ignore the group entry on switch
Group Entry timeout Secs Ports None
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When you set fast leave on all interfaces
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Multiple host mode for fast leave
To specify multiple mode, use the command
To specify single mode, use either of the commands
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Timer and counter relationships
Configurable Igmp timers and counters
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Software versions
Initial configuration
Each example modifies the following base configuration
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What these counters do
Default values
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Last Member Query Count and Last Member Query Interval
Last Member Query Interval 255 10secs
Potential problems with changing these counters
How to change these counters
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Last Member Query Count
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What this counter does
Potential problems with changing this counter
How to change this counter
Robustness Variable
How to change this timer
Default Query Interval
What this timer does
Potential problems with changing this timer
Query Response Interval
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Query Response Interval 100 10secs
Synchronisation of timers
Default Timeout Interval
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Default Timeout Interval = 2*130 + 100/10 = 270 seconds
Query Response Interval 200 10secs
Default Timeout Interval = 2*125 + 100/10 = 260 seconds
Default Timeout Interval 280 Secs
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Default Timeout Interval 180 Secs
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Default Query Interval 200 Secs Default Timeout Interval 410
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Example of bad choices for timer values
Imagine the following changes to the configuration
Commands to configure these settings are
Last Member Query Interval was set to 5, using the command
Problem 1 Last Member Query Interval too short
Problem 2 Query Response Interval short
Problem 3 Default Timeout Interval too short
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For more information, see Synchronisation of timers on
Stopping snoopers from snooping non-IGMP messages
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Ports 24
Configure the router
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Router uses Ospf
Ports 25
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Disabling All Groups entry for a port
Disabled All-groups Ports
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Preventing an All Groups entry for a port
Enabling All Groups entry again
Check the group entry timeout values
Reset port 24’s packet counters
Entry timeout 216 Secs
MulticastPkts
Check the group entry timeout values again
Entry timeout Secs
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Entry timeout 259 Secs
Enable Igmp debugging
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MulticastPkts 914
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Controlling which addresses create All Groups entries
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Configuring switch
224.0.0.5
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Configuring switches 1
Adding other router addresses
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Returning to the default list
224.0.0.254
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Using the other routermode options
Statically specifying that a port is a router port
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Check the current Igmp snooping entries
Stop port 6 from being a static router port
To remove the static configuration, simply delete it
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Statically add port 6 as a router port attached to Vlan
Igmp debugging
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Client joins a group
Several minutes later the group entry times out
IgmpSnoopMembershipQuery setting timer at 2 secs for group
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Client leaves a group
Snooped ports change
Manager Switch 3 del vlan=100 port=5
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Port entry times out
Report is filtered out
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Port in the All Groups list is unplugged
Output for show ip igmp changes
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State Forwarding
Switch
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Appendix STP state
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Manager Switch 3 show stp port=25-26