VoIP is the lab where a lot of CCNA students hit a wall: the phones power on, get an IP address, and then... nothing. No directory number, no dial tone, no call. The reason is almost never the part you typed — it's the one setting you didn't. This guide configures a working VoIP network in Cisco Packet Tracer end to end, from the voice VLAN to inter-site dial-peers, and explains why each piece matters so you can build and fix it yourself.
The short version: a VoIP lab in Packet Tracer is five things in order — a PoE switch to power the phones, a voice VLAN, a DHCP pool with option 150 (so phones find the call server), Call Manager Express (CME) on the router, and dial-peers to call between sites. Miss option 150 and the phones never register. If you'd rather skip the typing, NetPilot builds the whole VoIP lab from a plain-English prompt — "a router running CME, a PoE switch, and two IP phones that can call each other" — hands you a working
.pkt, and explains every line.
What a VoIP lab needs
| Piece | Why it's there |
|---|---|
| PoE switch | IP phones are powered over the Ethernet cable — a non-PoE port leaves the phone dead. |
| Voice VLAN | Keeps voice traffic separate from data so it can be prioritised and addressed cleanly. |
| DHCP + option 150 | Gives the phone an IP and tells it where the call server is. Option 150 is the make-or-break setting. |
| Call Manager Express | The call-control software running on the router itself — registers phones, assigns numbers. |
| Dial-peers | Routing for phone calls between two CME routers (multi-site labs). |
Step 1 — Switch, phones, and the voice VLAN
Cable each IP phone to the switch and create a voice VLAN for the phone ports:
vlan 10
name VOICE
!
interface range FastEthernet0/1 - 5
switchport mode access
switchport voice vlan 10The switchport voice vlan command tells the phone which VLAN to tag its voice traffic with. IP phones are powered over Ethernet, so either use a PoE-capable switch (in Packet Tracer the 3560 supplies PoE; the common 2960 does not) or add the power adapter to each phone on its Physical tab — a phone on a non-PoE port with no adapter stays dark.
Step 2 — Give the router an address on the voice VLAN
The router runs DHCP and CME, so it needs a live interface on the voice subnet. With the switch uplink set as a trunk, add a subinterface for the voice VLAN:
interface GigabitEthernet0/0.10
encapsulation dot1Q 10
ip address 192.168.10.1 255.255.255.0This 192.168.10.1 is the phones' default gateway, the DHCP option 150 target, and the CME ip source-address — all three point back to this interface, so nothing comes up until it's configured.
Step 3 — DHCP pool with option 150
The phones need addresses, and — critically — they need option 150 pointing at the router's voice interface, which is where CME lives:
ip dhcp pool VOICE
network 192.168.10.0 255.255.255.0
default-router 192.168.10.1
option 150 ip 192.168.10.1Option 150 is the single most common reason VoIP labs fail. Without it a phone gets a perfectly good IP address and then sits there forever, because it has no idea where the call manager is. If your phones get an IP but never show a number, check this first.
Step 4 — Call Manager Express (telephony-service)
CME runs on the router. Point it at the router's own voice interface and set capacity:
telephony-service
max-ephones 5
max-dn 5
ip source-address 192.168.10.1 port 2000
auto assign 1 to 5ip source-address is the address phones register to (port 2000 is the SCCP signalling port); max-ephones/max-dn cap how many phones and lines CME will handle; auto assign hands directory numbers to phones as they register.
Step 5 — Phone numbers (ephone-dn)
A directory number is the line; create one per phone and give it a number:
ephone-dn 1
number 1001
!
ephone-dn 2
number 1002With auto assign configured, CME attaches these to phones as they come up. (An ephone is the physical phone; an ephone-dn is the line on it — keeping the two straight is half the battle.)
At this point, two phones on the same router can call each other. Power-cycle them if they don't pick up a number immediately.
Step 6 — Calls between two sites (dial-peers)
When phones live behind two different CME routers, each router needs a VoIP dial-peer describing how to reach the other site's numbers:
dial-peer voice 1 voip
destination-pattern 2...
session target ipv4:10.0.0.2This says "for any four-digit number starting with 2, send the call over IP to 10.0.0.2." Put a matching dial-peer on the other router pointing back, make sure the two routers have IP connectivity, and a phone on site A can dial a phone on site B.
The faster path: describe it, get a working .pkt
Every step above is exact IOS that fails silently if one line is off. The alternative is to describe the lab and let an AI tutor build it:
"Build a Packet Tracer VoIP lab: a 2811 router running CME, a 3560 PoE switch, voice VLAN 10, DHCP with option 150, and three IP phones registered with extensions 1001–1003. Then add a second site and dial-peers so the sites can call each other."
NetPilot generates the whole topology with the voice VLAN, option 150, telephony-service, ephone-dns, and dial-peers already configured, hands you a .pkt to open in Packet Tracer, and explains why each setting is there — so you can defend the config or fix it when a phone won't register. It's tested against hundreds of real Packet Tracer scenarios, and you can verify the IOS on real Cisco CLIs in the cloud — no 870 MB download, no NetAcad account.
FAQ
What router and switch should I use for a VoIP lab in Packet Tracer?
Use a router that exposes Call Manager Express — the 2811 is the standard, reliable CME router in Packet Tracer (some newer models like the 2911 don't expose telephony-service in common PT builds). For the switch, IP phones need power, so use a PoE-capable switch (the 3560 supplies PoE in Packet Tracer) or add each phone's power adapter on its Physical tab. The router runs CME and DHCP; the switch carries the voice VLAN.
What's the difference between an ephone and an ephone-dn?
An ephone is the physical IP phone; an ephone-dn (directory number) is a line — the extension that can ring. You assign numbers to ephone-dn entries, and CME attaches those lines to phones as they register. Mixing the two up is one of the most common points of confusion when reading a CME config.
Do I need a separate Call Manager server in Packet Tracer?
No — Call Manager Express runs on the router itself, so for lab-sized topologies you don't need a dedicated CUCM server. The router's telephony-service handles registration and call control. That's exactly why CME is the standard way to do VoIP in Packet Tracer and CCNA labs.
How many IP phones can Call Manager Express handle in a Packet Tracer lab?
It's capped by the max-ephones and max-dn values you set under telephony-service — set them to at least the number of phones and lines you plan to register. If phones won't register even though everything else looks right, confirm these limits are high enough; a max-ephones of 2 will silently refuse a third phone.
Related guides: Why Won't My IP Phones Register in Cisco Packet Tracer? · Cisco Packet Tracer VoIP (build any VoIP lab in your browser) · Cisco Packet Tracer Online · Free CCNA Practice Lab
Want the lab without the typing? Describe your VoIP lab to NetPilot and get a working, fully explained .pkt in about two minutes — no download required.