Configuring ERSPAN

This chapter describes how to configure an encapsulated remote switched port analyzer (ERSPAN) to transport mirrored traffic in an IP network on Cisco NX-OS devices.

About ERSPAN

ERSPAN transports mirrored traffic over an IP network, which provides remote monitoring of multiple switches across your network. The traffic is encapsulated at the source router and is transferred across the network. The packet is decapsulated at the destination router and then sent to the destination interface. Another method is that the destination can be the analyzer itself, which needs to understand the ERSPAN encapsulation format to parse the packet and access the inner (SPAN copy) frame.

ERSPAN Sources

The interfaces from which traffic can be monitored are called ERSPAN sources. Sources designate the traffic to monitor and whether to copy ingress, egress, or both directions of traffic. ERSPAN sources include the following:

  • Ethernet ports (but not subinterfaces)

  • Port channels

  • The inband interface to the control plane CPU


    Note

    When you specify the supervisor inband interface as a SPAN source, the device monitors all packets that are sent by the Supervisor CPU.


    Note

    If you use the supervisor inband interface as a SPAN source, all packets generated by the supervisor hardware (egress) are monitored.

    Rx is from the perspective of the ASIC (traffic egresses from the supervisor over the inband and is received by the ASIC/SPAN).

  • VLANs

    • When a VLAN is specified as an ERSPAN source, all supported interfaces in the VLAN are ERSPAN sources.

    • VLANs can be ERSPAN sources only in the ingress direction, except for Cisco Nexus 9300-EX/-FX/-FX2/-FX3/-GX series platform switches, and Cisco Nexus 9500 series platform switches with -EX/-FX line cards.


Note
A single ERSPAN session can include mixed sources in any combination of the above.

ERSPAN Destination

Destination ports receive the copied traffic from ERSPAN sources. The destination port is a port that is connected to the device such as a Remote Monitoring (RMON) probe or security device that can receive and analyze the copied packets from single or multiple source port. Destination ports do not participate in any spanning tree instance or any Layer 3 protocols

Cisco Nexus 9200, 9300-EX, 9300-FX, and 9300-FX2 platform switches support an ERSPAN destination session configured on physical or port-channel interfaces in switchport mode through the use of GRE header traffic flow. The source IP address should be configured on the default VRF. Multiple ERSPAN destination sessions should be configured with the same source IP address.

ERSPAN Sessions

You can create ERSPAN sessions that designate sources to monitor.

Localized ERSPAN Sessions

An ERSPAN session is localized when all of the source interfaces are on the same line card.


Note

An ERSPAN session with a VLAN source is not localized

ERSPAN Truncation

Beginning with Cisco NX-OS Release 7.0(3)I7(1), you can configure the truncation of source packets for each ERSPAN session based on the size of the MTU. Truncation helps to decrease ERSPAN bandwidth by reducing the size of monitored packets. Any ERSPAN packet that is larger than the configured MTU size is truncated to the given size. For ERSPAN, an additional ERSPAN header is added to the truncated packet from 54 to 166 bytes depending on the ERSPAN header type. For example, if you configure the MTU as 300 bytes, the packets are replicated with an ERSPAN header size from 354 to 466 bytes depending on the ERSPAN header type configuration.

ERSPAN truncation is disabled by default. To use truncation, you must enable it for each ERSPAN session.

Prerequisites for ERSPAN

ERSPAN has the following prerequisites:

  • You must first configure the ports on each device to support the desired ERSPAN configuration. For more information, see the Cisco Nexus 9000 Series NX-OS Interfaces Configuration Guide.

Guidelines and Limitations for ERSPAN


Note

For scale information, see the release-specific Cisco Nexus 9000 Series NX-OS Verified Scalability Guide.

ERSPAN has the following configuration guidelines and limitations:

  • A maximum of 48 source interfaces are supported per ERSPAN session (Rx and Tx, Rx, or Tx).

  • ERSPAN destination handles jumbo frames for MTU differently based on the platform. For the following Cisco Nexus 9300 platform switches and Cisco Nexus 9500 platform switches with supporting line cards, ERSPAN destination drops the jumbo frames:

    • Cisco Nexus 9332PQ

    • Cisco Nexus 9372PX

    • Cisco Nexus 9372PX-E

    • Cisco Nexus 9372TX

    • Cisco Nexus 9372TX-E

    • Cisco Nexus 93120TX

    • Cisco Nexus 9500 platform switches with the following line cards:

      • Cisco Nexus 9564PX

      • Cisco Nexus 9464TX

      • Cisco Nexus 9464TX2

      • Cisco Nexus 9564TX

      • Cisco Nexus 9464PX

      • Cisco Nexus 9536PQ

      • Cisco Nexus 9636PQ

      • Cisco Nexus 9432PQ

    For the following Cisco Nexus 9200 platform switches and Cisco Nexus 9500 platform switches with supporting line cards, ERSPAN truncates the packets at port MTU, and issues a TX Output error:

