100 Chapter 4: QoS Support on the Catalyst 5000 Family of Switches
Enabling QoS Features on the Catalyst 5000 Family of
Switches
QoS must be globally enabled on the Catalyst 5000 Family of switches before the switch
enacts on classification, marking, and output scheduling configurations. To enable QoS on
the Catalyst 5000 Family of switches, enter the following command:
set qos {enable | disable}
Example 4-3 illustrates a user enabling QoS on a Catalyst 5000 Switch.
Input Scheduling
Similar to other access layer switches, the Catalyst 5000 Family of switches performs only
FIFO queuing of ingress packets. Input scheduling is not supported, but this does not pose
a significant issue if traffic does not exceed the backplane bandwidth. Backplane bandwidth
UDLD yes
AuxiliaryVlan no
SPAN source,destination
Console> (enable)
show port capabilities 3/1
Model WS-X5234
Port 3/1
Type 10/100BaseTX
Speed auto,10,100
Duplex half,full
Trunk encap type 802.1Q,ISL
Trunk mode on,off,desirable,auto,nonegotiate
Channel 3/1-2,3/1-4
Broadcast suppression percentage(0-100)
Flow control receive-(off,on),send-(off,on)
Security yes
Dot1x yes
Membership static,dynamic
Fast start yes
QOS scheduling rx-(none),tx-(1q4t)
CoS rewrite yes
ToS rewrite IP-Precedence
Rewrite yes
UDLD yes
AuxiliaryVlan 1..1000,untagged,dot1p,none
SPAN source,destination
Example 4-3 Enabling QoS Features on a Catalyst 5000 Switch
Console> (enable) set qos enable
QoS is enabled.
Example 4-2 Sample Output from the show port capabilities Command (Continued)
Input Scheduling 101
depends on the chassis model and supervisor engine. All Supervisor I and II Engines utilize
a single 1.2-Gbps system bus for the backplane architecture. The Supervisor III Engines
utilize three 1.2-Gbps system buses for total of 3.6-Gbps bandwidth in a three-system bus
chassis for the backplane architecture. The three-system bus chassis encompass the 5505,
5500, and 5509 models.
The three system buses on the 5505, 5500, and 5509 chassis aggregate at the supervisor
engine. The supervisor engine is responsible for moving traffic between the three buses. All
Ethernet line cards except the three-port, WS-X5403, and nine-port Gigabit Ethernet
modules utilize a single bus connector. With the exception of the WS-X5403 and WS-
X5410, all line cards attach to the first bus connector in a slot. The WS-X5403 attaches a
single front-panel Gigabit Ethernet port to each bus connector on the backplane, whereas
the WS-X5410 distributes traffic from all nine front-panel Gigabit ports to the three bus
connectors on the backplane. The switch references the three buses as bus A, B, and C,
respectively.
To distribute traffic across the buses for single bus connecting line cards, each chassis
employs a different bus connector layout per slot. In this manner, the switch distributes
traffic on a line card basis by placing the three backplane bus connectors in a different order
depending on a chassis slot. In a Catalyst 5505 chassis, for instance, the first bus connector
in slot 3 is A, whereas slots 4 and 5 utilize B and C, respectively, as the first bus connector.
Placing three single bus line cards in slots 3 to 5 results in traffic from each line card
occupying a different 1.2-Gbps system bus. Tables 4-3 to 4-6 illustrate the bus layout for
each of the Catalyst 5000 Family of switches chassis.
Table 4-3 Catalyst 5000 Chassis Bus Layout
Slot Backplane Connector
1A
2A
3A
4A
5A
Table 4-4 Catalyst 5505 Chassis Bus Layout
Slot Backplane Connector
1A B C
2A B C
3A B C
4B A C
5C B A
102 Chapter 4: QoS Support on the Catalyst 5000 Family of Switches
The Catalyst 5500 chassis utilizes slots 9 through 12 for ATM or Ethernet line modules.
This chassis only supports an ATM switch process in slot 13 and does not accept an
Ethernet line module in this slot.
In addition to referencing the system architecture, use the whichbus {mod/port} command
to determine which bus a line module utilizes.
Table 4-5 Catalyst 5509 Chassis Bus Layout
Slot Backplane Connector
1A B C
2A B C
3A B C
4A B C
5B A C
6B A C
7B A C
8C B A
9C B A
Table 4-6 Catalyst 5500 (13-Slot) Chassis Bus Layout
Slot Backplane Connector
1 A B C
2 A B C
3 A B C
4 A B C
5B A C
6B
7B
8B
9 B or ATM
10 C or ATM
11 C or ATM
12 C or ATM
13 Reserved for ATM switch processor
Input Scheduling 103
Example 4-4 illustrates a user enabling the whichbus {mod/port} command.
Because the Catalyst 5000 Family of switches does not support input scheduling,
maintaining backplane utilization within the 1.2 Gbps per system bus is important when
implementing a QoS architecture. When oversubscribing the system bus, the switch tail
drops frames from front-panel ports. Therefore, to avoid the arbitrary tail dropping of
frames, do not oversubscribe the bus. Use the show traffic command to view the current
and peak loads on each system bus as demonstrated in Example 4-5.
Use the show system command to view the collective utilization of all three buses.
Example 4-6 displays sample output of the show system command.
As a generally accepted practice when using the Catalyst 5000 Family of switches, avoid
utilizing more than 50 percent of a system bus’s bandwidth. For networks requiring more
bandwidth, use the Catalyst 3550 Family of switches, the Catalyst 4000 IOS Family of
switches, or the Catalyst 6500 Family of switches.
For more information regarding the system architecture of the Catalyst 5000 Family of
switches, refer to the following technical documents at Cisco.com:
• “Hardware Troubleshooting for Catalyst 5500/5000/2926G/2926 Series Switches”
Document ID: 18810
• “Preparing to Troubleshoot Hardware for Catalyst 5500/5000/2926G/2926 Series
Switches” Document ID: 18826
Example 4-4 Example of Using the whichbus Command
Console> (enable) whichbus 4/1
B
Example 4-5 Sample Output of the show traffic Command
Console> (enable) ss
ss
hh
hh
oo
oo
ww
ww
tt
tt
rr
rr
aa
aa
ff
ff
ff
ff
ii
ii
cc
cc
Threshold: 100%
Switching-Bus Traffic Peak Peak-Time
------------- ------- ---- -------------------------
A 3% 10% Sun Mar 30 2002, 09:52:14
B 5% 11% Sun Mar 30 2002, 09:52:14
C 17% 63% Sun Mar 30 2002, 09:52:14
Example 4-6 Sample Output of the show system Command
Console> (enable) ss
ss
hh
hh
oo
oo
ww
ww
ss
ss
yy
yy
ss
ss
tt
tt
ee
ee
mm
mm
(text deleted)
Modem Baud Traffic Peak Peak-Time
------- ----- ------- ---- -------------------------
disable 9600 7% 13% Sun Mar 30 2002, 09:52:14
(text deleted)
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