In an enterprise network with multiple VLANs, the switch must be configured for multicast to be routed correctly. Troubleshooting multicast issues can be time-consuming and without some tools almost impossible.
Linux has several terminal commands for checking Multicast status of an interface:
ip maddr show - list all multicast interfaces
Example:
ip maddr show
1: lo
inet 224.0.0.251
inet 224.0.0.1
2: wlp0s20f3
inet 224.0.0.251 users 4
inet 224.0.0.1
Example:
ip addr show wlp0s20f3
3: wlp0s20f3: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP group default qlen 1000
Example:
ip link show wlp0s20f3 | grep MULTICAST
3: wlp0s20f3: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP mode DORMANT group default qlen 1000
Enable/Disable Multicast
sudo ip link set dev <interface> multicast [on|off]netstat -g - Lists all multicast interfaces
Example:
netstat -g
IPv6/IPv4 Group Memberships
Interface RefCnt Group
--------------- ------ ---------------------
lo 1 224.0.0.251
lo 1 all-systems.mcast.net
enp60s0 1 all-systems.mcast.net
wlp0s20f3 4 224.0.0.251
wlp0s20f3 1 all-systems.mcast.net
Pinging Multicast groups
ping -r -I wlp0s20f3 -t 1 -c 2 224.0.0.1
PING 224.0.0.1 (224.0.0.1) from 192.168.10.183 wlp0s20f3: 56(84) bytes of data.
64 bytes from 192.168.10.52: icmp_seq=1 ttl=255 time=3.89 ms
64 bytes from 192.168.10.50: icmp_seq=1 ttl=64 time=4.20 ms (DUP!)
64 bytes from 192.168.10.51: icmp_seq=1 ttl=64 time=5.50 ms (DUP!)
64 bytes from 192.168.10.50: icmp_seq=2 ttl=64 time=1.55 ms
-r - Bypass the normal routing tables and send directly to a host on an attached interface. If the host is not on a directly-attached network, an error is returned. This option can be used to ping a local host through an interface that has no route through it provided the option -I is also used.
-I - interface is either an address, or an interface name. If interface is an address, it sets source address to specified interface address. If interface is an interface name, it sets source interface to specified interface.
-t - ttl ping only. Set the IP Time to Live.
-c - Count
On Linux, there are several free open source tools available for testing multicast. In this blog, I am going to demonstrate two tools
mcjoin - Simple multicast testing application for UNIX
omping - Open Multicast ping
The lab consists of:
Cisco 3750x switch running c3750e-universalk9-mz.152-3.E1 with an IP Services license
Ubuntu 18.04 laptop with IP Address 10.112.40.1/23
Ubuntu 18.04 laptop with IP Address 192.168.10.183/24
Vlan 10 - 192.168.10.0/24
Vlan 46 - 10.112.40.0.23
m c j o i n - tiny multicast testing tool
mcjoin is a very simple and easy-to-use tool to test IPv4 and IPv6 multicast. it features:an optional multicast generator (server)
an end device that can act as a data sink (client)
supports joining one or more groups:
ASM (*,G) support
SSM (S,G) support
IPv4
IPv6
Installing mcjoin
Download mcjoin_2.4_amd64.deb from mcjoin releases and double click to install.The manual page for mcjoin is very good. Open it by running
man mcjoin
Simple usage example
Sender - 192.160.10.183/24 Vlan 10Receiver - 10.112.40.1/23 Vlan46
sender$ mcjoin -s
receiver$ mcjoin
joined group 225.1.2.3 on eth0 ...
..................................................................
Received total: 66 packets
receiver$
In this example, you start mcjoin on the sender laptop with the -s switch and mcjoin with no options on the receiver laptop. After 30 seconds or so press ctrl+c to stop the process. If multicast was successful you see the number of packets that were received.
A more advanced example
Say you want to verify that your topology can forward 5 consecutive groups in the MCAST_TEST_NET, as defined in RFC5771. Simply add the following as a standalone argument to both the receiver and the sender: 233.252.0.1+5.On the sender
./mcjoin -s 233.252.0.1+5
On the Receiver
./mcjoin -t3 -i wlp0s20f3 233.252.0.1+5
joined group 233.252.0.1 on wlp0s20f3 ...
joined group 233.252.0.2 on wlp0s20f3 ...
joined group 233.252.0.3 on wlp0s20f3 ...
joined group 233.252.0.4 on wlp0s20f3 ...
joined group 233.252.0.5 on wlp0s20f3 ...
