Contents

Introduction

Prerequisites

Requirements

Components Used

Conventions

Troubleshoot Strategies

Check Source Packet Flow

Check Network Signaling

Troubleshoot PIM Sparse Mode

Check Network Packet Flow

Check Receiver Signaling

Check Receiver Packet Flow

Power CLI Tools

mstat

mrinfo

mtrace

ping

show Commands

show ip igmp groups

show ip igmp interface

show ip pim neighbor

show ip pim interface

show ip mroute summary

show ip mroute

show ip mroute active

show ip rpf

show ip mcache

show ip mroute count

show ip route

show ip pim rp mapping

debug Commands

debug ip igmp

debug ip mpacket

debug ip mrouting

debug ip pim

Related Information

Introduction

This document describes different tools and techniques used to troubleshoot multicast networks.

Prerequisites

Requirements

There are no specific requirements for this document.

Components Used

This document is not restricted to specific software and hardware versions.

The information in this document was created from the devices in a specific lab environment. All of the devices used in this document started with a cleared (default) configuration. If your network is live, ensure that you understand the potential impact of any command.

Conventions

Refer to Cisco Technical Tips Conventions for more information on document conventions.

Troubleshoot Strategies

When you troubleshoot multicast networks, it is good to consider the signaling protocol used in the network and packet flow.

The signaling protocol is used to setup and tear down the multicast sessions (such as PIM dense mode, PIM sparse mode, and DVMRP).

Packet flow is the actual sending, replicating, and receiving of the multicast packets between the source and receiver, based on the forwarding table created by the signaling process.

This table helps verify each piece information to troubleshoot and checks each section of the table works correctly:

Source

Network

Receivers

Signaling

NA

Check Network Signaling

Check Receiver Signaling

Packet Flow

Check Source Packet Flow

Check Network Packet Flow

Check Receiver Packet Flow

The next subsections detail the troubleshoot tools you can use to check and fix common problems.

Check Source Packet Flow

Complete these steps to determine if the source has sent the packets and that the correct packet fields are inserted:

1. Check the interface counters on the host. First, check the interface counters (if you are on a UNIX system, use the netstat command) on the source host to see if it sends packets. If it is not, check for misconfiguration or bugs in the host stack and application.

2. Use the show ip igmp groups <interface-name> command to check the upstream router to see if it received a join membership report at the interface directly connected to source.

3. Check the TTL value for the packets in the multicast application; it must be greater than 1. If the application sends packets with a TTL value less than 1, you must see the traffic dropped at the first upstream router. To verify, use the show ip traffic command and look for an increase in the value of the "bad hop count" counter. Any packet with a TTL value of 1, or less than the TTL threshold set by the interface with the ip multicast ttl-threshold command, is dropped and the "bad hop-count" counter is increased by one. Use the show ip igmp interface <interface-name> command to see the interface TTL threshold value.

4. Use the show ip mroute count and show ip mroute active commands to check the first upstream router or switch to see if it sees multicast packets from the source. The command output shows the traffic flow statistics for each (S,G) pair. If you do not observe any traffic, check receiver signaling.

5. Use the debug ip mpacket command on the nearest upstream router, with the detail or acl argument for granularity.

Caution: Use this command with caution when there is heavy multicast traffic on the network. Only if necessary, use the debug ip mpacket command on the route. Use the detail argument to show packet headers in the debug output, and access lists to check for traffic from specific sources. Remember that this command can have a serious performance impact on other traffic.

Check Network Signaling

This is the most complex and important piece to troubleshoot in any network.

It depends on the network signaling protocol used, such as PIM sparse mode, PIM dense mode, and DVMRP.

We recommend the multi-step approach described in this section.

Troubleshoot PIM Sparse Mode

Complete these steps to troubleshoot PIM sparse mode:

1. Check that IP multicast routing is enabled on all multicast routers.

2. Use the show ip pim neighbor command to check the expiration timer and mode to ensure successful PIM neighbor establishment, and look for any possible connectivity and timer issues that can inhibit the establishment of PIM neighbors. If necessary, use the ip pim [version] [dense-mode] [sparse-mode] [sparse-dense-mode] interface level subcommand to set the correct mode and version to successfully establish the PIM neighbors.

3. Use the show ip pim rp mapping command to ensure the correct RP-Group mapping and to check the expiration timer if auto-RP is configured. Use the debug ip pim auto-rp command to help figure out any auto-RP failures. If you do not see any PIM Group-to-RP Mappings, check the auto-RP configuration, or configure static Group-RP mappings with the ip pim rp-address ip address of RP [access-list] [named-accesslist] [override] command. The auto-RP configuration can be performed with the ip pim send-rp-announce interface-id scope TTL value and ip pim send-rp-discovery interface-id scope TTL value commands. These commands have to be configured only if there are auto-RP configurations.

