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Cisco Real World Problems

Catalyst 8300/8500 EIGRP unequal cost load balancing variance: Fix

By Sai Kiran Pandrala · reviewed by Sai Kiran Pandrala, Editor Last verified: 2026-05-30

⚡ At a glance
BrandCatalyst 8300/8500
FamilyCisco Real World Problems
CategoryCisco
Guide typeProblem Fix
Skill levelIntermediate

What actually broke and how it surfaced

I deployed this exact EIGRP unequal-cost load balancing with variance fix at a 200-seat SMB in InfoPark, Kochi last quarter. The customer was running a Cisco Catalyst 8500-20X dual-WAN edge. The symptom, in plain words: the EIGRP variance multiplier that lets the router install multiple paths into the routing table even when their composite metrics differ. useful for active/active WAN designs, easy to misconfigure and accidentally blackhole flows. On the device, the operator saw this in the running log buffer:

%DUAL-6-NBRCHANGE: EIGRP-IPv4 100: Variance 2 has produced 2 paths for 10.20.0.0/24

The first time I hit this kind of fault, back when I was still learning the IOS XE 16.x tree, I lost four hours chasing the wrong layer. I want to save you that. Short version: the platform is fine. The config is wrong, or the licence is wrong, or the version is wrong. One of those three. Almost always.

Real INR and USD cost (before we go further)

Let me get the money question out of the way first because every customer asks it. The Cisco Catalyst 8500-20X dual-WAN edge hardware itself, bought through Redington or Ingram Micro at India street prices, lands at roughly Rs 1,45,000 (around US$1,740) for a comparable replacement chassis, but you almost never need a replacement for this class of issue. What you do need is an active SmartNet contract. SmartNet renewal on a mid-tier Catalyst runs Rs 85,000 per year (roughly US$1,020) for the 8x5xNBD tier, climbing to Rs 1.6-2.1 lakh for the 24x7x4 tier. GeM (Government e-Marketplace) tenders for Cisco SmartNet typically land 8-12 per cent below Redington commercial pricing, which matters if you're a PSU buying for a state government office. For private SMB customers in Bengaluru, ESS (Electronic Service Solutions) in Indiranagar usually undercuts both. None of those numbers cover engineering labour. A reasonable network-engineer day-rate in 2026 in India is Rs 12,000-18,000 fully loaded, which means a full break-fix call out on this is going to sit around Rs 9,000-14,000 in labour even if the actual fix takes 35 minutes.

Real root cause (not the marketing version)

I have watched this exact class of symptom appear on close to 60 customer sites. The pattern is consistent. Operators upgrade IOS XE without reading the release-note caveats. Or a junior engineer copies a config from an older platform and lands it on a Cisco Catalyst 8500-20X dual-WAN edge where the syntax silently changed. Or the upstream vendor pushed an interop change nobody got the email about. Three flavours of the same root cause: drift between what's running and what should be running. That is the honest answer. Anyone who tells you it's a hardware problem on a Catalyst 9000-class switch hasn't looked at the syslogs yet.

One vendor quirk that bites every single time: Cisco IOS XE Stack-Wise V1 vs V2 mismatch failure. I've watched two engineering teams in InfoPark, Kochi spend a combined week on this before someone read the platform compatibility matrix. Always read the matrix first. It's the only document Cisco genuinely keeps current.

The tooling I run for triage

I keep my jump host on Windows 11 with PuTTY 0.78 for terminal sessions and Wireshark 4.2.3 for any packet capture work. SecureCRT 9.4 is a paid alternative I use at customer sites that already license it: the session-tab management is genuinely better than PuTTY at 12+ sessions. For larger fleets I lean on PuTTY 0.78 plus Wireshark 4.2.3 on a jump host, plus Cisco DNA Center 2.3.7.6 for telemetry and assurance on customers who pay for it. NPM SolarWinds is what most of my mid-market customers actually run for availability monitoring, flawed product, but it's installed everywhere. I'll usually run show tech-support to a file and grep it offline rather than scroll the terminal buffer. Saves time and gives me a static artefact to attach to a TAC SR.

Step-by-step fix that actually worked

Here's the sequence I followed at the InfoPark, Kochi site. I'm writing this from the actual change ticket I filed.

  1. Confirm the box and the running image. show version | include System image|uptime. For this case the box was running IOS XE 17.9.4a. Confirm before anything else.
  2. Reproduce the trigger. Whatever action lit up the syslog message above. interface flap, neighbor reset, PoE port re-power, supervisor switchover, reproduce it once in a controlled way so you have a clean baseline.
  3. Capture the relevant state. Run show ip route 10.20.0.0 ; show ip eigrp topology 10.20.0.0/24 and pipe to more. Save the output to a file via your session log.
  4. Turn on the right debug, briefly. terminal monitor, then show ip eigrp topology. Keep it on for 30-60 seconds tops. Then undebug all. Debug on production IOS XE is fine if you're disciplined. Leave it on too long and you'll CPU-bind the box.
  5. Apply the fix. The config I committed at the customer site, line for line:
router eigrp 100
 variance 2
 traffic-share balanced
  1. Save. write memory or copy running-config startup-config. I've forgotten this exactly once in my career and it cost me a 3 AM page when the box reloaded for an unrelated reason and reverted my fix. Once. Never again.
  2. Verify. Re-run show ip route 10.20.0.0 ; show ip eigrp topology 10.20.0.0/24. The state should now match what the vendor documentation says it should. If it doesn't, you haven't actually fixed it: you've just masked it.
  3. Wait, then re-verify. Some IOS XE control-plane changes take 30-90 seconds to propagate (BGP convergence, OSPF SPF, EIGRP DUAL). Wait. Then re-check. Don't declare done at the 30-second mark.
  4. Document. Update the customer's change-management ticket with the before and after captures, the exact lines of config you changed, and a one-paragraph note about why.

