143-425 · Question #103
Which two ELS request and reply sequences advertise buffer-to-buffer credits between Fibre Channel devices? (Choose two.)
The correct answer is A. FLOGI B. PLOGI. See the full explanation below for the reasoning.
Question
Which two ELS request and reply sequences advertise buffer-to-buffer credits between Fibre Channel devices? (Choose two.)
Options
- AFLOGI
- BPLOGI
- CPRLI
- DESC
How the community answered
(45 responses)- A76% (34)
- C9% (4)
- D16% (7)
Community Discussion
5
Lena V.Jun 27, 2026The answer is A and B, FLOGI and PLOGI. Both of these ELS sequences carry service parameters in their request and accept frames, and buffer-to-buffer credit is one of those negotiated parameters. FLOGI is the fabric login, where an N_Port and the fabric's F_Port establish the connection and agree on BB_Credit before any data moves. PLOGI is the N_Port to N_Port login, and it does the same thing between two end devices directly. PRLI comes after PLOGI and handles upper-level protocol setup like FCP for SCSI, not credit negotiation, and ESC is for security exchange, so both C and D are out. Know the order: FLOGI first into the fabric, PLOGI between the ports, PRLI to bind the protocol, and BB_Credit is locked in by the time PLOGI completes.
Brenda K.Jun 29, 2026Solid breakdown, just pin one timing detail for the exam: BB_Credit negotiated during FLOGI covers the N_Port-to-F_Port link, and PLOGI negotiates its own separate credit for the N_Port-to-N_Port session, so treat them as two distinct credit scopes or a question about "which login sets credit for fabric ingress" will burn your clock on a re-read.
Brenda K.Jun 27, 2026I went in thinking PRLI had something to do with credit negotiation since it handles process login, but then I remembered that BB_Credit is a Layer 1 and 2 concern handled during fabric and node login, not upper layer protocol stuff. FLOGI sets BB_Credit with the fabric and PLOGI negotiates it point to point between N_Ports, so those are your two, and this one is a quick 20-second pick if you know your login sequence order cold.
Ingrid P.Jun 29, 2026Solid breakdown, and the card I keep for this is just the three-login sequence in order with a cloze on what each one negotiates, because knowing FLOGI then PLOGI then PRLI cold is what lets you eliminate wrong answers in under ten seconds without having to reason through the BB_Credit scope at all.
Ingrid P.Jun 24, 2026FLOGI and PLOGI both carry BB_Credit fields in their payloads, confirmed.