Cisco 3G Wireless WAN Configuration Example

In this tutorial you will learn how to configure your Cisco router to use its 3G / UMTS / HSPDA WAN interface. I’m using a HWIC-3G-GSM WAN card but the configuration will be very similar for most of the cards out there. Even if you are using 4G / LTE this will be very useful.

Instead of just showing the commands I will explain the entire connection process and tell you why we need to use each command. Once the configuration is complete I’ll show you how to verify your work and how to use debug commands to fix any possible problems that might arise.

For your 3G wireless connection we require 3 items to establish a data connection:

  • SIM
  • Radio Modem
  • Router

The SIM card is used to identify the end user, the radio modem takes care of the physical layer and the router part is required for layer 2/3 (PPP and IP). For each of these items we have to configure a couple of things. The SIM card has to be unlocked with a PIN code, the radio modem requires AT dial commands to start the connection and the router requires some PPP commands.

Let’s walk through everything step by step!

Configuration

First we will check the interfaces of our router. Below you can see that my router has a Cellular0/1/0 interface:

Router#show ip interface brief
Interface                  IP-Address      OK? Method Status                Protocol
FastEthernet0/0            unassigned      YES unset  administratively down down    
FastEthernet0/1            unassigned      YES unset  administratively down down    
Serial0/0/0                unassigned      YES unset  administratively down down    
Cellular0/1/0              unassigned      YES unset  down                  down

That’s my HWIC-3G-GSM interface. All the show commands for the cellular interface are found under the show cellular command:

Router#show cellular 0/1/0 ?
  all         Display all the information
  connection  Current active connection and statistics
  hardware    Cellular modem hardware information
  network     Cellular network information
  profile     Profile information in the modem
  radio       Cellular modem radio information
  security    Modem security status

These commands are useful to check your signal strength and to see if you are connected to a network. The first thing we will do is check if we have a signal. Without a signal it will be hard to establish a connection:

Router#show cellular 0/1/0 radio 
Current Band = WCDMA 2100, Channel Number = 10637
Current RSSI = -88 dBm
Band Selected = Auto

Our radio is connected and the current RSSI (Received Signal Strength Indicator) is -88 dBm which is good enough for this tutorial. Cisco has a reference index to show you what RSSI values are acceptable:

  • Off: Low RSSI (under -100 dBm).
  • Slow Green Blink: Low or medium RSSI (-99 to -90 dBm).
  • Fast Green Blink: Medium RSSI (-89 to -70 dBm).
  • Solid Green: High RSSI (-69 dBm or higher).
  • Solid Yellow: No service or no RSSI detected.

A signal strength of -88 dBm indicates medium signal strength, not bad since this router is in an enclosed 42u rack cabinet. There are also some leds on the WIC but it’s probably easier to look at your console. Since we have a signal, let’s check to what network we are connected:

Router#show cellular 0/1/0 network 
Current Service Status = Emergency Only, Service Error = None
Current Service = Invalid
Packet Service = None
Packet Session Status = Inactive
Current Roaming Status = Roaming
Network Selection Mode = Automatic
Country = NLD, Network = NL KPN
Mobile Country Code (MCC) = 204
Mobile Network Code (MNC) = 8
Location Area Code (LAC) = 1190
Routing Area Code (RAC) = 0
Cell ID = 26561
Primary Scrambling Code = 97
PLMN Selection = Automatic

Above you can see that the service status is “Emergency Only”. This is because my SIM has a pincode and I have to unlock it first. There are no service errors and we are connected to the NL KPN network in The Netherlands. Let’s unlock the SIM card and see if it makes a difference:

Router#cellular 0/1/0 gsm sim unlock 0000
!!!WARNING: SIM will be unlocked with pin=0000(4), call will be disconnected!!!
Are you sure you want to proceed?[confirm]

After unlocking the SIM you will see that the service status is now normal:

Router#show cellular 0/1/0 network 
Current Service Status = Normal, Service Error = None
Current Service = Combined
Packet Service = UMTS/WCDMA (Attached)
Packet Session Status = Inactive
Current Roaming Status = Home
Network Selection Mode = Automatic
Country = NLD, Network = NL KPN
Mobile Country Code (MCC) = 204
Mobile Network Code (MNC) = 8
Location Area Code (LAC) = 1190
Routing Area Code (RAC) = 0
Cell ID = 26561
Primary Scrambling Code = 97
PLMN Selection = Automatic
Registered PLMN =  , Abbreviated = 
Service Provider = KPN