4. Use theshow ip rpf <ip address of source> command to check the RPF failure for the source address. PIM dense mode and PIM sparse mode send Prune messages back to the source if traffic arrives on a non-RPF point-to-point interface. The debug ip pim command helps identify possible reasons for a failure in a PIM network—it compares the typical output with what you see. Use this output to identify the three discrete stages in PIM sparse mode: joining, registering, and SPT-switchover. The show ip mroute command allows you to watch the null entries in the Outgoing Interface lists and pruned entries in the mroute table.

Check Network Packet Flow

Use these commands to check the flow of multicast packets across the network:

- Use the mtrace command to check multicast trace hop-by-hop

- mstat

- ping

- show ip mroute count

- show ip mroute active

- debug ip mpacket

Check Receiver Signaling

Complete these steps to check receiver signaling:

1. Use the show ip igmp groups command at the first upstream router connected to the receiver to check that the interface has joined the group.

2. Use the ping command to check the reachability of the host and the first upstream router.

3. Use the show ip igmp interface command to check the IGMP version of the interface.

Note: Remember that a router configured with IGMP version 1 considers IGMP version 2 packets received from the host as invalid. These IGMP packets do not join the group until the router receives an IGMP version 1 packet from the host.

4. Use the debug ip igmp command to further troubleshoot receiver signaling.

Check Receiver Packet Flow

Complete these steps to check the receiver packet flow:

1. Use the netstat command on a UNIX system to check the receiver interface statistics.

2. Check that the TCP/IP stack was installed and configured properly.

3. Check that the Multicast receiver client application was installed and configured properly.

4. Watch for duplicate multicast packets on a multiaccess segment.

Power CLI Tools

The commands in this section can also be useful when troubleshoot, especially when you test the network packet flow and find the points of failure in the multicast network.

mstat

This command shows the multicast path in ASCII graphic format. It traces the path between any two points in the network, shows drops and duplicates, TTLs, and delays at each node in the network.

It is very useful when you need to locate congestion points in the network or focus on a router with high drop/duplicate counts. Duplicates are indicated in the output as negative drops.

Router#mstat lwei-home-ss2 172.16.58.88 224.0.255.255

Type escape sequence to abort

Mtrace from 172.16.143.27 to 172.16.58.88 via group 224.0.255.255

>From source (lwei-home-ss2.cisco.com) to destination (lwei-ss20.cisco.com)

Waiting to accumulate statistics......

Results after 10 seconds:

Source        Response Dest    Packet Statistics For    Only For Traffic

172.16.143.27    172.16.62.144    All Multicast Traffic     From 172.16.143.27

|       __/  rtt 48   ms   Lost/Sent = Pct  Rate     To 224.0.255.255

v      /     hop 48   ms   ---------------------     --------------------

172.16.143.25   lwei-cisco-isdn.cisco.com

|     ^      ttl   1

v     |      hop 31   ms    0/12 = 0%      1 pps    0/1 = --%  0 pps

172.16.121.84

172.16.121.45   eng-frmt12-pri.cisco.com

|     ^      ttl   2

v     |      hop -17  ms    -735/12 = --%      1 pps    0/1 = --%  0 pps

172.16.121.4

172.16.5.27     eng-cc-4.cisco.com

|     ^      ttl   3

v     |      hop -21  ms    -678/23 = --%      2 pps    0/1 = --%  0 pps

172.16.5.21

172.16.62.130   eng-ios-2.cisco.com

|     ^      ttl   4

v     |      hop 5    ms    605/639 = 95%      63 pps    1/1 = --%  0 pps

172.16.62.144

172.16.58.65    eng-ios-f-5.cisco.com

|      \__   ttl   5

v         \  hop 0    ms        4         0 pps           0    0 pps

172.16.58.88    172.16.62.144

Receiver      Query Source

mrinfo

This command shows multicast neighbor router information, router capabilities and code version, multicast interface information, TTL thresholds, metrics, protocol, and status.

It is useful when you need to verify multicast neighbors, confirm that bi-directional neighbor adjacency exists, and verify that tunnels are up in both directions.

Router#mrinfo

192.168.7.37 (b.cisco.com) [version cisco 11.1] [flags: PMSA]:

192.168.7.37 -> 192.168.7.34 (s.cisco.com) [1/0/pim]

192.168.7.37 -> 192.168.7.47 (d.cisco.com) [1/0/pim]

192.168.7.37 -> 192.168.7.44 (d2.cisco.com) [1/0/pim]

192.168.9.26  -> 192.168.9.29 (su.bbnplanet.net) [1/32/pim]

The flags in the output indicate:

- P = prune-capable

- M = mtrace-capable

- S = SNMP-capable

- A = Auto-RP-capable

mtrace

This command shows the multicast path from the source to the receiver, and it traces the path between points in the networks, which shows TTL thresholds and delay at each node.

