Configuring Traffic Mirroring

This module describes the configuration of the traffic mirroring feature. Traffic mirroring is sometimes called port mirroring, or switched port analyzer (SPAN). You can then pass this traffic to a destination port on the same router.

Feature Release History

Release

Modification

Release 6.1.3

ERSPAN Traffic to a Destination Tunnel in a Default VRF was introduced.
Release 7.0.2

SPAN over Pseudo-Wire was introduced.
Release 7.1.2

SPAN to File was introduced.
Release 7.2.1

File Mirroring was introduced.
Release 7.3.1

PCAPng file format was introduced.
Release 7.5.2

Mirror first option in global configuration mode was introduced.
Release 7.5.3

ERSPAN Traffic to a Destination Tunnel in a Non-Default VRF was introduced.
Release 7.5.4

  • DSCP Marking on Egress GRE Tunnel in ERSPAN was introduced.

  • DSCP Bitmask to filter Ingress SPAN was introduced.

  • Mirroring Forward-Drop Packets was introduced.
Release 7.6.1

VLAN Sub-interface as Ingress or Egress Source for Traffic Mirroring was introduced.

Introduction to Traffic Mirroring

Traffic mirroring, also referred to as Port mirroring or Switched Port Analyzer (SPAN), is a Cisco proprietary feature that enables you to monitor network traffic passing in or out of a set of ports on a router. You can then mirror this traffic to a remote destination or a destination port on the same router.

Traffic mirroring copies traffic from one or more source ports and sends the copied traffic to one or more destinations for analysis by a network analyzer or other monitoring devices. Traffic mirroring does not affect the flow of traffic on the source interfaces or sub-interfaces. It allows the mirrored traffic to be sent to a destination interface or sub-interface.

For example, you can attach a traffic or network analyzer to the router and capture the ethernet traffic that is sent by host A to host B.

Figure 1. Traffic Mirroring Operation

Traffic Mirroring Terminology

  • Ingress Traffic — Traffic that comes into the router.

  • Egress Traffic — Traffic that goes out of the router.

  • Source port—A port that is monitored with the use of traffic mirroring. It is also called a monitored port.

  • Destination port—A port that monitors source ports, usually where a network analyzer is connected. It is also called a monitoring port.

  • Monitor session—A designation for a collection of SPAN configurations consisting of a single destination and, potentially, one or many source ports.

Characteristics of Source Port

A source port, also called a monitored port, is a routed port that you monitor for network traffic analysis. In a single traffic mirroring session, you can monitor source port traffic. The routers support a maximum of up to 800 source ports.

A source port has these characteristics:

  • It can be any data port type, such as Bundle Interface, 100 Gigabit Ethernet physical port, or 10 Gigabit Ethernet physical port.

  • Each source port can be monitored in only one traffic mirroring session.

  • When a port is used as a source port, the same port cannot be used as a destination port.

  • Each source port can be configured with a direction (ingress, egress, or both) to monitor local traffic mirroring. Remote traffic mirroring is supported both in the ingress and egress directions. For bundles, the monitored direction applies to all physical ports in the group.

Characteristics of Monitor Session

A monitor session is a collection of traffic mirroring configurations consisting of a single destination and, potentially, many source interfaces. For any given monitor session, the traffic from the source interfaces (called source ports) is sent to the monitoring port or destination port. If there are more than one source port in a monitoring session, the traffic from the several mirrored traffic streams is combined at the destination port. The result is that the traffic that comes out of the destination port is a combination of the traffic from one or more source ports.

Monitor sessions have these characteristics:

  • A single monitor session can have only one destination port.

  • A single destination port can belong to only one monitor session.

  • A monitor session can have a maximum of 800 source ports. This maximum limit is applicable only when the maximum number of source ports from all monitoring sessions does not exceed 800.

Characteristics of Destination Port

Each session must have a destination port or file that receives a copy of the traffic from the source ports.

A destination port has these characteristics:

  • A destination port cannot be a source port.

  • A destination port must reside on the same router as the source port for local traffic mirroring. For remote mirroring, the destination is always a GRE tunnel.

  • For remote mirroring, the destination is a GRE tunnel.

  • A destination port for local mirroring can be any Ethernet physical port, EFP, GRE tunnel interface, or bundle interface. It can be a Layer 2 or Layer 3 transport interface.

  • A destination port on router cannot be a VLAN subinterface.

  • At any time, a destination port can participate in only one traffic mirroring session. 
A destination port in one traffic mirroring session cannot be a destination port for a second traffic mirroring session. In other words, no two monitor sessions can have the same destination port.

Supported Scale

This list provides scale supported on the NCS 560 routers for traffic mirroring.

Restrictions

Generic Restrictions

The following are the generic restrictions related to traffic mirroring:

  • Partial mirroring and sampled mirroring are not supported.

  • From Release 7.6.1, sub-interface configured as source interface is supported on SPAN.

  • The destination bundle interfaces flap when:

    • both the mirror source and destination are bundle interfaces in the Link Aggregation Control Protocol (LACP) mode.

    • mirror packets next-hop is a router or a switch instead of a traffic analyzer.

    This behavior is observed due to a mismatch of LACP packets on the next-hop bundle interface due to the mirroring of LACP packets on the source bundle interface.

  • Subinterface with only one VLAN is supported as source for traffic mirroring.

  • Bridge group virtual interfaces (BVIs) are not supported as source ports or destination ports.

  • Bundle members cannot be used as destination ports.

  • Fragmentation of mirror copies is not handled by SPAN when SPAN destination MTU is less than the packet size. Existing behaviour if the MTU of destination interface is less than the packet size is as below:

    Platforms

    Rx SPAN

    Tx SPAN

    NCS 560

    Mirror copies are not fragmented. Receives whole packets as mirror copies.

    Mirror copies are fragmented.

    You can configure the SPAN destination with an MTU which is greater than the packet size.

  • Until Cisco IOS XR Software Release 7.6.1, SPAN only supports port-level source interfaces.

VLAN Sub-interface as Source Restrictions

  • Supports a maximum of 24 reception and transmission sessions together for mirroring. This restriction is applicable for sub-intefaces and ports as source.

  • When the port is in Egress Traffic Management (ETM) mode, the outbound or transmission mirroring is possible only on the sub-interface for which outbound traffic mirroring is configured.

  • Transmission mirroring is applicable on ETM mode only. Reception mirroring is applicable on both the ETM and non-ETM modes.

ACL-based SPAN Restrictions

The following restrictions apply to SPAN-ACL:

Table 1. SPAN-ACL Support

Platforms

Rx Direction

Tx Direction

NCS 540

Supported at the port level, that is, in the ingress direction for IPv4 or IPv6 ACLs.

Not supported.

  • MPLS traffic cannot be captured with SPAN-ACL.

    • ACL for any MPLS traffic is not supported.

  • Traffic mirroring counters are not supported.

  • ACL-based traffic mirroring is not supported with Layer 2 (ethernet-services) ACLs.

  • Main interface as span source interface and ACL with the capture keyword on same main interface's sub-interface are not supported.

  • If a SPAN session with the acl keyword is applied on an interface with no ACL rule attached to that interface, SPAN happens without any filtering.

ERSPAN Restrictions

This section provides the restrictions that apply to ERSPAN and multiple ERSPAN sessions.

The following restrictions apply to ERSPAN:

  • The value of ERSPAN session-ID is always zero. IOS XR command for configuring ERSPAN is not available.

  • ERSPAN next-hop must have ARP resolved. Any other traffic or protocol will trigger ARP.

  • ERSPAN packets with outgoing interface having MPLS encapsulation are not supported.

    • Additional routers may encapsulate in MPLS.

  • ERSPAN sessions can be created only on physical interfaces. The sessions cannot be created on sub-interfaces.

  • ERSPAN decapsulation is not supported.

  • ERSPAN does not work if the GRE next hop is reachable over sub-interface. For ERSPAN to work, the next hop must be reachable over the main interface.