    • Cisco Nexus 92160YC-X

    • Cisco Nexus 92304QC

    • Cisco Nexus 9272Q

    • Cisco Nexus 9232C

    • Cisco Nexus 9236C

    • Cisco Nexus 92300YC

    • Cisco Nexus 93108TC-EX

    • Cisco Nexus 93180LC-EX

    • Cisco Nexus 93180YC-EX

    • Cisco Nexus 9500 platform switches with the following line cards:

      • Cisco Nexus 9736C-EX

      • Cisco Nexus 97160YC-EX

      • Cisco Nexus 9732C-EX

      • Cisco Nexus 9732C-EXM

  • Using the ACL filter to ERSPAN subinterface traffic on the parent interface is not supported on the Cisco Nexus 9200 platform switches.

  • Using the ACL filter to ERSPAN subinterface traffic on the parent interface is not supported on the Cisco Nexus 9300-EX/FX/FX2/FX3/GX platform switches.

  • ERSPAN mirroring is not supported for PBR traffic.

  • ERSPAN with a Type three header is not supported in Cisco NX-OS Release 9.3(3).

  • For ERSPAN session limits, see the Cisco Nexus 9000 Series NX-OS Verified Scalability Guide.

  • The number of ERSPAN sessions per line card reduces to two if the same interface is configured as a bidirectional source in more than one session.

  • Configuring two SPAN or ERSPAN sessions on the same source interface with only one filter is not supported. If the same source is used in multiple SPAN or ERSPAN sessions either all the sessions must have different filters or no sessions should have filters.

  • Beginning with Cisco NX-OS Release 9.3(5), the following ERSPAN features are supported on Cisco Nexus 9300-GX platform switch:

    • ERSPAN Type III Header

    • ERSPAN Destination Support

  • Packets with FCS errors are not mirrored in an ERSPAN session.

  • TCAM carving is not required for SPAN/ERSPAN on the following line cards:

    • Cisco Nexus 9636C-R

    • Cisco Nexus 9636Q-R

    • Cisco Nexus 9636C-RX

    • Cisco Nexus 96136YC-R

    • Cisco Nexus 9624D-R2


    Note

    All other switches supporting SPAN/ERSPAN must use TCAM carving.

  • Statistics are not supported for the filter access group.

  • An access-group filter in an ERSPAN session must be configured as vlan-accessmap.

  • Control plane packets that are generated by the Supervisor cannot be ERSPAN encapsulated or filtered by an ERSPAN access control list (ACL).

  • ERSPAN is not supported for management ports.

  • ERSPAN does not support destinations on Layer 3 port-channel subinterfaces.

  • VLAN as a source is not supported with ERSPAN configuration on R-series linecards and N3K-C36180YC-R, N3KC36480LD-R2, and N3K-C3636C-R platform switches.

  • A VLAN can be part of only one session when it is used as an ERSPAN source or filter.

  • VLAN ERSPAN monitors only the traffic that leaves or enters Layer 2 ports in the VLAN.

  • If you enable ERSPAN on a vPC and ERSPAN packets must be routed to the destination through the vPC, packets that come through the vPC peer link cannot be captured.

  • ERSPAN is not supported over a VXLAN overlay.

  • ERSPAN copies for multicast packets are made before rewrite. Therefore, the TTL, VLAN ID, any remarking due to egress policy, and so on, are not captured in the ERSPAN copy.

  • The timestamp granularity of ERSPAN Type III sessions is not configurable through the CLI. It is 100 picoseconds and driven through PTP.

  • ERSPAN works on default and nondefault VRFs, but ERSPAN marker packets work only on the default VRF.

  • The same source can be part of multiple sessions.

The following guidelines and limitations apply to egress (Tx) ERSPAN:

  • The flows for post-routed unknown unicast flooded packets are in the ERSPAN session, even if the ERSPAN session is configured to not monitor the ports on which this flow is forwarded. This limitation applies to Network Forwarding Engine (NFE) and NFE2-enabled EOR switches and ERSPAN sessions that have TX port sources.

  • For ERSPAN Tx multicast for Layer 2, ERSPAN copies are created independent of multicast replication. Due to this, multicast and SPAN packet have different values for VLAN tag, which is the ingress interface VLAN ID.

  • The following guidelines and limitations apply to ingress (Rx) ERSPAN:

    • VLAN sources are spanned only in the Rx direction.

    • Session filtering functionality (VLAN or ACL filters) is supported only for Rx sources.

    • VLANs are supported as ERSPAN sources only in the ingress direction.

  • Priority flow control (PFC) ERSPAN has the following guidelines and limitations:

    • It cannot coexist with filters.

    • It is supported only in the Rx direction on physical or port-channel interfaces. It is not supported in the Rx direction on VLAN interfaces or in the Tx direction.

  • The following guidelines and limitations apply to FEX ports:

    • If the sources used in bidirectional ERSPAN sessions are from the same FEX, the hardware resources are limited to two ERSPAN sessions.

