PPP

Point-to-Point Protocol (PPP) in RouterOS mobile networking provides a method for establishing direct connections between two network nodes over serial interfaces, including cellular modems. While modern LTE interfaces typically use direct IP connectivity, PPP remains important for legacy modem support and specific use cases requiring PPP encapsulation.

Overview

PPP in the mobile networking context serves two primary purposes:

PPP Client: Connecting to cellular networks via modems that require PPP encapsulation (common with older 3G modems and certain LTE modems)
PPP Server: Accepting incoming PPP connections over cellular for remote access scenarios

PPP provides features not available with direct IP interfaces, including:

Authentication (PAP, CHAP, MS-CHAPv1, MS-CHAPv2)
Link quality monitoring
Dynamic IP address assignment
Compression negotiation
Error detection

PPP Client

The PPP client creates outbound PPP connections through cellular modems. This mode is used when the cellular network requires PPP authentication or when the modem operates in PPP mode.

Interface Creation

Create a PPP client interface for a cellular modem that exposes a serial port:

/interface ppp-client
add apn=internet dial-on-demand=no disabled=no port=usb1 \
    name=ppp-out1 password=internet user=internet

PPP Client Properties

Property	Description	Default
add-default-route	Add default route to peer	no
allow	Allowed authentication methods	mschap2,mschap1,chap,pap
apn	Access Point Name for the cellular network	-
default-route-distance	Distance for auto-added default route	-
dial-on-demand	Connect only when traffic is generated	no
disabled	Enable/disable the interface	yes
port	Serial or modem port to use	-
max-mru	Maximum Receive Unit	1500
max-mtu	Maximum Transmission Unit	1500
mrru	Maximum Reconstructed Receive Unit	disabled
name	Interface name	-
password	Authentication password	-
profile	PPP profile to use	default
user	Authentication username	-

Configuration Example

Basic PPP client for a modem on usb1:

/interface ppp-client
add apn=internet authentication=chap port=usb1 name=ppp-out1 \
    password=internet user=internet

/interface ppp-client enable ppp-out1

/interface ppp-client monitor ppp-out1

Expected output:

       status: connected
     dial-status: connected
        uptime: 2m23s
  service-name: internet
       ipaddress: 10.128.XXX.XXX
         dns-server: 10.128.XXX.XXX
       mtu: 1500
       mru: 1500

Adding Default Route

Automatically add a default route when PPP connects:

/interface ppp-client
add apn=internet add-default-route=yes default-route-distance=10 \
    port=usb1 name=ppp-out1 password=internet user=internet

Dial-on-Demand

Enable dial-on-demand to connect only when traffic requires it:

/interface ppp-client
add apn=internet dial-on-demand=yes port=serial0 name=ppp-out1 \
    password=internet user=internet

With dial-on-demand, the connection remains dormant until outbound traffic is generated, saving data usage.

PPP Server

The PPP server accepts incoming PPP connections, enabling remote access scenarios where clients dial into the router over cellular networks.

Enabling PPP Server

Configure the router to accept PPP connections:

/interface ppp-server
add name=ppp-in1

Server Properties

Property	Description	Default
authentication	Allowed authentication methods	pap,chap,mschap1,mschap2
data-channel	Data channel number	0
max-mru	Maximum Receive Unit for clients	1500
max-mtu	Maximum Transmission Unit for clients	1500
modem-init	Modem initialization string	-
mrru	Maximum Reconstructed Receive Unit	disabled
name	Server name	-
null-modem	Enable null-modem mode	no
port	Serial port to listen on	-
profile	PPP profile for incoming connections	default
ring-count	Number of rings before answering	1

User Authentication

Configure user credentials for PPP server access:

/ppp secret
add name=remoteuser password=SecretPass123 profile=default remote-address=10.0.0.100

/ppp secret
add name=mobileuser password=MobilePass456 profile=default-encryption service=any

PPP Server Example

Set up a PPP server for remote cellular access:

# Create PPP profile for remote users
/ppp profile
add local-address=10.0.0.1 name=remote-pool remote-address=10.0.0.100-10.0.0.200 \
    dns-server=8.8.8.8,8.8.4.4

# Add user credentials
/ppp secret
add name=remoteuser password=SecurePass123 profile=remote-pool

# Enable PPP server on serial port
/interface ppp-server
add profile=remote-pool port=serial0 name=ppp-in1

Monitoring and Troubleshooting

Connection Status

Monitor active PPP connections:

/interface ppp-client monitor ppp-out1

Monitor active sessions:

/ppp active print

Debug Logging

Enable PPP debugging to diagnose connection issues:

/system logging
add topics=ppp action=memory

View PPP-related logs:

/log print where message~"ppp"

Common Issues

Connection refused:

# Verify APN is correct
/interface ppp-client print

# Check authentication credentials
/ppp secret print

Modem not responding:

# Reset the LTE interface
/interface lte reset

# Check physical connection
/system resource usb print

Authentication failures:

# Verify username and password
/interface ppp-client set [find] password=correctpassword

# Check allowed authentication methods
/interface ppp-client set [find] allow=mschap2,chap

PPP Profiles

PPP profiles define connection parameters for both client and server scenarios:

/ppp profile
add name=cellular-profile local-address=10.0.0.1 remote-address=pool1 \
    dns-server=8.8.8.8 idle-timeout=30m use-encryption=required

Profile Properties

Property	Description
local-address	IP address for the router side of PPP
remote-address	IP address or pool for client
dns-server	DNS servers to assign to clients
idle-timeout	Disconnect after inactivity
use-encryption	Encryption requirement (yes, no, required, default)
rate-limit	Bandwidth limits (rx-rate/tx-rate)

Mobile Networking - Main mobile networking documentation
LTE/5G Interface - Direct LTE interface configuration
PPP AAA - PPP authentication and accounting
PPPoE - PPP over Ethernet for ISP connections

PPP

PPP