  • When you use the same ACEs defined in both the IPv4 and IPv6 ACLs, the router doesn’t perform ERSPAN mirroring for the ACLs that have the priority set as 2 ms.

  • ERSPAN decapsulation is not supported. Tunnel destination should be network analyzer.

Multiple ERSPAN Restrictions

  • All sessions under the source port should have SPAN access control list (ACL) enabled.

  • A few sessions with SPAN ACL and a few without SPAN ACLs in the same source interface are not supported.

  • No two sessions should have the same ACL in the same source interface. Each session should have a different ACL.

  • Multiple sessions without ACL in the same interface are not supported.

  • One SPAN session with the keyword ACL (use security acl as the keyword) and other SPAN sessions with the keyword SPAN ACL are not supported.

  • At a time, you can make only one mirror copy of a packet.

  • Capturing keywords is not required.

  • Multiple sessions under the same interface cannot have a combination of directions. Only RX is supported.

SPAN over Pseudowire Restrictions

SPAN over Psedowire (PW-SPAN) has the following restrictions:

  • PW-SPAN does not support the listed functionalities:

    • Monitor session statistics

    • Partial packet SPAN

    • Sampled SPAN

  • ETM mode must be enabled for outgoing (Tx) traffic on sub-interface.

SPAN-to-File Restrictions

SPAN to File has the following restrictions:

  • A maximum of 1000 source ports are supported across the system. Individual platforms may support lower numbers. The SPAN session may be any of these currently supported classes: Ethernet, IPv4, IPv6, MPLS-IPv4, and MPLS-IPv6.

  • Provides a buffer range of 1000-1000000 KB. The default buffer size is set to 1000 KB.

  • Provides support for SPAN source.

    • Each source port can be monitored in only one traffic mirroring session.

    • Each source port can be configured with a direction (ingress, egress, or both) to monitor local traffic mirroring.

  • Only port-level is supported.

  • VLAN interface as source port is not supported.

  • Bundle members as source interfaces are not supported.

  • Filtering based on Egress ACL is not supported.

  • Source port statistics is not supported.

  • Span to file mirror packets are punted from NPU to CPU at a maximum shaper rate of 40 mbps.

File Mirroring Restrictions

The following restrictions apply to file mirroring:

  • Supported only on Dual RP systems.

  • Supports syncing only from active to standby RP. If files are copied into standby /harddisk:/mirror location, it won’t be synced to active RP.

  • A slight delay is observed in show mirror command output when mirror checksum configuration is enabled.

  • Not supported on multichassis systems.

Forward-Drop Packets Mirroring Restrictions

These are some restrictions for Forward-Drop packets mirroring:

  • Only one global forward-drop session can be configured on a router.

  • When traffic-class is configured under monitor-session for forward-drop, the type of service (ToS) byte of the outgoing ERSPAN packet is overwritten with the configured traffic-class value.

  • In-band traffic destined to router management interface cannot be captured using this functionality.

SPAN Types, Supported Features, and Configurations

Local SPAN

This is the most basic form of traffic mirroring. The network analyzer or sniffer is attached directly to the destination interface. In other words, all monitored ports are located on the same router as the destination port.

Remote SPAN

Configure Remote Traffic Mirroring

Procedure

Step 1

configure

Example:


RP/0/RP0/CPU0:router# configure

Enters global configuration mode.

Step 2

monitor-session session-name

Example:


RP/0/RP0/CPU0:router(config)# monitor-session mon1 ethernet
RP/0/RP0/CPU0:router(config-mon)#

Defines a monitor session and enters monitor session configuration mode.

Step 3

destination interface subinterface

Example:


RP/0/RP0/CPU0:router(config-mon)# destination interface TenGigE 0/2/0/4.1

Specifies the destination subinterface to which traffic is replicated.

Step 4

exit

Example:


RP/0/RP0/CPU0:router(config-mon)# exit
RP/0/RP0/CPU0:router(config)#

Exits monitor session configuration mode and returns to global configuration mode.

Step 5

interface type number

Example:


RP/0/RP0/CPU0:router(config)# interface HundredGigE 0/0/1/0

Enters interface configuration mode for the specified source interface. The interface number is entered in rack /slot /module /port notation. For more information about the syntax for the router, use the question mark (?) online help function.

Step 6

monitor-session session-name ethernet direction rx-onlyport-only

Example:


RP/0/RP0/CPU0:router(config-if)# monitor-session mon1 ethernet 
direction rx-only port-only

Specifies the monitor session to be used on this interface. Use the direction keyword to specify that only ingress or egress traffic is mirrored.

Step 7

end or commit

Example:


RP/0/RP0/CPU0:router(config-if)# end

or 


RP/0/RP0/CPU0:router(config-if)# commit

Saves configuration changes.

  • When you issue the end command, the system prompts you to commit changes: 

    
Uncommitted changes found, commit them before exiting (yes/no/cancel)?
[cancel]:

    - Entering yes saves configuration changes to the running configuration file, exits the configuration session, and returns the router to EXEC mode.

    - Entering no exits the configuration session and returns the router to EXEC mode without committing the configuration changes.

    - Entering cancel leaves the router in the current configuration session without exiting or committing the configuration changes.

  • Use the commit command to save the configuration changes to the running configuration file and remain within the configuration session.

Use the commit command to save the configuration changes to the running configuration file and remain within the configuration session.

Step 8

show monitor-session [session-name] status [detail] [error]

Example:


RP/0/RP0/CPU0:router# show monitor-session

Displays information about the traffic mirroring session.

Example

This example shows the basic configuration for traffic mirroring with physical interfaces.
RP/0/RP0/CPU0:router# configure
RP/0/RP0/CPU0:router(config)# monitor-session ms1
RP/0/RP0/CPU0:router(config-mon)# destination interface HundredGigE0/2/0/15
RP/0/RP0/CPU0:router(config-mon)# commit
RP/0/RP0/CPU0:router# configure
RP/0/RP0/CPU0:router(config)# interface TenGigE0/2/0/19
RP/0/RP0/CPU0:router(config-if)# monitor-session ms1 port-level
RP/0/RP0/CPU0:router(config-if)# commit
RP/0/RP0/CPU0:router# configure
RP/0/RP0/CPU0:router(config)# interface TenGigE0/2/0/19
RP/0/RP0/CPU0:router(config-if)# monitor-session ms1 direction rx-only port-level
RP/0/RP0/CPU0:router(config-if)# commit
RP/0/RP0/CPU0:router# configure
RP/0/RP0/CPU0:router(config)# interface TenGigE0/2/0/19
RP/0/RP0/CPU0:router(config-if)# monitor-session ms1 direction tx-only port-level
RP/0/RP0/CPU0:router(config-if)# commit

This example shows sample output of the show monitor-session command with the status keyword:

RP/0/RSP0/CPU0:router# show monitor-session status
Monitor-session cisco-rtp1
Destination interface HundredGigE 0/5/0/38
================================================================================
Source Interface Dir Status
--------------------- ---- ----------------------------------------------------
TenGigE0/5/0/4 Both Operational
TenGigE0/5/0/17 Both Operational
RP/0/RSP0/CPU0:router# show monitor-session status detail
Monitor-session sess1
Destination interface is not configured
Source Interfaces
-----------------
TenGigE0/2/0/19
Direction: Both
ACL match: Disabled
Portion: Full packet
Status: Not operational (destination interface not known).
TenGigE0/1/0/1
Direction: Both
ACL match: Disabled
Portion: First 100 bytes

RP/0/RSP0/CPU0:router# show monitor-session status error
Monitor-session ms1
Destination interface TenGigE0/2/0/15 is not configured
================================================================================
Source Interface Dir Status
--------------------- ---- ----------------------------------------------------
Monitor-session ms2
Destination interface is not configured
================================================================================
Source Interface Dir Status
--------------------- ---- ----------------------------------------------------
RP/0/RP0/CPU0:router# show monitor-session test status
Monitor-session test (ipv4)
Destination Nexthop 255.254.254.4
=========================================================================================
Source Interface Dir Status
-----------------------------------------------------------------------------------------
Gi0/0/0/2.2 Rx Not operational (source same as destination)
Gi0/0/0/2.3 Rx Not operational (Destination not active)
Gi0/0/0/2.4 Rx Operational
Gi0/0/0/4 Rx Error: see detailed output for explanation
RP/0/RP0/CPU0:router# show monitor-session test status error
Monitor-session test
Destination Nexthop ipv4 address 255.254.254.4
===============================================================
Source Interface Status
---------------------------------------------------------------
Gi0/0/0/4 < Error: FULL Error Details >

SPAN on Subinterfaces

VLAN Subinterface as Ingress or Egress Source for Traffic Mirroring

Table 2. Feature History Table

Feature Name

Release Information

Feature Description

VLAN Subinterface as Ingress or Egress Source for Traffic Mirroring

 Release 7.6.1

You can now configure the VLAN subinterface as an egress or ingress source for traffic mirroring. This feature enables the monitoring of traffic mirrored on either egress or ingress or both directions.