    • FEX ports are supported as ERSPAN sources in the ingress direction for all traffic and in the egress direction only for known Layer 2 unicast traffic.

    • Cisco Nexus 9300 platform switches do not support ERSPAN destination being connected on a FEX interface. The ERSPAN destination must be connected to a front panel port.

    • VLAN and ACL filters are not supported for FEX ports. It cannot coexist with filters.

  • The following guidelines and limitations apply to ERSPAN destination:

    • Cisco Nexus 9200, 9300-EX, 9300-FX, and 9300-FX2 platform switches support an ERSPAN destination session that is configured on physical or port-channel interfaces in switchport mode by using GRE header traffic flow.

    • ERSPAN destination cannot coexist with other tunnel features such as MPLS and VXLAN for Cisco Nexus 9200, 9300, 9300-EX, 9300-FX, and 9300-FX2 platform switches.

    • On Cisco Nexus 9300-GX switches, dot1q-tagged broadcast or multicast packets passing through a device where the ERSPAN destination session is active, get tagged with the native VLAN instead of the correct VLAN due to a hardware limitation.

    • ERSPAN destination supports only default VRF.

    • Cisco Nexus 9300-EX/FX switches cannot serve as an ERSPAN destination for Cisco Nexus 3000 and non-EX/FX Cisco Nexus 9000 switches.

  • Beginning with Cisco NX-OS Release 10.1(2), ERSPAN is supported on the Cisco Nexus N9K-X9624D-R2 Line Card.

Default Settings

The following table lists the default settings for ERSPAN parameters.

Table 1. Default ERSPAN Parameters

Parameters

Default

ERSPAN sessions

Created in the shut state

Configuring ERSPAN


Note

Be aware that the Cisco NX-OS commands for this feature may differ from those commands used in Cisco IOS.

Configuring an ERSPAN Source Session

You can configure an ERSPAN session on the local device only. By default, ERSPAN sessions are created in the shut state.


Note

ERSPAN does not monitor any packets that are generated by the supervisor, regardless of their source.

Procedure

  Command or Action Purpose

Step 1

configure terminal

Example:

switch# configure terminal
switch(config)#

Enters global configuration mode.

Step 2

monitor erspan origin ip-address ip-address global or

Example:

switch(config)# monitor erspan origin ip-address 10.0.0.1 global

Configures the ERSPAN global origin IP address.

Step 3

no monitor session {session-number | all}

Example:

switch(config)# no monitor session 3

Clears the configuration of the specified ERSPAN session. The new session configuration is added to the existing session configuration.

Step 4

monitor session {session-number | all} type erspan-source [shut]

Example:

switch(config)# monitor session 3 type erspan-source
switch(config-erspan-src)#

Configures an ERSPAN Type II source session. By default the session is bidirectional. The optional keyword shut specifies a shut state for the selected session.

Step 5

description description

Example:

switch(config-erspan-src)# description erspan_src_session_3

Configures a description for the session. By default, no description is defined. The description can be up to 32 alphanumeric characters.

Step 6

source {interface type [ tx | rx |both] vlan {number | range} [rx]}

Example:

switch(config-erspan-src)# source interface
ethernet 2/1-3, ethernet 3/1 rx

Example:

switch(config-erspan-src)# source interface
port-channel 2

Example:

switch(config-erspan-src)# source interface
sup-eth 0 rx

Example:

switch(config-erspan-src)# source vlan 3, 6-8 rx

Example:

switch(config-erspan-src)# source interface
ethernet 101/1/1-3

Configures the sources and traffic direction in which to copy packets. You can enter a range of Ethernet ports, a port channel, an inband interface, a range of VLANs, or a satellite port or host interface port channel on the Cisco Nexus 2000 Series Fabric Extender (FEX).

You can configure one or more sources, as either a series of comma-separated entries or a range of numbers. You can specify the traffic direction to copy as ingress, egress, or both.

For a unidirectional session, the direction of the source must match the direction specified in the session.

Note

 

Source VLANs are supported only in the ingress direction. Source FEX ports are supported in the ingress direction for all traffic and in the egress direction only for known Layer 2 unicast traffic.

Supervisor as a source is only supported in the Rx direction.

Step 7

(Optional) Repeat Step 7 to configure all ERSPAN sources.

(Optional)

—

Step 8

filter vlan {number | range}

Example:

switch(config-erspan-src)# filter vlan 3-5, 7

Configures which VLANs to select from the configured sources. You can configure one or more VLANs, as either a series of comma-separated entries or a range of numbers. For information on the VLAN range, see the Cisco Nexus 9000 Series NX-OS Layer 2 Switching Configuration Guide.

Note

 

A FEX port that is configured as an ERSPAN source does not support VLAN filters.

Step 9

(Optional) Repeat Step 9 to configure all source VLANs — to filter.

