I have a number of EM7455 modems, full Sierra models running the latest firmware, that are performing in a very odd way.
When we attempt to use Linux pppd to establish connectivity the IP addresses between the provider cell network and the IPCP negotiation are wrong.
In our chat script we used to send the AT+CGDCONT=1 command to set up our private APN before establishing ppp negotiation with AT99***1#. With this setup the modem would drop its LTE connection to the cellular network, reestablish and receive a new IP address.
HOWEVER the PPP IPCP negotiation provides the PREVIOUSLY KNOWN IP address from the LTE peering connection. If we remove the AT+CGDCONT command it has worked MOST of the time.
It is as if the modem has two halves of a brain and are not working together.
Given the NEW IP address I am able to send ICMP requests and hear responses from the LTE side of the modem. Because the IP Address from the PPP IPCP negotiation is wrong the packets do not make it into the Linux system so no services are available to communicate.
Has anyone else seen this problem?