You could configure mirror functionality only at the main interface level in earlier releases.

VLAN subinterface provides the flexibility to monitor ingress or egress, or both ingress/egress traffic from all the active subinterfaces of the source VLAN. The active subinterfaces in the source VLAN are considered as source subinterfaces. When subinterfaces are added or removed from the source VLAN, the corresponding traffic is added or removed from the monitoring sources.

VLAN Interface as Ingress Source for Traffic Mirroring

Configuration Example

Router# configure
Router(config)# monitor-session mon1 ethernet
Router(config-mon)# destination interface tunnel-ip 3
Router(config-mon)# exit
Router(config)# interface HundredGigE 0/1/0/1.10
Router(config-subif)# 
Router(config-if-mon)# commit
Running Configuration

Router# show run monitor-session mon1
monitor-session mon1 ethernet
 destination interface tunnel-ip3
!


Router# show run interface HundredGigE 0/1/0/1.10
 interface HundredGigE0/1/0/1.10
  encapsulation dot1q 10
   ipv4 address 101.1.2.1 255.255.255.252
    monitor-session mon1 ethernet 
    !
   !
  !
Verification
Router# show monitor-session status
Monitor-session mon1
Destination interface tunnel-ip3
================================================================================
Source Interface Dir Status
--------------------- ---- ----------------------------------------------------
HundredGigE 0/1/0/1.10  Both Operational

VLAN Interface as Egress Source for Traffic Mirroring

Configuration Example
Running Configuration

Router# show run monitor-session mon1
monitor-session mon1 ethernet
 destination interface tunnel-ip3
!


Router# show run interface HundredGigE 0/1/0/1.10
interface HundredGigE0/1/0/1.10
 encapsulation dot1q 20
  ipv4 address 102.1.2.1 255.255.255.252
   monitor-session mon1 ethernet 
   !
  !
 !
Verification
Router# show monitor-session status
Monitor-session mon1
Destination interface tunnel-ip3
================================================================================
Source Interface Dir Status
--------------------- ---- ----------------------------------------------------
HundredGigE 0/1/0/1.10  Both Operational

Monitoring Traffic Mirroring on a Layer 2 Interface

This section describes the configuration for monitoring traffic on a Layer 2 interface.

Configuration

To monitor traffic mirroring on a Layer 2 interface, configure the monitor under l2transport sub-config of the interface: 

RP/0/RP0/CPU0:router(config)# interface TenGigE0/0/0/42
RP/0/RP0/CPU0:router(config-if)# l2transport
RP/0/RP0/CPU0:router(config-if-l2)# monitor-session EASTON ethernet port-level

Verification

RP/0/RP0/CPU0:router# show monitor-session status 
Thu Aug 29 21:42:22.829 UTC
Monitor-session EASTON
Destination interface TenGigE0/0/0/20
=============================================
Source Interface      Dir   Status
--------------------- ----  -----------------
Te0/0/0/42 (port)     Both  Operational

ACL-based SPAN

Traffic is mirrored based on the configuration of the interface ACL.

You can mirror traffic based on the definition of an interface access control list. When you mirror Layer 3 traffic, the ACL is configured using the ipv4 access-list or the ipv6 access-list command with the capture option. The permit and deny commands determine if the packets in the traffic are permitted or denied. The capture option designates the packet is to be mirrored to the destination port, and it is supported only on permit type of Access Control Entries (ACEs).


Note

  • Prior to Release 6.5.1, ACL-based traffic mirroring required the use of UDK (User-Defined TCAM Key) with the enable-capture option so that the capture option can be configured in the ACL.

  • ACL must be defined before attaching the ACL name to SPAN source interface.

Configuring Security ACLs for Traffic Mirroring

This section describes the configuration for creating security ACLs for traffic mirroring.

In ACL-based traffic mirroring, traffic is mirrored based on the configuration of the interface ACL. You can mirror traffic based on the definition of an interface access control list. When you're mirroring Layer 3 or Layer 2 traffic, the ACL is configured using the ipv4 access-list or the ipv6 access-list command with the capture option. The permit and deny commands determine the behavior of the regular traffic.

Configure an IPv4 ACL for Traffic Mirroring

Use the following steps to configure ACLs for traffic mirroring.

/* Create an IPv4 ACL (TM-ACL) for traffic mirroring */ 
Router(config)# ipv4 access-list TM-ACL 
Router(config-ipv4-acl)# 10 permit udp 10.1.1.0 0.0.0.255 eq 10 any capture
Router(config-ipv4-acl)# 20 permit udp 10.1.1.0 0.0.0.255 eq 20 any 
Router(config-ipv4-acl)# exit
Router(config)# commit 

/* Validate the configuration */
Router(config)# show run
Thu May 17 11:17:49.968 IST
Building configuration...
!! IOS XR Configuration 0.0.0
!! Last configuration change at Thu May 17 11:17:47 2018 by user
…
ipv4 access-list TM-ACL
 10 permit udp 10.1.1.0 0.0.0.255 eq 10 any capture
 20 permit udp 10.1.1.0 0.0.0.255 eq 20 any
!
…

You have successfully configured an IPv4 ACL for traffic mirroring.

Configuring UDF-Based Security ACL for Traffic Mirroring

Before you begin

This section describes the configuration steps for UDF-based security ACLs for traffic mirroring.

Procedure

Step 1

configure

Example:


RP/0/RP0/CPU0:router# configure

Enters global configuration mode.

Step 2

udf udf-name header {inner | outer} {l2 | l3 | l4} offset offset-in-bytes length length-in-bytes

Example:


RP/0/RP0/CPU0:router(config)# udf udf3 header outer l4 offset 0 length 1
(config-mon)#

Example:


RP/0/RP0/CPU0:router(config)# udf udf3 header inner l4 offset 10 length 2 
(config-mon)#

Example:


RP/0/RP0/CPU0:router(config)# udf udf3 header outer l4 offset 50 length 1
(config-mon)#

Configures individual UDF definitions. You can specify the name of the UDF, the networking header from which offset, and the length of data to be extracted.

The inner or outer keywords indicate the start of the offset from the unencapsulated Layer 3 or Layer 4 headers, or if there is an encapsulated packet, they indicate the start of offset from the inner L3/L4.

Note

 

The maximum offset allowed, from the start of any header, is 63 bytes

The length keyword specifies, in bytes, the length from the offset. The range is from 1 to 4.

Step 3

ipv4 access-list acl-name

Example:


RP/0/RP0/CPU0:router(config))# ipv4 access-list acl1

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

Step 4

permit regular-ace-match-criteria udf udf-name1 value1 ... udf-name8 value8

Example:


RP/0/RP0/CPU0:router(config-ipv4-acl)# 10 permit ipv4 any any udf udf1 0x1234 0xffff udf3 0x56 0xff capture
RP/0/RP0/CPU0:router(config-ipv4-acl)# 30 permit ipv4 any any dscp af11 udf udf5 0x22 0x22 capture

Configures ACL with UDF match.

