A unidirectional link failure is a classic scenario where STP may fail to block a loop. STP relies on BPDUs traveling in both directions. If a fiber strand fails or a transceiver malfunctions, traffic can flow in one direction but not the other, creating a loop that STP cannot detect and block, leading to intermittent traffic loss.

For real-time applications like VoIP, fast roaming protocols (802.11r, FT) are critical. They reduce the authentication handshake time during a roam from hundreds of milliseconds to near-zero, preventing audio dropouts. Checking and enabling these features, along with key caching (802.11k/v), is the primary design solution for seamless roaming.

The preference value (or administrative distance) determines route selection. Lower values are preferred. Dynamic protocols like OSPF have defaults around 10-110. A static route with preference 100 is less preferred than most dynamic routes (e.g., OSPF internal route pref 10) and will only appear in the routing table if those better routes are withdrawn, making it an effective backup path.

On a hybrid port, frames for the Port VLAN ID (PVID) are sent untagged. If the port’s PVID is not set (or is set to an unused VLAN like the default VLAN 1), and the port is only tagged for VLANs 10 and 20, the PC will send untagged frames that the switch associates with the PVID. If this PVID is not the intended data VLAN (e.g., VLAN 10), the PC’s DHCP discovery will be in the wrong broadcast domain. The fix is to set `port hybrid pvid vlan 10` and `port hybrid untagged vlan 10`.

The RD’s sole purpose is to create uniqueness. It is prepended to the customer’s IPv4 route, transforming it into a unique VPNv4 address (e.g., 65000:1:10.1.1.0/24). This allows the service provider’s BGP to hold identical IPv4 prefixes from multiple customers without conflict. The RD itself does not imply topology or policy; that is the role of the Route Target (RT).

While source IP identifies the host, the combination of IP Protocol (e.g., 6 for TCP, 17 for UDP) and particularly the Destination Port is the key to application identification. For example, destination port 443 points to HTTPS/SSL, 80 to HTTP, 5060 to SIP, etc. This L4 information, exported by NetStream, is essential for moving beyond ‘who’ is using bandwidth to understanding ‘what’ they are using it for.

In a switch stack, typically only the master switch runs the routing protocol control plane (RPU). The standby and member switches forward traffic (data plane) based on the master’s FIB. If, after an upgrade, the synchronization of the FIB/LIB from the master to the standby is incomplete or faulty, the standby may not forward OSPF hello packets correctly, causing neighbors to see missed hellos and drop the adjacency, while the master’s adjacencies remain fine.

MACsec provides hop-by-hop encryption at Layer 2. Its operation fundamentally depends on key establishment. This can be done statically using a pre-shared Connectivity Association Key (CAK), or dynamically and more securely using the MACsec Key Agreement (MKA) protocol, which can interface with a central key server (like a KS/CA). It does not require IP (it secures all L2 frames), encrypts all traffic on the secured link, and works on both fiber and copper.

For a link to be eligible to join an Eth-Trunk, its physical and logical configuration must be identical to the Eth-Trunk interface itself. This includes speed, duplex mode, VLAN membership (allowed VLANs, PVID), and other layer 2 settings. A mismatch in any of these parameters on a member port will cause it to be placed in a down or unselected state, preventing it from carrying traffic.

A unidirectional link failure is a classic scenario where STP may fail to block a loop. STP relies on BPDUs traveling in both directions. If a fiber strand fails or a transceiver malfunctions, traffic can flow in one direction but not the other, creating a loop that STP cannot detect and block, leading to intermittent traffic loss.0