When troubleshooting, use the mtrace command to find where multicast traffic flow stops, to verify the path of multicast traffic, and to identify sub-optimal paths.

Router#mtrace 192.168.215.41 192.168.215.67 239.254.254.254

Type escape sequence to abort.

Mtrace from 192.168.215.41 to 192.168.215.67 via group 239.254.254.254

From source (?) to destination (?)

Querying full reverse path...

0  192.168.215.67

-1  192.168.215.67 PIM  thresh^ 0  0 ms

-2  192.168.215.74 PIM  thresh^ 0  2 ms

-3  192.168.215.57 PIM  thresh^ 0  894 ms

-4  192.168.215.41 PIM  thresh^ 0  893 ms

-5  192.168.215.12 PIM  thresh^ 0  894 ms

-6  192.168.215.98 PIM  thresh^ 0  893 ms

ping

When troubleshoot, the ping command is the easiest way to generate multicast traffic in the lab to test the multicast tree because it pings all members of the group, and all members respond.

R3#ping 239.255.0.1

Type escape sequence to abort.

Sending 1, 100-byte ICMP Echos to 239.255.0.1, timeout is 2 seconds:

Reply to request 0 from 172.16.12.2, 16 ms

Reply to request 0 from 172.16.7.2, 20 ms

show Commands

The commands in this section help you gather useful information when troubleshoot a multicast problem. Refer to the Cisco IOS IP Multicast Command Reference Guide for more extensive information on these show commands.

Tip: If your show command responses are sluggish, the most probable reason is that router currently performs an IP domain lookup for IP addresses in the show command. You can disable IP domain lookup, use the no ip domain-lookup command, under the router global configuration mode to disable IP domain lookup. This stops the IP domain lookup and increases the show command output speed.

show ip igmp groups

This command shows which multicast groups are directly connected to the router, and which are learned via Internet Group Management Protocol (IGMP). You can use this command to verify that a source or receiver has actually joined the target group on the router interface. The Last Reporter column shows only one IGMP host, which indicates that it has sent either an unsolicited IGMP Join or IGMP Report in response to an IGMP Query from the PIM router for that particular group. You must only see one Last Reporter per Group Address.

R1#show ip igmp groups

IGMP Connected Group Membership

Group Address    Interface      Uptime          Expires         Last Reporter

239.255.0.1      Ethernet1      00:10:54        00:01:10        192.168.9.1

224.0.1.40       Ethernet0      01:36:27        00:02:45        192.168.10.2

224.0.1.40       Ethernet1      01:48:15        never           192.168.9.3

show ip igmp interface

Use this command to display multicast-related information about an interface, and to verify that IGMP is enabled, the correct version runs, the timers, Time To Live (TTL) threshold value, and IGMP querier router are properly set. IGMP does not need to be configured on an interface. It is enabled by default when you configure ip pim {dense-mode|sparse-mode|sparse-dense-mode}.

R1#show ip igmp interface

Ethernet1 is up, line protocol is up

Internet address is 192.168.9.3/24

IGMP is enabled on interface

Current IGMP version is 2

CGMP is disabled on interface

IGMP query interval is 60 seconds

IGMP querier timeout is 120 seconds

IGMP max query response time is 10 seconds

Last member query response interval is 1000 ms

Inbound IGMP access group is not set

IGMP activity: 22 joins, 18 leaves

Multicast routing is enabled on interface

Multicast TTL threshold is 0

Multicast designated router (DR) is 192.168.9.5

IGMP querying router is 192.168.9.3 (this system)

Multicast groups joined (number of users):

224.0.1.40(1)

show ip pim neighbor

Use this command to list the Protocol Independent Multicast (PIM) neighbors discovered by the Cisco IOS Software.

R1#show ip pim neighbor

PIM Neighbor Table

Neighbor          Interface                Uptime/Expires    Ver   DR

Address                                                            Prio/Mode

10.10.10.1        Ethernet0/0              02:19:41/00:01:38 v2    1 / DR B S

Details of each field are explained here:

- Neighbor Address- Specifies a PIM neighbor IP address

- Interface- An interface where a PIM neighbor was discovered

- Uptime- The total uptime of neighbor

- Expires- The time before a neighbor is timed out and until next PIM hello is received

- Ver- The version of PIM on neighbor interface

- DR Prio- The possible values are 0 to 4294967294 or N

This is a new column which tracks the priority of a PIM interface for DR election. The feature to configure a DR based on highest priority versus highest IP address was introduced in Cisco IOS Software Releases 12.1(2)T and 12.2 and Cisco IOS images with Bidir-PIM. You can use theip pim dr-priority <0-4294967294>interface command to set the DR priority. The default DR priority is set to 1. For interoperability, if a PIM neighbor runs an older Cisco IOS version which does not support the DR priority feature, the "DR Prior" column shows as N. If the neighbor is the only router that shows N for the interface, it becomes the DR regardless of which router actually has the highest IP address. If there are several PIM neighbors with N listed under this column, the tie breaker is the highest IP address among them.

