EtherChannel: bundle two links between switches with LACP
- Switching
- Intermediate
- 12 min
- 3 steps
- Cisco IOS-style
Bundle two parallel links between SW1 and SW2 into a single Port-channel using LACP (mode active). The bundle appears as one logical iface to STP, doubling the available bandwidth without triggering loop avoidance.
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Free · no install · no account
Scenario
Two parallel links between the same pair of switches normally trigger STP to *block* one of them — that's exactly the loop- prevention design. EtherChannel is the workaround: it tells STP to treat both physical links as a single logical port, doubling bandwidth and load-balancing flows across the members. `` SW1 ════════ SW2 (one logical Port-channel = two physical links) ` Three negotiation modes: - on — static, no negotiation. Both ends must say on. Fastest, but a misconfigured single side (one on, one off) causes a loop because the other end doesn't bundle. - active / passive (LACP) — IEEE 802.3ad standard. Active sends LACPDUs, passive only responds. At least one side must be active. - desirable / auto (PAgP) — Cisco proprietary. Same idea as LACP, different protocol. Associate-tier reflex: always use LACP active/active` in modern designs unless you have a vendor-mix reason to do otherwise.
Topology
2 × switch · Cisco IOS-style
SW1— switchSW2— switch
What you will do
On SW1, add both Eth0 and Eth1 to channel-group 1 with LACP mode
active.Now configure SW2 — but with mode
desirable(PAgP), not LACP. We're deliberately introducing a mismatch to see what happens.Fix SW2 to use LACP
activeto match SW1. The bundle should then form andshow etherchannel summaryreports SU (in-use).
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This lab in other languages
EtherChannel: zwei Links zwischen Switches mit LACP bündelnEtherChannel: agrupa dos enlaces entre switches con LACPEtherChannel: agrupe dois links entre switches com LACPEtherChannel : agréger deux liens entre switches avec LACPEtherChannel: LACP से switches के बीच दो links bundle करेंEtherChannel：用 LACP 把交换机间的两条链路捆绑成一个EtherChannel: aggrega due link tra switch con LACPEtherChannel: スイッチ間の 2 本のリンクを LACP で束ねるEtherChannel: LACP 로 스위치 간 두 링크를 번들EtherChannel: связать два линка между свитчами через LACPEtherChannel: LACP ile switch'ler arasında iki link'i bundle yapEtherChannel: bó hai link giữa switch bằng LACP