Three quick predictions before we start. You won't be scored — this just primes your brain to notice the answers as they show up below.
- Q. AutoVPN tunnels use IPsec — true or false? (watch Section 1)
- Q. For 50 sites, is full-mesh or hub-and-spoke the saner choice? (Section 2)
- Q. Which outbound UDP ports must reach the Meraki cloud for AutoVPN to work? (Section 4)
Why this matters — the chai-tapri version
Think of an IPsec VPN the old way: two routers, matching crypto maps, a shared secret, and a public IP on both ends. Add a 30th branch and you are editing 29 configs. Now picture a WhatsApp group instead. You don't dial each member's number — you join the group and you can instantly message everyone. Meraki AutoVPN is that group. Each MX checks in with a cloud "directory", and the directory tells every member how to reach every other member. You tick one box; the tunnels build themselves.
Imagine every branch office is a kid in a classroom. Normally, for two kids to pass secret notes, they'd each need the other's exact desk address — and you'd rewrite all of them every time a new kid joins. Meraki AutoVPN is like a friendly class monitor (the cloud) who knows where everyone sits. Each kid tells the monitor "here I am", and the monitor whispers everyone's seat to everyone else. Now any two kids can pass encrypted notes directly. You didn't set up a single address by hand.
In production this is the difference between a 3-week VPN rollout and a 3-day one. Interviewers love it too: "How does Meraki form a VPN without you configuring IPsec?" is a top-5 question in any Meraki or SD-WAN screen. Get the registry story right and you sound like you've actually deployed it.
Four words you'll hear in every Meraki VPN conversation
The cloud "directory". Each MX checks in every 10 seconds; it hands out everyone's public IP + port so peers can reach each other. No registry = no AutoVPN.
How two MX boxes behind NAT reach each other. Each opens an outbound UDP flow; the registry swaps the port mappings so the tunnel forms without inbound port-forwarding.
An MX set to "Hub" tunnels to every other Hub and to any spoke that lists it. Datacentre MXs are hubs; for scale, keep them dedicated.
An MX in one-armed mode (no LAN routing) that only terminates VPN tunnels. The classic datacentre design — it aggregates spokes, nothing else.
① AutoVPN & the registry — watch a tunnel form
Here's the climax reveal: AutoVPN does use IPsec under the hood — but you never touch a crypto map. The MX negotiates IPsec automatically once the registry has introduced the two peers. So the pre-quiz answer is "true, but you don't configure it." That's the part most freshers get wrong in interviews.
Let's trace it. Aditya at a Pune branch wants to reach the HQ file server. His MX has never spoken to the HQ MX before. Press Play and watch the handshake.
▶ Watch AutoVPN form a tunnel
Click Play. Each stage lights up as the two MX appliances meet through the cloud registry.
Aditya enables Site-to-site VPN on the Pune MX and picks the HQ as its hub. Within ~40 seconds the dashboard shows a green tunnel. He didn't open a single inbound firewall port on the branch router — UDP hole punching did it. His teammate asks "where are the pre-shared keys?" Aditya's answer: "There aren't any I typed. The cloud brokered it."
The actual config — three clicks
Type: ◉ Spoke (HQ MX = ◉ Hub) Hubs: [ HQ-Datacentre ▼ ] Default route: ☐ Local networks in VPN: VLAN 20 10.20.0.0/24 ☑ Use VPN: yes NAT traversal: ◉ Automatic → Save
Peer Status Last contact NAT type HQ-Datacentre ● Online 3 sec ago Friendly Tunnel: 10.20.0.0/24 ⇄ 10.0.0.0/16 (AES, up 41s)
If the Meraki cloud registry went completely offline for 10 minutes, would your existing AutoVPN tunnels keep passing data? Decide before you reveal.
A junior engineer claims "Meraki AutoVPN is its own protocol, it doesn't use IPsec." How do you correct them?
② Hub-and-spoke vs full-mesh — pick the right shape
Every site can be a Hub or a Spoke. That one toggle decides your whole topology. The trap: full-mesh feels "better" because every site talks to every site directly — lowest latency. But the tunnel count explodes.
The math is N×(N-1)/2. Ten sites = 45 tunnels. Fifty sites = 1,225 tunnels. Each MX has a finite tunnel + route capacity, so mesh quietly hits a ceiling. Cisco's own best practice: for scale, use hub-and-spoke with dedicated hubs.