- Mode- Information about the DR and other PIM capabilities.

This column lists the DR in addition to any capabilities supported by the PIM neighbor:

DR- The PIM neighbor is Designated Router

B- Bidirectional PIM (Bidir-PIM) capable

S- State refresh capable (applies only for dense mode)

When you troubleshoot, use this command to verify that all neighbors are up and that they use the proper mode, version, and expiration timer. You can also check the router configuration, or use the  show ip pim interface  command to verify the mode (PIM sparse or dense mode). Use the  debug ip pim  command to observe the pim-query message exchange.

show ip pim interface

Use this command to display information about interfaces configured for PIM. In addition, you can use this command to verify that the correct PIM mode (dense or sparse) is configured on the interface, the neighbor count is correct, and the designated router (DR) is correct (which is critical for PIM sparse mode). Multi-access segments (such as Ethernet, Token Ring, FDDI) elect a DR based on highest IP address. Point-to-Point links do not display DR information.

R1#show ip pim interface

Address          Interface          Version/Mode    Nbr   Query     DR

Count Intvl

192.168.10.1     Ethernet0          v2/Sparse-Dense  1    30     192.168.10.2

192.168.9.3      Ethernet1          v2/Sparse-Dense  1    30     192.168.9.5

show ip mroute summary

Use this command to display the summarized contents of the IP multicast routing table. You can also use it to verify the active multicast group(s) and which multicast senders are active when you look at the timers and flags.

R1#show ip mroute summary

IP Multicast Routing Table

Flags: D - Dense, S - Sparse, C - Connected, L - Local, P - Pruned

R - RP-bit set, F - Register flag, T - SPT-bit set, J - Join SPT

M - MSDP created entry, X - Proxy Join Timer Running

A - Advertised via MSDP

Outgoing interface flags: H - Hardware switched

Timers: Uptime/Expires

Interface state: Interface, Next-Hop or VCD, State/Mode

(*, 239.255.0.1), 01:57:07/00:02:59, RP 192.168.7.2, flags: SJCF

(192.168.33.32, 239.255.0.1), 01:56:23/00:02:59, flags: CJT

(192.168.9.1, 239.255.0.1), 01:57:07/00:03:27, flags: CFT

(*, 224.0.1.40), 1d00h/00:00:00, RP 192.168.7.2, flags: SJPCL

show ip mroute

Use this command to display the full contents of the IP multicast routing table. When you troubleshoot, use this command to verify:

- The (S,G) and (*,G) state entries from the flags.

- The incoming interface is correct. If it is not, check the unicast routing table.

- The outgoing interface(s) is correct. If it is incorrectly pruned, check the state in the downstream router.

R1#show ip mroute

IP Multicast Routing Table

Flags: D - Dense, S - Sparse, C - Connected, L - Local, P - Pruned

R - RP-bit set, F - Register flag, T - SPT-bit set, J - Join SPT

M - MSDP created entry, X - Proxy Join Timer Running

A - Advertised via MSDP

Outgoing interface flags: H - Hardware switched

Timers: Uptime/Expires

Interface state: Interface, Next-Hop or VCD, State/Mode

(*, 239.255.0.1), 01:55:27/00:02:59, RP 192.168.7.2, flags: SJCF

Incoming interface: Ethernet0, RPF nbr 192.168.10.2

Outgoing interface list:

Ethernet1, Forward/Sparse, 01:55:27/00:02:52

(192.168.33.32 , 239.255.0.1), 01:54:43/00:02:59, flags: CJT

Incoming interface: Ethernet0, RPF nbr 192.168.10.2

Outgoing interface list:

Ethernet1, Forward/Sparse, 01:54:43/00:02:52

(192.168.9.1, 239.255.0.1), 01:55:30/00:03:26, flags: CFT

Incoming interface: Ethernet1, RPF nbr 0.0.0.0

Outgoing interface list:

Ethernet0, Forward/Sparse, 01:55:30/00:03:12

(*, 224.0.1.40), 1d00h/00:00:00, RP 192.168.7.2, flags: SJPCL

Incoming interface: Ethernet0, RPF nbr 192.168.10.2

Outgoing interface list: Null

show ip mroute active

Use this command to display the active traffic sources and groups over the threshold. When you troubleshoot, use it to verify active source groups, the traffic rate for each source group (S,G) pair (you must have switched to Shortest Path Tree (SPT)), and to check if the target group multicast traffic is received. If the traffic is not received, look for active traffic that starts from the source towards the receiver.

R1#show ip mroute active

Active IP Multicast Sources - sending >= 4 kbps

Group: 239.255.0.1, (?)

