Network designers plan to interconnect two geographically separated data centers using an Ethernet-over-MPLS pseudowire. Within that design, the link between the sites is stable, there are no apparent

Running 802.1d on one site and 802.1w on the other forces RSTP to fall back to slow 802.1d convergence timers network-wide, which is poor design practice and does not address the STP diameter risk.

When two data center STP domains are merged over an EoMPLS pseudowire, the combined spanning tree diameter - the maximum bridge count along any path between two endpoints - may exceed the default IEEE 802.1D limit of 7 hops. Exceeding this limit causes MaxAge and Hello timer violations that lead to indirect loops, spurious topology change notifications, or loss of connectivity to the peer data center, so the designer must verify and reduce the diameter before interconnecting the sites.

UDLD detects physical unidirectional link conditions at the data-link layer and does not address spanning tree diameter or timer-related issues that arise when merging two large Layer 2 broadcast domains.

Root guard prevents a port from accepting superior BPDUs to protect the root bridge placement, but it does not mitigate connectivity issues caused by a spanning tree diameter that exceeds timer-supported limits.