IGMP Overview with Ruckus ICX and VOIP Pageing

Ruckus ICX Multicast and IGMP – Complete Reference

This document summarizes key concepts, terminology, best practices, and FAQs related to multicast, IGMP snooping, and VoIP paging on Ruckus ICX switches. Targeted for K-12 networks and small to medium enterprises.

Note: Command syntax is based on Ruckus FastIron 08.0.90+ firmware. Always verify commands against your specific firmware version.

1. Key Terms and Concepts

VLAN

  • A Virtual LAN separates traffic into broadcast domains.
  • Multicast traffic within a VLAN can be controlled via IGMP snooping.

Multicast

  • A method to send one copy of data to multiple receivers.
  • Destination IP addresses range from 224.0.0.0 to 239.255.255.255.
  • Useful for VoIP paging, IPTV, video conferencing, and mDNS discovery.

Multicast Address Space

  • 224.0.0.0 – 224.0.0.255: Reserved for local network control (IGMP, routing protocols). Not snooped by switches - these are flooded to maintain control plane functionality.
  • 224.0.1.0 – 238.255.255.255: Globally-scoped and internetwork control applications. Includes well-known addresses (e.g., NTP at 224.0.1.1).
  • 239.0.0.0 – 239.255.255.255: Administratively-scoped (private) addresses for enterprise use like paging systems and internal IPTV.

Important: Addresses in the 224.0.0.x range are flooded by design and cannot be controlled via IGMP snooping.

IGMP (Internet Group Management Protocol)

  • A Layer 3 protocol used by hosts to join or leave multicast groups.
  • Versions: IGMPv1, v2, v3 (v2 is most common for VoIP phones).
  • Works between hosts and queriers/routers within a VLAN.
  • IGMP messages are control traffic, not the multicast data itself.

IGMP Snooping

  • A Layer 2 switch feature that listens to IGMP control packets.
  • Builds a forwarding table mapping multicast groups → switch ports.
  • Forwards multicast traffic only to ports with interested receivers.
  • Requires an active querier to maintain and refresh membership tables.
  • Without snooping, multicast floods to all ports in the VLAN (inefficient but functional).

IGMP Querier

  • The device that periodically sends IGMP Query messages (typically every 125 seconds).
  • Ensures switches maintain up-to-date multicast membership tables.
  • Can be a Layer 3 router (your gateway) or a Layer 2 switch with an IP interface on the VLAN.
  • Only one active querier per VLAN; if multiple queriers exist, the one with the lowest IP address wins the election.

Active vs Passive Mode

  • Active Mode: Switch acts as IGMP querier and sends query messages.
    • Use when: No router is present, or in standalone Layer 2 networks.
    • Only enable on ONE switch per VLAN.
  • Passive Mode: Switch forwards queries but does not send them.
    • Use when: A router or another switch is the querier.
    • Default mode for most deployments.

Multicast Router Port

  • A port connected to a multicast router (PIM-enabled) that can route multicast between VLANs/subnets.
  • Only required if multicast traffic must traverse multiple VLANs.
  • Not required for single-VLAN multicast (e.g., VoIP paging within one voice VLAN).
  • Can be learned automatically or configured statically.

Static Group

  • Manually configured multicast group on a switch.
  • Forces multicast traffic for that group to specified ports.
  • Useful for devices that don’t send IGMP join messages (some legacy equipment).
  • Acts as a proxy - the switch sends membership reports on behalf of the group.

Fast Leave

  • fast-leave-v2 for IGMPv2: Switch immediately removes a port from the group when receiving an IGMP Leave message.
  • No group-specific query is sent before removing the port.
  • Safe ONLY when: One device per access port.
  • NEVER enable on trunk ports or ports with multiple devices (e.g., IP phone + PC pass-through).

Querier Address

  • The IP address the switch uses to send IGMP queries when in active mode.
  • Must be a local IP address on that VLAN (the VE interface IP).
  • Configured automatically if you have a VE interface; manual configuration rarely needed.

2. How Multicast Works on a Layer 2 Switch

Normal Operation Flow

  1. Querier sends IGMP General Queries periodically to 224.0.0.1 (all-hosts multicast group).
  2. Interested hosts respond with IGMP Membership Reports for the groups they want to join.
  3. Switches with IGMP snooping enabled:
    • Listen to these control messages
    • Build a forwarding table: multicast group → interested ports
    • Forward multicast data traffic only to ports with active memberships
  4. When membership queries stop or timeout:
    • Entries age out (typically 260 seconds)
    • Traffic stops being forwarded to those ports

What Happens Without a Querier?

