12-Network Management and Monitoring Configuration Guide

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14-Packet capture configuration
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Configuring the packet capture

Overview

The packet capture feature captures incoming packets that are to be forwarded in CPU. The feature displays the captured packets in real time, and allows you to save the captured packets to a .pcap file for future analysis.

The packet capture supports capture filters and display filters. You can use expressions to match packets to capture or display.

Packet capture modes

The device supports the following packet capture modes: local packet capture, remote packet capture, and feature image-based packet capture.

Local packet capture

Local packet capture displays the captured packets at the CLI or saves the captured packets to a remote file on an FTP server or to a local file.

Remote packet capture

Remote packet capture sends captured packets to the Wireshark packet analyzer installed on a PC.

Before using remote packet capture, you must install the Wireshark software on a PC and connect the PC to the device.

Feature image-based packet capture

Feature image-based packet capture saves the captured packets to a local file or displays the captured packets on the terminal. This mode can also display contents of .pcap and .pcapng files.

To use this mode, you must install the packet capture feature image by using the boot-loader, install, or issu command. For more information about image installation, see software upgrade or ISSU in Fundamentals Configuration Guide.

Filter elements

A capture or display filter contains a keyword string or multiple keyword strings that are connected by operators.

Keywords include the following types:

·     Qualifiers—Fixed keyword strings. For example, you must use the ip qualifier to specify the IPv4 protocol.

·     Variables—Values supplied by users in the required format. For example, you can set an IP address to 2.2.2.2 or any other valid values.

A variable must be modified by one or multiple qualifiers. For example, to capture any packets sent from the host at 2.2.2.2, use the filter src host 2.2.2.2.

Operators include the following types:

·     Logical operatorsPerform logical operations, such as the AND operation.

·     Arithmetic operatorsPerform arithmetic operations, such as the ADD operation.

·     Relational operatorsIndicate the relation between keyword strings. For example, the = operator indicates equality.

This document provides basic information about these elements. For more information about capture and display filters, go to the following websites:

·     http://wiki.wireshark.org/CaptureFilters.

·     http://wiki.wireshark.org/DisplayFilters.

Capture filter keywords

Table 1 and Table 2 describe the qualifiers and variables for capture filters, respectively.

Table 1 Qualifiers for capture filters

Category

Description

Examples

Protocol

Matches a protocol.

If you do not specify a protocol qualifier, the filter matches any supported protocols.

·     arp—Matches ARP.

·     icmp—Matches ICMP.

·     ip—Matches IPv4.

·     ipv6—Matches IPv6.

·     tcp—Matches TCP.

·     udp—Matches UDP.

Direction

Matches packets based on its source or destination location (an IP address or port number).

If you do not specify a direction qualifier, the src or dst qualifier applies.

·     src—Matches the source IP address field.

·     dst—Matches the destination IP address field.

·     src or dst—Matches the source or destination IP address field.

NOTE:

The src or dst qualifier applies if you do not specify a direction qualifier. For example, port 23 is equivalent to src or dst port 23.

Type

Specifies the direction type.

·     host—Matches the IP address of a host.

·     net—Matches an IP subnet.

·     port—Matches a service port number.

·     portrange—Matches a service port range.

NOTE:

The host qualifier applies if you do not specify any type qualifier. For example, src 2.2.2.2 is equivalent to src host 2.2.2.2.

To specify an IPv6 subnet, you must specify the net qualifier.

Others

Any other qualifiers than the previously described qualifiers.

·     broadcast—Matches broadcast packets.

·     multicast—Matches multicast and broadcast packets.

·     less—Matches packets that are less than or equal to a specific size.

·     greater—Matches packets that are greater than or equal to a specific size.

·     len—Matches the packet length.

·     vlan—Matches VLAN packets.

 

 

NOTE:

The broadcast, multicast, and all protocol qualifiers cannot modify variables.

 

Table 2 Variable types for capture filters

Variable type

Description

Examples

Integer

Represented in binary, octal, decimal, or hexadecimal notation.