Step 5

exit

Example:


RP/0/RP0/CPU0:router(config-ipv4-acl)# exit

Exits IP ACL configuration mode and returns to global configuration mode.

Step 6

interfacetype number

Example:


RP/0/RP0/CPU0:router(config)# interface HundredGigE 0/0/1/0

Configures interface and enters interface configuration mode.

Step 7

ipv4 access-group acl-name ingress

Example:


RP/0/RP0/CPU0:router(config-if)# ipv4 access-group acl1 ingress

Applies access list to an interface.

Step 8

commit

Example:


RP/0/RP0/CPU0:router(config-if)# commit

Applies access list to an interface.

Verifying UDF-based Security ACL

Use the show monitor-session status detail command to verify the configuration of UDF on security ACL. 

RP/0/RP0/CPU0:leaf1# show monitor-session 1 status detail 

Fri May 12 19:40:39.429 UTC
Monitor-session 1
  Destination interface tunnel-ip3
  Source Interfaces
  -----------------
  TenGigE0/0/0/15
    Direction:  Rx-only
    Port level: True
    ACL match:  Enabled
    Portion:    Full packet
    Interval:   Mirror all packets
    Status:     Not operational (destination not active)

DSCP Bitmask to Filter Ingress SPAN Traffic

Table 3. Feature History Table

Feature Name

Release Information

Feature Description

DSCP Bitmask to Filter Ingress SPAN Traffic

 Release 7.5.4

You can now mirror multiple traffic flows for matched Differentiated Service Code Point (DSCP) value of IP header on the SPAN. The matched DSCP value is based on the DSCP value and the bitmask configured in Access Control List (ACL) rule.

Earlier, you could monitor single traffic flow by setting the RFC 4594 defined DSCP values in the IP header.

This feature introduces the following changes:

Starting Release 7.5.4, You can configure an ACL rule with DSCP bitmask on the SPAN to mirror specific traffic flows.

Without ACL rule, SPAN mirrors all the traffic on the incoming port. When ACL is configured with DSCP and DSCP mask on the SPAN, SPAN mirrors the traffic whose DSCP value lies within the combination of DSCP value and the specified mask.

A DSCP value is mapped to a single traffic class as per the defined value in RFC2474. Masking the DSCP value in ACL rule allows to mirror multiple traffic flows. DSCP value and mask operate similar to IPv4 address and mask.


Note

ACL must be defined before attaching the ACL name to SPAN source interface.

Configure DSCP Bitmask to Filter Ingress SPAN Traffic

Configuration Example for IPv4

This example shows how you can configure DSCP bitmask on ingress SPAN for IPv4 traffic.

Running Configuration
Router(config)# show running-config ipv4 access-list
ipv4 access-list acl1
 10 permit ipv4 host 192.0.2.1 any dscp af22 bitmask 0x3f
!

interface HundredGigE0/0/0/6
 ipv4 address 192.0.2.51 255.255.255.0
 monitor-session TEST ethernet direction rx-only port-level  acl ipv4 acl1
!
!
Configuration Example for IPv6

This example shows how you can configure DSCP bitmask on ingress SPAN for IPv6 traffic.

/*configure the ACL*/
Router# config
Router(config)# ipv6 access-list acl1 
Router(config-ipv6-acl)# 10 permit ipv6 host 2001:DB8::2/32 any dscp 33 bitmask 0x3f
Router(config-ipv6-acl)# commit
Router(config-ipv6-acl)# exit

/* Perform the following configurations to attach the created ACL to an interface*/
Router(config)# interface HundredGigE 0/0/10/3
Router(config-if)# ipv6 address 2001:DB8::1/32

/* Monitor the ingress ACL applied and DSCP masked IPv4 traffic on ERPSAN*/
Router(config-if)# monitor-session TEST ethernet direction rx-only port-level acl ipv6 acl1
Router(config-if)# commit
Running Configuration
Router(config)# show running-config ipv6 access-list
ipv6 access-list acl1
 10 permit ipv6 acl1 host 2001:DB8::2/32 any dscp 33 bitmask 0x3f
!
interface HundredGigE0/0/10/3
 ipv6 address 2001:db8::1/32
 monitor-session TEST ethernet direction rx-only port-level acl ipv6 acl1
!
!

Attaching the Configurable Source Interface

Procedure

Step 1

configure

Example:


RP/0/RP0/CPU0:router# configure

Enters global configuration mode.

Step 2

interface type number

Example:


RP/0/RP0/CPU0:router(config)# interface HundredGigE 0/0/1/0

Enters interface configuration mode for the specified source interface. The interface number is entered in rack /slot /module /port notation. For more information about the syntax for the router, use the question mark (?) online help function.

Step 3

ipv4 access-group acl-name {ingress | egress}

Example:


RP/0/RP0/CPU0:router(config-if)# ipv4 access-group acl1 ingress

Controls access to an interface.

Step 4

monitor-session session-name ethernet direction rx-onlyport-level acl

Example:


RP/0/RP0/CPU0:router(config-if)# monitor-session mon1 ethernet direction rx-only port-level acl
RP/0/RP0/CPU0:router(config-if-mon)#

Attaches a monitor session to the source interface and enters monitor session configuration mode.

Note

 

rx-only specifies that only ingress traffic is replicated.

Step 5

acl

Example:


RP/0/RP0/CPU0:router(config-if-mon)# acl

Specifies that the traffic mirrored is according to the defined ACL.

Note

 

If an ACL is configured by name, then this step overrides any ACL that may be configured on the interface.

Step 6

exit

Example:


RP/0/RP0/CPU0:router(config-if-mon)# exit
RP/0/RP0/CPU0:router(config-if)#

Exits monitor session configuration mode and returns to interface configuration mode.

Step 7

end or commit

Example:


RP/0/RP0/CPU0:router(config-if)# end

or 


RP/0/RP0/CPU0:router(config-if)# commit

Saves configuration changes.

  • When you issue the end command, the system prompts you to commit changes: 

    
Uncommitted changes found, commit them before exiting (yes/no/cancel)?
[cancel]:

    - Entering yes saves configuration changes to the running configuration file, exits the configuration session, and returns the router to EXEC mode.

    - Entering no exits the configuration session and returns the router to EXEC mode without committing the configuration changes.

    - Entering cancel leaves the router in the current configuration session without exiting or committing the configuration changes.

  • Use the commit command to save the configuration changes to the running configuration file and remain within the configuration session.

Step 8

show monitor-session [session-name] status [detail] [error]

Example:


RP/0/RP0/CPU0:router# show monitor-session status

Displays information about the monitor session.

ERSPAN

Encapsulated Remote Switched Port Analyzer (ERSPAN) transports mirrored traffic over an IP 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.

Encapsulated Remote SPAN (ERSPAN) enables generic routing encapsulation (GRE) for all captured traffic and allows it to be extended across Layer 3 domains.

ERSPAN involves mirroring traffic through a GRE tunnel to a remote site. For more information on configuring the GRE tunnel that is used as the destination for the monitor sessions, see the chapter Configuring GRE Tunnels.


Note

A copy of every packet includes the Layer 2 header if the ethernet keyword is configured. As this renders the mirrored packets unroutable, the end point of the GRE tunnel must be the network analyzer.

Introduction to ERSPAN Egress Rate Limit

With ERSPAN egress rate limit feature, you can monitor traffic flow through any IP network. This includes third-party switches and routers.

ERSAPN operates in the following modes:

  • ERSPAN Source Session – box where the traffic originates (is SPANned).

  • ERSPAN Termination Session or Destination Session – box where the traffic is analyzed.

This feature provides rate limiting of the mirroring traffic or the egress traffic. With rate limiting, you can limit the amount of egress traffic to a specific rate, which prevents the network and remote ERSPAN destination traffic overloading. Be informed, if the egress rate-limit exceeds then the system may cap or drop the monitored traffic.