 (Optional)

—

Step 10

(Optional) filter access-group acl-filter

Example:

switch(config-erspan-src)# filter access-group
ACL1
(Optional)

Associates an ACL with the ERSPAN session. (You can create an ACL using the standard ACL configuration process. For more information, see the Cisco Nexus 9000 Series NX-OS Security Configuration Guide.)

Note

 

Before executing this command, configure ip access list and associated vlan access map. See Configuring ERSPAN ACL.

Step 11

destination ip ip-address

Example:

switch(config-erspan-src)# destination ip 10.1.1.1

Configures the destination IP address in the ERSPAN session.

Note

 

Only one destination IP address is supported per ERSPAN source session.

Step 12

erspan-id erspan-id

Example:

switch(config-erspan-src)# erspan-id 5

Configures the ERSPAN ID for the ERSPAN source session. The ERSPAN range is from 1 to 1023.

Step 13

vrf vrf-name

Example:

switch(config-erspan-src)# vrf default

Configures the virtual routing and forwarding (VRF) instance that the ERSPAN source session uses for traffic forwarding. The VRF name can be any case-sensitive, alphanumeric string up to 32 characters.

Step 14

(Optional) ip ttl ttl-number

Example:

switch(config-erspan-src)# ip ttl 25
 (Optional)

Configures the IP time-to-live (TTL) value for the ERSPAN traffic. The range is from 1 to 255.

Step 15

(Optional) ip dscp dscp-number

Example:

switch(config-erspan-src)# ip dscp 42
 (Optional)

Configures the differentiated services code point (DSCP) value of the packets in the ERSPAN traffic. The range is from 0 to 63.

Step 16

no shut

Example:

switch(config-erspan-src)# no shut

Enables the ERSPAN source session. By default, the session is created in the shut state.

Step 17

exit

Example:

switch(config-erspan-src)# exit
switch(config)#

Exits the monitor configuration mode.

Step 18

(Optional) show monitor session {all | session-number | range session-range} [brief]

Example:

switch(config)# show monitor session 3
 (Optional)

Displays the ERSPAN session configuration.

Step 19

(Optional) show running-config monitor

Example:

switch(config)# show running-config monitor
 (Optional)

Displays the running ERSPAN configuration.

Step 20

(Optional) show startup-config monitor

Example:

switch(config)# show startup-config monitor
 (Optional)

Displays the ERSPAN startup configuration.

Step 21

(Optional) copy running-config startup-config

Example:

switch(config)# copy running-config startup-config
 (Optional)

Copies the running configuration to the startup configuration.

Shutting Down or Activating an ERSPAN Session

You can shut down ERSPAN sessions to discontinue the copying of packets from sources to destinations. You can shut down one session in order to free hardware resources to enable another session. By default, ERSPAN sessions are created in the shut state.

You can enable ERSPAN sessions to activate the copying of packets from sources to destinations. To enable an ERSPAN session that is already enabled but operationally down, you must first shut it down and then enable it. You can shut down and enable the ERSPAN session states with either a global or monitor configuration mode command.

Procedure

  Command or Action Purpose

Step 1

configure terminal

Example:

switch# configure terminal
switch(config)#

Enters global configuration mode.

Step 2

monitor session {session-range | all} shut

Example:

switch(config)# monitor session 3 shut

Shuts down the specified ERSPAN sessions. By default, sessions are created in the shut state.

Step 3

no monitor session {session-range | all} shut

Example:

switch(config)# no monitor session 3 shut

Resumes (enables) the specified ERSPAN sessions. By default, sessions are created in the shut state.

If a monitor session is enabled but its operational status is down, then to enable the session, you must first specify the monitor session shut command followed by the no monitor session shut command.

Step 4

monitor session session-number type erspan-source

Example:

switch(config)# monitor session 3 type erspan-source
switch(config-erspan-src)#

Enters the monitor configuration mode for the ERSPAN source type. The new session configuration is added to the existing session configuration.

Step 5

shut

Example:

switch(config-erspan-src)# shut

Shuts down the ERSPAN session. By default, the session is created in the shut state.

Step 6

no shut

Example:

switch(config-erspan-src)# no shut

Enables the ERSPAN session. By default, the session is created in the shut state.

Step 7

exit

Example:

switch(config-erspan-src)# exit
switch(config)#

Exits the monitor configuration mode.

Step 8

(Optional) show monitor session all

Example:

switch(config)# show monitor session all
 (Optional)

Displays the status of ERSPAN sessions.

Step 9

(Optional) show running-config monitor

Example:

switch(config)# show running-config monitor
 (Optional)

Displays the ERSPAN running configuration.

Step 10

(Optional) show startup-config monitor

Example:

switch(config)# show startup-config monitor
 (Optional)

Displays the ERSPAN startup configuration.

Step 11

(Optional) copy running-config startup-config

Example:

switch(config)# copy running-config startup-config
 (Optional)

Copies the running configuration to the startup configuration.