The port 23 expression matches traffic sent to or from port number 23.

Integer range

Represented by hyphenated integers.

The portrange 100-200 expression matches traffic sent to or from any ports in the range of 100 to 200.

IPv4 address

Represented in dotted decimal notation.

The src 1.1.1.1 expression matches traffic sent from the IPv4 host at 1.1.1.1.

IPv6 address

Represented in colon hexadecimal notation.

The dst host 1::1 expression matches traffic sent to the IPv6 host at 1::1.

IPv4 subnet

Represented by an IPv4 network ID or an IPv4 address with a mask.

Both of the following expressions match traffic sent to or from the IPv4 subnet 1.1.1.0/24:

·     src 1.1.1.

·     src net 1.1.1.0/24.

IPv6 network segment

Represented by an IPv6 address with a prefix length.

The dst net 1::/64 expression matches traffic sent to the IPv6 network 1::/64.

 

Capture filter operators

Capture filters support logical operators (Table 3), arithmetic operators (Table 4), and relational operators (Table 5). Logical operators can use both alphanumeric and nonalphanumeric symbols. The arithmetic and relational operators can use only nonalphanumeric symbols.

Logical operators are left associative. They group from left to right. The not operator has the highest priority. The and and or operators have the same priority.

Table 3 Logical operators for capture filters

Nonalphanumeric symbol

Alphanumeric symbol

Description

!

not

Reverses the result of a condition.

Use this operator to capture traffic that matches the opposite value of a condition.

For example, to capture non-HTTP traffic, use not port 80.

&&

and

Joins two conditions.

Use this operator to capture traffic that matches both conditions.

For example, to capture non-HTTP traffic that is sent to or from 1.1.1.1, use host 1.1.1.1 and not port 80.

||

or

Joins two conditions.

Use this operator to capture traffic that matches either of the conditions.

For example, to capture traffic that is sent to or from 1.1.1.1 or 2.2.2.2, use  host 1.1.1.1 or host 2.2.2.2.

 

Table 4 Arithmetic operators for capture filters

Nonalphanumeric symbol

Description

+

Adds two values.

-

Subtracts one value from another.

*

Multiplies one value by another.

/

Divides one value by another.

&

Returns the result of the bitwise AND operation on two integral values in binary form.

|

Returns the result of the bitwise OR operation on two integral values in binary form.

<< 

Performs the bitwise left shift operation on the operand to the left of the operator. The right-hand operand specifies the number of bits to shift.

>> 

Performs the bitwise right shift operation on the operand to the left of the operator. The right-hand operand specifies the number of bits to shift.

[ ]

Specifies a byte offset relative to a protocol layer. This offset indicates the byte where the matching begins.

You must enclose the offset value in the brackets and specify a protocol qualifier. For example, ip[6] matches the seventh byte of payload in IPv4 packets (the byte that is six bytes away from the beginning of the IPv4 payload).

 

Table 5 Relational operators for capture filters

Nonalphanumeric symbol

Description

=

Equal to.

For example, ip[6]=0x1c matches an IPv4 packet if its seventh byte of payload is equal to 0x1c.

!=

Not equal to.

For example, len!=60 matches a packet if its length is not equal to 60 bytes.

Greater than.

For example, len>100 matches a packet if its length is greater than 100 bytes.

Less than.

For example, len<100 matches a packet if its length is less than 100 bytes.

>=

Greater than or equal to.

For example, len>=100 matches a packet if its length is greater than or equal to 100 bytes.

<=

Less than or equal to.

For example, len<=100 matches a packet if its length is less than or equal to 100 bytes.

 

Display filter keywords

Table 6 and Table 7 describe the qualifiers and variables for display filters, respectively.

Table 6 Qualifiers for display filters

Category

Description

Examples

Protocol

Matches a protocol.

·     eth—Matches Ethernet.

·     ftp—Matches FTP.