If IGMP snooping is enabled but there is no active querier:

  1. Membership tables age out after ~260 seconds (2x query interval + grace period)
  2. Once tables are empty, multicast behavior depends on switch configuration:
    • Default behavior: Multicast traffic is dropped (no forwarding)
    • If flood-unregistered is enabled: Multicast floods to all ports
  3. This is why a querier is critical - without periodic queries, memberships cannot be maintained

Example: VoIP Paging Flow

Scenario: VLAN 101, Voice VLAN, ICX Switch with VE interface as querier, IP phones on access ports

  1. Switch (querier) sends General Query → 224.0.0.1 every 125 seconds
  2. Phones respond with Membership Reports for paging group 239.10.10.1
  3. Switch updates forwarding table: 239.10.10.1 → ports 1-24
  4. Paging server sends audio stream to 239.10.10.1
  5. Switch forwards stream only to ports 1-24 (phones), not to uplinks or other ports
  6. Querier continues sending periodic queries to maintain memberships

3. Ruckus ICX Configuration Best Practices

Basic VLAN Multicast Configuration

Enable multicast on the VLAN (enables IGMP snooping in passive mode by default):

ICX7150(config)# vlan 101
ICX7150(config-vlan-101)# router-interface ve 101
ICX7150(config-vlan-101)# multicast passive

Note: multicast passive is the default when you enable multicast. Explicitly stating it is optional.

Configuring Active Querier

To make a switch act as the IGMP querier (active mode):

ICX7150(config)# vlan 101
ICX7150(config-vlan-101)# multicast active

Prerequisites:

  • Switch must have a VE (Virtual Ethernet) interface configured on the VLAN
  • VE interface must have an IP address assigned
ICX7150(config)# vlan 101
ICX7150(config-vlan-101)# router-interface ve 101
ICX7150(config-vlan-101)# exit
ICX7150(config)# interface ve 101
ICX7150(config-if-ve-101)# ip address 10.10.101.1 255.255.255.0

The switch will use the VE interface IP (10.10.101.1) as the querier source address.

Setting IGMP Version

Set IGMP version globally (applies to all VLANs unless overridden):

ICX7150(config)# ip multicast version 2

Or set per-VLAN:

ICX7150(config)# vlan 101
ICX7150(config-vlan-101)# multicast version 2

Recommendations:

  • Use IGMPv2 for most VoIP deployments (broadest compatibility)
  • Use IGMPv3 if you need source-specific multicast (SSM) or source filtering

Enabling Fast Leave

Enable fast-leave for IGMPv2 on a VLAN:

ICX7150(config)# vlan 101
ICX7150(config-vlan-101)# multicast fast-leave-v2

CRITICAL WARNING:

  • Only enable on access ports with a single device
  • Never enable on trunk ports
  • Never enable on ports with IP phones that have PC pass-through
  • Fast-leave bypasses leave-wait timers - if multiple devices are on a port, traffic stops prematurely

Configuring Static Groups

If you have devices that don’t send IGMP joins, configure static groups:

ICX7150(config)# vlan 101
ICX7150(config-vlan-101)# multicast static-group 239.1.1.1 ethernet 1/1/1 to 1/1/10

This forces traffic for 239.1.1.1 to ports 1/1/1 through 1/1/10.

Optional: Disable static group proxy behavior (prevents switch from sending membership reports):

ICX7150(config)# vlan 101
ICX7150(config-vlan-101)# multicast static-grp-fwd-disable

Configuring Static Router Ports

Force multicast traffic to specific uplink ports (useful for ensuring traffic reaches routers):

ICX7150(config)# vlan 101
ICX7150(config-vlan-101)# multicast router-port ethernet 1/3/1

Global IGMP Snooping Enable/Disable

Enable IGMP snooping globally (usually enabled by default):

ICX7150(config)# ip multicast

Disable IGMP snooping globally (causes flooding - not recommended):

ICX7150(config)# no ip multicast

Adjusting IGMP Timers

Modify query interval (default 125 seconds):

ICX7150(config)# ip multicast query-interval 60

Modify group membership age-out time (default 260 seconds):

ICX7150(config)# ip multicast group-membership-time 200

Modify leave-wait time for IGMPv2 (default 2 seconds):

ICX7150(config)# ip multicast leave-wait-time 1

4. Verification Commands

Display Global IGMP Configuration

ICX7150# show ip multicast

Sample Output:

Summary of all vlans. Please use "sh ip mu vlan <vlan-id>" for details
Version=2, Intervals: Query=125, Group Age=260, Max Resp=10, Other Qr=255, Leave Wait=2
VL101: cfg V2, glb cfg active, 5 grp, 5 (*G) cache, no rtr port, 
       My Query address: 10.10.101.1 (configured)

What to look for:

  • active or passive mode
  • Query address (should match your VE interface)
  • Number of groups learned

Display VLAN-Specific Multicast Info

ICX7150# show ip multicast vlan 101

Display IGMP Group Memberships

ICX7150# show ip multicast group

Sample Output:

Group Address    VLAN  Port         Type    
239.1.1.1        101   1/1/5        Dynamic  
239.1.1.1        101   1/1/8        Dynamic
239.10.10.1      101   1/1/1-1/1/24 Static

Display Multicast Forwarding Cache (mcache)

ICX7150# show ip multicast mcache

This shows actual data streams being forwarded (not just group memberships).

