HPE7-A04 · Question #22
You need to design a network that supports transmitting RDMA traffic over multiple IP hops. Which protocols must the switches support? (Select all that apply.)
The correct answer is A. ETS B. IP ECN C. PFC. Designing a lossless RDMA-over-IP (RoCEv2) fabric requires three complementary DCB mechanisms working together. ETS (A) provides bandwidth scheduling and traffic class isolation so RDMA flows get dedicated priority lanes. PFC (C) delivers hop-by-hop lossless flow control - it…
Question
You need to design a network that supports transmitting RDMA traffic over multiple IP hops. Which protocols must the switches support? (Select all that apply.)
Options
- AETS
- BIP ECN
- CPFC
- DQCN
How the community answered
(32 responses)- A72% (23)
- D28% (9)
Explanation
Designing a lossless RDMA-over-IP (RoCEv2) fabric requires three complementary DCB mechanisms working together. ETS (A) provides bandwidth scheduling and traffic class isolation so RDMA flows get dedicated priority lanes. PFC (C) delivers hop-by-hop lossless flow control - it pauses a specific priority queue rather than dropping packets, which RDMA's stateless transport cannot recover from. IP ECN (B) handles end-to-end congestion signaling across IP hops; algorithms like DCQCN rely on ECN marks to throttle senders before PFC triggers, keeping the network stable.
QCN (D) is wrong because it is an IEEE 802.1Qau Layer 2 mechanism - it cannot cross IP (Layer 3) boundaries. In a multi-hop routed network, QCN messages have no way to reach the traffic source, making it useless for RoCEv2 deployments.
Memory tip: Think of it as the "PEE" stack for RoCEv2 - PFC + ETS + ECN. QCN gets "Quit at L2, Cannot cross iP" - it stays trapped at the Ethernet segment and never reaches across routed hops.
Topics
Community Discussion
No community discussion yet for this question.