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IP Multicast on Cat2960 issue

Wolfgang Maier

Hi @all,


I have a weird multicast problem.


I´ve  setup multicast routing in our network.


Multicast is working so far but the Receivers attached to the Catalist 2960 Switches receive the stream in a very poor quality (pixel images, distorted sound, choppy image flow)

The Source is a VLC Stream to the group with a TTL=12 . However the same stream on the same VLAN only on a Catalyst 3560 or 2950 is playing smoothly. Based on this information, I think there´s something wrong at the 2960 end but I can´t fugure what. igmp snooping is active and I can see the mroute and querier.

I had a look at the network utilization and on the receivers where the stream is working (attached to 3560/2950) have a network utilization of around 1Mbit/s The other receiver where the stream is choppy the network stream is around 4Mbit/s....weird.

Can someone help me out? Thank you


Wolfgang Maier

Now I´ve found out that if I connect the 2960 Switch to the 3560CX switch streaming works *confused*


Peter Paluch
Hall of Fame Cisco Employee Hall of Fame Cisco Employee
Hall of Fame Cisco Employee

Hello Christian,

This issue is confusing indeed.

One thing, though: Can you confirm that when you had your 2960-PST connected directly to the SiteB switch, all ports on the 2960-PST and the corresponding port on the SiteB switch were operating at at least 100 Mbps, full duplex? Are you configuring any of these parameters (speed and/or duplex) manually at any point in your network?

Best regards,

Good day Peter,

thank you for your reply. Yes, the trunk ports are all 1Gbit/s and the ports towards the receivers are 100Mbit/s.

I also noticed a lot of drops on the interfaces towards the receivers but only when the 2960-PST is directly connected to the 6509-V-E (Site B)


FastEthernet0/2 is up, line protocol is up (connected)
  Hardware is Fast Ethernet, address is 6899.cd3d.ad82 (bia 6899.cd3d.ad82)
  MTU 1500 bytes, BW 100000 Kbit/sec, DLY 100 usec,
     reliability 255/255, txload 12/255, rxload 1/255
  Encapsulation ARPA, loopback not set
  Keepalive set (10 sec)
  Full-duplex, 100Mb/s, media type is 10/100BaseTX
  input flow-control is off, output flow-control is unsupported
  ARP type: ARPA, ARP Timeout 04:00:00
  Last input never, output 00:00:01, output hang never
  Last clearing of "show interface" counters never
  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 1772366
  Queueing strategy: fifo
  Output queue: 0/40 (size/max)
  5 minute input rate 0 bits/sec, 0 packets/sec
  5 minute output rate 4992000 bits/sec, 454 packets/sec
     5666 packets input, 747531 bytes, 0 no buffer
     Received 1479 broadcasts (1108 multicasts)
     0 runts, 0 giants, 0 throttles
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
     0 watchdog, 1108 multicast, 0 pause input
     0 input packets with dribble condition detected

This drops are constantly increasing which would explain the bad quality of the stream. But why are these packets dropped?

I thought OK, lets check the core switch there must be something. And here is what i found out :

IP statistics:
  Rcvd:  2032682421 total, 574453407 local destination
         0 format errors, 0 checksum errors, 40270311 bad hop count
         6 unknown protocol, 528722 not a gateway
         0 security failures, 0 bad options, 8527652 with options
  Opts:  4 end, 0 nop, 0 basic security, 0 loose source route
         0 timestamp, 0 extended security, 4 record route
         0 stream ID, 0 strict source route, 8527648 alert, 0 cipso, 0 ump
         0 other
  Frags: 3 reassembled, 0 timeouts, 0 couldn't reassemble
         2213 fragmented, 0 couldn't fragment
  Bcast: 115203121 received, 3150421 sent
  Mcast: 22500620 received, 20975346 sent
  Sent:  630567240 generated, 1135212704 forwarded
  Drop:  78437506 encapsulation failed, 0 unresolved, 0 no adjacency
         3172490 no route, 0 unicast RPF, 0 forced drop
         0 options denied, 0 source IP address zero


This counter is increasing also. But this would mean that the multicast stream has a TTL issue. On the source I´ve double checked  VLC. These are the stream options

:sout=#rtp{dst=,port=5004,mux=ts,ttl=12} :sout-all :sout-keep

If there is indeed a TTL issue, why does the stream work flawlessly on a 2950 and 3560 ?

I dont have any clues.


Best regards,



To exclude any issues with TTL I´ve measured the multicast traffic on Site B:



All packets are send with a ttl value of 10.. so this wouldn´t be a issue