·     http—Matches HTTP.

·     icmp—Matches ICMP.

·     ip—Matches IPv4.

·     ipv6—Matches IPv6.

·     tcp—Matches TCP.

·     telnet—Matches Telnet.

·     udp—Matches UDP.

Packet field

Matches a field in packets by using a dotted string in the protocol.field[.level1-subfield]…[.leveln-subfield] format.

·     tcp.flags.syn—Matches the SYN bit in the flags field of TCP.

·     tcp.port—Matches the source or destination port field.

 

 

NOTE:

The protocol qualifiers cannot modify variables.

 

Table 7 Variable types for display filters

Variable type

Description

Integer

Represented in binary, octal, decimal, or hexadecimal notation.

For example, to display IP packets that are less than or equal to 1500 bytes, use one of the following expressions:

·     ip.len le 1500.

·     ip.len le 02734.

·     ip.len le 0x436.

Boolean

This variable type has two values: true or false.

This variable type applies if you use a packet field string alone to identify the presence of a field in a packet.

·     If the field is present, the match result is true. The filter displays the packet.

·     If the field is not present, the match result is false. The filter does not display the packet.

For example, to display TCP packets that contain the SYN field, use tcp.flags.syn.

MAC address (six bytes)

Uses colons (:), dots (.), or hyphens (-) to break up the MAC address into two or four segments.

For example, to display packets that contain a destination MAC address of ffff.ffff.ffff, use one of the following expressions:

·     eth.dst==ff:ff:ff:ff:ff:ff.

·     eth.dst==ff-ff-ff-ff-ff-ff.

·     eth.dst ==ffff.ffff.ffff.

IPv4 address

Represented in dotted decimal notation.

For example:

·     To display IPv4 packets that are sent to or from 192.168.0.1, use ip.addr==192.168.0.1.

·     To display IPv4 packets that are sent to or from 129.111.0.0/16, use ip.addr==129.111.0.0/16.

IPv6 address

Represented in colon hexadecimal notation.

For example:

·     To display IPv6 packets that are sent to or from 1::1, use ipv6.addr==1::1.

·     To display IPv6 packets that are sent to or from 1::/64, use ipv6.addr==1::/64.

String

Character string.

For example, to display HTTP packets that contain the string HTTP/1.1 for the request version field, use http.request version=="HTTP/1.1".

 

Display filter operators

Display filters support logical operators (Table 8) and relational operators (Table 9). Both operator types can use alphanumeric and nonalphanumeric symbols.

Logical operators are left associative. They group from left to right. Table 8 displays logical operators by priority, from the highest to the lowest. The and and or operators have the same priority:

Table 8 Logical operators for display filters

Nonalphanumeric

symbol

Alphanumeric

symbol

Description

[ ]

No alphanumeric symbol is available.

Used with protocol qualifiers. For more information, see "The proto[…] expression."

!

not

Displays packets that do not match the condition connected to this operator.

&&

and

Joins two conditions.

Use this operator to display traffic that matches both conditions.

||

or

Joins two conditions.

Use this operator to display traffic that matches either of the conditions.

 

Table 9 Relational operators for display filters

Nonalphanumeric

symbol

Alphanumeric

symbol

Description

==

eq

Equal to.

For example, ip.src==10.0.0.5 displays packets with the source IP address as 10.0.0.5.

!=

ne

Not equal to.

For example, ip.src!=10.0.0.5 displays packets whose source IP address is not 10.0.0.5.

gt

Greater than.

For example, frame.len>100 displays frames with a length greater than 100 bytes.

lt

Less than.

For example, frame.len<100 displays frames with a length less than 100 bytes.

>=

ge

Greater than or equal to.

For example, frame.len ge 0x100 displays frames with a length greater than or equal to 256 bytes.

<=

le

Less than or equal to.

For example, frame.len le 0x100 displays frames with a length less than or equal to 256 bytes.

 

Building a capture filter

This section provides the most commonly used expression types for capture filters.

