Cisco router configuration for Australian 3G or 4G connectivity

There is very little in the way of solid documentation on configuring Cisco devices with cellular interfaces to work with Australian carriers, especially Optus.

The first thing to note is that Optus only support static public IPs on 3G connections, while by default the cellar interfaces will connect at 4G if coverage is available. To get around this, we need to force 3G.

Forcing 3G

Firstly, shut down all all Cellular interfaces with the shutdown command, then run Cellular 0/0/0 lte technology umts.

Configuring a cellular profile

The default profile will have an empty APN and allow both IPv6 and 6. It also specifies no authentication settings. With Optus, we need to specify the APN of yesbusiness as this is the APN required for static IP support, and CHAP credentials of optus/optus. These were details provided by Optus support.

router# cellular 0/0/0 lte profile create 1 yesbusinessip chap optus optus ipv4

Warning: You are attempting to modify the attach profile.
Please consult the service provider before doing so.
Modem power cycle required for change to take effect.

PDP Type = IPv4v6
Access Point Name (APN) =
Authentication = NONE

Profile 1 already exists with above parameters. Do you want to overwrite? [confirm]

Profile 1 will be overwritten with the following values:

PDP type = IPv4
APN = yesbusinessip
Username = optus
Password = optus
Authentication = CHAP

Are you sure? [confirm]
Profile 1 written to modem

Configure the Cellular interface

We then configure the cellular interface, which is very similar to a standard Dialer interface used with ADSL services in Australia.

interface Cellular0/0/0
 description -- Link to Optus 3G --
 ip address negotiated
 ip nat outside
 ip virtual-reassembly in
 encapsulation slip
 load-interval 60
 dialer in-band
 dialer idle-timeout 300
 dialer string INTERNET
 dialer-group 1
 async mode interactive

I have left out the usual NAT overload configuration, there is nothing special here and will be identical to other connection types.

Configuring the chat script

The chat script defines the command the modem needs to execute in order to connect. This seems unnecessarily low level and reminds be of the dial up days, but it is actually fairly simple. Most routers will come with a default chat script, but I like to define my own (even if it’s identical).

router(config)#chat-script INTERNET "" "AT!CALL" TIMEOUT 20 "OK"
chat-script INTERNET "" "ATDT*99#" TIMEOUT 30 CONNECT

Configure the Line

Finally, we configure the line. To determine which line we need to configure, we can check show line and to find the line which corresponds with the Cellular interface.

router#show line
   Tty Line Typ     Tx/Rx    A Modem  Roty AccO AccI  Uses  Noise Overruns  Int
*     0    0 CTY              -    -      -    -    -     0      0    0/0      -
      1    1 AUX   9600/9600  -    -      -    -    -     0      0    0/0      -
      2    2 TTY   9600/9600  -    -      -    -    -     0      0    0/0      -
I 0/0/0    3 TTY              - inout     -    -    -     0      0    0/0    Ce0/0/0
  0/0/1    4 TTY              -    -      -    -    -     0      0    0/0    Ce0/0/1
    132  132 VTY              -    -      -    -    -     0      0    0/0      -
    133  133 VTY              -    -      -    -    -     0      0    0/0      -
    134  134 VTY              -    -      -    -    -     0      0    0/0      -
    135  135 VTY              -    -      -    -    -     0      0    0/0      -
    136  136 VTY              -    -      -    -    -     0      0    0/0      -

This is where we specify the chat script defined in the first step.

(config)#line 0/0/0
router(config-line)#script dialer INTERNET
router(config-line)#exec

Send traffic through the interface

As the cellular connection is triggered by traffic, that is, the connection will not come up until there is data to route, we need to define a route and push some traffic through.

dialer-list 1 protocol ip permit
ip route 0.0.0.0 0.0.0.0 Cellular0/0/0 10 name Failover-Optus-3G

That’s it. Your cellular service should now be usable.

A final tip, I’ve found the cellular service can take a few minutes to come up and start passing traffic when the router is reloaded, so some patience is needed.