Source: 192.168.33.32 (?)

Rate: 10 pps/115 kbps(1sec), 235 kbps(last 23 secs), 87 kbps(life avg)

show ip rpf

Use this command to display how IP multicast routing does Reverse Path Forwarding (RPF). When you troubleshoot, use it to verify that the RPF information is correct. If it is not, check the unicast routing table for the source address. Also use the ping and trace commands on the source address to verify that unicast routing works. You can use Distance Vector Multicast Routing Protocol (DVMRP) routes or static mroutes to fix any unicast-multicast inconsistencies.

R1#show ip rpf 192.168.33.32

RPF information for ? (192.168.33.32)

RPF interface: Ethernet0

RPF neighbor: ? (192.168.10.2)

RPF route/mask: 192.168.33.0/16

RPF type: unicast (eigrp 1)

RPF recursion count: 0

Doing distance-preferred lookups across tables

show ip mcache

This command can verify the IP multicast fast switching cache and debug fast-switching bugs.

R1#show ip mcache

IP Multicast Fast-Switching Cache

(192.168.33.32/32, 239.255.0.1), Ethernet0, Last used: 00:00:00

Ethernet1       MAC Header: 01005E7F000100000C13DBA90800

(192.168.9.1/32, 239.255.0.1), Ethernet1, Last used: 00:00:00

Ethernet0       MAC Header: 01005E7F000100000C13DBA80800

show ip mroute count

Use this command to verify that multicast traffic is received and to check on its flow rates and drops. If no traffic is received, work from the source to the receiver until you find where the traffic stops. You can also use this command to verify that traffic is forwarded. If it is not, use the  show ip mroute  command to look for "Null Outgoing interface list" and RPF failures.

R1#show ip mroute count

IP Multicast Statistics

routes using 2406 bytes of memory

2 groups, 1.00 average sources per group

Forwarding Counts: Pkt Count/Pkts per second/Avg Pkt Size/Kilobits per second

Other counts: Total/RPF failed/Other drops(OIF-null, rate-limit etc)

Group: 239.255.0.1, Source count: 2, Group pkt count: 11709

RP-tree: Forwarding: 3/0/431/0, Other: 3/0/0

Source: 192.168.33.32/32, Forwarding: 11225/6/1401/62, Other: 11225/0/0

Source: 192.168.9.1/32, Forwarding: 481/0/85/0, Other: 490/0/9

Group: 224.0.1.40, Source count: 0, Group pkt count:

show ip route

Use this command to check the unicast routing table and fix the RPF failures in the mroute table.

R2#show ip route

Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP

D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area

N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2

E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP

i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area

* - candidate default, U - per-user static route, o - ODR

P - periodic downloaded static route

Gateway of last resort is not set

D    192.168.9.0/24 [90/307200] via 192.168.10.1, 00:59:45,    Ethernet0

C    192.168.10.0/24 is directly connected, Ethernet0

D    192.168.4.0/24 [90/11040000] via 192.168.7.1, 23:21:00,    Serial0

D    192.168.5.0/24 [90/11023872] via 192.168.7.1, 23:21:02,    Serial0

C    192.168.7.0/24 is directly connected, Serial0

D    192.168.33.0/16 [90/2195456] via 192.168.7.1, 1d23h, Serial0

D    192.168.1.0/24 [90/11552000] via 192.168.7.1, 22:41:27,    Serial0

show ip pim rp mapping

Use this command to check the RP assignment by multicast group range, and to verify that the source of RP learning (static or auto-RP) and the mapping are correct. If you find an error, check the local router configuration or auto-RP configuration.

R1#show ip pim rp mapping

PIM Group-to-RP Mappings

Group(s) 224.0.1.40/32

RP 192.168.7.2 (?), v1

Info source: local, via Auto-RP

Uptime: 2d00h, expires: never

Group(s): 224.0.0.0/4, Static

RP: 192.168.7.2 (?)

debug Commands

This section is designed to show you how certain debug command outputs must look in a functioning network. When you troubleshoot, you can distinguish between correct debug output and that which points to a problem in your network. For more extensive information on these debug commands, refer to the Cisco IOS Debug Command Reference.

debug ip igmp

Use the debug ip igmp command to display IGMP packets received and transmitted, as well as IGMP-host related events. The no form of this command disables debug output.

This output helps you discover whether the IGMP processes function. In general, if IGMP does not work, the router process never discovers another host on the network that is configured to receive multicast packets. In PIM dense mode, this means the packets are delivered intermittently (a few every three minutes). In PIM sparse mode, they are never delivered.

