Dialer Interface; Dhcp - Teldat -3Ge-USB User Manual

3 Configuring in Generic mode

3.1.1 Dialer Interface

Configuring the Cisco router for WWAN connectivity through the Teldat-3Ge-USB with PPPoE is based on the cre-
ation of a dialer interface. The router establishes a PPPoE session through said interface and uses it to negotiate
and establish a PPP link with the WWAN mobile network. In the PPPoE session, the router acts as client and the
Teldat-3Ge-USB as server.
The dialer interface configuration shows the PPP parameters configuration (user and password), the MTU definition,
which should not exceed 1492 bytes in PPPoE. There are also commands for configuring NAT port forwarding, and
the definition of the pool and the dialer interface group.
Configuring the maximum size of the TCP segment (MSS) is very important with PPPoE to avoid problems. Set a
maximum size of 1452 bytes for the TCP segment, to take into account the 20 byte IP header and the 20 byte TCP
header (MTU –20 –20 = 1452). If you do not configure this setting, a host (a PC with a default MTU value of 1500
bytes), could negotiate a 1500 byte MSS. This results in packets being received in the Teldat-3Ge-USB, through the
3G modem, bigger than 1492 bytes. These are dropped as they cannot be encapsulated in PPPoE to the router.
interface Dialer1
ip address negotiated
ip mtu 1492
ip nat outside
ip virtual-reassembly
ip tcp adjust-mss 1452
encapsulation ppp
dialer pool 1
dialer-group 1
no cdp enable
ppp chap hostname internet
ppp chap password 0 internet

3.1.2 DHCP

The Cisco router is the DHCP server for the Teldat-3Ge-USB. This protocol is used to configure certain parameters
in the Teldat-3Ge-USB, such as the SIM PIN number, the WWAN mobile network APN and the parameter telling the
Teldat-3Ge-USB to operate in generic mode.
ip dhcp pool ethant
host 172.24.78.28 255.255.0.0
client-identifier 7465.6c64.6174
bootfile fwethant.img
next-server 172.24.78.29
option 43 ascii antenna&routertype=generic&apn=internet.es&pin=5710
default-router 172.24.78.29
Use the bootfile option to give the Teldat-3Ge-USB the filename containing its application. Said application is auto-
matically downloaded from the indicated TFTP server, through the next-server option (provided this contains a more
updated version than the one currently running on the Teldat-3Ge-USB).
The client-identifier specifies the client-id the router must receive in order to accept the DHCP request from the
Teldat-3Ge-USB. This is "teldat" in ASCII (74656c646174 in hexadecimal).
The configuration parameters needed, so the Teldat-3Ge-USB can operate, are sent through option 43.
• The sent sentence syntax consists of parameters separated by the & signal.
• Not all parameters are necessary.
• If a parameter is not sent, the result depends on the default parameter value.
• If you have to enter a special character, use the % symbol followed by the ascii value with 2 hexadecimal digits.
For example, the character ' &' would be %26. So to enter an apn equal to access&network.es, enter it as
apn=access%26network.es.
• Some parameters have a shortened version. For example, routertype in short is rt.
The first word contained in option 43 should be antenna so the Teldat-3Ge-USB accepts the address offered by the
router. The Teldat-3Ge-USB will not accept said address if this word is not entered.
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Teldat S.A.
Teldat-3Ge-USB User Manual