© 2004 Cisco Systems, Inc. All rights reserved. Printed in USA.
Presentation_ID.scr
313131
© 2004 Cisco Systems, Inc. All rights reserved.
RST-3508
9805_05_2004_c2
High CPU Usage: Cisco IOS Supervisors
• CPU usage is not indicative of forwarding
performance on any supervisor
• Forwarding decisions are made in hardware
• Packets sent to the CPU
Control packets: STP, CDP, PAgP, LACP, UDLD
Routing protocol updates
IPX/Appletalk
SNMP/telnet/
ARP responses to ARP requests
Packets with IP options/expired TTL or non-ARPA encaps
Packets with special handling, i.e. tunneling, encryption
ACL logging enabled
Input ACL drops
MTU check failure
Adjacency same interface
323232
© 2004 Cisco Systems, Inc. All rights reserved.
RST-3508
9805_05_2004_c2
Extras: QoS on the CPU Port
CPU Queues
• Protects important traffic when CPU usage is high
BPDUs/routing updates get priority
Can still telnet or SNMP query when CPU is high
…
1: Control
2: Host Learning
15: MTU Fail/Invalid
3–5: L3 Forwarding
Packets to
the CPU
9–10: L3 Rx (Telnet/SNMP)
0: ESMP
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