Port-channel
Cisco term for an aggregated link: 2-8 physical ports bundled into one logical link. Bandwidth: N× single-port; redundancy if one link fails. Standard between switches + from switch to server NIC team.
Protocols: LACP (802.3ad open standard, default) or PAgP (Cisco proprietary). Hash-based distribution of flows across links — a flow stays on one link (no reordering), but different flows are distributed. Hash can be src-MAC, dst-MAC, IP-pair, etc. Classic perf trap: 4×10 Gbps port-channel where all traffic between two specific hosts lands on one link → 10 Gbps cap. MC-LAG / vPC: port-channel span over two physical switches for chassis redundancy.