You can configure the QoS parameters on the traffic monitor session.

  • Traffic Class (0 through 7)

    • Traffic class 0 has the lowest priority and 7 the highest.

    • The default traffic class is the same as that of the original traffic class.

  • The Discard Class (0 through 2):

    • The default is 0.

    • The discard class configuration is used in WRED.

Benefits

With ERSPAN Egress rate limit feature, you can limit the egress traffic or the mirrored and use the mirrored traffic for data analysis.

Topology

Figure 2. Topology for ERSPAN Egress Rate Limit

The encapsulated packet for ERSPAN is in ARPA/IP format with GRE encapsulation. The system sends the GRE tunneled packet to the destination box identified by an IP address. At the destination box, SPAN-ASIC decodes this packet and sends out the packets through a port. ERSPAN egress rate limit feature is applied on the router egress interface to rate limit the monitored traffic.

The intermediate switches carrying ERSPAN traffic from source session to termination session can belong to any L3 network.

Configure ERSPAN Egress Rate Limit

Use the following steps to configure ERSPAN egress rate limit:

monitor-session ERSPAN ethernet
destination interface tunnel-ip1
!
RP/0/RP0/CPU0:pyke-008#sh run int tunnel-ip 1
interface tunnel-ip1
ipv4 address 4.4.4.1 255.255.255.0
tunnel mode gre ipv4
tunnel source 20.1.1.1
tunnel destination 20.1.1.2
!

RP/0/RP0/CPU0:pyke-008#sh run int hundredGigE 0/0/0/16

interface HundredGigE0/0/0/16
ipv4 address 215.1.1.1 255.255.255.0
ipv6 address 3001::2/64
monitor-session ERSPAN ethernet direction rx-only port-level
  acl
!
ipv4 access-group ACL6 ingress
Running Configuration
!! Policy-map to be used with the ERSPAN Destination (egress interface)
!! Traffic class is set to 5. For packets in this class, apply shaping
!! as well as WRED.
class-map match-any TC5
 match traffic-class 5 
 end-class-map
! 
policy-map shape-foo
 class TC5
  random-detect discard-class 0 10000 bytes 40000 bytes 
  random-detect discard-class 1 40000 bytes 80000 bytes 
  random-detect discard-class 2 80000 bytes 200000 bytes 
  shape average percent 15 
 !  
 class class-default
 ! 
 end-policy-map
! 
!!GRE Tunnel Interface
interface Loopback49
 ipv4 address 49.49.49.49 255.255.255.255
!
interface tunnel-ip100
 ipv4 address 130.100.1.1 255.255.255.0
 tunnel mode gre ipv4
 tunnel source 49.49.49.49
 tunnel destination 10.8.1.2
!
!!ERSPAN Monitor Session with GRE tunnel as the Destination Interface, and with QoS configuration
monitor-session FOO ethernet
 destination interface tunnel-ip100
 traffic-class 5
 discard-class 1
!
!!ERSPAN Source Interface
interface TenGigE0/6/0/4/0
 description connected to TGEN 9/5
 ipv4 address 10.4.90.1 255.255.255.0
 monitor-session FOO ethernet port-level
 !
!
!!ERSPAN Destination ip-tunnel00’s underlying interface, with egress policy-map shape-foo attached
interface TenGigE0/6/0/9/0
 service-policy output shape-foo
 ipv4 address 10.8.1.1 255.255.255.0
Verification
RP/0/RP0/CPU0:ios#show monitor-session FOO status detail   
Wed May  2 15:14:05.762 UTC
Monitor-session FOO
  Destination interface tunnel-ip100
  Source Interfaces
  -----------------
  TenGigE0/6/0/4/0
    Direction:  Both
    Port level: True
    ACL match:  Disabled
    Portion:    Full packet
    Interval:   Mirror all packets
    Status:     Operational
RP/0/RP0/CPU0:ios#
show monitor-session <sess-id> status internal

RP/0/RP0/CPU0:ios#show monitor-session FOO status internal 
Wed May  2 15:13:06.063 UTC
Information from SPAN Manager and MA on all nodes:
Monitor-session FOO (ID 0x00000001) (Ethernet)
SPAN Mgr: Destination interface tunnel-ip100 (0x0800001c)
          Last error: Success
          Tunnel data:
            Mode: GREoIPv4
            Source IP: 49.49.49.49
            Dest IP: 10.8.1.2
            VRF: 
            ToS: 0 (copied)
            TTL: 255
            DFbit: Not set
0/6/CPU0: Destination interface tunnel-ip100 (0x0800001c)
          Tunnel data:
            Mode: GREoIPv4
            Source IP: 49.49.49.49
            Dest IP: 10.8.1.2
            VRF: 
            ToS: 0 (copied)
            TTL: 255
            DFbit: Not set

Information from SPAN EA on all nodes:
Monitor-session 0x00000001 (Ethernet)
0/6/CPU0: Name 'FOO', destination interface tunnel-ip100 (0x0800001c)
Platform, 0/6/CPU0:

  Dest Port: 0xe7d

  ERSPAN Encap:
    Tunnel ID: 0x4001380b
    ERSPAN Tunnel ID: 0x4001380c
    IP-NH Grp key: 0x3140000cc5
    IP-NH hdl: 0x308a5fa5e0
    IP-NH IFH: 0x30002a0
    IP-NH IPAddr: 10.4.91.2

  NPU   MirrorRx     MirrorTx    
  00    0x00000003   0x00000004
  01    0x00000003   0x00000004
  02    0x00000003   0x00000004
  03    0x00000003   0x00000004
  04    0x00000003   0x00000004
  05    0x00000003   0x00000004
RP/0/RP0/CPU0:ios#

ERSPAN Traffic to a Destination Tunnel in a Default VRF

Table 4. Feature History Table

Feature Name

Release Information

Description

ERSPAN Traffic to a Destination Tunnel in a Default VRF

Release 6.1.3

Encapsulated Remote Switched Port Analyzer (ERSPAN) now transports mirrored traffic through GRE tunnels that belongs to the default VRF thus ensuring a network design with a single Layer 3 device.

This feature enables the tunnels to be grouped under the default VRF domain towards which you can segregate the traffic.

Running Configuration

The following example shows a tunnel interface configured with endpoints in a default VRF (vrf: green ): 

Router#show run int tunnel-ip 2
Thu Feb  3 06:18:28.075 UTC
interface tunnel-ip2
 ipv4 address 102.1.1.100 255.255.255.0
 tunnel tos 32
 tunnel mode gre ipv4
 tunnel source 120.1.1.100
 tunnel vrf green
 tunnel destination 120.1.1.1
Router#show monitor-session status
Thu Feb  3 06:18:11.061 UTC
Monitor-session ERSPAN-2
Destination interface tunnel-ip2
===============================================================
Source Interface      Dir   Status
--------------------- ----  ----------------------------------------------------
Te0/0/0/5 (port)      Rx    Operational

Verification

The following CLI output shows how to verify the default VRF configuration:

Router#show monitor-session ERSPAN-2 status internal
Thu Feb  3 06:19:50.014 UTC

Information from SPAN Manager and MA on all nodes:
Monitor-session ERSPAN-2 (ID 0x00000003) (Ethernet)
SPAN Mgr: Destination interface tunnel-ip2 (0x20008024)
          Last error: Success
          Tunnel data:
            Mode: GREoIPv4
            Source IP: 120.1.1.100
            Dest IP: 120.1.1.1
            VRF: green
            VRF TBL ID: 0
            ToS: 32
            TTL: 255
            DFbit: Not set

ERSPAN Traffic to a Destination Tunnel in a Non-Default VRF

Table 5. Feature History Table

Feature Name

Release Information

Description

ERSPAN Traffic to a Destination Tunnel in a Non-Default VRF

Release 7.5.3

The tunnels are grouped under the VRFs and you can segregate the traffic towards a specific VRF domain.