Configuring an ERSPAN ACL

You can create an IPv4 ERSPAN ACL on the device and add rules to it.

Before you begin

To modify the DSCP value or the GRE protocol, you need to allocate a new destination monitor session. A maximum of four destination monitor sessions are supported.

Procedure

  Command or Action Purpose

Step 1

configure terminal

Example:

switch# configure terminal
switch(config)#

Enters global configuration mode.

Step 2

ip access-list acl-name

Example:

switch(config)# ip access-list erspan-acl
switch(config-acl)#

Creates the ERSPAN ACL and enters IP ACL configuration mode. The acl-name argument can be up to 64 characters.

Step 3

[sequence-number] {permit | deny} protocol source destination [set-erspan-dscp dscp-value] [set-erspan-gre-proto protocol-value]

Example:

switch(config-acl)# permit ip 192.168.2.0/24 any 
set-erspan-dscp 40 set-erspan-gre-proto 5555

Example:

switch(config)# ip access-list match_11_pkts
switch(config-acl)# permit ip 10.0.0.0/24 any
switch(config-acl)# exit

Creates a rule in the ERSPAN ACL. You can create many rules.

The sequence-number argument can be a whole number between 1 and 4294967295.

The permit and deny commands support many ways of identifying traffic.

The set-erspan-dscp option sets the DSCP value in the ERSPAN outer IP header. The range for the DSCP value is from 0 to 63. The DSCPvalue configured in the ERSPAN ACL overrides the value configured in the monitorsession. If you do not include this option in the ERSPAN ACL, 0 or the DSCP value configured in the monitor session will be set.

The set-erspan-gre-proto option sets the protocol value in the ERSPAN GRE header. The range for the protocol value is from 0 to 65535. If you do not include this option in the ERSPAN ACL, the default value of 0x88be will be set as the protocol in the GRE header for ERSPAN-encapsulated packets

Each access control entry (ACE) with the sset-erspan-gre-proto or set-erspan-dscp action consumes one destination monitor session. A maximum of three ACEs with one of these actions is supported per ERSPAN ACL. For example, you can configure one of the following:

  • One ERSPAN session with an ACL having a maximum of three ACEs with the set-erspan-gre-proto or set-erspan-dscp action

  • One ERSPAN session with an ACL having two ACEs with the set-erspan-gre-proto or set-erspan-dscp action and one additional local or ERSPAN session

  • A maximum of two ERSPAN sessions with an ACL having one ACE with the set-erspan-gre-proto or set-erspan-dscp action

Step 4

show ip access-lists name

Example:

switch(config-acl)# show ip access-lists erpsan-acl

Displays the ERSPAN ACL configuration.

Step 5

show monitor session {all | session-number | range session-range} [brief]

Example:

switch(config-acl)# show monitor session 1

Displays the ERSPAN session configuration.

Step 6

(Optional) copy running-config startup-config

Example:

switch(config-acl)# copy running-config startup-config
(Optional)

Copies the running configuration to the startup configuration.

Configuring UDF-Based ERSPAN

You can configure the device to match on user-defined fields (UDFs) of the outer or inner packet fields (header or payload) and to send the matching packets to the ERSPAN destination. Doing so can help you to analyze and isolate packet drops in the network.

Before you begin

Make sure that the appropriate TCAM region (racl, ifacl, or vacl) has been configured using the hardware access-list tcam region command to provide enough free space to enable UDF-based ERSPAN. For information, see the "Configuring ACL TCAM Region Sizes" section in the Cisco Nexus 9000 Series NX-OS Security Configuration Guide.

Procedure

  Command or Action Purpose

Step 1

configure terminal

Example:

switch# configure terminal
switch(config)#

Enters global configuration mode.

Step 2

udf udf-name offset-base offset length

Example:

switch(config)# udf udf-x packet-start 12 1
switch(config)# udf udf-y header outer l3 20 2

Defines the UDF as follows:

  • udf-name—Specifies the name of the UDF. You can enter up to 16 alphanumeric characters for the name.

  • offset-base—Specifies the UDF offset base as follows, where header is the packet header to consider for the offset: packet-start | header {outer | inner {l3 | l4}} .

  • offset—Specifies the number of bytes offset from the offset base. To match the first byte from the offset base (Layer 3/Layer 4 header), configure the offset as 0.

  • length—Specifies the number of bytes from the offset. Only 1 or 2 bytes are supported. To match additional bytes, you must define multiple UDFs.

You can define multiple UDFs, but Cisco recommends defining only required UDFs.

Step 3

hardware access-list tcam region {racl | ifacl | vacl }qualify udf udf-names

Example:

switch(config)# hardware access-list tcam region
racl qualify udf udf-x udf-y

Attaches the UDFs to one of the following TCAM regions:

  • racl—Applies to Layer 3 ports.—Applies to layer 2 and Layer 3 ports.

  • ifacl—Applies to Layer 2 ports.

  • vacl—Applies to source VLANs.

