More redundancy always means more availability. Do you agree?
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Say this first
No. Redundancy helps only while the failover mechanism works, and every mechanism (STP, FHRP, stacking, MLAG, routing) brings its own failure modes, more configuration to keep consistent and more room for operator error. Past two of something the gain is usually tiny and the complexity is real. I add redundancy where the business impact justifies it, use the simplest failover mechanism that meets the target, and test it regularly.
Go deeper
How redundancy hurts
- New failure modes. A virtual pair can go dual-active when its links fail. A unidirectional link can stop BPDUs and make a blocked STP port forward, creating a loop. An MLAG peer link failure can isolate the wrong switch.
- Untested paths. Backup paths often fail when needed because nobody exercised them: an expired license on the standby firewall, a missing VLAN on the second uplink.
- Shared fate. Two routers running the same software version share the same bug. Two circuits in one duct fail together. Redundancy that is not independent is not redundancy.
- Operators. More boxes and more protocols mean longer troubleshooting and more chances to make a mistake. Human error is a leading cause of outages.
How I balance it
- Quantify: what does an hour of outage cost, and how much does each option reduce expected downtime?
- Prefer layer 3 and ECMP over layer 2 tricks, and open standards the team understands.
- Two independent paths, not three. The third rarely changes the math but always adds work.
- Make failover automatic and fast, and test it in maintenance windows.
- Standardize so every site fails the same way.
A quick number to quote
Two independent components at 99.9 percent in parallel give about 99.9999 percent. A third adds almost nothing on paper, and in practice the limit becomes software bugs and human error, which extra boxes do not fix.
They will ask next
Give an example where removing redundancy improved a design.
A classic one: a layer 2 square of four switches with redundant links everywhere, where STP blocked unpredictable ports and every failure caused a 30 second reconvergence. Replacing it with two routed uplinks per access switch, a triangle with ECMP, has fewer links and converges in well under a second.
Traps
- Saying "two of everything" with no mention of cost, testing or shared fate.