Logical expression

Use this type of expression to capture packets that match the result of logical operations.

Logical expressions contain keywords and logical operators. For example:

·     not port 23 and not port 22—Captures packets with a port number that is not 23 or 22.

·     port 23 or icmp—Captures packets with a port number 23 or ICMP packets.

In a logical expression, a qualifier can modify more than one variable connected by its nearest logical operator. For example, to capture packets sourced from IPv4 address 192.168.56.1 or IPv4 network 192.168.27, use either of the following expressions:

·     src 192.168.56.1 or 192.168.27.

·     src 192.168.56.1 or src 192.168.27.

The expr relop expr expression

Use this type of expression to capture packets that match the result of arithmetic operations.

This expression contains keywords, arithmetic operators (expr), and relational operators (relop). For example, len+100>=200 captures packets that are greater than or equal to 100 bytes.

The proto [ expr:size ] expression

Use this type of expression to capture packets that match the result of arithmetic operations on a number of bytes relative to a protocol layer.

This type of expression contains the following elements:

·     proto—Specifies a protocol layer.

·     []—Performs arithmetic operations on a number of bytes relative to the protocol layer.

·     expr—Specifies the arithmetic expression.

·     size—Specifies the byte offset. This offset indicates the number of bytes relative to the protocol layer. The operation is performed on the specified bytes. The offset is set to 1 byte if you do not specify an offset.

For example, ip[0]&0xf !=5 captures an IP packet if the result of ANDing the first byte with 0x0f is not 5.

To match a field, you can specify a field name for expr:size. For example, icmp[icmptype]=0x08 captures ICMP packets that contain a value of 0x08 in the Type field.

The vlan vlan_id expression

Use this type of expression to capture 802.1Q tagged VLAN traffic.

This type of expression contains the vlan vlan_id keywords and logical operators. The vlan_id variable is an integer that specifies a VLAN ID. For example, vlan 1 and ip6 captures IPv6 packets in VLAN 1.

To capture packets of a VLAN, set a capture filter as follows:

·     To capture tagged packets that are permitted on the interface, you must use the vlan vlan_id expression prior to any other expressions. For example, use the vlan 3 and src 192.168.1.10 and dst 192.168.1.1 expression to capture packets of VLAN 3 that are sent from 192.168.1.10 to 192.168.1.1.

·     To capture an untagged packet that is received on the interface, follow these rules:

¡     If the device adds a VLAN tag to the packet header, add "vlan xx" to the capture filter expression. For Layer 3 packets, the xx represents the default VLAN ID of the outgoing interface. For Layer 2 packets, the xx represents the default VLAN ID of the incoming interface.

¡     If the device does not add a VLAN tag to the packet header, do not add "vlan xx" to the capture filter expression.

Building a display filter

This section provides the most commonly used expression types for display filters.

Logical expression

Use this type of expression to display packets that match the result of logical operations.

Logical expressions contain keywords and logical operators. For example, ftp or icmp displays all FTP packets and ICMP packets.

Relational expression

Use this type of expression to display packets that match the result of comparison operations.

Relational expressions contain keywords and relational operators. For example, ip.len<=28 displays IP packets that contain a value of 28 or fewer bytes in the length field.

Packet field expression

Use this type of expression to display packets that contain a specific field.

Packet field expressions contain only packet field strings. For example, tcp.flags.syn displays all TCP packets that contain the SYN bit field.

The proto[…] expression

Use this type of expression to display packets that contain specific field values.

This type of expression contains the following elements:

·     proto—Specifies a protocol layer or packet field.

·     []—Matches a number of bytes relative to a protocol layer or packet field. Values for the bytes to be matched must be a hexadecimal integer string. The expression in brackets can use the following formats:

¡     [n:m]—Matches a total of m bytes after an offset of n bytes from the beginning of the specified protocol layer or field. To match only 1 byte, you can use both [n] and [n:1] formats. For example, eth.src[0:3]==00:00:83 matches an Ethernet frame if the first three bytes of its source MAC address are 0x00, 0x00, and 0x83. The eth.src[2] == 83 expression matches an Ethernet frame if the third byte of its source MAC address is 0x83.