R1#debug ip igmp

12:32:51.065: IGMP: Send v2 Query on Ethernet1 to 224.0.0.1

12:32:51.069: IGMP: Set report delay time to 9.4 seconds for 224.0.1.40 on Ethernet1

12:32:56.909: IGMP: Received v1 Report from 192.168.9.1 (Ethernet1) for 239.255.0.1

12:32:56.917: IGMP: Starting old host present timer for 239.255.0.1 on Ethernet1

12:33:01.065: IGMP: Send v2 Report for 224.0.1.40 on Ethernet1

12:33:01.069: IGMP: Received v2 Report from 192.168.9.4 (Ethernet1) for 224.0.1.40

12:33:51.065: IGMP: Send v2 Query on Ethernet1 to 224.0.0.1

The previous output shows that the router sends an IGMP version 2 query out interface Ethernet 1 at multicast address 224.0.0.1 (All multicast systems on this subnet). Interface Ethernet 1 itself is a member of group 224.0.1.40 (you can use the  show ip igmp interface  command to determine this), which sets a report delay time of 9.4 seconds (randomly determined). Because it does not receive any report from another system for multicast group 224.0.1.40 for the next 9.4 seconds, it sends a version 2 report of its membership, which is received by the router itself on Ethernet 1. It also receives IGMP report version 1 from host 192.168.9.1, which is directly connected to the interface Ethernet 1 for group 239.255.0.1.

This debug output is useful when you verify that the router interface sends queries and to determine the query interval (in the previous case, 60 seconds). You can also use the command to determine the version of IGMP used by the clients.

debug ip mpacket

Use the debug ip mpacket command to display all received and transmitted IP multicast packets. The no form of this command disables debug output.

R1#debug ip mpacket 239.255.0.1 detail

13:09:55.973: IP: MAC sa=0000.0c70.d41e (Ethernet0), IP last-hop=192.168.10.2

13:09:55.977: IP: IP tos=0x0, len=892, id=0xD3C1, ttl=12, prot=17

13:09:55.981: IP: s=192.168.33.32 (Ethernet0) d=239.255.0.1 (Ethernet1) len 906, mforward

This command decodes the multicast packet and shows whether the packet is forwarded (mforward) or dropped. It is useful when you debug packet flow problems in the network to look at the TTL value and the reason a packet was dropped.

Caution: Use caution when you turn on packet-level debug output, especially when the router services high multicast packet loads.

debug ip mrouting

This command is useful for routing table maintenance purposes. Use it to verify that the (S,G) mroute is installed in the mrouting table, or if it is not, why not. The key information in this output is the RPF interface. If there is an RPF check failure, the (S,G) mroute fails to install in the mrouting table.

R1#debug ip mrouting 239.255.0.1

13:17:27.821: MRT: Create (*, 239.255.0.1), RPF Null, PC 0x34F16CE

13:17:27.825: MRT: Create (192.168.33.32/32, 239.255.0.1), RPF Ethernet0/192.168.10.2,

PC 0x34F181A

13:17:30.481: MRT: Create (192.168.9.1/32, 239.255.0.1), RPF Ethernet1/0.0.0.0,

PC 0x34F18

debug ip pim

Use the debug ip pim command to display PIM packets received and transmitted, as well as PIM related events. The no form of this command disables debug output.

This section uses an example to help you understand the debug output of PIM sparse mode, and to show a typical debug output.

Here is the output of debug ip pim on R1:

R1#debug ip pim

PIM: Send v2 Hello on Ethernet0

PIM: Send v2 Hello on Ethernet1

PIM: Received v2 Hello on Ethernet0 from 192.168.10.2

PIM: Send v2 Hello on Ethernet0

PIM: Send v2 Hello on Ethernet1

PIM: Building Join/Prune message for 239.255.0.1

PIM: v2, for RP, Join-list: 192.168.7.2/32, RP-bit, WC-bit, S-bit

PIM: Send v2 periodic Join/Prune to RP via 192.168.10.2 (Ethernet0)

PIM: Received RP-Reachable on Ethernet0 from 192.168.7.2 for group 239.255.0.1

PIM: Update RP expiration timer (270 sec) for 239.255.0.1

Here is what each line of output denotes: R1 and R2 establish PIM neighbors when Hello messages are exchanged. These periodic Hello messages, exchanged at Query-Interval seconds between R1 (E0) and R2 (E0), keep track of PIM neighbors.

R1 sends a Join/Prune message to the RP address 192.168.7.2. The RP (R2) replies with a Received RP Reachable message back to R1 for group 239.255.0.1. This in turn updates the RP expiration timer at R1. The expiration timer sets a checkpoint to make sure the RP still exists; otherwise, a new RP must be discovered. Use the show ip pim rp command to observe the RP expiry time.

Now, look at the debug output between R1 and R2 when a multicast receiver for group 239.255.0.1 joins R1.

