The reMarkable shows as an Ethernet device when plugged into a computer via USB. It runs a DHCP server and will listen on 10.11.99.1 by default, assigning IP addresses in the 10.11.99.2 to 10.11.99.6 range (see also Changing the USB Network IP). The DHCP server configuration is in /etc/udhcpd.usb0.conf and the network configuration is in /usr/lib/systemd/network/rndis.network.