¡     [n-m]—Matches a total of (m-n+1) bytes, starting from the (n+1)th byte relative to the beginning of the specified protocol layer or packet field. For example, eth.src[1-2]==00:83 matches an Ethernet frame if the second and third bytes of its source MAC address are 0x00 and 0x83, respectively.

Configuration restrictions and guidelines

Before configuring this feature, make sure no other users are using this feature on the device.

To capture packets forwarded through chips, first configure a traffic behavior to mirror the traffic to the CPU. To capture packets forwarded by the CPU, enable packet capture directly.

Packet capture configuration task list

Tasks at a glance

Remarks

Configuring local packet capture

Perform one of the tasks.

Configuring remote packet capture

Configuring feature image-based packet capture

 

Configuring local packet capture

To display the captured packets on the local device, use the packet-capture read command. To display the captured packets on the FTP server, use the Wireshark client connected to the FTP server. To stop the capture, use the packet-capture stop command.

To configure local packet capture:

 

Task

Command

Remarks

Configure local packet capture.

packet-capture local interface interface-type interface-number [ capture-filter capt-expression | limit-frame-size bytes | autostop filesize kilobytes | autostop duration seconds ] * write { filepath | url url [ username username [ password { cipher | simple } string ] ] }

After this command is executed, you can still configure other commands from the CLI. The operation does not affect the packet capture.

 

Configuring remote packet capture

Task

Command

Remarks

Configure remote packet capture.

packet-capture remote interface interface-type interface-number [ port port ]

To stop the capture, use the packet-capture stop command.

 

To display the captured packets, perform the following tasks:

1.     Connect the Wireshark client to the device that captures packets.

2.     Start Wireshark and select Capture > Options.

3.     Select Remote from the Interface list.

4.     Enter the IP address of the remote interface and the RPCAP service port number on the window that appears, and click OK.

Make sure the interface IP address is reachable for the Wireshark. If you do not specify the RPCAP service port number, the default RPCAP service port 2002 is used.

5.     Click Start.

Figure 1 Configuring Wireshark capture options

 

Configuring feature image-based packet capture

IMPORTANT

IMPORTANT:

To capture or display desired packets, make sure the filter expressions do not conflict. The system does not check for logic errors.

 

Feature image-based packet capture captures only packets that are forwarded through CPU. To capture packets that are forwarded through chips, you must configure flow mirroring to mirror packets to the CPU. For more information about flow mirroring, see "Configuring flow mirroring."

The capture displays captured packets in real time. You can configure the capture to save captured packets to a file or filter packets to display.

You cannot configure the device from the CLI while the capture is operating. To stop the capture while it is capturing packets, press Ctrl+C. There might be a delay for the capture to stop because of heavy traffic.

To capture packets:

 

Task

Command

Capture incoming packets on an interface.

·     Save captured packets to a file:
packet-capture interface interface-type interface-number [ capture-filter capt-expression | limit-captured-frames limit | limit-frame-size bytes | autostop filesize kilobytes | autostop duration seconds | autostop files numbers | capture-ring-buffer filesize kilobytes | capture-ring-buffer duration seconds | capture-ring-buffer files numbers ] * write filepath [ raw | { brief | verbose } ] *

·     Filter packets to display:
packet-capture interface interface-type interface-number [ capture-filter capt-expression | display-filter disp-expression | limit-captured-frames limit | limit-frame-size bytes | autostop duration seconds ] * [ raw | { brief | verbose } ] *

 

Displaying the contents in a packet file

Task

Command

Remarks

Display the contents in a packet file.

packet-capture read filepath [ verbose ] [ display-filter disp-expression ] [ raw | { brief | verbose } ] *

A packet file must use the .pcap or .pcapng extension.

