Arista switch: MAC table full

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

What this guide covers

Fix MAC table full on a Arista switch.

Full fix path

1. Check current MAC table utilisation.
2. Identify the offending VLAN or port.
3. Enable storm-control on access ports.
4. Enable port-security with a hard MAC limit.
5. Long-term, refresh to a switch with a larger MAC table.

CLI / commands

show interfaces status
show interfaces Ethernet1 detail
show inventory

When the issue persists

• Open a Arista TAC case with the tech-support bundle.
• Provide the timeline + recent changes.

Frequently asked questions

Will this work on my specific Arista EOS version?

The procedure reflects current Arista EOS behaviour. Older releases may need minor syntax adjustments, use the CLI help (? or tab-completion) to verify.

Should I open a Arista TAC case immediately?

Open one if you suspect hardware failure or the symptom persists after a maintenance-window reload. Make sure your support entitlement is active first.

Where can I find the Arista official documentation?

https://www.arista.com/en/support/toi. search the product family + feature name.

Is this procedure safe in production?

Test in a lab or maintenance window first. Capture pre-change state so you can roll back.

Related guides

• All Arista fix guides → /arista/
• All vendor guides → /vendors/

References

• Arista support portal: https://www.arista.com/en/support
• Arista knowledge base: https://www.arista.com/en/support/toi
• Arista security advisories: https://www.arista.com/en/support/advisories-notices
• Open a case: https://www.arista.com/en/support/customer-support

Reference material, not professional advice. Validate against your specific Arista EOS version and test in a non-production environment before applying.

What changed recently?

Fault diagnosis on a Arista device goes faster when you map the symptom to a recent change:

• Did firmware update in the last 7 days?
• Did the network (router, ISP, VPN) change?
• Was the device moved physically?
• Did paired devices (phone, hub, app) update?
• Were any accessories swapped in or out?

The answer narrows the root cause to a manageable subset.

Safety + preconditions

Before any work on a Arista device:

• Unplug from mains for any internal-access procedure.
• Discharge stored energy (capacitors in PSUs, residual battery charge) per manufacturer guidance.
• Use ESD-safe handling for boards and modules, no carpet, no wool sleeves.
• Avoid moisture; never apply liquids near vents or connectors.
• If you smell smoke, see scorch marks, or feel uneven heat, stop and escalate.

Confirm it stuck

Before you walk away from a Arista device fix, run through:

1. Reproduce the original trigger: does the issue reappear? 2. Check the device's status / health screen for any new alerts. 3. Confirm paired devices (app, hub, controller) reconnected. 4. Save / commit any configuration changes per the device's normal workflow. 5. Note the change in your maintenance log with date + firmware version.

Escalation guide

For a Arista device, the right escalation depends on impact:

• Cosmetic / minor: log a ticket via the Arista app or web portal. Response 1-3 business days.
• Mid-impact: phone support. Have your serial number ready.
• Critical (production down, safety issue): in-person dealer / TAC visit. Bring proof of purchase.
• Out of warranty: third-party repair shop with manufacturer-certified technicians.

More frequently asked questions

Does this affect other devices on my network?

Generally no. The procedure is local to this device. Network-side changes (firmware updates that affect TLS, SMB, or routing) are flagged explicitly in the steps.

What if the fix returns after a reboot?

Persistent fault returns mean either: a hardware fault (escalate), a configuration that's being overwritten by a sync source (check cloud profiles), or a regression in a recent firmware update (rollback).

Can I roll this back if something breaks?

Yes for software-level changes (firmware rollback, config rollback). Hardware changes are usually one-way. Always back up settings before starting.

Why is this happening on a brand-new unit?

Out-of-box defects do occur. If you've owned the device under 30 days and the symptom persists after a factory reset, escalate to the seller for replacement under DOA terms before opening a manufacturer support case.

Should I update firmware first or last?

Update firmware first if a release note specifically mentions your symptom. Otherwise, finish the troubleshooting flow first, then update; that way you can isolate whether the update or the underlying fix solved it.

Field notes from real incidents on Arista

When I work on Arista switch: MAC table full the rhythm I lean on is the one I have built over years of these tickets. EOS-API (eAPI) over HTTPS is the cleanest way to script Arista at scale; do not wrap CLI screen-scraping when eAPI returns JSON. Arista EOS lets you reload a module without reloading the chassis on most platforms, I use that capability more than people realise. CloudVision Portal alerts are noisy unless you tune them; I disable the defaults and re-enable the ones that map to actual production events.

