用一台Cisco Catalyst 3750G-24TS交换机连接服务器，服务器提供NAT功能，让内部网络通过NAT后访问Internet。3750G交换机IOS使用12.2(50)SE:
3750G-S1#show version
Cisco IOS Software, C3750 Software (C3750-IPSERVICES-M), Version 12.2(50)SE, RELEASE SOFTWARE (fc1)
Copyright (c) 1986-2009 by Cisco Systems, Inc.
Compiled Fri 27-Feb-09 23:05 by weiliu
Image text-base: 0x00003000, data-base: 0x01C00000
ROM: Bootstrap program is C3750 boot loader
BOOTLDR: C3750 Boot Loader (C3750-HBOOT-M) Version 12.2(44)SE5, RELEASE SOFTWARE (fc1)
3750G-S1 uptime is 8 hours, 2 minutes
System returned to ROM by power-on
System restarted at 12:54:31 GMT+8 Fri Mar 20 2009
System image file is "flash:/c3750-ipservices-mz.122-50.SE.bin"
cisco WS-C3750G-24TS (PowerPC405) processor (revision R0) with 118784K/12280K bytes of memory.
Processor board ID FDO1302Z0T5
Last reset from power-on
2 Virtual Ethernet interfaces
28 Gigabit Ethernet interfaces
The password-recovery mechanism is enabled.
512K bytes of flash-simulated non-volatile configuration memory.
Base ethernet MAC Address : 00:24:98:AC:F8:80
Motherboard assembly number : 73-7058-15
Power supply part number : 341-0045-02
Motherboard serial number : FDO13020B6Z
Power supply serial number : PHI1217L1BE
Model revision number : R0
Motherboard revision number : A0
Model number : WS-C3750G-24TS-S
System serial number : FDO1203Z0T9
Top Assembly Part Number : 800-21894-08
Top Assembly Revision Number : B0
Version ID : V08
CLEI Code Number : COMUH10ARA
Hardware Board Revision Number : 0x09
Switch Ports Model SW Version SW Image
------ ----- ----- ---------- ----------
* 1 28 WS-C3750G-24TS 12.2(50)SE C3750-IPSERVICES-M
Configuration register is 0xF
在没流量的情况下，交换机的CPU利用率也在10%左右。在300M流量时，CPU利用情况如下：
3750G-S1#sh processes cpu sorted
CPU utilization for five seconds: 32%/12%; one minute: 31%; five minutes: 31%
PID Runtime(ms) Invoked uSecs 5Sec 1Min 5Min TTY Process
9 1928177 5591015 344 15.01% 15.31% 15.57% 0 ARP Input
200 12026 107093 112 0.15% 0.06% 0.03% 0 Spanning Tree
2 0 5733 0 0.00% 0.00% 0.00% 0 Load Meter
3 0 1 0 0.00% 0.00% 0.00% 0 CEF RP IPC Backg
4 38288 3416 11208 0.00% 0.09% 0.10% 0 Check heaps
6 0 2 0 0.00% 0.00% 0.00% 0 Timers
1 0 9 0 0.00% 0.00% 0.00% 0 Chunk Manager
8 0 1 0 0.00% 0.00% 0.00% 0 Crash writer
5 9 3 3000 0.00% 0.00% 0.00% 0 Pool Manager
7 0 1 0 0.00% 0.00% 0.00% 0 HRPC asic-stats
11 0 1 0 0.00% 0.00% 0.00% 0 AAA_SERVER_DEADT
12 0 2 0 0.00% 0.00% 0.00% 0 AAA high-capacit
10 0 1 0 0.00% 0.00% 0.00% 0 CEF MIB API
14 9 4 2250 0.00% 0.00% 0.00% 0 Entity MIB API
15 0 47 0 0.00% 0.00% 0.00% 0 EEM ED Syslog
16 0 1 0 0.00% 0.00% 0.00% 0 IFS Agent Manage
17 0 480 0 0.00% 0.00% 0.00% 0 IPC Dynamic Cach
18 0 1 0 0.00% 0.00% 0.00% 0 IPC Zone Manager
13 0 1 0 0.00% 0.00% 0.00% 0 Policy Manager
20 0 1 0 0.00% 0.00% 0.00% 0 IPC Managed Time
......
从上面可以看出ARP Input 占用CPU较多。 但实际上该交换机上ARP 表较小，只有10多条，搞不清楚到底什么地方出了问题。