First, look at the output on R1:

1 PIM: Check RP 192.168.7.2 into the (*, 239.255.0.1) entry

2 PIM: Send v2 Join on Ethernet0 to 192.168.10.2 for (192.168.8.7.2/32, 239.255.0.1), WC-bit, RPT-bit, S-bit

3 PIM: Building batch join message for 239.255.0.1

4 PIM: Building Join/Prune message for 239.255.0.1

5 PIM: v2, for RP, Join-list: 192.168.7.2/32, RP-bit, WC-bit, S-bit

6 PIM: Send v2 periodic Join/Prune to RP via 192.168.10.2 (Ethernet0)

7 PIM: Received RP-Reachable on Ethernet0 from 192.168.7.2 : for group 239.255.0.1

8 PIM: Update RP expiration timer (270 sec) for 239.255.0.1

9 PIM: Building Join/Prune message for 239.255.0.1

10 PIM: v2, for RP, Join-list: 192.168.7.2/32, RP-bit, WC-bit, S-bit

11 PIM: Send v2 periodic Join/Prune to RP via 192.168.10.2 (Ethernet0)

Now, look at the output on R2:

12 PIM: Received v2 Join/Prune on Ethernet0 from 192.168.10.1, to us

13 PIM: Join-list: (*, 239.255.0.1) RP 192.168.7.2

14 PIM: Check RP 192.168.7.2 into the (*, 239.255.0.1) entry, RPT-bit set, WC-bit set, S-bit set

15 PIM: Add Ethernet0/192.168.10.1 to (*, 239.255.0.1), Forward state

16 PIM: Building Join/Prune message for 239.255.0.1

17 PIM: Received v2 Join/Prune on Ethernet0 from 192.168.10.1, to us

18 PIM: Join-list: (*, 239.255.0.1) RP 192.168.7.2, RPT-bit set, WC-bit set, S-bit set

19 PIM: Add Ethernet0/192.168.10.1 to (*, 239.255.0.1), Forward state

20 PIM: Building Join/Prune message for 239.255.0.1

21 PIM: Send RP-reachability for 239.255.0.1 on Ethernet0

22 PIM: Received v2 Join/Prune on Ethernet0 from 192.168.10.1, to us

23 PIM: Join-list: (*, 239.255.0.1) RP 192.168.7.2, RPT-bit set, WC-bit set, S-bit set

24 PIM: Add Ethernet0/192.168.10.1 to (*, 239.255.0.1), Forward state

25 PIM: Building Join/Prune message for 239.255.0.1

In line 1 previous, the multicast receiver for group 239.255.0.1 joins R1. This installs a (*, 239.255.0.1) entry in the mroute table. Then, in line 2, the multicast receiver sends an IGMP Join to R2 (RP) to join the shared tree.

When the IGMP join arrives on R2, R2 installs a (*, 239.255.0.1) mroute, as shown in lines 12 through 15 of the R2 output.

Once R2 installs (*, 239.255.0.1) in its mrouting table, it adds the interface from which it received the Join/Prune message to its Outgoing-interface-list (OIL) in the forward state. It then sends an RP-reachability message back on the interface on which it received the Join/Prune message. This transaction is shown in lines 15 through 21 of the R2 output.

R1 receives the RP-reachable message for group 239.255.0.1 and updates its expiration timer for RP. This exchange repeats itself once a minute by default and refreshes its multicast forwarding state as shown in lines 7 and 8 of the R1 output.

In the next lines, the debug output between R2 (RP) and R3 is seen. The source (directly connected to R3) started to send packets for the group 239.255.0.1.

First, look at the output on R3:

1 PIM: Check RP 192.168.7.2 into the (*, 239.255.0.1) entry

2 PIM: Building Join/Prune message for 239.255.0.1

3 PIM: For RP, Join-list: 192.168.7.2/32, RP-bit, WC-bit

4 PIM: Send periodic Join/Prune to RP via 192.168.7.2 (Serial4/0)

5 PIM: Received RP-Reachable on Serial4/0 from 192.168.7.2

6 PIM: Update RP expiration timer (270 sec) for 239.255.0.1

7 PIM: Send Register to 192.168.7.2 for 192.168.33.32, group 239.255.0.1

8 PIM: Send Register to 192.168.7.2 for 192.168.33.32, group 239.255.0.1

9 PIM: Received Join/Prune on Serial4/0 from 192.168.7.2

10 PIM: Join-list: (192.168.33.32/32, 239.255.0.1), S-bit set

11 PIM: Add Serial4/0/192.168.7.2 to (192.168.33.32/32, 239.255.0.1), Forward state

12 PIM: Received Register-Stop on Serial4/0 from 192.168.7.2

13 PIM: Clear register flag to 192.168.7.2 for (192.168.33.32/32, 239.255.0.1)

14 PIM: Received Register-Stop on Serial4/0 from 192.168.7.2

15 PIM: Clear register flag to 192.168.7.2 for (192.168.33.32/32, 239.255.0.1)

Here is the output of R2, the RP:

