Network PC World

In this post, we will configure Multiple Spanning Tree (MST) , a protocol designed to optimize spanning tree instances by mapping multiple VLANs to fewer instances. This reduces overhead on network devices, enhances scalability, and speeds up convergence. We'll configure MST on both core/root switches and access switches , ensuring that only the required VLANs are active on each switch. The configuration will focus on assigning VLANs to specific MST instances, defining root priorities, and controlling VLAN availability on trunk links between switches. This setup ensures efficient traffic flow, minimizes network downtime, and improves overall stability. We'll also define MST regions and revision numbers to maintain consistency across the network. By following this guide, you'll optimize spanning tree operations while maintaining flexibility in VLAN creation and deployment across your infrastructure. Configuration for Core-SW1 (Primary Root for Instance 1) ! Define MST re...

 Here's a simple guide on when to use BPDU Guard and BPDU Filter : BPDU Guard : Purpose : To protect the network from unauthorized devices or switches that could participate in the spanning tree process and potentially cause loops. When to Use : On access ports where end devices (like PCs, printers, or servers) are connected. When you want to automatically shut down a port if a BPDU is received, indicating that another switch or device with STP capabilities is connected. Ensures the network remains loop-free by disabling the port when an unexpected BPDU is detected. BPDU Filter : Purpose : To suppress the sending and receiving of BPDUs on a port, effectively preventing STP participation. When to Use : On edge ports (access ports) where you want to prevent STP interactions but don't want to shut the port down upon BPDU reception. In specific scenarios like when you are sure that no switch will be connected, but you don’t want to disrupt the port's operation if a BPDU is...

The format of the original 802.1d bridge ID was redefined from two byte priority + MAC address to System ID extension mainly due to the advent of multiple spanning trees as supported by Per VLAN Spanning Tree Plus (PVST+) and IEEE 802.1s Multiple Spanning Trees (MST). With the old-style bridge ID format, a switch’s bridge ID for each STP instance (possibly one per VLAN) was identical if the switch used a single MAC address when building the bridge ID. Having multiple STP instances with the same bridge ID was confusing, so vendors such as Cisco Systems used a different Ethernet BIA for each VLAN when creating the old-style bridge IDs. This provided a different bridge ID per VLAN, but it consumed a large number of reserved BIAs in each switch.  The System ID Extension allows a network to use multiple instances of STP, even one per VLAN,  but without the need to consume a separate BIA on each switch for each STP instance. The System ID E...

This error is returned by Cisco IOS, when the trunking encapsulation is not set on one side of the switch and the other hand switch is configured properly. One of the case may be, when trunking between the port of a switch on one side and port of Switch-type interface on the router on other side. As you know that Dynamic Trunking Protocol, DTP, is not run by the Router so the Trunking can not be negotiated at this situation. To mitigate the error at this situation do the following steps; networkpcworld(config-if)#switchport mode trunk   Command rejected: An interface whose trunk encapsulation is "Auto" can not be configured to "trunk" mode.   Go to the desired Interface where you are getting this error networkpcworld (config)#int fa0/0/1 Enable trunk ecnapsulation manually  networkpcworld (config-if)#switchport trunk encapsulation dot1q Note:-  After setting encapsulation, most probably the switch interface would be converted to trunk by switchport mo...