Priya is asked to connect 60 retail stores to two datacentres. She almost sets every store as a Hub for "fast store-to-store". Then she does the math — 60 hubs would mean 1,770 mesh tunnels and the small MX67s would choke. She switches the stores to Spokes pointing at two dedicated MX450 hubs. Store-to-store traffic transits a hub (one extra hop, fine for retail). Tunnel count per store drops to two.
Architect note: when you need spoke-to-spoke without hub transit, you can still keep hub-and-spoke and rely on the spokes learning each other's routes via the hub — but true direct spoke-to-spoke needs the spokes to also be hubs, which reintroduces the mesh scaling problem. The clean answer for large fleets is dual dedicated hubs for redundancy, and accept the single hub-transit hop for inter-spoke flows.
You set a branch MX to "Hub" by mistake instead of "Spoke", in an org that already has 40 hubs. What happens to that branch's tunnel count?
A 25-site deployment is configured full-mesh. The team plans to grow to 80 sites next year. What should you flag in design review?
③ SD-WAN+ — send the right traffic over the right link
Branches usually have two uplinks — say a fibre line and a 4G/LTE backup. Plain failover only switches when a link dies. SD-WAN is smarter: it watches latency, jitter, and loss, then moves sensitive traffic to the better link before the user notices.
On Meraki this lives in two controls. Flow preferences pin a flow to a chosen uplink (e.g. "Office 365 always over WAN1"). Performance classes define the quality bar — the built-in VoIP class, or a custom one — and traffic fails over when the active link breaches it. SD-WAN+ (the upgraded licence) adds Internet flow preferences on top.
▶ Watch a VoIP call get steered
A Teams call is on WAN1 (fibre). Jitter spikes. Watch SD-WAN move it to WAN2 mid-call.
Building a VoIP-steering policy
Uplink selection > SD-WAN policies > Add a preference Traffic filter: Custom — Protocol UDP, dst port 16384-32767 (RTP) Source: 10.20.0.0/24 Preferred uplink: WAN 1 Fail over if: Performance class = VoIP (latency/jitter/loss bar) → Save
Flow: voice 10.20.0.55 active uplink: WAN2 (failover) reason: VoIP class breach WAN1 jitter 62ms (bar ~20ms) WAN2 jitter 9ms Bulk flow 10.20.0.71 active uplink: WAN1 (unchanged)
Karthik's branch users complain Teams calls "go robotic around 2pm" daily. Ping looks perfect — because ICMP isn't shaped. He builds a VoIP performance class and a flow preference for RTP. Now at 2pm, when the shared fibre saturates, voice silently rides the LTE uplink and the robotic audio disappears. The bulk file sync stays on fibre. Users notice nothing — which is the point.
A branch has only ONE uplink (no LTE backup). You build a VoIP performance class anyway. Does it do anything useful?
You built a VoIP flow preference but testing with continuous ping across the WAN shows no uplink change during congestion. Why?
④ "Tunnel won't form" — the 4-step playbook
This is the single most common Meraki VPN ticket. The good news: ~90% of cases are one of four causes, and you can rule them out in under two minutes from the dashboard.
▶ Diagnose a stuck tunnel
A spoke shows red in VPN status. Step through the diagnosis ladder.
- Symptom: tunnel never forms, both MXs show online in the org. → Cause: upstream firewall blocks the registry. Allow outbound
UDP 9350–9381from the MX WAN to the Meraki cloud. - Symptom: VPN status reads "NAT type: Unfriendly". → Cause: a symmetric / strict NAT upstream defeats UDP hole punching. Switch NAT traversal to
Manual: Port forwardingand forward the port. - Symptom: tunnel forms but some apps hang / large file transfers stall. → Cause: MTU / fragmentation on a low-MTU path (often DSL/PPPoE). Lower the VPN MSS/MTU.
- Symptom: a single branch shows dozens of tunnels and flaps. → Cause: it was set to
Hubin a multi-hub org. Set it back toSpoke. - Symptom: routes don't appear / "subnet conflict". → Cause: two sites advertise overlapping subnets (both 192.168.1.0/24). Re-IP one side; AutoVPN won't install conflicting routes.