 

Displaying and maintaining packet capture

Execute display commands in any view.

 

Task

Command

Display the local or remote packet capture status.

display packet-capture status

 

Packet capture configuration examples

Remote packet capture configuration example

Network requirements

As shown in Figure 2, capture packets on GigabitEthernet 1/0/1 and use Wireshark to display the captured packets.

Figure 2 Network diagram

 

 

Configuration procedure

1.     Apply a QoS policy to the incoming direction of GigabitEthernet 1/0/1 on the switch to capture packets destined for 20.1.1.0/16 that are forwarded through chips:

# Create an IPv4 advanced ACL to match packets that are destined for 20.1.1.0/16.

<Switch> system-view

[Switch] acl advanced 3000

[Switch-acl-ipv4-adv-3000] rule permit ip destination 20.1.1.0 255.255.0.0

[Switch-acl-ipv4-adv-3000] quit

# Configure a traffic behavior to mirror traffic to the CPU.

[Switch] traffic behavior behavior1

[Switch-behavior-behavior1] mirror-to cpu

[Switch-behavior-behavior1] quit

# Configure a traffic class to use the ACL to match traffic.

[Switch] traffic classifier classifier1

[Switch-classifier-class1] if-match acl 3000

[Switch-classifier-class1] quit

# Configure a QoS policy. Associate the traffic class with the traffic behavior.

[Switch] qos policy user1

[Switch-qospolicy-user1] classifier classifier1 behavior behavior1

[Switch-qospolicy-user1] quit

# Apply the QoS policy to the incoming direction of GigabitEthernet 1/0/1.

[Switch] interface gigabitethernet 1/0/1

[Switch-GigabitEthernet1/0/1] qos apply policy user1 inbound

[Switch-GigabitEthernet1/0/1] quit

[Switch] quit

2.     Configure remote packet capture on GigabitEthernet 1/0/1. Set the RPCAP service port number to 2014.

<Switch> packet-capture remote interface gigabitethernet 1/0/1 port 2014

3.     Display captured packets on the PC:

a.     Start Wireshark and select Capture > Options.

b.     Select Remote from the Interface list.

c.     Enter the IP address of the switch and a port number of 2014, and click OK. Ensure the IP connectivity between the IP address of the switch and the Wireshark client.

d.     Click Start.

The captured packets are displayed on the Wireshark client.

Feature image-based packet capture configuration example

Network requirements

As shown in Figure 3, capture the following incoming IP packets on GigabitEthernet 1/0/1:

·     Packets forwarded through the CPU.

·     Packets that are sourced from 192.168.56.1 0 and are forwarded through chips.

Figure 3 Network diagram

 

Configuration procedure

# Create an IPv4 advanced ACL to match packets that are sourced from 192.168.56.1 0.

<SwitchA> system-view

[SwitchA] acl advanced 3000

[SwitchA-acl-ipv4-adv-3000] rule permit ip source 192.168.56.1 0

[SwitchA-acl-ipv4-adv-3000] quit

# Configure a traffic behavior to mirror traffic to the CPU.

[SwitchA] traffic behavior behavior1

[SwitchA-behavior-behavior1] mirror-to cpu

[SwitchA-behavior-behavior1] quit

# Configure a traffic class to use the ACL to match traffic.

[SwitchA] traffic classifier classifier1

[SwitchA-classifier-classifier1] if-match acl 3000

[SwitchA-classifier-classifier1] quit

# Associate the traffic class with the traffic behavior in a QoS policy.

[SwitchA] qos policy user1

[SwitchA-qospolicy-user1] classifier classifier1 behavior behavior1

[SwitchA-qospolicy-user1] quit

# Apply the QoS policy to the incoming traffic of GigabitEthernet 1/0/1.

[SwitchA] interface gigabitethernet 1/0/1

[SwitchA-GigabitEthernet1/0/1] qos apply policy user1 inbound

[SwitchA-GigabitEthernet1/0/1] quit

[SwitchA] quit

# Capture incoming traffic on GigabitEthernet 1/0/1.

<SwitchA> packet-capture interface gigabitethernet 1/0/1

Capturing on 'Gigabitethernet1/0/1'