Encapsulated Remote Switched Port Analyzer (ERSPAN) now transports mirrored traffic through GRE tunnels with multiple VRFs, helping you design your network with multiple Layer 3 partitions.

In earlier releases, ERSPAN transported mirrored traffic through GRE tunnels that belonged to only default VRF.

Here, the tunnel interface, where the traffic mirroring is destined, is now in a VRF.

The traffic coming out of the interfaces of a router do not have any grouping. By configuring a specific VRF, you can now identify the incoming traffic group.

Configuration

Use the following command to configure a specific VRF:

RP/0/RP0/CPU0:router# configure 
RP/0/RP0/CPU0:router(config)# interface tunnel-ip 2
RP/0/RP0/CPU0:router(config)# tunnel vrf red

For more information on enabling the tunnel mode in GRE, see Configuring GRE Tunnels.

Configuration example

The following example shows a tunnel interface configured with endpoints in a non-default VRF (vrf: red ): 

Router#show run int tunnel-ip 2
Thu Feb  3 06:18:28.075 UTC
interface tunnel-ip2
 ipv4 address 102.1.1.100 255.255.255.0
 tunnel tos 32
 tunnel mode gre ipv4
 tunnel source 120.1.1.100
 tunnel vrf red
 tunnel destination 120.1.1.1
Router#show monitor-session status
Thu Feb  3 06:18:11.061 UTC
Monitor-session ERSPAN-2
Destination interface tunnel-ip2
===============================================================
Source Interface      Dir   Status
--------------------- ----  ----------------------------------------------------
Te0/0/0/5 (port)      Rx    Operational

Verification

The following CLI output shows how to verify, if the configured tunnel VRF is programmed in the session:

Router#show monitor-session ERSPAN-2 status internal
Thu Feb  3 06:19:50.014 UTC

Information from SPAN Manager and MA on all nodes:
Monitor-session ERSPAN-2 (ID 0x00000003) (Ethernet)
SPAN Mgr: Destination interface tunnel-ip2 (0x20008024)
          Last error: Success
          Tunnel data:
            Mode: GREoIPv4
            Source IP: 120.1.1.100
            Dest IP: 120.1.1.1
            VRF: red
            VRF TBL ID: 0
            ToS: 32
            TTL: 255
            DFbit: Not set

DSCP Marking on Egress GRE Tunnel in ERSPAN

Table 6. Feature History Table

Feature Name

Release Information

Feature Description

DSCP Marking on Egress GRE Tunnel in ERSPAN

Release 7.5.4

You can now set or modify Differentiated Service Code Point (DSCP) value on the ERSPAN GRE tunnel header. This feature allows you to control the QoS for your network's ERSPAN GRE tunnel traffic and eases the effort to control your customers' bandwidth across next-hop routers.

Starting Cisco IOS XR Release 7.5.4, you can set or modify DSCP marking on ERSPAN GRE tunnels. ERSPAN uses GRE encapsulation to route SPAN capture traffic.

SPAN over Pseudowire

Pseudo-wire traffic mirroring (known as PW-SPAN) is an extra functionality on the existing SPAN solutions. The existing SPAN solutions are monitored on a destination interface or through a GRE tunnel or RSPAN. In PW-SPAN, the traffic mirroring destination port is configured to be a pseudo-wire rather than a physical port. Here, the designated traffic on the source port is mirrored over the pseudo-wire to a central location. This allows the centralization of expensive network traffic analysis tools.

Because the pseudo-wire carries only mirrored traffic, this traffic is unidirectional. Incoming traffic from the remote provider edge is not allowed. Typically, a monitor session should be created with a destination pseudo-wire. This monitor session is one of the L2VPN xconnect segments. The other segment of the L2VPN VPWS is a pseudowire.

Configure SPAN over Pseudowire

Use the following steps to configure SPAN over Pseudowire:

Configure SPAN monitor session 

RP/0/RP0/CPU0:router#config
RP/0/RP0/CPU0:router(config)#monitor-session M1
RP/0/RP0/CPU0:router(config-mon)#destination pseudowire 
RP/0/RP0/CPU0:router(config-mon)#commit

Configure SPAN source 

RP/0/RP0/CPU0:router#config
Fri Sep  6 03:49:59.312 UTC
RP/0/RP0/CPU0:router(config)#interface Bundle-Ether100
RP/0/RP0/CPU0:router(config-if)#monitor-session M1 ethernet port-level
RP/0/RP0/CPU0:router(config-if-mon)#commit

Configure l2vpn xconnect 

RP/0/RP0/CPU0:router(config)#l2vpn
RP/0/RP0/CPU0:router(config-l2vpn)#pw-class span
RP/0/RP0/CPU0:router(config-l2vpn-pwc)#encapsulation mpls
RP/0/RP0/CPU0:router(config-l2vpn-pwc-mpls)#transport-mode ethernet
RP/0/RP0/CPU0:router(config-l2vpn)#xconnect group 1
RP/0/RP0/CPU0:router(config-l2vpn-xc)#p2p 2
RP/0/RP0/CPU0:router(config-l2vpn-xc-p2p)#monitor-session M1              
RP/0/RP0/CPU0:router(config-l2vpn-xc-p2p)#neighbor ipv4 10.10.10.1 pw-id 2
RP/0/RP0/CPU0:router(config-l2vpn-xc-p2p)#pw-class span
RP/0/RP0/CPU0:router(config-l2vpn-xc-p2p)#commit

Verify SPAN over Pseudowire

The following examples show how to verify SPAN over Pseudowire configuration.

To check monitor session status:

RP/0/RP0/CPU0:router#show run monitor-session M1           
monitor-session M1 ethernet
 destination pseudowire

RP/0/RP0/CPU0:router#show monitor-session M1 status        
Monitor-session M1
Destination pseudowire 
Source Interface      Dir   Status
BE100 (port)          Both  Operational
BE400 (port)          Both  Operational

RP/0/RP0/CPU0:router#show monitor-session M1 status detail 
Monitor-session M1
  Destination pseudowire 
  Source Interfaces
  -----------------
  Bundle-Ether100
    Direction:  Both
    Port level: True
    ACL match:  Disabled
    Portion:    Full packet
    Interval:   Mirror all packets
    Status:     Operational
  Bundle-Ether400
    Direction:  Both
    Port level: True
    ACL match:  Disabled
    Portion:    Full packet
    Interval:   Mirror all packets
    Status:     Operational

To check underlying l2vpn xconnect:

RP/0/RP0/CPU0:router#show run l2vpn 
l2vpn
 pw-class span
  encapsulation mpls
   transport-mode ethernet
  !
  !
  p2p 2
   monitor-session M1
   neighbor ipv4 10.10.10.1 pw-id 2
   pw-class span
   !
  !
  p2p 10
   monitor-session M2
   neighbor ipv4 10.10.10.1 pw-id 10
    pw-class span
   !
  !
 !
!
RP/0/RP0/CPU0:router#show l2vpn xconnect 
Fri Sep  6 03:41:15.691 UTC
Legend: ST = State, UP = Up, DN = Down, AD = Admin Down, UR = Unresolved,
        SB = Standby, SR = Standby Ready, (PP) = Partially Programmed

XConnect                   Segment 1                       Segment 2                
Group      Name       ST   Description            ST       Description            ST    
------------------------   -----------------------------   -----------------------------
1          2          UP   M1                     UP       10.10.10.1         2      UP    
----------------------------------------------------------------------------------------
1          10         UP   M2                     UP       10.10.10.1         10     UP    
----------------------------------------------------------------------------------------

SPAN-to-File

SPAN-to-File is an extension of the pre-existing SPAN feature that allows network packets to be mirrored to a file instead of an interface. This simplifies the analysis of the packets at a later stage. The file format is PCAP, which helps that data to be used by tools, such as tcpdump or Wireshark.


