Cisco Catalyst SPAN and Remote SPAN Configuration

To analyze network traffic passing through ports or VLANs you can configure SPAN or remote SPAN to mirror the traffic to another port on the switch or on another switch that has been connected to a network analyzer. The network analyzer can be Wireshark or Riverbed Cascade Pilot what capture or analyze the traffic. Cascade Pilot is here quite interesting because you can filter the traffic before and then send it to Wireshark for a deep analysis.

Back to the configuration, SPAN mirrors traffic received or sent (or both) on source ports or source VLANs to a destination port for analysis. The SPAN session does not affect the switching of network traffic on the source. Except for traffic on the destination, ports do not receive or forward traffic there are shown as monitoring interfaces.

 

Configure local SPAN session:

Define the source interface which traffic you want to mirror

monitor session 1 source interface GigabitEthernet 0/41

or VLAN as source

monitor session 1 source vlan 500

Define the destination interface

monitor session 1 destination interface GigabitEthernet 0/10

 

Configure remote SPAN session (1st switch):

At first create an remote SPAN VLAN

vlan 2010
  name RSPAN_VLAN
  remote-span
  exit

Then like the local SPAN session define the source

monitor session 1 source interface gi 0/47

or VLAN

monitor session 1 source vlan 500

At the end of the configuration of the 1st switch you configure the remote SPAN VLAN as destination

monitor session 1 destination remote vlan 2010

 

Configure remote SPAN session (2nd switch):

Like on the other switch you need to create at first an remote SPAN VLAN

vlan 2010
  name RSPAN_VLAN
  remote-span
  exit

Then as source you configure the RSPAN VLAN

monitor session 1 source remote vlan 2010

In the end the destination interface

monitor session 1 destination interface gi 0/18

Important is to verify that the RSPAN VLAN is allowed between these two switches on thier Trunk Interfaces!

 

With the following command you can verify the monitoring session you configured

show monitor session 1

ASA and PPPoE example

Just a short example what you need to configure when use PPPoE on Cisco ASA…

vpdn group myconnection request dialout pppoe
vpdn group myconnection localname [email protected]
vpdn group myconnection ppp authentication pap
vpdn username [email protected] password aeb1puj43

interface Vlan 2
	nameif outside
	security-level 0
	pppoe client vpdn group myconnection
	ip address pppoe setroute
	no shutdown
	exit

Redirect Cisco show commands

Short overview of how to redirect Cisco show commands… quite useful sometimes 😉

show <command> | redirect URL

The syntax to redirect the command output to the file location specified in the URL. The pipe (|) is required. Prefixes can be local file locations, like flash: or disk0:. Alternatively, you can specify network locations using the following:

ftp://username:[email protected]/directory/filename
tftp://location/directory/filename

Rcp: prefix is not supported.

Example: Redirect show tech-support

show tech-support | redirect tftp://10.1.1.100/show-tech_c2960s-01.txt

Bug in Cisco Catalyst 2960S

I found a new bug in the IOS 12.2(55) on our c2960s where we had a high cpu usage and lot of traceback syslog messages.

Here is the info from the Cisco TAC about the problem:

Symptom:
C2960S switch getting the following message:

%SUPERVISOR-4-UNEXPECTED: rfd_idx = 56B hwptr 64D75AC queue 8 
-Traceback= 12ECA7C 12EF254 12EF5DC 1382180 137C680 137C628 13821F0 1383128 137C730 184AA64 184AA3C 1848974

Conditions:
WS-C2960S running IOS earlier than 12.2(58)SE

Workaround:
Temporary workaround is reload, fix is in 12.2(58)SE
Action Plan
1. As a temporary workaround we can reload the switch.
2. For permanent solution please upgrade the switch to 12.2(58)SE.

Cisco FlexLink Configuration Examples

Here you can find some configuration examples for the Cisco Flexlink.

This example shows how to configure an interface with a backup interface and to verify the configuration:

Switch# configure terminal
Switch(conf)# interface fastethernet1/1
Switch(conf-if)# switchport backup interface fastethernet1/2
Switch(conf-if)# end
Switch# show interface switchport backup

Switch Backup Interface Pairs:

Active Interface        Backup Interface        State
------------------------------------------------------------------------
FastEthernet1/1         FastEthernet1/2         Active Up/Backup Standby
FastEthernet1/3         FastEthernet1/4         Active Up/Backup Standby
Port-channel1           GigabitEthernet1/1      Active Up/Backup Standby

This example shows how to configure preemption mode as bandwidth for a  backup interface pair and to verify the configuration:

Switch# configure terminal
Switch(conf)# interface gigabitethernet1/0/1
Switch(conf-if)# switchport backup interface gigabitethernet1/2
Switch(conf-if)# switchport backup interface gigabitethernet1/2 preemption mode forced
Switch(conf-if)# switchport backup interface gigabitethernet1/2 preemption delay 50
Switch(conf-if)# end
Switch# show interface switchport backup detail

Active Interface     Backup Interface     State
------------------------------------------------------------------------
GigabitEthernet1/21     GigabitEthernet1/2     Active Down/Backup Down

Interface Pair : Gi1/21, Gi1/2
Preemption Mode : forced
Preemption Delay : 50 seconds
Bandwidth : 10000 Kbit (Gi1/1), 10000 Kbit (Gi1/2)
Mac Address Move Update Vlan : auto

To configure VLAN load balancing on Flex Links,  follow these steps:
In this example, VLANs 1 to 50, 60, and 100 to 120 are configured on the  switch:

Switch(config)# interface fastethernet 1/6
Switch(config-if)# switchport backup interface fastethernet 1/0/8 prefer vlan 60,100-120

When both interfaces are up, Fast Ethernet port1/0/8 forwards traffic for VLANs 60 and 100 to 120 and Fast Ethernet port 1/0/6 forwards traffic for VLANs 1 to 50

Switch# show interfaces switchport backup

Switch Backup Interface Pairs:

Active Interface     Backup Interface     State
------------------------------------------------------------------------
FastEthernet1/6     FastEthernet1/8     Active Up/Backup Standby

Vlans Preferred on Active Interface: 1-50
Vlans Preferred on Backup Interface: 60, 100-120