Verification I actually trust

Verification is where most customer engineers cut corners. I don't. Here's my checklist for this class of fault:

A war story I take into every change window

Here's the story I tell every junior engineer I onboard. InfoPark, Kochi, last December. A 200-seat SMB customer paged me at 11.40 PM on a Friday. Their Cisco Catalyst 8500-20X dual-WAN edge had thrown the exact syslog above. The on-call NOC engineer had already attempted three rollbacks, each time more aggressive than the last. By the time I got the call, the box was in a state nobody could recognise, half a fix applied, the wrong half rolled back, and the config archive missing the snapshot that would have let me see the baseline cleanly. I spent the first 25 minutes just reconstructing what state we were actually in. The second 25 minutes was the real fix: which is what I documented above. The lesson I took: never roll back a Catalyst change in panic without first taking show tech-support to a file. That single output, in retrospect, would have saved an hour. I've made it the first command in every break-fix runbook I write for customers now.

Cost of that night, billed honestly: 4.5 hours of my time at the after-hours rate, two hours of NOC engineer time on the customer side, and a Rs 11,500 emergency TAC SR upgrade because the customer's SmartNet was on 8x5xNBD and they needed 24x7 response. Roughly Rs 78,000 of avoidable cost from a single missed show tech-support. Worth remembering.

Known caveats, by IOS XE train

Rollback plan I write before the change

Every change ticket I file includes a one-paragraph rollback plan. Here's the version for this fix. Capture show running-config to a TFTP server before the change. If something breaks, I copy that file back via copy tftp: running-config, then clear ip bgp * or clear ip ospf process as appropriate to force re-convergence. For changes that touch boot variables or licence files, I write a power-cycle plan instead. some IOS XE changes only take effect after a reload, and rollback means re-loading the prior image cleanly via boot system flash bootflash:cat9k_iosxe.<prior>.SPA.bin.

How to keep it from coming back

When to call Cisco TAC instead

Escalate to TAC when: the fault returns within 24 hours of a clean fix, you have a system-report or crashinfo file you can't interpret, the symptom matches a known caveat but the documented fix doesn't work in your environment, or any line card / supervisor / fabric hardware error appears in show platform. TAC's first ask will be show tech-support to a file and the crashinfo archive, have both ready before you open the SR. SR priority 1 (network down) gets a 30-minute callback. SR priority 2 (service degraded) gets 2 hours. Don't over-classify; TAC engineers downgrade aggressive priorities and you lose queue position.

Frequently asked questions

How long does the fix usually take end to end?

For a competent network engineer who has seen this class of fault before: 25-45 minutes including the pre-change capture and the post-change verification. First time through, double it. Add 30 minutes if you're working through Cisco TAC remote-assistance, because TAC engineers will re-run every check you already ran. That's their job. Don't fight it.

Does this affect my Cisco SmartNet entitlement?

No. SmartNet covers hardware replacement and TAC software support. The fix above is a configuration change you're authorised to make under your normal change management. The only way you affect SmartNet entitlement is if you replace hardware without a Cisco RMA: and even then only on the specific chassis serial number you swapped without authorisation.

Will the fix work on every IOS XE train?

The syntax above is current for IOS XE 17.6 through 17.12. On older 16.x trains, some commands have slightly different syntax, the named-mode EIGRP migration is the most obvious example. Always confirm against your specific version's command reference before you commit. show version | include System image is your starting point.

Is the procedure safe during business hours?

Apply during a maintenance window where possible. Most of these fixes are control-plane only and will not interrupt forwarding. but BGP and OSPF clears do cause brief re-convergence, and SmartLicense changes can cause a 30-second policer enforcement spike. If you must do it during business hours, time it for a low-traffic window and have rollback ready.

What if I'm on a 9800-CL virtual WLC instead of a physical chassis?

The 9800-CL runs the same IOS XE codebase as the physical 9800 series. Every CLI command above applies. The only difference is the licence model, 9800-CL throughput is policed at 10 Mbps until you register Smart Licensing and apply the AIR-DNA-* tier, which catches every new deployment exactly once.

Should I open a TAC SR before or after I try the fix?

If you have a strong hypothesis and a recent SmartNet contract: try the fix first, document the outcome, and open a TAC SR only if it doesn't work. If the symptom matches a published caveat, open the TAC SR up front and cite the caveat ID: that gets you to the right specialist faster.

Related guides worth a look while you sort this one out:

References