You can attach up to 8 UDFs to a TCAM region.

Note

 

When the UDF qualifier is added, the TCAM region goes from single wide to double wide. Make sure enough free space is available; otherwise, this command will be rejected. If necessary, you can reduce the TCAM space from unused regions and then re-enter this command. For more information, see the "Configuring ACL TCAM Region Sizes" section in the Cisco Nexus 9000 Series NX-OS Security Configuration Guide.

Note

 

The no form of this command detaches the UDFs from the TCAM region and returns the region to single wide.

Step 4

copy running-config startup-config

Example:

switch(config)# copy running-config startup-config

Saves the change persistently through reboots and restarts by copying the running configuration to the startup configuration.

Step 5

reload

Example:

switch(config)# reload

Reloads the device.

Note

 

Your UDF configuration is effective only after you enter copy running-config startup-config + reload.

Step 6

ip access-list erspan-acl

Example:

switch(config)# ip access-list erspan-acl-udf-only
switch(config-acl)#

Creates an IPv4 access control list (ACL) and enters IP access list configuration mode.

Step 7

Enter one of the following commands:

  • permit udf udf-name value mask
  • permit ip source destination udf udf-name value mask

Example:

switch(config-acl)# permit udf udf-x 0x40 0xF0 udf-y 0x1001 0xF00F

Example:

switch(config-acl)# permit ip 10.0.0.0/24 any udf udf-x 0x02 0x0F udf-y 0x1001 0xF00F

Configures the ACL to match only on UDFs (example 1) or to match on UDFs along with the current access control entries (ACEs) for the outer packet fields (example 2).

A single ACL can have ACEs with and without UDFs together. Each ACE can have different UDF fields to match, or all ACEs can match for the same list of UDFs.

Step 8

(Optional) copy running-config startup-config

Example:

switch(config)# copy running-config startup-config
 (Optional)

Copies the running configuration to the startup configuration.

Configuring ERSPAN Truncation

You can configure truncation for local and ERSPAN source sessions only.

Procedure

  Command or Action Purpose

Step 1

configure terminal

Example:

switch# configure terminal
switch(config)#

Enters global configuration mode.

Step 2

monitor session session-number type erspan-source

Example:

switch(config)# monitor session 10 type erspan-source
switch(config-erspan-src)#

Enters monitor configuration mode for the specified ERSPAN session.

Step 3

source interface type slot/port [rx | tx | both]

Example:

switch(config-erspan-src)# source interface ethernet 1/5 both

Configures the source interface.

Step 4

mtu size

Example:

switch(config-erspan-src)# mtu 512

Example:

switch(config-erspan-src)# mtu ?
<512-1518> Enter the value of MTU truncation size for
ERSPAN packets (erspan header + truncated original packet)

Configures the MTU size for truncation. Any ERSPAN packet that is larger than the configured MTU size is truncated to the configured size. The MTU ranges for ERSPAN packet truncation are:

  • The MTU size range is 512 to 1518 bytes for Cisco Nexus 9300-EX Series switches.

  • The MTU size range is 64 to 1518 bytes for Cisco Nexus 9300-FX Series switches.

  • The MTU size range is 512 to 1518 bytes for Cisco Nexus 9500 platform switches with 9700-EX and 9700-FX line cards.

Step 5

destination interface type slot/port

Example:

switch(config-erspan-src)# destination interface Ethernet 1/39

Configures the Ethernet ERSPAN destination port.

Step 6

no shut

Example:

switch(config-erspan-src)# no shut

Enables the ERSPAN session. By default, the session is created in the shut state.

Step 7

(Optional) show monitor session session

Example:

switch(config-erspan-src)# show monitor session 5
(Optional)

Displays the ERSPAN configuration.

Step 8

copy running-config startup-config

Example:

switch(config-erspan-src)# copy running-config startup-config

Copies the running configuration to the startup configuration.

Configuring an ERSPAN Destination Session

You can configure a ERSPAN destination session to copy packets from a source IP address to destination ports on the local device. By default, ERSPAN destination sessions are created in the shut state.

Before you begin

Ensure that you have already configured the destination ports in switchport monitor mode.

Procedure

  Command or Action Purpose

Step 1

configure terminal

Example:

switch# configure terminal
switch(config)#

Enters global configuration mode.

Step 2

interface ethernet slot/port[-port]

Example:

switch(config)# interface ethernet 2/5
switch(config-if)#

Enters interface configuration mode on the selected slot and port or range of ports.

Step 3

switchport

Example:

switch(config-if)# switchport

Configures switchport parameters for the selected slot and port or range of ports.

Step 4

switchport mode [access | trunk]

Example:

switch(config-if)# switchport mode trunk

Configures the following switchport modes for the selected slot and port or range of ports:

  • access

  • trunk

Step 5

switchport monitor

Example:

switch(config-if)# switchport monitor

Configures the switchport interface as an ERSPAN destination.