Display IGMP Snooping Groups (Alternative)

ICX7150# show igmp-snooping groups

Display Multicast Traffic Statistics

ICX7150# show ip multicast traffic

Useful for troubleshooting - shows queries sent/received, reports received, etc.

Check Router Ports

ICX7150# show ip multicast router-port

5. Common Scenarios and Outcomes

ScenarioIGMP SnoopingQuerier PresentResult
Baseline (proper config)EnabledYes (Active)✅ Efficient forwarding, minimal bandwidth waste
No querier configuredEnabledNo❌ Tables age out → multicast stops after ~260 sec
Snooping disabledDisabledN/A⚠️ Multicast floods to all ports (works but wastes bandwidth)
Multiple queriers configuredEnabledMultiple✅ Lowest IP wins election, others go passive (auto-resolves)
Static groups onlyEnabledOptional⚠️ Traffic forwarded to static ports only, dynamic joins ignored
Multicast router port configuredEnabledYes✅ Multicast can route between VLANs (requires PIM on router)
Fast-leave on trunk portEnabledYes❌ Can break multicast (traffic removed prematurely)

6. Frequently Asked Questions

Q: Can a Layer 2 switch act as an IGMP querier?

A: Yes, absolutely. Any Ruckus ICX switch with a VE interface (Layer 3 VLAN interface) on the VLAN can act as a querier in active mode. The switch does NOT need to be the default gateway - it just needs a local IP on that VLAN.

Q: Do other switches in the topology need to know who the querier is?

A: No. Other switches automatically discover the querier by listening to IGMP query messages. They operate in passive mode and forward queries throughout the VLAN.

Q: Does the querier send the actual multicast data?

A: No! The querier only sends IGMP Query control messages. The actual multicast data comes from the application server (e.g., your VoIP paging server, IPTV head-end, etc.). The querier’s job is purely maintaining group memberships.

Q: When is a multicast router port required?

A: Only when multicast traffic must cross VLAN boundaries. For example:

  • Paging server in VLAN 100, phones in VLAN 101 → needs router port + PIM routing
  • All devices in same VLAN → no router port needed

Q: What happens if multiple switches are configured as active queriers?

A: IGMP has a querier election process. The switch with the lowest IP address on the VLAN wins and becomes the active querier. All others automatically become passive. However, it’s best practice to configure only ONE switch as active to avoid unnecessary elections.

Q: Why did my paging system work when I disabled IGMP snooping?

A: Disabling snooping causes the switch to flood all multicast traffic to every port in the VLAN (like a broadcast). This is inefficient and wastes bandwidth, but it does ensure all devices receive the stream. It’s a temporary workaround, not a solution.

Q: What is the purpose of static-group entries?

A: Static groups are for devices that don’t send IGMP join messages (some legacy paging devices, cameras, etc.). The switch acts as a proxy and tells the querier “I have members for this group” even though no IGMP joins were received. Traffic is then forwarded to the configured static ports.

Q: Can I run both multicast routing (PIM) and IGMP snooping on the same VLAN?

A: No. On Ruckus ICX, you cannot enable PIM routing on a VE interface and IGMP snooping on the same VLAN simultaneously. They are mutually exclusive. Choose one:

  • IGMP snooping for Layer 2 multicast within a VLAN
  • PIM routing for Layer 3 multicast across VLANs/subnets

Q: My multicast stopped working after 260 seconds. What happened?

A: Your querier is either down or not configured. Without queries, IGMP group memberships age out (default 260 seconds = 2x query interval + margin). Check:

  1. Is there an active querier? (show ip multicast)
  2. Is the VE interface up? (show interface ve 101)
  3. Is multicast set to active or passive? (show ip multicast vlan 101)

Q: Should I use IGMPv2 or IGMPv3?

A: For most K-12 and SMB deployments with VoIP paging:

  • Use IGMPv2 - simpler, widely supported by all phones
  • Use IGMPv3 only if you need source-specific multicast (SSM) or advanced filtering

IGMPv3 adds source filtering (e.g., “I want group 239.1.1.1 but ONLY from source 10.1.1.100”). Most paging systems don’t require this.

