Mobile L2TP Technical
An L2TP tunnel is established using the pre-agreed IP addresses, hostname and shared secret. Note that if your LNS rejects the tunnel connection, or fails to respond to the SCCRQ or a subsequent HELLO, then it will be black listed for 5 minutes allowing further connections to go to the fall-back LNSs.
Once the tunnel is established, a session is established for each connecting data SIM.
ICRQ
| Attribute | Meaning | |
| Assigned Session ID | 14 | Session ID |
| Call Serial Number | 15 | Present if received from mobile network |
| Calling Number | 22 | 19 digit ICCID of SIM, starting 8944 |
Limitations
- Only available on data SIMs.
- Called Number is a fixed APN and not the one entered on the phone, which is ignored.
- Reduced MTU of 1450 is in operation when L2TP is run over the internet. This restriction can be removed to allow full 1500 byte MTU where direct *Baby-jumbo frame links are available from us to your LNS.
- User-Name passed is what is provided by the mobile which is usually blank. Do not use the password 'password' as this will not be passed through.
- IPv6 is not available yet, but is planned for the future if possible.