A4:5F:B9 is a 24-bit MA-L block registered to DreamBig Semiconductor, Inc., a US fabless chip company founded in 2019 and headquartered at 2860 Zanker Road, Suite 210, San Jose, CA. Unlike a consumer brand, DreamBig builds datacenter and AI networking silicon — its flagship Mercury is an 800G AI-SuperNIC with a hardware-offloaded RoCE v2 and UEC RDMA engine, built on the chiplet-based Mars platform (Ares networking, Deimos hub, Phobos extensibility chiplets). The practical consequence for OUI work: a MAC in A4:5F:B9 space almost certainly belongs to enterprise datacenter hardware — AI training/inference racks, GPU clusters, and high-performance compute nodes carrying SmartNICs or DPUs — not consumer, mobile, or IoT gear. An address from this block surfacing outside a datacenter context is therefore worth investigating. The company raised a $75M Series B in July 2024 (co-led by Samsung Catalyst Fund and the Sutardja family) and was acquired by Arm in a roughly $265M cash deal announced in late 2025, so the silicon may increasingly ship under the Arm umbrella even though the IEEE registration remains under DreamBig's name. No public CVEs or vulnerability disclosures for DreamBig products were found as of June 2026; the standard datacenter network-adapter risk posture applies — RDMA/RoCE-capable NICs in shared GPU fabrics are high-value targets if segmentation is weak.
- IEEE assignment
- A4:5F:B9 → DreamBig Semiconductor, Inc. [Confirmed] — IEEE oui.csv (enrichment/registries/oui.csv, line 736); vendor corroborated at https://www.dreambigsemi.com/
- Registry / block size
- MA-L (24-bit OUI), single prefix A4:5F:B9 [Confirmed] — IEEE oui.csv (MA-L block); no matching row in mam.csv (MA-M) or oui36.csv (MA-S). NOTE: IEEE's public OUI data publishes NO assignment/registration date (oui.csv columns are only Registry, Assignment, Organization Name, Organization Address); any "date registered" on third-party tools is a database artifact, not an IEEE fact.
- HQ / country
- 2860 Zanker Road, Suite 210, San Jose, CA 95134, US [Confirmed] — IEEE oui.csv registry address; matches https://www.dreambigsemi.com/our-company
- Company status
- active; acquired by Arm (~$265M cash, announced late 2025) [Confirmed] — https://www.sdxcentral.com/news/arm-to-acquire-ai-networking-chipmaker-dreambig-in-265m-deal/
- Founded
- 2019, US fabless semiconductor company [Confirmed] — https://www.dreambigsemi.com/our-company
- Device types
- datacenter and AI networking silicon — AI SuperNICs (Mercury, 800G), SmartNICs, DPUs, and chiplet-based networking components for AI/HPC/cloud; enterprise/datacenter PCIe adapters and chiplets, not consumer or IoT end-user devices [Confirmed] — https://www.dreambigsemi.com/our-products, https://www.dbdpu.com/
- Notable products
- Mercury (800G AI-SuperNIC with hardened RoCE v2 + UEC RDMA engine); Mars Chiplet Platform (Ares networking, Deimos chiplet hub, Phobos extensibility) [Confirmed] — https://www.prnewswire.com/news-releases/dreambig-announces-world-leading-800g-ai-supernic-chip-mercury-with-fully-hw-offloaded-roce-v2--uec-rdma-engine-302342748.html
- Funding
- $75M Series B, July 2024, co-led by Samsung Catalyst Fund and the Sutardja family [Confirmed] — https://www.prnewswire.com/news-releases/dreambig-closes-75m-series-b-funding-round-co-led-by-samsung-catalyst-fund-and-sutardja-family-to-enable-ai-inference-and-training-solutions-to-the-masses-302197507.html
- Assignment / registration date
- Unknown — IEEE publishes no OUI registration dates; oui.csv has no date column and no third-party scrape date is recorded here [Confirmed that none exists] — IEEE oui.csv
- Security context
- no DreamBig-specific CVEs or public vulnerability disclosures found as of June 2026; datacenter RDMA/RoCE NIC risk posture applies (high-value targets in shared GPU fabrics if poorly segmented) [Likely] — single-angle web check, no advisory found; https://www.dreambigsemi.com/our-products
- Related vendors
- Arm (acquirer, ~$265M deal announced late 2025; IEEE registration still under DreamBig) [Confirmed] — https://www.sdxcentral.com/news/arm-to-acquire-ai-networking-chipmaker-dreambig-in-265m-deal/
- Analyst note
- an A4:5F:B9 address identifies enterprise datacenter networking silicon (AI/HPC servers, GPU clusters), not consumer or IoT hardware; an appearance outside a datacenter context warrants investigation.