Step 6

Repeat Steps 2 to 5 to configure monitoring on additional ERSPAN destinations.

—

Step 7

no monitor session {session-number | all}

Example:

switch(config-if)# no monitor session 3

Clears the configuration of the specified ERSPAN session. The new session configuration is added to the existing session configuration.

Step 8

monitor session {session-number | all} type erspan-destination

Example:

switch(config-if)# monitor session 3 type erspan-destination
switch(config-erspan-dst)#

Configures an ERSPAN destination session.

Step 9

description description

Example:

switch(config-erspan-dst)# description erspan_dst_session_3

Configures a description for the session. By default, no description is defined. The description can be up to 32 alphanumeric characters.

Step 10

source ip ip-address

Example:

switch(config-erspan-dst)# source ip 10.1.1.1

Configures the source IP address in the ERSPAN session. The source IP address is a locally configured IP address. The source IP address in an ERSPAN destination session must match the destination IP address configured in the ERSPAN source session from which the encapsulated data is received. Only one source IP address is supported per ERSPAN destination session.

Step 11

destination {[interface [type slot/port[-port]]] [port-channel channel-number]]}

Example:

switch(config-erspan-dst)# destination interface ethernet 2/5

Configures a destination for copied source packets. You can configure a destination interface.

Note

 

You can configure destination ports as trunk ports.

Step 12

(Optional) Repeat Step 11 to configure all ERSPAN destinations.

 (Optional)

—

Step 13

erspan-id erspan-id

Example:

switch(config-erspan-dst)# erspan-id 5

Configures the ERSPAN ID for the ERSPAN session. The range is from 1 to 1023.

Step 14

no shut

Example:

switch(config-erspan-dst)# no shut

Enables the ERSPAN destination session. By default, the session is created in the shut state.

Step 15

exit

Example:

switch(config-erspan-dst)# exit

Exits monitor configuration mode.

Step 16

exit

Example:

switch(config)# exit

Exits global configuration mode.

Step 17

(Optional) show monitor session {all | session-number | range session-range}

Example:

switch(config)# show monitor session 3
 (Optional)

Displays the ERSPAN session configuration.

Step 18

(Optional) show running-config monitor

Example:

switch(config-erspan-src)# show running-config monitor
 (Optional)

Displays the running ERSPAN configuration.

Step 19

(Optional) show startup-config monitor

Example:

switch(config-erspan-src)# show startup-config monitor
 (Optional)

Displays the ERSPAN startup configuration.

Step 20

(Optional) copy running-config startup-config

Example:

switch(config-erspan-src)# copy running-config startup-config
 (Optional)

Copies the running configuration to the startup configuration.

Verifying the ERSPAN Configuration

To display the ERSPAN configuration, perform one of the following tasks:

Command

Purpose

show monitor session {all | session-number | range session-range} [brief]

Displays the ERSPAN session configuration.

show running-config monitor

Displays the running ERSPAN configuration.

show startup-config monitor

Displays the ERSPAN startup configuration.

Configuration Examples for ERSPAN

Configuration Example for a Unidirectional ERSPAN Session

This example shows how to configure a unidirectional ERSPAN session: 

switch# configure terminal
switch(config)# interface ethernet 14/30
switch(config-if)# no shut
switch(config-if)# exit
switch(config)# no monitor session 3
switch(config)# monitor session 3 rxswitch(config-erspan-src)# source interface ethernet 2/1-3 rx
switch(config-erspan-src)# erspan-id 1
switch(config-erspan-src)# ip ttl 16
switch(config-erspan-src)# ip dscp 5
switch(config-erspan-src)# vrf default
switch(config-erspan-src)# destination ip 10.1.1.2
switch(config-erspan-src)# no shut
switch(config-erspan-src)# exit
switch(config)# show monitor session 1

Configuration Example for an ERSPAN ACL

This example shows how to configure an ERSPAN ACL: 

switch# configure terminal
switch(config)# ip access-list match_10_pkts
switch(config-acl)# permit ip 10.0.0.0/24 any
switch(config-acl)# exit
switch(config)# ip access-list match_172_pkts
switch(config-acl)# permit ip 172.16.0.0/24 any
switch(config-acl)# exit

In the case of different ERSPAN destinations where the interesting traffic is chosen based on the defined ACL filters, the last configured session would always have the higher priority.

For example, if Monitor Session 1 is configured; then Monitor Session 2 is configured; then ERSPAN traffic filter works as intended. But, if the user goes back to Monitor Session 1 and re-applies one of the existing configuration line (no new changes in the config); then the spanned traffic switches back to Monitor Session 1.

