Quiz: LACP / Link Aggregation

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3 questions

L0 (1 questions)

1. What are the two LACP modes and what happens if both sides are set to passive?

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Active mode sends LACP PDUs and actively tries to form a bond. Passive mode responds to LACP PDUs but does not initiate. If both sides are set to passive, no bond is formed because neither side initiates negotiation. At least one side must be active.

L1 (1 questions)

1. Why does a single TCP flow not benefit from the increased bandwidth of a LACP bond, and what hash policy gives the best traffic distribution for IP-based workloads?

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Traffic distribution across bond members uses hashing, not round-robin. A single TCP flow always hashes to the same link, so it is limited to one link's bandwidth. Aggregate bandwidth only benefits from many concurrent flows. The layer3+4 hash policy (source/destination IP + port) gives the best distribution for IP traffic because it incorporates both endpoints and ports, spreading different connections across links.

L2 (1 questions)

1. A Linux server has a mode 4 (802.3ad) bond with two interfaces, but only one link carries traffic. How do you diagnose and fix this?

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1. Check bond status: cat /proc/net/bonding/bond0 — verify both interfaces show as 'up' and 'Aggregator ID' matches on both.
2. Check LACP partner info to confirm the switch is participating.
3. Verify switch-side LACP config matches (both sides must agree on LAG membership).
4. Check hash policy — with layer2 hashing and only one destination MAC, all traffic hashes to one link. Fix by setting xmit_hash_policy to layer3+4: ip link set bond0 type bond xmit_hash_policy layer3+4.
5. Ensure miimon is set for link monitoring: ip link set bond0 type bond miimon 100.