16 PIM: Received Join/Prune on Serial0 from 192.168.7.1, to us

17 PIM: Send RP-reachability for 239.255.0.1 on Serial0

18 PIM: Received Register on Serial0 from 192.168.7.1 for 192.168.33.32, group 239.255.0.1

19 PIM: Forward decapsulated data packet for 239.255.0.1 on Ethernet0

10 PIM: Forward decapsulated data packet for 239.255.0.1 on Serial0

21 PIM: Send Join on Serial0 to 192.168.7.1 for (192.168.33.32/32, 239.255.0.1), S-bit

22 PIM: Send Join on Serial0 to 192.168.7.1 for (192.168.33.32/32, 239.255.0.1), S-bit

23 PIM: Send Register-Stop to 192.168.7.1 for 192.168.33.32, group 239.255.0.1

24 PIM: Received Join/Prune on Serial0 from 192.168.7.1, to us

25 PIM: Prune-list: (192.168.33.32/32, 239.255.0.1)

26 PIM: Received v2 Join/Prune on Ethernet0 from 192.168.10.1, to us

27 PIM: Join-list: (*, 239.255.0.1) RP 192.168.7.2, RPT-bit set, WC-bit set, S-bit set

28 PIM: Add Ethernet0/192.168.10.1 to (*, 239.255.0.1), Forward state

29 PIM: Add Ethernet0/192.168.10.1 to (192.168.33.32/32, 239.255.0.1)

30 PIM: Join-list: (192.168.33.32/32, 239.255.0.1), S-bit set

31 PIM: Add Ethernet0/192.168.10.1 to (192.168.33.32/32, 239.255.0.1), Forward state

32 PIM: Building Join/Prune message for 239.255.0.1

33 PIM: For 192.168.7.1, Join-list: 192.168.33.32/32

34 PIM: For 192.168.10.1, Join-list: 192.168.9.1/32

35 PIM: Send v2 periodic Join/Prune to 192.168.10.1 (Ethernet0)

36 PIM: Send periodic Join/Prune to 192.168.7.1 (Serial0)

37 PIM: Received Join/Prune on Serial0 from 192.168.7.1, to us

38 PIM: Join-list: (*, 239.255.0.1) RP 192.168.7.2, RP-bit set, WC-bit set, S-bit set

39 PIM: Add Serial0/192.168.7.1 to (*, 239.255.0.1), Forward state

40 PIM: Add Serial0/192.168.7.1 to (192.168.33.32/32, 239.255.0.1)

41 PIM: Add Serial0/192.168.7.1 to (192.168.9.1/32, 239.255.0.1)

42 PIM: Join-list: (192.168.9.1/32, 239.255.0.1), S-bit set

43 PIM: Add Serial0/192.168.7.1 to (192.168.9.1/32, 239.255.0.1), Forward state

44 PIM: Join-list: (*, 239.255.0.1) RP 192.168.7.2, RP-bit set, WC-bit set, S-bit set

45 PIM: Add Serial0/192.168.7.1 to (*, 239.255.0.1), Forward state

Line 1 shows that R3, which is directly connected via Ethernet0/0 to the source, receives multicast traffic for group 239.255.0.1. It creates a (* , 239.255.0.1) entry and sends a Join message to the RP.

Lines 16 and 17 show that R2, which is the RP, also receives the Join/Prune message and sends RP reachability information back to R3.

In lines 5 and 6, R3 updates its RP expiration timer after it receives the RP reachable information. Lines 7 and 8 previous show that R3 uses its (*,G) entry to send the data to RP encapsulated in a Register packet with the source that initiates transmission to group 239.255.0.1.

Lines 18 to 20 show that R2 received the Register packet, de-encapsulated and forwarded it down the tree with a preexisting (*, 239.255.0.1) entry in route table.

Lines 21 and 29 show that R2 sends a Join message towards R3 and installs an (S,G) (192.168.33.32, 239.255.0.1) entry in the mroute table.

Lines 9 to 11 show that R3 receives the Join message from R2, installs an (S,G) (192.168.33.32,239.255.0.1) entry in mroute table, and puts the interface connected to RP in forward mode, which builds the (S,G) multicast SPT tree toward the source.

In line 23, R2 begins to receive (S,G) traffic down SPT and sends a Register-Stop message (and a Join message) toward the source.

Lines 12 to 15 show that R3 receives the Register-Stop message, clears the register flag, and stops the encapsulation (S,G) traffic.

Periodic Join/Prune messages are exchanged between the RP and R3 to maintain the multicast tree.

Related Information

- IP Multicast Troubleshooting Guide

- Multicast Quick-Start Configuration Guide

- IP Multicast Support Page

- IP Routing Support Page

- Cisco Technical Support & Downloads