Ethernet as transport
In one line
Ethernet is the universal L2 framing from the access edge to 400G+ and out into the WAN as Carrier / Metro Ethernet.
Speeds, lanes, and optics
1 / 10 / 25 / 40 / 100 / 400G. Higher speeds use multiple lanes (40G = 4x10G, 100G = 4x25G, 400G = 8x50G PAM4), enabling breakout. At 25G and above, auto-negotiation and FEC matter - a mismatch shows up as a down link or CRC errors, a classic gotcha.
MTU / jumbo frames
Standard 1500 vs jumbo ~9000-9216. MTU must be consistent end-to-end; overlays (VXLAN/MPLS) add encapsulation overhead, and storage / RoCE need jumbo plus lossless headroom (see Lossless fabric - PFC, ECN, DCQCN).
Carrier / Metro Ethernet
Ethernet as a WAN service: E-Line (point-to-point), E-LAN (multipoint), E-Tree (rooted), delivered as EVCs; QinQ stacks customer tags. This is a common enterprise WAN access method (see WAN and last-mile transport selection).
Design drivers
Speed roadmap, breakout / port economics, MTU planning, and avoiding autoneg/FEC mismatches.
IPv6 / dual-stack note
Dual-stack rides identical framing; plan MTU / PMTUD so v6 (no in-path fragmentation) isn't black-holed.
Related
- Physical mediums - fiber and copper
- Optical transport - CWDM vs DWDM
- WAN and last-mile transport selection
Spaced repetition
Why do 25G+ Ethernet links require attention to autoneg and FEC?
Without matched auto-negotiation/FEC the link fails to come up or shows CRC errors; high-speed serdes depends on FEC.
Jumbo frames matter for overlays and storage because [...]; MTU must be [...].
Jumbo frames matter for overlays and storage because encapsulation adds overhead and RoCE/storage need large MTU (plus lossless headroom); MTU must be consistent end-to-end.
Name the three Carrier-Ethernet service types.
E-Line (P2P), E-LAN (multipoint), E-Tree (rooted multipoint).
Sources
- IEEE 802.3; MEF Carrier Ethernet; Cisco Press, End-to-End QoS (MTU/overlay notes).