Datalink Layer

Etherchannel allows a method of doubling (or more) bandwidth between switches without spanning tree protocol (STP) blocking one of the links. Multiple physical links to be grouped into a single logical link, called an Etherchannel or port channel as defined in the 802.3AD link aggregation specification. The multiple physical links that form the logical link…

The most common method of establishing a trunk port is statically setting it in the configuration using switchport mode trunk. Cisco does provide a method where the port can be negotiated as a trunk automatically with Dynamic Trunking Protocol (DTP) Dynamic trunk ports are established by the switch by sending DTP packets across the link…

VLAN Trunking Protocol (VTP) is a protocol with the aim of reducing the administrative overhead of provisioning VLANs on switches. Switches that participate in the same VTP domain can have a VLAN created once on a VTP server which is propagated across the VTP domain. Three versions of VTP exist with version 1 being the…

Goal: To experiment with MSP (Multiple Spanning Tree) Topology and Setup In this deployment we’ll test with three L2/L3 switches in the following topology On switches 1,2,3: Configure the hostname SW1(config)#hostname SW1 Configure VLANs 2,3,4,5 SW1(config)#vlan 2,3,4,5 Change spanning tree mode to MST SW1(config)#spanning-tree mode mst Map VLANs 2,3,4,5 to instance 1 SW1(config)#spanning-tree mst configuration…

The Multiple Spanning Tree topology is contained with the internal multiple spanning tree area. The region boundary is defined when a port connects to a switch that is in a different Multiple Spanning Tree region or a non-MSTP port (Such as 802.1D or 802.1W) The instances will never interact outside of their region. MST enabled…

Assigning VLANs to the IST Caution should be taken when assigning VLANs to the Internal Spanning Tree instance as it runs across every link to deliver the BPDUs regardless of the VLAN configured on it. This can mean that a VLAN access port may become blocked if assigned to the Internal Spanning Tree VLAN rather…

Similar to other spanning tree protocol configurations, the cost and port priority of Multiple Spanning Tree can be tweaked. The command is different though to tweak the cost for Multiple Spanning Tree: spanning-tree mst X cost Y Substitute X with the instance number of the Multiple Spanning Tree process and Y with the chosen cost.…

Multiple Spanning Tree can be configured on a Cisco Switch with these instructions: In global configuration mode, enter the command spanning-tree mode mst to change the spanning tree mode on the switch to Multiple Spanning Tree. Define the Multiple Spanning Tree Instance priority by following one of the two methods below in global configuration mode…

Multiple Spanning Tree uses a special instance called the Internal Spanning Tree which runs on the first instance with the instance number of 0. A typical Cisco round can support up to 16 MSTs. MSTs 1 to 15 can be assigned to specific VLANs. This special instance runs on all switch port interfaces in the…

The original Spanning Tree Protocol standard only supported one STP instance / process for the entire switched network with all VLANs within the same topology. A disadvantage of having all the VLANs within the same process is it does not allow simple load balancing to occur by filtering the port for one VLAN and allowing…