Re: (ASCEND) Multicast weirdness

[Matt Holdrege <matt@ascend.com>]

At 01:18 PM 1/8/98 +0100, Andre Beck wrote:
>Hi,
>
>I've posted on this here already but no answer yet. I'd like to try
>out the multicasting capabilities of several Ascend boxes I have
>around. I basically have two obstacles:
>
>1) Documentation, or better lack thereof. I can't find where the
>   multicast stuff for Ascend boxes is documented. Neither the
>   "ISP Guide" nor the "Reference Guide" from the beta download
>   area (I assumed them to be the newest) had a single word on
>   it. Searching www.ascend.com reveals some release notes that
>   may have information, but the WWW server fails to retrieve them.
>   I'll have a look on FTP later, but this is a really bad example
>   for documentation: We are at least one major version after the
>   releases where multicast was added (4.6Bi or such) but still have
>   no documentation besides what may hang around in a giant backlog
>   of change release notes.

Your manual must be old. You should ask for a new one. Attached is the most
recent HTML file for Multicast.

Title: Setting Up IP Multicast Forwarding

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Setting Up IP Multicast Forwarding

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This chapter covers these topics:

Configuring multicast forwarding

Administering multicast interfaces

Configuring multicast forwarding

The multicast backbone (MBONE) is a virtual network layered on top of the Internet to support IP multicast routing across point-to-point links. It is used for transmitting audio and video on the Internet in real-time, because multicasting is a much cheaper and faster way to communicate the same information to multiple hosts.

To the MBONE, the MAX looks like a multicast client. It responds as a client to IGMP (Internet Group Membership Protocol) packets it receives from MBONE routers, which may be IGMP version-1 or version-2, including IGMP MTRACE (multicast trace) packets.

To multicast clients on a WAN or Ethernet interface, the MAX looks like a multicast router. Like a router, it sends those clients IGMP queries, receives responses, and forwards multicast traffic. In this implementation, multicast clients are not allowed to source multicast packets-if they do, the MAX discards the packets.

These are the parameters for configuring multicast forwarding:

Ethernet
      Mod Config
            Multicast...
                  Forwarding=Yes
                  Mbone Profile=
                  Client=No
                  Rate Limit=5 
                  HeartBeat Addr=224.0.1.1
                  HeartBeat Udp Port=123
                  HeartBeat Slot Time=10
                  HeartBeat Slot Count=10
                  Alarm threshold=3
                  Source Addr=128.232.0.0
                  Source Mask=0.0.0.0

Ethernet
      Connections
              Ip options...
                  Multicast Client=No
                  Multicast Rate Limit=5

For details on each parameter, see the MAX Reference Guide.

Understanding the multicast parameters

This section provides some background information about multicast parameters.

• Enabling multicast forwarding

  The Forwarding parameter turns on multicast forwarding in the MAX.

  Note: When you change the Forwarding parameter from No to Yes, the multicast subsystem reads the values in the Ethernet profile and initiates the forwarding function. If you modify a multicast value in the Ethernet profile, you must set this parameter to No and then set it to Yes again to force a read of the new value.

• Specifying the MBONE interface

  The MBONE interface is where the multicast router resides. If it resides across the WAN, the Mbone Profile parameter must specify the name of a resident Connection profile to that router. If the Mbone Profile name is null and Multicast Forwarding is turned on, the MAX assumes that its Ethernet is the MBONE interface.

• Monitoring the multicast heartbeat

  When it is running as a multicast forwarder, the MAX is continually receiving multicast traffic. The heartbeat-monitoring feature enables the administrator to monitor possible connectivity problems by continuously polling for this traffic and generating an SNMP alarm trap if there is a traffic breakdown. This is the SNMP alarm trap:

  Trap type: TRAP_ENTERPRISE
  Code: TRAP_MULTICAST_TREE_BROKEN (19)
  Arguments:
  1) Multicast group address being monitored (4 bytes),
  2) Source address of last heartbeat packet received (4 bytes)
  3) Slot time interval configured in seconds (4 bytes),
  4) Number of slots configured (4 bytes).
  5) Total number of heartbeat packets received before the MAX started sending SNMP Alarms (4bytes).
  

  Note: Heartbeat monitoring is optional. It is not required for multicast forwarding.

  To set up heartbeat monitoring, you configure several parameters that define what packets will be monitored, how often and for how long to poll for multicast packets, and the threshold for generating an alarm. These are the related parameters:

  • What packets will be monitored
    HeartBeat Addr specifies a multicast address. If specified, the MAX listens for packets to and from this group.

