Technical data

1. Documentation of the base package

1.1. Introduction

ﬂi4l is a Linux-based router, capable of handling ISDN, DSL, UMTS, and ethernet connections,

with little hardware requirements: an USB stick used for booting, an Intel Pentium MMX

processor, 64 MiB RAM as well as (at least) one ethernet network adapter are completely

suﬃcient. The necessary boot medium can be created under Linux, Mac OS X or MS Windows.

You don’t need any speciﬁc Linux knowledge, but it is deﬁnitely helpful. However, you should

possess basic knowledge about networking, TCP/IP, DNS, and routing. For developing your

own extensions exceeding the basic conﬁguration, you will need a working Linux system as

well as Linux skills.

ﬂi4l supports various boot media, among them USB sticks, hard disks, CDs, and last but

not least booting over the network. An USB stick is in many respects ideal: Today, almost

every PC can boot from it, it is relatively cheap, it is big enough, and installing ﬂi4l onto it

is relatively easy under both MS Windows and Linux. In contrast to a CD it is writable and

thus additionally able to hold non-volatile conﬁguration data (as e.g. DHCP leases).

• General features

– Creation of boot media under Linux (Page 251), Mac OS X (Page 251), and MS Win-

dows (Page 254)

– Conﬁguration through ﬂat ASCII/UTF-8 ﬁles

– Support for IP masquerading and port forwarding

– Least Cost Routing (LCR): automatic provider selection based on daytime

– Displaying/Computing/Logging of connection times and costs

– MS Windows/Linux client imonc talking to imond and telmond

– Upload of updated conﬁguration ﬁles via MS Windows client imonc or via SCP

under Linux

– Boot media use the VFAT ﬁle system as permanent storage

– Packet ﬁlter: External access to blocked ports is logged

– Uniform mapping of WAN interfaces to so-called circuits

– Running ISDN and DSL/UMTS circuits in parallel is possible

• Router basics

– Linux kernel 3.14

– Packet ﬁlter and IP masquerading

– Local DNS server in order to reduce the number of DNS queries to external DNS

servers