Configuration Example for a Marker Packet

This example shows how to enable the ERSPAN marker packet with an interval of 2 seconds: 

switch# configure terminal
switch(config)# monitor erspan origin ip-address 172.28.15.250 global
switch(config)# monitor session 1 type erspan-source
switch(config-erspan-src)# header-type 3
switch(config-erspan-src)# erspan-id 1
switch(config-erspan-src)# ip ttl 16
switch(config-erspan-src)# ip dscp 5
switch(config-erspan-src)# vrf default
switch(config-erspan-src)# destination ip 10.1.1.2
switch(config-erspan-src)# source interface ethernet 1/15 both
switch(config-erspan-src)# marker-packet 100
switch(config-erspan-src)# no shut
switch(config-erspan-src)# show monitor session 1
session 1
---------------
type              : erspan-source
state             : up
granularity       : nanoseconds
erspan-id         : 1
vrf-name          : default
destination-ip    : 10.1.1.2
ip-ttl            : 16
ip-dscp           : 5
header-type       : 3
origin-ip         : 172.28.15.250 (global)
source intf       :
    rx            : Eth1/15
    tx            : Eth1/15
    both          : Eth1/15
    rx            :
marker-packet     : enabled
packet interval   : 100
packet sent       : 25
packet failed     : 0
egress-intf       :

Configuration Examples for UDF-Based ERSPAN

This example shows how to configure UDF-based ERSPAN to match on the inner TCP flags of an encapsulated IP-in-IP packet using the following match criteria:

  • Outer source IP address: 10.0.0.2

  • Inner TCP flags: Urgent TCP flag is set

  • Bytes: Eth Hdr (14) + Outer IP (20) + Inner IP (20) + Inner TCP (20, but TCP flags at 13th byte)

  • Offset from packet-start: 14 + 20 + 20 + 13 = 67

  • UDF match value: 0x20

  • UDF mask: 0xFF 

udf udf_tcpflags packet-start 67 1
hardware access-list tcam region racl qualify udf udf_tcpflags
copy running-config startup-config
reload
ip access-list acl-udf
permit ip 10.0.0.2/32 any udf udf_tcpflags 0x20 0xff
monitor session 1 type erspan-source
source interface Ethernet 1/1
filter access-group acl-udf

This example shows how to configure UDF-based ERSPAN to match regular IP packets with a packet signature (DEADBEEF) at 6 bytes after a Layer 4 header start using the following match criteria:

  • Outer source IP address: 10.0.0.2

  • Inner TCP flags: Urgent TCP flag is set

  • Bytes: Eth Hdr (14) + IP (20) + TCP (20) + Payload: 112233445566DEADBEEF7788

  • Offset from Layer 4 header start: 20 + 6 = 26

  • UDF match value: 0xDEADBEEF (split into two-byte chunks and two UDFs)

  • UDF mask: 0xFFFFFFFF 

udf udf_pktsig_msb header outer l3 26 2
udf udf_pktsig_lsb header outer l3 28 2
hardware access-list tcam region racl qualify udf udf_pktsig_msb udf_pktsig_lsb
copy running-config startup-config
reload
ip access-list acl-udf-pktsig
permit udf udf_pktsig_msb 0xDEAD 0xFFFF udf udf_pktsig_lsb 0xBEEF 0xFFFF
monitor session 1 type erspan-source
source interface Ethernet 1/1
filter access-group acl-udf-pktsig

Configuration Example for ERSPAN Truncation

This example shows how to configure ERSPAN truncation for use with MPLS stripping: 

mpls strip
ip access-list mpls
  statistics per-entry
  20 permit ip any any redirect Ethernet1/5

interface Ethernet1/5
  switchport
  switchport mode trunk
  mtu 9216
  no shutdown

monitor session 1
  source interface Ethernet1/5 tx
  mtu 64
  destination interface Ethernet1/6
  no shut
monitor session 21 type erspan-source
  description "ERSPAN Session 21"
  header-type 3
  erspan-id 21
  vrf default
  destination ip 10.1.1.2
  source interface Ethernet1/5 tx
  mtu 64
  no shut
monitor session 22 type erspan-source
  description "ERSPAN Session 22"
  erspan-id 22
  vrf default
  destination ip 10.2.1.2
  source interface Ethernet1/5 tx
  mtu 750
  no shut
monitor session 23 type erspan-source
  description "ERSPAN Session 23"
  header-type 3
  marker-packet 1000
  erspan-id 23
  vrf default
  destination ip 10.3.1.2
  source interface Ethernet1/5 tx
  mtu 1000
  no shut

Configuration Example for an ERSPAN Destination Session

This example shows how to configure an ERSPAN destination session:

The destination interface eth1/1 is in switchport monitor mode. This interface can not co-exist with mpls strip, tunnel, nv overlay, vn-segment-vlan-based, mpls segment-routing, mpls evpn, mpls static, mpls oam, mpls l3vpn , mpls ldp, and nv overlay evpn features. 

switch# monitor session 1 type erspan-destination
switch(config)# erspan-id 1
switch(config-erspan-dst)# source ip 10.1.1.1
switch(config-erspan-dst)# destination interface eth1/1
switch(config-erspan-dst)# no shut
switch(config-erspan-dst)# exit