    HeartBeat Udp Port specifies a UDP port number. If specified, the MAX listens only to packets received on that port.

    Source Addr and Source Mask specify an IP address and netmask. If specified, the MAX ignores packets from that source for monitoring purposes.

    How often and for how long to poll for multicast packets

    HeartBeat Slot Time specifies an interval (in seconds). The MAX polls for multicast traffic, waits for this interval, and then polls again.

    HeartBeat Slot Count specifies how many times to poll before comparing the number of heartbeat packets received to the Alarm Threshold.

    The threshold for generating an alarm

    Alarm Threshold specifies a number. If the number of monitored packets falls below this number, the SNMP alarm trap is sent.

• Configuring multicast forwarding on a client interface

  Each local or WAN interface that supports multicast clients must set the Client (or Multicast Client) parameter to Yes. With this setting, the MAX begins handling IGMP requests and responses on the interface. It does not begin forwarding multicast traffic until the rate limit is set.

  The Rate Limit specifies the rate at which the MAX accepts multicast packets from its clients. It does not affect the MBONE interface.

  Note: By default, the Rate Limit parameter is set to 100. This disables multicast forwarding on the interface. The forwarder handles IGMP packets, but does not accept packets from clients or forward multicast packets from the MBONE router.

  To begin forwarding multicast traffic on the interface, you must set the Rate Limit parameter to a number less than 100. For example if you set it to 5, the MAX accepts a packet from multicast clients on the interface every 5 seconds. Any subsequent packets received in that 5-second window are discarded.

• An implicit priority setting for dropping multicast packets

  For high-bandwidth data, voice, and audio multicast applications, the MAX supports both multicast rate limiting (described immediately above) and prioritized packet dropping. If the MAX is the receiving device under extremely high loads, it drops packets according to a priority ranking, which is determined by these UDP port ranges:

  • Traffic on ports 0-16384 (unclassified traffic) has the lowest priority (50).

  • Traffic on ports 16385-32768 (Audio traffic) has the highest priority (70).

  • Traffic on ports 32769-49152 (Whiteboard traffic) has medium priority (60).

  • Traffic on ports 49153-65536 (Video traffic) has low priority (55).

Multicast forwarding from an MBONE router on Ethernet

Figure  11-1 shows a local multicast router on one of the MAX unit's Ethernet interfaces and dial-in multicast clients.

Figure 11-1. MAX forwarding multicast traffic to dial-in multicast clients

Note:   Heartbeat monitoring is an optional feature. You can operate multicast forwarding 
without it if you prefer.

This sample profile specifies the MBONE interface as the Ethernet port, and uses the heartbeat group address of 224.1.1.1:

1. Open Ethernet>Mod Config>Multicast.

2. Enable multicast forwarding, and leave the default values for the Mbone profile, Client, and Rate Limit parameters.

   Ethernet
         Mod Config
               Multicast...
                     Forwarding=Yes
                     Mbone Profile=
                     Client=No
                     Rate Limit=5 
   

3. Specify a heartbeat group address and UDP port for monitoring heartbeat packets.

                       HeartBeat Addr=224.1.1.1
                     HeartBeat Udp Port=16387
   

4. Specify the time, count, and alarm threshold parameters.

                     HeartBeat Slot Time=10
                     HeartBeat Slot Count=10
                     Alarm threshold=3
                     Source Addr=0.0.0.0
                     Source Mask=0.0.0.0
   

5. Close the Ethernet profile.

To enable multicasting on WAN interfaces:

1. Open the Connection profile for a multicast client site.

2. Open the IP options subprofile and set Multicast Client to Yes. If appropriate, specify a rate limit other than the default 5.

   Ethernet
         Connections
               Ip options...
                     Multicast Client=Yes
                     Multicast Rate Limit=5
   

3. Close the Connection profile.

Multicast forwarding from an MBONE router on a WAN link

Figure  11-2 shows a multicast router on the WAN with local and dial-in multicast clients.

Figure 11-2. MAX acting as a multicast forwarder on Ethernet and WAN interfaces

Note:   This example does not use heartbeat monitoring. If you want to configure the MAX for 
heartbeat monitoring, see the example settings in "Multicast forwarding from an MBONE 
router on Ethernet" .

This sample profile specifies the MBONE interface as a WAN link accessed through a Connection profile #20. To configure the MAX for to respond to multicast clients on Ethernet:

1. Open Ethernet>Mod Config>Multicast.

2. Enable multicast forwarding, specify the number of the Connection profile for the MBONE interface, and set Client to Yes.