..................................^C
Group 233.252.0.1 received 40 packets
Group 233.252.0.2 received 40 packets
Group 233.252.0.3 received 40 packets
Group 233.252.0.4 received 40 packets
Group 233.252.0.5 received 40 packets
Received total: 200 packets
Using omping (open multicast ping)
omping is available from the same github site as mcjoin.Install omping
https://github.com/troglobit/omping/
Simple example with two hosts. You can use more than two hosts.
Run the following on both laptops
./omping 10.112.40.1 192.168.10.183
10.112.40.1 : waiting for response msg
10.112.40.1 : joined (S,G) = (*, 232.43.211.234), pinging
10.112.40.1 : unicast, seq=1, size=69 bytes, dist=1, time=1.669ms
10.112.40.1 : unicast, seq=2, size=69 bytes, dist=1, time=3.906ms
10.112.40.1 : multicast, seq=2, size=69 bytes, dist=1, time=4.177ms
10.112.40.1 : unicast, seq=3, size=69 bytes, dist=1, time=3.564ms
10.112.40.1 : multicast, seq=3, size=69 bytes, dist=1, time=3.860ms
^C
10.112.40.1 : unicast, xmt/rcv/%loss = 3/3/0%, min/avg/max/std-dev = 1.669/3.046/3.906/1.205
10.112.40.1 : multicast, xmt/rcv/%loss = 3/2/33% (seq>=2 0%), min/avg/max/std-dev = 3.860/4.019/4.177/0.224
On the Switch
IGMP Connected Group Membership
Group Address Interface Uptime Expires Last Reporter Group Accounted
233.89.188.1 Vlan10 02:12:24 00:02:37 192.168.10.50
239.255.255.254 Vlan10 02:12:24 00:02:41 192.168.10.221
239.255.255.250 Vlan10 02:12:25 00:02:40 192.168.10.239
232.43.211.234 Vlan10 00:00:02 00:02:57 192.168.10.183
232.43.211.234 Vlan46 00:00:13 00:02:46 10.112.40.1
224.0.1.60 Vlan10 02:12:24 00:02:43 192.168.10.239
224.0.1.40 Vlan10 01:52:28 00:02:36 192.168.10.52
224.0.1.140 Vlan10 02:12:24 00:02:39 192.168.10.254
Using omping to test multicast with a specified multicast IP and port
From 192.168.10.183./omping -m 233.252.0.1 -p 9106 10.112.40.1 192.168.10.183
10.112.40.1 : waiting for response msg
10.112.40.1 : waiting for response msg
10.112.40.1 : joined (S,G) = (*, 233.252.0.1), pinging
10.112.40.1 : unicast, seq=1, size=69 bytes, dist=1, time=1.574ms
10.112.40.1 : multicast, seq=1, size=69 bytes, dist=1, time=53.798ms
10.112.40.1 : unicast, seq=2, size=69 bytes, dist=1, time=2.608ms
10.112.40.1 : multicast, seq=2, size=69 bytes, dist=1, time=2.608ms
10.112.40.1 : unicast, seq=3, size=69 bytes, dist=1, time=1.679ms
10.112.40.1 : multicast, seq=3, size=69 bytes, dist=1, time=1.809ms
10.112.40.1 : unicast, seq=4, size=69 bytes, dist=1, time=1.595ms
10.112.40.1 : multicast, seq=4, size=69 bytes, dist=1, time=1.901ms
10.112.40.1 : unicast, seq=5, size=69 bytes, dist=1, time=1.811ms
10.112.40.1 : multicast, seq=5, size=69 bytes, dist=1, time=2.043ms
10.112.40.1 : waiting for response msg
10.112.40.1 : server told us to stop
10.112.40.1 : unicast, xmt/rcv/%loss = 5/5/0%, min/avg/max/std-dev = 1.574/1.853/2.608/0.432
10.112.40.1 : multicast, xmt/rcv/%loss = 5/5/0%, min/avg/max/std-dev = 1.809/12.432/53.798/23.126
On the switch
sh ip igmp groups
IGMP Connected Group Membership
Group Address Interface Uptime Expires Last Reporter Group Accounted
233.89.188.1 Vlan10 02:13:26 00:02:34 192.168.10.50
239.255.255.254 Vlan10 02:13:26 00:02:33 192.168.10.221
239.255.255.250 Vlan10 02:13:27 00:02:40 192.168.10.239