Warning
Be cautious when you apply this feature to files located on interfaces with high traffic.

When a file is configured as a destination for a SPAN session, a buffer is created on each node to which the network packets are logged. The buffer is for all packets on the node regardless of which interface they are from, that is, multiple interfaces may be providing packets for the same buffer. The buffers are deleted when the session configuration is removed. The file is written by each node to a location on the active RP which contains the node ID of the node on which the buffer was located.

If multiple interfaces are attached to a session, then interfaces on the same node are expected to have their packets sent to the same file. Bundle interfaces can be attached to a session with a file destination, which is similar to attaching individual interfaces.

SPAN-to-File Enhancements

Table 7. Feature History Table

Feature Name

Release Information

Feature Description

Configure SPAN-to-File

Use the following command to configure SPAN to File:

monitor-session <name> [ethernet|ipv4|ipv6|mpls-ipv4|mpls-ipv6]
    destination file [size <kbytes>] [buffer-type linear]

The monitor-session <name> [ethernet|ipv4|ipv6|mpls-ipv4|mpls-ipv6] part of the command creates a monitor-session with the specified name and class and is a pre-existing chain point from the current SPAN feature. The destination file [size <kbytes>] [buffer-type linear] part of the command adds a new “file” option to the existing “destination”.

destination file has the following configuration options:

  • Buffer size.

  • Two types of buffer:

    • Circular: Once the buffer is full, the start is overwritten.

    • Linear: Once the buffer is full, no further packets are logged.


Note

The default buffer-type is circular. Only linear buffer is explicitly configurable. Changing any of the parameters (buffer size or type) recreates the session, and clears any buffers of packets.

All configuration options which are applied to an attachment currently supported for other SPAN types should also be supported by SPAN to file. This may include:

  • ACLs

  • Write only first X bytes of packet.

  • Mirror interval from 512 to 16k.


Note

These options are implemented by the platform when punting the packet.

Once a session has been created, then interfaces may be attached to it using the following configuration:

interface GigabitEthernet 0/0/0/0
    monitor-session <name> [ethernet|ipv4|ipv6|mpls-ipv4|mpls-ipv6]

The attachment configuration is unchanged by SPAN-to-File feature.


Note

Once the SPAN-to-File session is attached to source interface, mirroring starts and packets are punted from NPU to CPU and dropped at CPU until the packet-collection start action command is executed.

Configuration Examples

To configure a mon1 monitor session, use these commands: 

monitor-session mon1 ethernet
          destination file size 230000 
         !

In the above example, omitting the buffer-type option results in default circular buffer.

To configure a mon2 monitor session with the linear buffer type, use these commands: 

monitor-session mon2 ethernet
          destination file size 1000 buffer-type linear
         !

To attach monitor session to a physical or bundle interface, use these commands:

interface Bundle-Ether1
monitor-session ms7 ethernet
!

Running Configuration

!! IOS XR Configuration 7.1.1.124I
!! Last configuration change at Tue Nov 26 19:29:05 2019 by root
!
hostname OC
logging console informational
!
monitor-session mon2 ethernet
 destination file size 1000 buffer-type linear

!
interface Bundle-Ether1
monitor-session ms7 ethernet
end

Verification

To verify packet collection status:

RP/0/RP0/CPU0:router#show monitor-session status
Monitor-session mon1
Destination File - Packet collecting
=============================================
Source Interface      Dir   Status
--------------------- ----  ------------------
Hu0/9/0/2             Rx    Operational
 
Monitor-session mon2
Destination File - Packet collecting
=========================================
Source Interface      Dir   Status
--------------------- ----  --------------
BE2.1                 Rx    Operational

If packet collection is not active, the following line is displayed:


Monitor-session mon2
Destination File - Not collecting

Here, Status-Operational and Destination File - Not collecting indicates that mirroring has started and packets are being punted from NPU to CPU but getting dropped at CPU until the packet-collection start action command is executed.

Action Commands for SPAN-to-File

Action commands are added to start and stop network packet collection. The commands may only be run on sessions where the destination is a file. The action command auto-completes names of globally configured SPAN to File sessions. See the table below for more information on action commands.

Table 8. Action Commands for SPAN-to-File

Action

Command

Description

Start

monitor-session <name> packet-collection start

Issue this command to start writing packets for the specified session to the configured buffer.

Once the SPAN is configured and operational, the packets are punted to CPU and dropped by CPU until the monitor-session <name> packet-collection start command is executed.

Stop

monitor-session <name> packet-collection stop [ discard-data | write directory <dir> filename <filename> ]

Issue this command to stop writing packets to the configured buffer.

  • discard-data: Specify this option to clear the buffer.

  • discard-data: Specify this option to write the buffer to the disk before it is cleared.

The buffer is written in .pcap format in this location: /<directory>/<node_id>/<filename>.pcap.

The .pcap extension that the user adds to the filename is removed automatically to avoid a duplicate file extension.

File Mirroring

Prior to Cisco IOS XR Software Release , the router did not support file mirroring from active RP to standby RP. Administrators had to manually perform the task or use EEM scripts to sync files across active RP and standby RP. Starting with Cisco IOS XR Software Release , the file mirroring feature enables the router to copy files or directories automatically from /harddisk:/mirror location in active RP to /harddisk:/mirror location in standby RP or RSP without user intervention or EEM scripts.

Two new CLIs have been introduced for the file mirroring feature:

  • mirror enable

    The /harddisk:/mirror directory is created by default, but file mirroring functionality is only enabled by executing the mirror enable command from configuration terminal. Status of the mirrored files can be viewed with show mirror status command.

  • mirror enable checksum

    The mirror enable checksum command enables MD5 checksum across active to standby RP to check integrity of the files. This command is optional.

Configure File Mirroring

File mirroring has to be enabled explicitly on the router. It is not enabled by default.

RP/0/RSP0/CPU0:router#show run mirror

Thu Jun 25 10:12:17.303 UTC
mirror enable
mirror checksum

Following is an example of copying running configuration to harddisk:/mirror location: 

RP/0/RSP0/CPU0:router#copy running-config harddisk:/mirror/run_config
Wed Jul  8 10:25:51.064 PDT
Destination file name (control-c to abort): [/mirror/run_config]?
Building configuration..
32691 lines built in 2 seconds (16345)lines/sec
[OK]

Verification

To verify the syncing of file copied to mirror directory, use the show mirror command. 

RP/0/RSP0/CPU0:router#show mirror 
Wed Jul  8 10:31:21.644 PDT
% Mirror rsync is using checksum, this show command may take several minutes if you have many files. Use Ctrl+C to abort
MIRROR DIR: /harddisk:/mirror/
% Last sync of this dir ended at Wed Jul  8 10:31:11 2020
Location   |Mirrored |MD5 Checksum                     |Modification Time
--------------------------------------------------------------------------
run_config |yes      |76fc1b906bec4fe08ecda0c93f6c7815 |Wed Jul  8 10:25:56 2020

If checksum is disabled, show mirror command displays the following output: 

RP/0/RSP0/CPU0:router#show mirror
Wed Jul 8 10:39:09.646 PDT
MIRROR DIR: /harddisk:/mirror/
% Last sync of this dir ended at Wed Jul  8 10:31:11 2020
Location   |Mirrored |Modification Time 
-----------------------------------------
run_config |yes         |Wed Jul  8 10:25:56 2020

If there is a mismatch during the syncing process, use show mirror mismatch command to verify. 

RP/0/RP0/CPU0:router# show mirror mismatch
Wed Jul  8 10:31:21.644 PDT
 MIRROR DIR: /harddisk:/mirror/
 % Last sync of this dir ended at Wed Jul  8 10:31:11 2020 
 Location  |Mismatch Reason     |Action Needed 
------------------------------------------------
 test.txt  |newly created item. |send to standby

Forward-Drop Packets Mirroring

In a network, packets are forwarded from one device to another until they reach their destination. However, in some cases, routers may drop packets during this forwarding process. These packets are known as forward-drop packets.

