在交换机上抓包，一般可排查一些网络问题。
下面是总结的在各厂商交换机上抓包方式。
H3C交换机抓包：在华三交换机上可使用：packet-capture 命令，在用户视图下执行。
具体操作可查看这：https://www.h3c.com/cn/d_202009/1327093_30005_0.htm
代码语言：javascript复制#做流统匹配抓包流量
acl advanced 3000
description test
rule 0 permit ip source 192.168.1.1 0 destination 192.168.2.1 0
traffic classifier class_test operator and
if-match acl 3000
#
traffic behavior behavior_test
accounting packet # 做流量统计
mirror-to cpu # 镜像到CPU，必须镜像到CPU才能抓包
#
qos policy policy_test
classifier class_test behavior behavior_test
#
interface Ten-GigabitEthernet1/3/1
qos apply policy policy_test inbound
packet-capture local interface Ten-GigabitEthernet 1/3/1 autostop filesize 50000 write flash:/isp1.cap
packet-capture stop # 及时停止。需要注意的几点：
抓包时尽量使用acl匹配精确的流在traffic behavior中，必须配置流量镜向到CPU。mirror-to cpu, 否则不能抓到包。抓包时做好文件大小限制，autostop filesze 50000, 因为交换机的硬盘都很小，防止把交换机硬盘打满。抓包时尽量选择流量低峰期。配置accounting packet 流量统计后，可通过display qos policy interface 查看匹配情况。华为交换机抓包：华为交换机抓包使用：capture-packet 命令，在用户视图下执行。
https://support.huawei.com/hedex/hdx.do?lib=EDOC110010122531180BDB&docid=EDOC1100101225&lang=zh&v=02&tocLib=EDOC110010122531180BDB&tocV=02&id=ZH-CN_CLIREF_0141119899&tocURL=resources%2fdc%2fcapture%2dpacket%2ehtml&p=t&fe=1&ui=3&keyword=capture
代码语言：javascript复制capture-packet interface 10GE 1/0/5 acl 3000 destination file file.cap packet-num 1000 packet-len 1000
undo capture-packet # 关闭报文捕获。注意事项：做好抓包限制，防止打满硬盘。
锐捷交换机抓包：锐捷交换机抓包使用packet captur命令，在用户视图下执行。
代码语言：javascript复制packet capture ?
file Packet capture file #设置抓包文件保存路径
point Packet capture point
rule Packet capture rule # 抓包规则
start Start to capture packets # 开启抓包
stop Stop to capture packets # 停止抓包
packet capture file ?
flash: Save info into the flash file system
sata0: Save info into the sata file system
sd0: Save info into the sd0 file system
tmp: Save info into the tmp file system
usb0: Save info into the usb file system
packet capture rule test filter ?
acl Debug efmp packet acl
dst_mac Destination MAC address
etype Specify eth type
icmpv4_code ICMP code
icmpv4_type ICMP type
icmpv6_code ICMPv6 code
icmpv6_type ICMPv6 type
ipv4_dip Destination IP address
ipv4_dport IPv4 destination port
ipv4_sip Source IP address
ipv4_sport IPv4 source port
ipv6_dip Destination IPv6 address
ipv6_dport IPv6 destination port
ipv6_sip Source IPv6 address
ipv6_sport IPv6 source port
src_mac Source MAC address
v4_protocol IP protocol
v6_protocol IPv6 protocol
代码语言：javascript复制Arista#
**bash**
Arista Networks EOS shell
[admin@Arista ~]$
**tcpdump -****help**
tcpdump version 4.2.1
libpcap version 1.1.1
Usage: tcpdump [-aAbdDefhHIKlLnNOpqRStuUvxX] [ -B size ] [ -c count ]
[ -C file_size ] [ -E algo:secret ] [ -F file ]
[ -G seconds ]
[ -i interface ] [ -M secret ]
[ -r file ] [ -s snaplen ] [ -T type ] [ -w file ]
[ -W filecount ] [ -y datalinktype ] [ -z command ]
[ -Z user ] [ -@ file_index ] [ expression ]Cisco交换机抓包：Cisco nexus 抓包使用ethanalyze命令。在用户视图下执行。
“ 注：该命令只能捕获去交换机自身和自身发出去的流量。
不能捕获：捕获在硬件中转发的数据平面流量。不支持特定于接口的捕获
如果需要抓取CPU的流量，需要将端口流量镜像到CPU，然后使用ethanalyze抓取。
在抓端口镜像（转发层面的）包时，设备不能配置sflow。
ERROR: SFLOW is configured. Please delete all SFLOW data sources before configuring SPANs
”
“ https://www.cisco.com/c/en/us/support/docs/switches/nexus-9000-series-switches/215329-nexus-9000-cloud-scale-asic-nx-os-span-t.html?dtid=osscdc000283
”
https://www.cisco.com/c/en/us/support/docs/switches/nexus-7000-series-switches/116136-trouble-ethanalyzer-nexus7000-00.html
代码语言：javascript复制 ethanalyzer local interface inband ?
> Redirect it to a file
>> Redirect it to a file in append mode
autostop Capture autostop condition
capture-filter Filter on ethanalyzer capture
capture-ring-buffer Capture ring buffer option
decode-internal Include internal system header decoding
detail Display detailed protocol information
display-filter Display filter on frames captured
limit-captured-frames Maximum number of frames to be captured (default is 10)
limit-frame-size Capture only a subset of a frame
mirror Filter mirrored packets
raw Hex/Ascii dump the packet with possibly one line summary
write Filename to save capture to
| Pipe command output to filter
# 配置SPAN到CPU的监视器会话
N9K# **configure terminal**
Enter configuration commands, one per line. End with CNTL/Z.
N9K-1(config)# **monitor session 1** N9K-1(config-monitor)# **source interface Ethernet1/10 rx**N9K-1(config-monitor)# **destination interface sup-eth0** N9K-1(config-monitor)# **no shut**
N9K-1(config-monitor)# **end**
# 确认SPAN到CPU监视器会话已启动
N9K# **show running-config monitor**
N9K# **show monitor**
# 在控制平面中查看复制的数据包
# ethanalyze 可以用来复制到思科Nexus 9000设备的控制平面视图流量。Ethanalyzer命令中的**mirror**关键字可以过滤流量，以便仅显示SPAN到CPU监视器会话复制的流量。Ethanalyzer捕获和显示过滤器可用于进一步限制显示的流量。
9K# **ethanalyzer** **local** **interface inband mirror display-filter** **"icmp && ip.addr==192.168.10.10"** **limit-captured-frames 0**
# 使用Control-C组合键可以退出Ethanalyzer控制平面数据包捕获实用程序。
# 通过在Ethanalyzer命令中包含**detail**关键字，可以查看有关此流量的详细信息。下面显示了单个ICMP Echo Request数据包的示例。
N9K# **ethanalyzer** **local** **interface inband mirror display-filter** **"icmp && ip.addr==192.168.10.10"** **limit-captured-frames 0 detail**
# 以管理方式关闭SPAN到CPU监视器会话
# 在SPAN到CPU监视器会话的上下文中使用**shutdown** configuration命令可以正常关闭SPAN到CPU监视器会话，并停止将流量复制到Cisco Nexus 9000设备的控制平面。
N9K# **configure terminal**
Enter configuration commands, one per line. End with CNTL/Z.
N9K-1(config)# **monitor session 1** N9K-1(config-monitor)# **shut**
N9K-1(config-monitor)# **end**
N9K#