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Zorluk: ZorHigh Availability and Redundancy Concepts

An enterprise deployment connects dual-homed application servers to two separate top-of-rack access switches using LACP (IEEE 802.3ad) NIC teaming for link redundancy, while two core routers run Virtual Router Redundancy Protocol (VRRP) to provide default gateway resiliency. Following a network migration, users report intermittent traffic loss during router failover tests, and LACP bundles on the servers fail to form properly. Which TWO of the following technical misconfigurations or architectural oversights are the primary causes of these issues?

  1. LACP was configured across two independent, non-stacked access switches without implementing Multi-Chassis Link Aggregation (mLAG) or switch stacking between them.Cevap
  2. Host default gateway addresses were statically configured with the physical IP address of the primary router instead of the VRRP Virtual IP (VIP) address.Cevap
  3. C
    Spanning Tree Protocol (STP) root bridge priority was set to 0 on the primary switch, forcing all server-facing LACP ports into an STP blocking state.
  4. D
    VRRP preemption was disabled on both routers, forcing both appliances into active master mode simultaneously and causing IP collisions on the virtual MAC address.
  5. E
    LACP active mode was configured on the server NIC team while LACP passive mode was configured on the access switch ports.

Cevap

The primary causes are that LACP was configured across separate standalone switches without Multi-Chassis Link Aggregation (mLAG), and host default gateways were set to the physical router IP address rather than the VRRP Virtual IP (VIP).
LACP requires a single logical switch plane (achieved via switch stacking or multi-chassis link aggregation / mLAG) when bundling interfaces connected across physical switch chassis. Furthermore, VRRP requires endpoints to target the shared Virtual IP (VIP) address rather than physical interface IP addresses to maintain seamless default gateway failover.

Adım Adım Çözüm

1
Analyze the LACP negotiation failure across distinct access switches.
Standard LACP (IEEE 802.3ad) requires all bundle members to terminate on a single logical control plane. Split connections across non-stacked standalone switches fail to establish a combined aggregation bundle without mLAG or stacking technology.
LACP Control Protocol Data Units (LACPDUs) from different physical switches carry different system IDs, preventing unified link group formation.
2
Evaluate host gateway reachability during VRRP failover.
Hosts configured with the physical interface IP of the primary router continue directing traffic to that specific hardware address during failover, causing connection drops.
VRRP relies on hosts sending default gateway traffic to the shared Virtual IP (VIP) and virtual MAC address so the backup router can take over seamlessly upon primary device failure.

Anahtar Kavram

Multi-Chassis Link Aggregation (mLAG) requirements and First Hop Redundancy Protocol (FHRP) Virtual IP host configuration.
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High Availability and Redundancy Concepts

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