  1   0.000000 192.168.56.1 -> 192.168.56.2 TCP 62 6325 > telnet [SYN] Seq=0 Win

=65535 Len=0 MSS=1460 SACK_PERM=1

  2   0.000061 192.168.56.1 -> 192.168.56.2 TCP 60 6325 > telnet [ACK] Seq=1 Ack

=1 Win=65535 Len=0

  3   0.024370 192.168.56.1 -> 192.168.56.2 TELNET 60 Telnet Data ...

  4   0.024449 192.168.56.1 -> 192.168.56.2 TELNET 78 Telnet Data ...

  5   0.025766 192.168.56.1 -> 192.168.56.2 TELNET 65 Telnet Data ...

  6   0.035096 192.168.56.1 -> 192.168.56.2 TELNET 60 Telnet Data ...

  7   0.047317 192.168.56.1 -> 192.168.56.2 TCP 60 6325 > telnet [ACK] Seq=42 Ac

k=434 Win=65102 Len=0

  8   0.050994 192.168.56.1 -> 192.168.56.2 TCP 60 6325 > telnet [ACK] Seq=42 Ac

k=436 Win=65100 Len=0

  9   0.052401 192.168.56.1 -> 192.168.56.2 TCP 60 6325 > telnet [ACK] Seq=42 Ac

k=438 Win=65098 Len=0

 10   0.057736 192.168.56.1 -> 192.168.56.2 TCP 60 6325 > telnet [ACK] Seq=42 Ac

k=440 Win=65096 Len=0

10 packets captured

Packet file display configuration example

Network requirements

As shown in Figure 4:

·     Capture 10 incoming packets on GigabitEthernet 1/0/1 and save the packets to a packet file.

·     Display contents in the file.

Figure 4 Network diagram

 

Configuration procedure

# Capture packets on GigabitEthernet 1/0/1. Set the maximum number of captured packets to 10. Save the packets to the file flash:/a.pcap.

<SwitchA> packet-capture interface gigabitethernet 1/0/1 limit-captured-frames 10 write flash:/a.pcap

Capturing on 'Gigabitethernet1/0/1'

# Display the contents in the packet file.

<SwitchA> packet-capture read flash:/a.pcap

  1   0.000000 192.168.56.1 -> 192.168.56.2 TCP 62 6325 > telnet [SYN] Seq=0 Win

=65535 Len=0 MSS=1460 SACK_PERM=1

  2   0.000061 192.168.56.1 -> 192.168.56.2 TCP 60 6325 > telnet [ACK] Seq=1 Ack

=1 Win=65535 Len=0

  3   0.024370 192.168.56.1 -> 192.168.56.2 TELNET 60 Telnet Data ...

  4   0.024449 192.168.56.1 -> 192.168.56.2 TELNET 78 Telnet Data ...

  5   0.025766 192.168.56.1 -> 192.168.56.2 TELNET 65 Telnet Data ...

  6   0.035096 192.168.56.1 -> 192.168.56.2 TELNET 60 Telnet Data ...

  7   0.047317 192.168.56.1 -> 192.168.56.2 TCP 60 6325 > telnet [ACK] Seq=42 Ac

k=434 Win=65102 Len=0

  8   0.050994 192.168.56.1 -> 192.168.56.2 TCP 60 6325 > telnet [ACK] Seq=42 Ac

k=436 Win=65100 Len=0

  9   0.052401 192.168.56.1 -> 192.168.56.2 TCP 60 6325 > telnet [ACK] Seq=42 Ac

k=438 Win=65098 Len=0

 10   0.057736 192.168.56.1 -> 192.168.56.2 TCP 60 6325 > telnet [ACK] Seq=42 Ac

k=440 Win=65096 Len=0

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