OSPF roles are defined in RSTP. The Port role values of the Alternate port and the Backup port are consistent in the Flags field of the packet, both are 01.

Question

Options

• ATRUE
• BFALSE

• A
  77% (23)
• B
  23% (7)

Explanation

Option A is correct because in IEEE 802.1w RSTP, the Flags field of a BPDU uses bits 3–2 to encode the port role, and both the Alternate port and Backup port share the same encoded value of 01 - this is intentional in the standard, as both roles represent blocked/discarding ports that serve as backups to active paths. The distinction between Alternate and Backup ports lies in their function (Alternate backs up the root path; Backup backs up a designated path on the same segment), not in how they're flagged in the packet. Option B is wrong because it contradicts the IEEE 802.1w specification, which explicitly assigns value 01 to both of these port roles in the Flags field. Note: the question's opening phrase "OSPF roles are defined in RSTP" appears to be a translation artifact or typo - the actual subject is RSTP port roles, not OSPF; the meaningful testable claim is the second sentence about the 01 encoding.

Memory tip: Think "01 = One-Blocked" - both Alternate and Backup ports are blocked/discarding roles, so they share a single code (01). Root port = 10, Designated port = 11, Unknown = 00. The two "active" roles (10, 11) each get their own code; the two "standby" roles share 01.

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