Re: Catalyst 9k multicast

mr.richardb · ‎05-27-2021

Hi all,

I have a multicast new IPTV configuration on a catalyst 9k platform and seeing hundreds of megabits of traffic on the uplinks which I think it should not be there. The streams are good and the TVs are working normally but the unnecessary traffic worries me.

The setup is simple. All traffic is within the same vlan but on several switches.

Receivers and sources are connected to 3 different access switch and those access switches are connected to a collapsed core where the the SVI is for the particular VLAN. The uplinks are L2 port-channels with ~40Gbit/s BW.

IGMP snooping has been enabled all switches for that vlan.

The core switch has ip multicast routing enabled and ip pim sparse-mode too on the SVI.

There is a document that states that CGMP should be enabled, but not 100% sure that will help.

https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst9500/software/release/16-12/configuration_guide/ip_mcast_rtng/b_1612_ip_mcast_rtng_9500_cg/constraining_ip_multicast_in_switched_ethernet.html

"The default behavior for a Layer 2 switch is to forward all multicast traffic to every port that belongs to the destination LAN on the switch. This behavior reduces the efficiency of the switch, whose purpose is to limit traffic to the ports that need to receive the data. This behavior requires a constraining mechanism to reduce unnecessary multicast traffic, which improves switch performance."

Can anybody advise on that?

Reza Sharifi · ‎05-27-2021

Hi,

CGMP is not needed. As long as you have IGMP snooping enabled and PIM on the SVIs for communicating between vlans, that should be sufficient. We have never enabled CGMP for IPTV and everything has been working just fine.

HTH

mr.richardb · ‎06-01-2021

Hi,

I understand that CGMP is not needed ( Something is not right with that doc I think), but than something is missing. I don't really believe that we should see gigabits of traffic on the trunk interfaces. This interface on the core is dedicated to that multicast traffic now.

Port-channel116 is up, line protocol is up (connected) 
  Hardware is EtherChannel, address is 0476.b06d.d642 (bia 0476.b06d.d642)
  Description: x6
  MTU 1500 bytes, BW 40000000 Kbit/sec, DLY 10 usec, 
     reliability 255/255, txload 1/255, rxload 18/255
  Encapsulation ARPA, loopback not set
  Keepalive set (10 sec)
  Full-duplex, 10Gb/s, link type is auto, media type is N/A
  input flow-control is on, output flow-control is unsupported 
  Members in this channel: Twe1/0/2 Twe1/0/4 Twe2/0/2 Twe2/0/4 
  ARP type: ARPA, ARP Timeout 04:00:00
  Last input 00:00:01, output 00:00:11, output hang never
  Last clearing of "show interface" counters never
  Input queue: 0/2000/0/0 (size/max/drops/flushes); Total output drops: 0
  Queueing strategy: fifo
  Output queue: 0/40 (size/max)
  5 minute input rate 2885977000 bits/sec, 263309 packets/sec
  5 minute output rate 15426000 bits/sec, 1537 packets/sec
     46297474191 packets input, 63428593363455 bytes, 0 no buffer
     Received 46294803323 broadcasts (46294766588 multicasts)
     0 runts, 0 giants, 0 throttles 
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
     0 watchdog, 3345093628 multicast, 0 pause input
     0 input packets with dribble condition detected
     282691487 packets output, 356376964711 bytes, 0 underruns
     Output 337862 broadcasts (0 multicasts)
     0 output errors, 0 collisions, 2 interface resets
     0 unknown protocol drops
     0 babbles, 0 late collision, 0 deferred
     0 lost carrier, 0 no carrier, 0 pause output
     0 output buffer failures, 0 output buffers swapped out

The SVI on the core switch

sh int vlan 1260
Vlan1260 is up, line protocol is up , Autostate Enabled
  Hardware is Ethernet SVI, address is 8c94.1fac.61bf (bia 8c94.1fac.61bf)
  Description: IPTV_Multicast
  Internet address is 10.202.70.1/24
  MTU 1500 bytes, BW 1000000 Kbit/sec, DLY 10 usec, 
     reliability 255/255, txload 9/255, rxload 255/255
  Encapsulation ARPA, loopback not set
  Keepalive not supported 
  ARP type: ARPA, ARP Timeout 04:00:00
  Last input 00:00:02, output 00:00:00, output hang never
  Last clearing of "show interface" counters never
  Input queue: 0/375/132/0 (size/max/drops/flushes); Total output drops: 0
  Queueing strategy: fifo
  Output queue: 0/40 (size/max)
  5 minute input rate 13743237000 bits/sec, 1252006 packets/sec
  5 minute output rate 35848000 bits/sec, 3349 packets/sec
     1985604231381 packets input, 2720747639162645 bytes, 0 no buffer
     Received 0 broadcasts (330499 IP multicasts)
     0 runts, 0 giants, 0 throttles 
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
     4769357464 packets output, 6359605866433 bytes, 0 underruns
     Output 0 broadcasts (0 IP multicasts)
     0 output errors, 2 interface resets
     0 unknown protocol drops
     0 output buffer failures, 0 output buffers swapped out

There is a RP configured on the core switch. Is it possible that all traffic is sent to it from the sources? ( but RP should get only traffic that receivers are subscribed, not?)

Richard