150-820 · Question #204
You need to configure two separate VCS fabrics for connectivity to each other. The fabrics must remain independent fabrics. Maximum throughput and redundancy is required for the links between them…
The correct answer is D. vLAG. See the full explanation below for the reasoning.
Question
You need to configure two separate VCS fabrics for connectivity to each other. The fabrics must remain independent fabrics. Maximum throughput and redundancy is required for the links between them. Which technology would meet these requirements?
Options
- AMPLS
- BISLtrunking
- CSPB
- DvLAG
How the community answered
(17 responses)- B18% (3)
- C12% (2)
- D71% (12)
Community Discussion
11
Brenda K.Feb 21, 2026The answer is D, vLAG, and this one should not cost you more than 30 seconds once you lock in the phrase "independent fabrics." ISL trunking is the trap here because ISL extends a VCS fabric outward, which merges the two domains into a single fabric, directly violating the independence requirement. SPB creates a unified fabric as well, so eliminate it immediately. vLAG lets you bond multiple physical links between two VCS fabrics that remain completely separate from each other, giving you aggregated bandwidth for maximum throughput and multiple paths for redundancy without either fabric absorbing the other. Bookmark this one as a quick point, 20 seconds max, and move on.
Hiroshi T.Mar 10, 2026The correct answer is D, vLAG. The Brocade VCS fabric guide specifies that vLAG (Virtual Link Aggregation Group) is the designated mechanism for connecting two independent VCS fabrics without merging them into a single fabric domain, which is exactly what the question describes. ISL trunking, option B, actually extends fabric membership across the link and would cause the two fabrics to merge rather than remain separate, so it fails the independence requirement directly. vLAG bundles multiple physical links between the two edge RBridges using LACP, giving you both the maximum throughput from aggregated bandwidth and the redundancy from multiple active paths, satisfying every condition in the question simultaneously.
Bao N.Feb 26, 2026vLAG is the right call here because it lets you bond multiple inter-switch links between the two independent VCS fabrics while keeping the fabrics logically separate, which rules out SPB and ISL trunking since those either merge the fabrics or lack the redundancy piece. Quick question though, do you understand why MPLS gets eliminated so fast on this one, or is that still fuzzy for you?
Bartosz H.Feb 20, 2026The key word the exam writers are testing is "independent," because if you trunk those ISLs together you are merging the two fabrics into one, which blows the requirement right out of the water. So ask yourself what gives you aggregated bandwidth and link redundancy across a fabric boundary without collapsing the principal-switch election into a single domain, and that should narrow it down fast.
Prof. SaraFeb 23, 2026Solid framing, though worth spelling out for newer folks that the aggregated bandwidth piece is precisely why vPC peer-links often tempt people here, but vPC is an intra-switch construct and cannot span fabrics, so the only mechanism that satisfies all three conditions at once is inter-fabric traffic engineering via separate VSANs mapped over dedicated ISLs, each fabric keeping its own principal-switch election intact.
Prof. SaraFeb 14, 2026vLAG is your answer because it bonds links across both fabric borders for bandwidth and redundancy without merging the two VCS domains into one, which is exactly the trap ISL trunking sets for you since ISL collapses them into a single fabric. I sat this exact scenario on my 150-820 and almost penciled in B before I caught the phrase "remain independent," and that one word is the whole key.
Yusuf A.Feb 15, 2026My senior drilled that same point into me and added that ISL also collapses the spanning tree domains into one, so a topology change in either fabric bleeds across the boundary, which makes "remain independent" an even stronger signal to rule it out beyond just the VCS domain merge.
Yusuf A.Mar 7, 2026ISL trunking is exactly what my senior walked me through when we had two separate VCS fabrics that needed to talk to each other, because it lets you bundle multiple physical links between the switches for both redundancy and maximum throughput while keeping each fabric completely independent. The key thing he drilled into me is that ISL is designed specifically for inter-switch fabric connectivity, so B has to be the right call here.
Prof. SaraMar 7, 2026Yusuf, your senior was describing ISL trunking in the context of intra-fabric connectivity, meaning it links switches together to form or expand a single VCS fabric, not to bridge two already separate, independent fabrics. The scenario describes two distinct fabrics that need to communicate, which is exactly the use case D addresses through fabric interconnect, where each fabric retains its autonomy while a dedicated logical connection is established between them.
Viktor S.Feb 15, 2026SPB keeps fabrics independent while bridging them, that is the point.
Bao N.Feb 18, 2026Viktor, the correct answer is actually D, shortest path bridging uses a link state protocol to build a full topology map so every node can independently compute optimal paths, which is what makes it different from older spanning tree approaches. The "independent fabrics" description fits more of a proprietary fabric virtualization concept, not what SPB is actually doing under the hood.