Cisco IOS: Can I have MPLS-TE tunnels use FRR when using dynamic paths

The client switchport or the server switchport can be monitored. A third switchport can be configured as a mirror port. This means that this mirror port will receive copies of all packets on the corresponding original port, while the original traffic won't be affected.

For example, on the Catalyst 3560:

1. Enter configuration mode:

   conf t
   

2. Define the source and set the session number:

   monitor session 1 source interface fa 0/24
   

   Here, the session number can be from 1 to 66, you could also specify a VLAN or an ethernet channel. Also, interface ranges such as fa 0/25 - 26 are possible, and interface list, such as fa 0/24,fa 0/26, if you would like to monitor several clients at the same time. Also by repeating the command you can add ports, or remove using no. Mixing ports and VLANs is not possible in the same session, another restriction is that you cannot use a destination port as a source port.

3. Define the destination port:

   monitor session 1 destination interface gi 0/1
   

   You can use a normal port, but not a VLAN. Similarly to above, a destination port cannot be a source port: a port used here can either be a source or a destination port, and only of one session. Again, you can specify multiple ports like above.

4. You may want to exit configiration mode and save the config.

5. You may have a look at your defined session - here multiple ports, tried like above:

   #show monitor session 1
   Session 1
   ---------
   Type                   : Local Session
   Source Ports           :
       Both               : Fa0/24,Fa0/25-26
   Destination Ports      : Fa0/48,Gi0/1
       Encapsulation      : Native
             Ingress      : Disabled
   

   You can see an encapsulation here - optionally you can set it to replicate for replicating the source interface encapsulation method, such as by adding encapsulation replicate after the source interface. Furthermore, you can specify a direction (tx, rx, both), filter VLANs and more. The Ingress: Disabled line means that the switch will not accept any frames presented to it by your capture device on a destination port. For such finer details and for further restrictions and default settings have a look at the command reference of the IOS version of your switch.

Once you configured source and destination port, you can capture the traffic using your laptop connected to the destination port, for example with Wireshark.

The number of source sessions can be limited, for example the 3560 supports a maximum of 2.

After the capturing, don't forget to remove this session configuration.

We can use the alias command in global conf mode:

alias <mode> <command-alias> <original-command>

<mode> is one of the many IOS command modes. If you need it in different modes, you have to call it for each one - type alias ? to get a long list of modes.

An example for checking for a dhcp snooped IP, type in global conf mode

alias exec snoop show ip dhcp snooping binding | include

Now you can simply type snoop 172.16.20.12 to check for this IP or snoop 801 for checking all IPs in VLAN 801, for example. Do similarly for show mac-address-table | include and you're faster in searching and troubleshooting.

Further tipps:

• document your aliases for you and for your collegues
• sh aliases shows your aliases plus the predefined ones
• while no alias <mode> <command> can be guessed for removing an alias, no alias <mode> deletes the aliases for a complete mode - so you can clear several at once, default alias <mode> works similarly, as expected
• if you decide to use aliases, deploy them once everywhere you may need them
• tools like Cisco Prime can help in deploying
• don't forget the original commands ;-)