233.252.0.1 Vlan10 00:00:09 00:00:01 192.168.10.183
233.252.0.1 Vlan46 00:00:13 00:02:46 10.112.40.1
224.0.1.60 Vlan10 02:13:27 00:02:37 192.168.10.239
224.0.1.40 Vlan10 01:53:31 00:02:41 192.168.10.52
224.0.1.140 Vlan10 02:13:26 00:02:36 192.168.10.254
Switch Configuration
3750x(config)#ip multicast-routing distributed
interface vl 10
ip address 192.168.10.52 255.255.255.0
no ip redirects
ip pim sparse-mode
end
interface Vlan46
ip address 10.112.41.254 255.255.254.0
ip helper-address 192.168.10.221
ip pim sparse-mode
end
Create a loopback to use as the rendezvous point (RP)
interface Loopback0
ip address 10.10.10.10 255.255.255.255
end
Create the Rendevouz point (RP)
ip pim rp-address 10.10.10.10
Show the rendezvous point
sh ip pim rp
Group: 233.89.188.1, RP: 10.10.10.10, next RP-reachable never
Group: 239.255.255.254, RP: 10.10.10.10, next RP-reachable never
Group: 239.255.255.250, RP: 10.10.10.10, next RP-reachable never
Group: 233.252.0.1, RP: 10.10.10.10, next RP-reachable never
Group: 224.0.1.60, RP: 10.10.10.10, next RP-reachable never
Group: 224.0.1.40, RP: 10.10.10.10, next RP-reachable never
Group: 224.0.1.140, RP: 10.10.10.10, next RP-reachable never
sh ip multicast
Multicast Routing: enabled
Multicast Multipath: disabled
Multicast Route limit: No limit
Multicast Fallback group mode: Dense
Number of multicast boundaries configured with filter-autorp option: 0
MoFRR: Disabled
From the Cisco multicast manual - Mulitcast configuration on an SVI
An SVI—A VLAN interface created by using the interface vlan vlan-id global configuration command. You will also need to enable IP PIM sparse-dense-mode on the VLAN, join the VLAN as a statically connected member to an IGMP static group, and then enable IGMP snooping on the VLAN, the IGMP static group, and physical interface. These interfaces must have IP addresses assigned to them.
sparse-mode - Enables sparse mode of operation. If you configure sparse mode, you must also configure an RP.
sh ip igmp snooping
Global IGMP Snooping configuration:
-------------------------------------------
IGMP snooping : Enabled
IGMPv3 snooping (minimal) : Enabled
Report suppression : Enabled
TCN solicit query : Disabled
TCN flood PortFast : Disabled
TCN flood query count : 2
Robustness variable : 2
Last member query count : 2
Last member query interval : 1000
Vlan 10:
--------
IGMP snooping : Enabled
IGMPv2 immediate leave : Disabled
Multicast router learning mode : pim-dvmrp
CGMP interoperability mode : IGMP_ONLY
Robustness variable : 2
Last member query count : 2
Last member query interval : 1000
Vlan 46:
--------
IGMP snooping : Enabled
IGMPv2 immediate leave : Disabled
Multicast router learning mode : pim-dvmrp
CGMP interoperability mode : IGMP_ONLY
Robustness variable : 2
Last member query count : 2
Last member query interval : 1000
References
Multicast testing, made easy!
How can I know if IP Multicast is enabled
Multicast Driver Testing Quick How-To v 0.3
10 “ping” Command Usage Examples in Linux
How can I know if IP Multicast is enabled
Multicast Driver Testing Quick How-To v 0.3
10 “ping” Command Usage Examples in Linux
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