Packets can be dropped for several reasons such as congestion on the network, errors in the packet header or payload, blocking by firewall or access control lists (ACL), and so on. These forward-drop packets are typically discarded before they can reach their intended destination, and may have to be re-transmitted by the source device. This feature supports mirroring of these forward-drop packets at the ingress (Rx direction) to another destination. When a global forward-drop session is configured for the router, the forward-drop packets at the ingress are mirrored or copied to the configured destination. You can configure the mirror destination as a file (for SPAN-to-file sessions) or an IPv4 GRE tunnel ID (for ERSPAN).

Mirror Forward-Drop Packets

Table 9. Feature History Table

Feature Name

Release Information

Description

Mirror Forward-Drop Packets

Release 7.5.4

Mirroring forward-drop packets feature copies or mirrors the packets that are dropped during the forwarding process at the router ingress to a configured destination. These mirrored packets can be captured and analyzed using network monitoring tools. The analysis of dropped packets helps you understand the types of traffic that are blocked, analyze potential security threats, troubleshoot, and optimize network performance.

This feature introduces the following changes:

Mirroring forward-drop packets to a suitable destination for analysis can help in the following:

  • Network visibility: By mirroring and analyzing forward-drop packets, network administrators gain better visibility into the types of traffic that are blocked by the firewalls and access control lists (ACL).

  • Threat detection: As the original dropped packet is forwarded without any change, it helps in identifying the source of potential security threats.

  • Troubleshooting: Analyzing forward-drop packets helps in troubleshooting network issues that may be causing the packet drop. This helps in taking proactive measures to avoid escalation of the issue.

Configure Forward-Drop Mirroring

Perform the following tasks on the router to configure a global session for mirroring forward-drop packets:

  1. Configure the tunnel mode.

  2. Configure the tunnel source.

  3. Configure the tunnel destination.

  4. Configure a traffic mirroring session.

  5. Associate a destination interface with the traffic mirroring session.

  6. Run forward-drop rx command to start mirroring forward-drop packets.

This example shows how to configure a global traffic mirroring session for forward-drop packets.

Router(config)# interface tunnel-ip 2
Router(config-if)# tunnel mode gre ipv4
Router(config-if)# tunnel source 20.20.20.20
Router(config-if)# tunnel destination 192.1.1.3 
Router(config-if)!
Router(config)# monitor-session mon2 ethernet 
Router(config)#destination interface tunnel-ip2 
Router(config)#forward-drop rx
Router(config)#!
Running Configuration

This section shows forward-drop running configuration.

RP/0/RSP0/CPU0:router#sh running-config
interface tunnel-ip 2
tunnel mode gre ipv4
tunnel source 20.20.20.20
tunnel destination 192.1.1.3 
!
monitor-session mon2 ethernet 
destination interface tunnel-ip2 
forward-drop rx
!
Verification

Verify the forward-drop packets are mirrored using the show monitor-session command. 

Router#show monitor-session mon2 status detail
Mon Aug 15 19:14:31.975 UTC
Monitor-session mon2
   Destination interface tunnel-ip2
   All forwarding drops:
      Direction: Rx
Source Interfaces
-----------------

Troubleshoot Traffic Mirroring

When you encounter any issue with traffic mirroring, begin troubleshooting by checking the output of the show monitor-session status command. This command displays the recorded state of all sessions and source interfaces: 


# show monitor-session status
Monitor-session 5
rx destination interface tunnel-ip5
tx destination is not specified
================================================================================
Source Interface  Dir  Status
--------------------- ---- ----------------------------------------------------
Te0/0/0/23 (port) Rx   Operational

In the preceding example, the line marked as <Session status> can indicate one of these configuration errors:

Session Status

Explanation

Session is not configured globally

The session does not exist in global configuration. Review the show run command output and ensure that a session with a correct name has been configured.

Destination interface <intf> (<down-state>)

The destination interface is not in Up state in the Interface Manager. You can verify the state using the show interfaces command. Check the configuration to determine what might be keeping the interface from coming up (for example, a sub-interface needs to have an appropriate encapsulation configured).

The <Source interface status> can report these messages:

Source Interface Status

Explanation

Operational

Everything appears to be working correctly in traffic mirroring PI. Please follow up with the platform teams in the first instance, if mirroring is not operating as expected.

Not operational (Session is not configured globally)

The session does not exist in global configuration. Check the show run command output to ensure that a session with the right name has been configured.

Not operational (destination not known)

The session exists, but it either does not have a destination interface specified, or the destination interface named for the session does not exist. For example, if the destination is a sub-interface that has not been created.

Not operational (source same as destination)

The session exists, but the destination and source are the same interface, so traffic mirroring does not work.

Not operational (destination not active)

The destination interface or pseudowire is not in the Up state. See the corresponding Session status error messages for suggested resolution.

Not operational (source state <down-state>)

The source interface is not in the Up state. You can verify the state using the show interfaces command. Check the configuration to see what might be keeping the interface from coming up (for example, a sub-interface needs to have an appropriate encapsulation configured).

Error: see detailed output for explanation

Traffic mirroring has encountered an error. Run the show monitor-session status detail command to display more information.

The show monitor-session status detail command displays full details of the configuration parameters and any errors encountered. For example:

RP/0/RP0/CPU0:router show monitor-session status detail 


Monitor-session sess1
 Destination interface is not configured
 Source Interfaces
 -----------------
 TenGigE0/0/0/1
  Direction: Both
  ACL match: Disabled
  Portion:  Full packet
  Status:  Not operational (destination interface not known)
 TenGigE0/0/0/2
  Direction: Both
  ACL match: Disabled
  Portion:  First 100 bytes
  Status: Not operational (destination interface not known). Error: 'Viking SPAN PD' detected the 'warning' condition 'PRM connection 
          creation failure'.
Monitor-session foo
 Destination next-hop TenGigE 0/0/0/0
 Source Interfaces
 -----------------
 TenGigE 0/0/0/1.100:
  Direction: Both
  Status:  Operating
 TenGigE 0/0/0/2.200:
  Direction: Tx
  Status:  Error: <blah>

Monitor session bar
 No destination configured
 Source Interfaces
 -----------------
 TenGigE 0/0/0/3.100:
  Direction: Rx
  Status:  Not operational(no destination)

Here are additional trace and debug commands: 


RP/0/RP0/CPU0:router# show monitor-session trace ?

 platform  Enable platform trace
 process   Filter debug by process(cisco-support)

RP/0/RP0/CPU0:router# show monitor-session trace platform ?

 errors  Display error traces(cisco-support)
 events  Display event traces(cisco-support)

RP/0/RP0/CPU0:router#show monitor-session trace platform events location all ?

usrtdir  Specify directory to collect unsorted traces(cisco-support)
|        Output Modifiers
<cr>

RP/0/RP0/CPU0:router#show monitor-session trace platform errors location all ?

usrtdir  Specify directory to collect unsorted traces(cisco-support)
|        Output Modifiers
<cr>

#

 

RP/0/RP0/CPU0:router# debug monitor-session process all

RP/0/RP0/CPU0:router# debug monitor-session process ea

RP/0/RP0/CPU0:router# debug monitor-session process ma

RP/0/RP0/CPU0:router# show monitor-session process mgr

 detail  Display detailed output
 errors  Display only attachments which have errors
 internal Display internal monitor-session information
 |     Output Modifiers

RP/0/RP0/CPU0:router# show monitor-session status

RP/0/RP0/CPU0:router# show monitor-session status errors

RP/0/RP0/CPU0:router# show monitor-session status internal

RP/0/RP0/CPU0:router# show tech-support span ?

 file       Specify a valid file name (e.g. disk0:tmp.log)
 list-CLIs  list the commands that would be run (don't execute)(cisco-support)
 location   Specify a location(cisco-support)
 rack       Specify a rack(cisco-support)
 time-out   per show command timeout configuration(cisco-support)
 <cr>