Medianet Reference Guide - Cisco

Cisco Network Analysis Module
Chapter 6
Medianet Management and Visibility Design Considerations
Port Rx-No-Pkt-Buff RxPauseFrames TxPauseFrames PauseFramesDrop
Gi1/1 0 0 0 0
Gi1/2 0 0 0 0
...
Gi1/48 0 0 0 0
Port UnsupOpcodePause
Gi1/1 0
Gi1/2 0
...
Gi1/48 0
The first two highlighted sections can provide information regarding how many unicast and multicast
packets have crossed the interface in the inbound or outbound direction. Multicast traffic is often used
to support real-time and VoD broadcasts. The multicast packet count within the switch interface
increments from when the switch was reloaded or the counters were manually cleared. Because of this,
and because the information does not include the byte count, you cannot use the statistics alone to
determine the data rate of multicast traffic across the interface. However, you may be able to gain some
useful information regarding the percentage of multicast traffic on the interface based on the ratio of the
unicast to multicast packets seen.
The third highlighted section provides two additional pieces of information. First, it indicates the number
of queues per interface. Because the output above is from a Cisco Catalyst 4948 switch, four transmit
queues per interface are supported. Second, the output indicates the amount of traffic, in bytes, that has
been transmitted per queue per interface. Because this is a summation of bytes since the counters were
last cleared or the switch reloaded, you must run the command multiple times over a time interval to get
a rough estimate of the byte rate over that time period. This can be used to gain an idea of the current
data rate of a particular traffic service class across the switch interface.
The final two highlighted sections indicate the number of packets dropped in the egress direction, per
transmit queue. You can use this information to assist in troubleshooting a video application
performance issue or fault condition caused by packet loss. Note that Dbl-Drops are drops that are the
result of the dynamic buffer limiting (DBL) algorithm, which attempts to fairly allocate buffer usage per
flow through the Cisco Catalyst 4500 switch. You have the option of enabling or disabling DBL per
service class on the switch.
To make use of information regarding transmit queues drops shown in Example 6-17, you must
understand which traffic classes are assigned to which transmit queues. For Cisco Catalyst 4500 Series
switches with classic supervisors as well as Cisco Catalyst 4900 Series switches, the show qos maps
command can be used to display which DSCP values are mapped to which transmit queues on the switch,
as shown in Example 6-18.
Example 6-18
Output from Cisco Catalyst 4948 show qos maps Command
tp-c2-4948-1#show qos maps
DSCP-TxQueue Mapping Table (dscp = d1d2) ! Provides mapping of DSCP value to transmit
! queue on the switch
d1 : d2 0 1 2 3 4 5 6 7 8 9
-------------------------------------
0 : 02 01 01 01 01 01 01 01 01 01
1 : 01 01 01 01 01 01 04 02 04 02
2 : 04 02 04 02 04 02 04 02 04 02
3 : 04 02 03 03 04 03 04 03 04 03
4 : 03 03 03 03 03 03 03 03 04 04
5 : 04 04 04 04 04 04 04 04 04 04
6 : 04 04 04 04
Policed DSCP Mapping Table (dscp = d1d2)
d1 : d2 0 1 2 3 4 5 6 7 8 9
6-52
Medianet Reference Guide
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