- Keep hubs dedicated. A datacentre MX that's also serving LAN clients and terminating 200 spokes will hit CPU before it hits bandwidth. Use a one-armed VPN concentrator.
- Patch the AnyConnect DoS. CVE-2025-20271 (CVSS 8.6) lets an unauthenticated attacker restart the MX AnyConnect VPN server. If you use AnyConnect with client-cert auth, upgrade to fixed firmware (e.g. 18.107.13 / 18.211.6 / 19.1.8 branches) via Organization > Firmware upgrades.
The registry is control plane only. Data never tunnels through the Meraki cloud — it rides directly MX-to-MX. If an interviewer asks "isn't that a privacy risk, Meraki seeing my traffic?", the answer is no: the cloud brokers introductions, your encrypted data stays on your own internet path.
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📝 Wrap-up — six more
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✍️ In your own words
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📖 Glossary — the terms in this lesson
- AutoVPN
- Meraki's cloud-brokered site-to-site VPN. You tick Hub/Spoke; the cloud automates IPsec peer discovery and key exchange.
- VPN registry
- The Meraki cloud directory that introduces MX peers and tracks keepalives. Control plane only — no user data passes through it.
- UDP hole punching
- Technique letting two NAT'd MXs reach each other via outbound UDP flows the registry coordinates — no inbound port-forward needed.
- Hub / Spoke
- Topology roles. A Hub tunnels to every Hub + listing spoke; a Spoke tunnels only to its chosen hub(s).
- VPN concentrator
- A one-armed MX that only terminates VPN tunnels (no LAN routing) — the scalable datacentre aggregation design.
- SD-WAN
- Policy-based steering of app traffic across multiple WAN links by performance, not just up/down state.
- SD-WAN+
- The higher Meraki licence tier; unlocks Internet flow preferences and richer SD-WAN policy.
- Flow preference
- A rule pinning a matched flow to a chosen uplink (e.g. O365 over WAN1).
- Performance class
- A latency/jitter/loss quality bar (built-in VoIP or custom). Breach it and matching flows fail over.
Quick reference — last-minute revision card
| Topic | Key fact | Where |
|---|---|---|
| Enable AutoVPN | Set Hub or Spoke, tick subnets, Save | Security & SD-WAN > Configure > Site-to-site VPN |
| Registry ports | Outbound UDP 9350–9381 to Meraki cloud | Upstream firewall |
| Keepalive | Every 10s; >6 missed = node marked down | Registry |
| NAT "Unfriendly" | Set NAT traversal = Manual: Port forwarding | Site-to-site VPN settings |
| Scale topology | Hub-and-spoke + dedicated hubs; mesh = N(N-1)/2 tunnels | Design choice |
| SD-WAN+ models | MX67/68/75/85/95/105/250/450 (and more) | Licensing |
| VoIP steering | VoIP performance class + RTP flow preference | SD-WAN & traffic shaping |
| ICMP gotcha | ICMP is NOT traffic-shaped — ping won't show steering | Testing |
| 2025 advisory | CVE-2025-20271 AnyConnect DoS — patch firmware | Organization > Firmware upgrades |
📚 Sources
- Cisco Meraki Documentation — Meraki Auto VPN — Configuration and Troubleshooting. documentation.meraki.com
- Cisco Meraki Documentation — Configuring Hub-and-spoke VPN Connections on the MX Security Appliance & Auto VPN General Best Practices.
- Cisco Meraki Documentation — SD-WAN and Traffic Shaping & MX Load Balancing and Flow Preferences.
- The Meraki Community — AutoVPN Troubleshooting & AutoVPN tunnels not re-establishing after WAN drop. community.meraki.com
- Hummingbird Networks — Hardening Meraki Auto VPN for High-Scale Performance (practitioner war-stories).
- Cisco Security Advisory — CVE-2025-20271: Meraki MX & Z Series AnyConnect VPN DoS (CVSS 8.6, June 2025).
- Cisco — Engineering Cisco Meraki Solutions (ECMS) 500-220 exam blueprint (Design/Implement/Operate/Troubleshoot).
What's next?
The MX isn't just a router — it's a full security appliance. Next we open the Layer-7 side: content filtering, the Cisco AMP malware engine, and the Snort-based IDS/IPS that inspects traffic inline.
— Techclick Team