This distinction is the most frequently misunderstood point in Spectrum-X architecture, so state it clearly before anything else: BlueField-3 appears only in DGX B200. DGX H100 and DGX H200 use ConnectX-7 HCA (CX7). GH200 Grace-Hopper Superchip also uses ConnectX-7. There is no configuration or firmware upgrade that turns a CX7 into a BF3 SuperNIC. They are different silicon.

The reason BF3 is required for full Spectrum-X adaptive routing is the RoCEv2 Go-Back-N retransmission protocol. RoCEv2 uses a Selective Acknowledgement-like mechanism at the QP (Queue Pair) level, but the Go-Back-N behaviour is triggered by out-of-order packet arrival. When a ConnectX-7 receives packets out of order — which per-packet adaptive routing actively produces, because packets from the same flow spray across different spine paths — the CX7 sends a NACK for the first out-of-order packet and requests retransmission from the last in-order sequence number. The sender retransmits the entire window from that point. At scale, with millions of packets per second per flow and per-packet routing producing routine reordering, retransmit storms consume 30–40% of link bandwidth on CX7 deployments with aggressive adaptive routing.

The BlueField-3 SuperNIC solves this with a dedicated reorder buffer implemented in hardware on the BF3 silicon. Before packets are delivered to the RDMA QP, they pass through the reorder buffer, which holds out-of-order packets until the sequence gap is filled. The QP sees an in-order stream regardless of how the network transported the packets. The Go-Back-N protocol is never triggered because out-of-order delivery is invisible to it.

The 16 ARM Cortex-A78AE cores on the BF3 run a full DPU operating system independently of the host. Three operating modes exist. DPU mode: ARM cores run a DOCA application stack with full eSwitch control, packet processing offload, and host isolation — this is the security-focused deployment mode. NIC mode: BF3 acts as a transparent high-speed NIC, ARM cores idle, no DPU functions active. SuperNIC mode: DPU OS runs for management and DOCA telemetry, but the reorder buffer is activated and adaptive routing integration is enabled — this is the Spectrum-X deployment mode.

DOCA runtime in SuperNIC mode exposes three primary applications. DOCA Flow provides a programmable packet processing pipeline where you can insert match-action rules in the BF3 eSwitch, offloading functions like NAT, ACL enforcement, and encapsulation/decapsulation from the host CPU. DOCA Compress offloads data compression and decompression to BF3 hardware engines, relevant for checkpoint compression to storage. DOCA App Shield monitors process integrity on the host from the isolated DPU OS — the host cannot tamper with App Shield because it runs in a separate security domain.

# On DGX B200 host: verify BF3 SuperNIC mode is active
dgx-b200-01$ mst status
MST modules:
MST PCI module loaded

MST devices:
/dev/mst/mt41692_pciconf0  - PCI configuration cycles access
                             domain:bus:dev.fn=0000:03:00.0 addr.reg=88 data.reg=92
                             type: BlueField3(rev:0)

dgx-b200-01$ doca_nic_config --query-mode
Device: BlueField-3 [MT41692]
Current mode: SuperNIC
Reorder buffer: ENABLED
AR integration: ENABLED
Reorder buffer depth: 256 packets per flow

# On DGX H100/H200: ConnectX-7, no reorder buffer available
dgx-h100-01$ mst status | grep -i type
type: ConnectX-7(rev:0)
# No SuperNIC mode, no reorder buffer — this is correct and expected