We are connected to the network but before we can do anything we need to configure a profile. This is where you configure the APN (Access Point Name) and authentication (if required). Let’s see if we already have a profile:

Router#show cellular 0/1/0 profile 
 * - Default profile

We don’t have any profiles so let’s create a new one:

Router#cellular 0/1/0 gsm profile create 1 prepaidinternet
Profile 1 will be created with the following values:
APN = prepaidinternet
Are you sure? [confirm]
Profile 1 written to modem

My provider doesn’t require any authentication but I do have to set the APN which is “prepaidinternet”.  Now we have to configure a chat script which tells the modem to connect using old-school AT dial commands:

Router#configure terminal
Router(config)#chat-script gsm "" "ATDT*99*1#" TIMEOUT 30 "CONNECT"

The name of my chat script is “gsm” and it will dial to number 99. The *1 refers to the profile that we just configured, if you only have one profile you can remove it if you want. I like to keep it for clarity or in case I want to use another profile in the future.

This takes care of the profile and the chat script, now we can configure the cellular interface and PPP settings:

Router(config)#interface Cellular 0/1/0 
Router(config-if)#dialer in-band
Router(config-if)#dialer pool-member 1
Router(config-if)#ppp chap hostname prepaidinternet
Router(config-if)#ppp chap password 0 fakepassword

The dialer in-band and dialer pool-member 1 commands tell the interface to use a dialer interface which we will configure in a second. I didn’t require authentication for the profile but I do have to configure PPP authentication. This depends on your ISP but in my case the hostname has to match the APN and for that password I can configure whatever I like. There’s nothing else we require on the cellular interface, we’ll have to use the dialer interface:

Router(config)#interface Dialer 1
Router(config-if)#ip address negotiated 
Router(config-if)#encapsulation ppp
Router(config-if)#dialer pool 1
Router(config-if)#dialer string gsm
Router(config-if)#dialer persistent
Router(config-if)#ppp ipcp dns request
Router(config-if)#no cdp enable

First we tell the router to request the IP address through PPP with the ip address negotiated command and the dialer pool command binds the dialer interface to the cellular interface. Our dialer string refers to the chat-script called “gsm” and dialer persistent is required to tell the router to initiate the connection immediately. If you don’t use this it will only establish a connection when you try to send traffic out of the 3G interface.

Some providers force you to use their DNS servers so that’s why I added the ppp ipcp dns request command. Once the router establishes a PPP connection it will request the ISP to send the IP addresses of the DNS servers. Last but not least, we disable CDP (Cisco Discovery Protocol) because there’s no point sending these packets towards the service provider.

The final step is adding the chat script to the line that comes with your cellular interface:

Router(config)#line 0/1/0
Router(config-line)#script dialer gsm

If everything went OK, you will see your cellular and dialer interface going up:

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Forum Replies

  1. Hi Matt,

    I don’t think it’s an issue. There are different radios, firmware and IOS versions. It could be a cosmetic bug.

    You might want to configure it, see if it works. If it doesn’t, you could try to install the latest firmware and/or try another IOS image.

    Rene

  2. Hmm good question, I doubt you can automatically receive the APN. Normally we configure it manually on the router.

  3. Hi Rene, i am trying to play with 4g-lte-ga and when Im trying to configure

    dialer pool-member 1

    i get

    %Remove Leagacy DDR configuration first

    can you help me out here please ?

    thanks

  4. Hello Maksym

    It seems that Legacy Dial-on-Demand routing (DDR) is configured on the router. This means that one or more of the following commands are enabled on the router:

    In Global Configuration mode:

    dialer dtr or dialer inband <em>parity</em>

    On some interface:

    dialer string ...
    dialer map
    dialer-list
    dialer-group
    dialer enable-timeout
    dialer wait-for-carrier-time
    dialer priority
    

    Check both physical and virtual (dialer and otherwise) interfaces for any such configurations and remove them.

    You might find some additional information here: http://www.cisco.c

    ... Continue reading in our forum

  5. Hi Guys,

    For some reason my cellular interface on the router is not telnet/ssh able.
    When the cellular interface comes up its pingable but we cant telnet/ssh it.

    Did a wire shark,

    tcp syn
    tcp syn ack
    ack
    sshv2
    

    then loads of the errrors below before timing out.

    5591	283.604252	x.x.x.x	x.x.x.x	TCP	82	[TCP Retransmission] 64464→22 [PSH, ACK] Seq=1 Ack=1 Win=65392 Len=28

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