Tools I actually reach for

For Arista switch: MAC table full on Arista the cheapest signal I can land usually comes from a known order of operations, not a kitchen-sink approach. I start with show tech-support (capture for TAC) because it is the lowest-friction way to confirm the failure is real and reproducible. If that returns ambiguous data, I escalate to ping vrf <vrf> <target>, show platform hardware capacity, show logging last 200, packet capture on the ingress interface (TAC will ask for it), and finally to traceroute vrf <vrf> <target> only when the cheaper tools cannot reach the layer the failure lives in. That ordering matches the failure surfaces I have actually seen on Arista units over the last few years, not an abstract taxonomy. The cheap signals gate the expensive ones so the investigation does not balloon into a multi-hour exercise.

Verification I run before I close the ticket

Before I mark Arista switch: MAC table full resolved on a Arista unit, the verification loop below is what I actually run. Each step proves a different layer is green, and the order matters - the cheap checks gate the more expensive ones so I never burn an hour on a deep test that a shallow one would have failed in seconds.

show interfaces <int> | include errors|drops|CRC

If that one comes back clean, move to the next check. If it does not, stop and dig in there before layering more verification on top of a red signal.

show ip route <prefix>  # confirm best path post-change

If that one comes back clean, move to the next check. If it does not, stop and dig in there before layering more verification on top of a red signal.

show bgp summary  # confirm session state after route changes

If that one comes back clean, move to the next check. If it does not, stop and dig in there before layering more verification on top of a red signal.

show logging | include %LINK|%LINEPROTO|%BGP|%OSPF

Only when every line above runs clean do I close the ticket and update the runbook with the timestamps. A green verification that nobody can reproduce is not a fix, it is luck waiting to regress.

Where I check first when the docs disagree

When two sources contradict each other on a Arista detail, the disambiguation order I lean on is stable across products and across years. Arista TAC knowledge base is where I start for the ground-truth view. github.com/aristanetworks for open-source tooling like Ansible roles is where I start for the ground-truth view. eos.arista.com for the official software documentation is where I start for the ground-truth view. Random blog posts and reseller wikis are signal, not ground truth, and I treat them as such until the references above either confirm or contradict the claim. The cost of trusting an unauthoritative source on Arista switch: MAC table full is rarely worth the time it saved.

Pitfalls I have walked into on this exact path

The shortcuts that look smart on Arista switch: MAC table full have a habit of biting back. The pitfalls below are the ones I have personally walked into on a Arista unit, not things I read about. Arista EOS lets you reload a module without reloading the chassis on most platforms. I use that capability more than people realise. Show tech-support detail is the artifact Arista TAC expects on call one; bundle it with the agent logs before you open the ticket. CloudVision Portal alerts are noisy unless you tune them; I disable the defaults and re-enable the ones that map to actual production events. When in doubt I revert to the slower path that the manual prescribes - the time I save by skipping it is always smaller than the time I spend cleaning up afterwards.

What I tell the next on-call

When I hand Arista switch: MAC table full off to the next person on rotation, the three lines I leave in the runbook are these. First, the symptom signature on Arista - not a paraphrase, the exact string that surfaces in logs or on the screen. Second, the diagnostic that gave the highest signal in the least time. Third, the exact verification command whose green output justified closing the ticket. That trio is what turns a one-off fix into a runbook entry the next engineer can use without paging me at three in the morning.

I also add a one-line note on the cost of getting this wrong. For Arista switch: MAC table full on a Arista unit, the cost is rarely the replacement part or the patch itself. It is the downtime, the second site visit, and the trust deficit you spend with whoever owns the asset when the fix does not hold. That framing keeps the next on-call from choosing the cheap-looking shortcut that ends up costing the most in elapsed hours and goodwill.

Related fixes

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

• Arista router: MAC table full
• Arista switch: MAC address flapping between ports
• Arista router: MAC address flapping between ports
• Arista switch: ARP poisoning / spoofing detected
• Arista switch: asymmetric routing detected
• Arista switch: DHCP clients not receiving IP