Cisco Commands – Understanding ‘Show Interface Switchport’ Output

ciscocisco-commandsswitchvlanvtp

The show interface switchport command shows a specific row Pruning VLANs Enabled. The field description is Lists the VLANs that are pruning-eligible but I cannot understand what that row is meaning.

Best Answer

With VTP, you can mark VLANs as eligible to be pruned for a trunk link. When pruning is enabled in VTP, the eligible VLANs will be pruned if there is nothing downstream of the trunk link using those VLANs.

This Cisco document shows how to configure VTP pruning and how to add VLANs to the pruning eligible list.

switch(config-if)# switchport trunk pruning vlan [add | remove | except | none | all] VLAN-IDs

It is a good practice to prune VLANs from links where they are not needed. This will eliminate broadcast traffic for those VLANs being sent to switches which don't have those VLANs.

Related Solutions

Switch – Cisco CatOS – show port usage output

As you found, the port is plugged into a phone; so until the phone cycles the port will stay up.

Regarding the portfast command; when a switchport comes up, spanning-tree moves through a series of states to bring the port up. Legacy spanning-tree took 15 seconds in the Listening state and another 15 seconds learning. During that time, the port cannot actually transmit traffic. portfast is a shortcut to make the port transition to a forwarding state very quickly, which is what you want as long as no switches are connected to the port.

Vlan – Setting up PIM Sparse mode

My questions are:

Should we setup on our core network switch OSPF with a router ID of 1.1.1.1 and then not set any OSPF settings on any other switch?

OSPF is not necessary for this implementation.

Would PIM Sparse Mode only need to be enabled on the core switches or on all of the switches in the network?

Pim-SM needs to be enabled on each L3 interface on which you want to allow the multicast traffic. For example, if you wish to contain the traffic to Vlans 15 and 14, you would have to do the following on your core:

configure
ip multicast
ip igmp
ip pim sparse
interface vlan 14
ip igmp
ip pim
interface vlan 15
ip igmp
ip pim
exit

If you want the traffic to traverse all Vlans, then you will need the appropriate interface configuration under each Vlan. Your L2 switches will need IGMP snooping turned on (ideally on all interfaces via the global configuration).

configure
ip igmp snooping 
bridge multicast filtering

For a very basic multicast setup like this, these should be the only features that you would need.

Best Answer

Related Solutions

Switch – Cisco CatOS – show port usage output

Vlan – Setting up PIM Sparse mode

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