3. Set Multicast Rate Limit to a number lower than the default 100.

   Ethernet
         Mod Config
               Multicast...
                     Forwarding=Yes
                     Mbone Profile=20
                     Client=Yes
                     Rate Limit=5
   

4. Close the Ethernet profile.

To configure the MBONE interface:

1. Open the Connection profile for a MBONE interface (in this example, profile #20).

2. Open the IP options subprofile and set Multicast Rate Limit to a number lower than the default 100.

   Ethernet
         Connections
               profile #20...
                     Ip options...
                           Multicast Client=No
                           Multicast Rate Limit=5
   

3. Close the Connection profile.

To enable multicasting on WAN interfaces:

1. Open the Connection profile for a multicast client site.

2. Open the IP options subprofile and set Multicast Client to Yes.

3. Set Multicast Rate Limit to a number lower than the default 100.

   Ethernet
         Connections
               Ip options...
                     Multicast Client=Yes
                     Multicast Rate Limit=5
   

4. Close the Connection profile.

Administering multicast interfaces

The terminal server command-line interface provides commands to support IP multicast functionality. To see the options, invoke the terminal server interface (System>Sys Diag>Term Serv) and type:

ascend% show igmp ?

show igmp ?         Display help information
show igmp stats     Display IGMP Statistics
show igmp groups    Display IGMP groups Table
show igmp clients   Display IGMP clients

and:

ascend% show mrouting ?

show mrouting ?     Display help information
show mrouting stats Display MROUTING Statistics

Displaying the multicast forwarding table

To display active multicast group addresses and clients (interfaces) registered for each group:

ascend% show igmp groups

IGMP Group address Routing Table Up Time: 0:0:22:17
 Hash      Group Address    Members    Expire time   Counts
  10       224.0.2.250  
                             2           0:3:24       3211 :: 0 S5
                             1           0:3:21       145 :: 0 S5
                             0(Mbone)    ......       31901 :: 0 S5

The output contains these fields:

• Hash is an index to a hash table (displayed for debugging purposes only).

• Group address is the IP multicast address used in this packet.

  Note: The IP multicast address being monitored is marked with an asterisk, meaning that this address is joined by local application.

• Members is the interface ID on which the membership resides. 0 represents the Ethernet interface. Other numbers represent WAN interfaces, numbered according to when they became active. The interface labeled "Mbone" is the interface on which the multicast router resides.

• Expire time indicates when this membership expires. The MAX sends out IGMP queries every 60 seconds, so the expiration time is usually renewed. If the expiration time is reached, the entry is removed from the table. When this field contains periods, it means that this membership never expires.

• Counts shows the number of packets forwarded to the client, the number of packets dropped due to lack of resources, and the state of the membership (the state is displayed for debugging purposes).

Listing multicast clients

To display a list of multicast clients, type:

ascend% show igmp clients

IGMP Clients

Client      Version  RecvCount  CLU      ALU
  0(Mbone)      1       0          0       0
  2             1      39         68       67
  1             1   33310         65       65

The output contains these fields:

• Client indicates the interface ID on which the client resides. 0 represents the Ethernet. Other numbers are WAN interfaces, numbered according to when they became active. The interface labeled "Mbone" is the interface on which the multicast router resides.

• Version is the version of IGMP being used.

• RecvCount is the number of IGMP messages received on that interface.

• CLU (current line utilization) and ALU (average line utilization) show the percentage of bandwidth utilized across this interface. If bandwidth utilization is high, some IGMP packet types will not be forwarded.

Displaying multicast activity

To display the number of IGMP packet types sent and received:

ascend% show igmp stats

            46 packets received.
        0 bad checksum packets received.
        0 bad version packets received.
        0 query packets received.
       46 response packets received.
        0 leave packets received.
       51 packets transmitted.
       47 query packets sent.
        4 response packets sent.
        0 leave packets sent.

To display the number of multicast packets received and forwarded:

ascend% show mrouting stats

34988 packets received.
    57040 packets forwarded.
        0 packets in error.
       91 packets dropped.
        0 packets transmitted.

In many cases, the number of packets forwarded will be greater than the number of packets received, because packets may be duplicated and forwarded across multiple links.

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techpubs@eng.ascend.com

Copyright © 1997, Ascend Communications, Inc. All rights reserved.

Matt Holdrege		http://www.ascend.com	matt@ascend.com

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References:

• (ASCEND) Multicast weirdness
• From: Andre Beck <beck@ibh-dd.de>

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