Q: How do I troubleshoot multicast not working?

Step-by-step checklist:

  1. Verify snooping is enabled:

    show ip multicast

    Look for “glb cfg active” or “glb cfg passive”

  2. Check for an active querier:

    show ip multicast vlan 101

    Look for “My Query address: X.X.X.X” - should show your VE IP

  3. Verify group memberships exist:

    show ip multicast group

    You should see entries for your multicast groups

  4. Check if traffic is flowing:

    show ip multicast mcache

    Mcache entries appear when actual data traffic flows

  5. Look for error counters:

    show ip multicast traffic

    Check for drops, resource exhaustion, etc.

  6. Test with flooding (temporary):

    no ip multicast

    If it works now, the issue is with your querier/snooping config

Q: What’s the difference between “group” and “mcache”?

A:

  • Group table (show ip multicast group): Shows IGMP control plane - who wants to receive which groups (based on IGMP joins)
  • Mcache (multicast cache) (show ip multicast mcache): Shows data plane - which multicast streams are actually being forwarded through the switch

Both should align. If you see groups but no mcache entries, data isn’t flowing.

Q: Can I see IGMP query messages in packet captures?

A: Yes! IGMP queries are sent to 224.0.0.1 (all-hosts multicast). Filter your capture for:

  • Destination IP: 224.0.0.1
  • Protocol: IGMP
  • Type: Membership Query (0x11)

IGMP Membership Reports are sent to the specific group address (e.g., 239.1.1.1).

7. Common Mistakes and Misconceptions

❌ Mistake: Enabling fast-leave on all ports

Problem: Breaks multicast on trunk ports and ports with multiple devices.
Fix: Only enable fast-leave on access ports with a single endpoint.

❌ Mistake: Configuring multiple switches as active queriers

Problem: Causes unnecessary querier elections and can confuse debugging.
Fix: Configure only ONE switch per VLAN as active. All others should be passive.

❌ Mistake: Disabling snooping to “fix” multicast

Problem: Floods multicast everywhere, wastes bandwidth, creates network load.
Fix: Enable snooping and configure a proper querier.

❌ Misconception: “The querier sends the multicast traffic”

Reality: The querier only sends IGMP control queries. Multicast data comes from your application server.

❌ Misconception: “I need PIM for VoIP paging”

Reality: Only if paging crosses VLAN boundaries. Single-VLAN paging only needs IGMP snooping.

❌ Mistake: Using a device IP as querier address instead of the VE interface

Problem: Queries won’t be sent from the correct IP, memberships won’t be maintained.
Fix: Always use the switch’s VE interface IP as the querier address (automatic if VE is configured).

❌ Misconception: “224.0.0.x addresses can be controlled with snooping”

Reality: The 224.0.0.0/24 range is reserved and always flooded - snooping doesn’t apply to these addresses.

8. Key Takeaways

✅ IGMP is control plane, multicast is data plane - they’re related but separate.

✅ Snooping requires an active querier - without queries, memberships age out and multicast stops.

✅ Active mode = querier, Passive mode = listener - only one active querier per VLAN is needed.

✅ Fast-leave is only safe on access ports with single devices - never enable on trunks.

✅ Static groups are for devices that don’t send IGMP joins - use sparingly.

✅ Flooding (no snooping) works but wastes bandwidth - querier + snooping is best practice.

✅ Multicast router ports are only for cross-VLAN routing - not needed for single-VLAN deployments.

✅ Always verify with show commands - check groups, mcache, and traffic statistics regularly.

✅ You cannot run PIM routing and IGMP snooping on the same VLAN - they’re mutually exclusive.

9. Additional Resources

  • Ruckus FastIron IP Multicast Configuration Guide - Official documentation for your firmware version
  • Ruckus Community Forums - Real-world troubleshooting and configuration examples
  • RFC 2236 - IGMPv2 Protocol Specification
  • RFC 3376 - IGMPv3 Protocol Specification

Document Version

Version: 2.0
Last Updated: October 2025
Target Firmware: Ruckus FastIron 08.0.90 and newer
Target Audience: K-12 Networks, Small to Medium Enterprises

Changelog

  • v2.0: Complete revision with accurate CLI syntax, improved explanations, additional FAQs
  • v1.0: Initial ChatGPT-generated draft (contained syntax errors and unclear explanations)

This document is provided as-is for educational purposes. Always test configurations in a lab environment before deploying to production. Command syntax may vary between firmware versions - consult official Ruckus documentation for your specific platform.