Net-HOWTO

Introduction

This is the first release of the GOLEM Network Howto, this document aims to be a sort of unofficial update of the Linux Networking Howto.

General Information about Networking

Sources of non-linux-specific network information

If you are looking for general TCP/IP networking information, here you can find some resources:

• IBM TCP/IP Tutorial and Technical Overview

Generic Network Configuration Information

Network tools

iproute2: IP Routing Utilities

nftables: Linux kernel packet control tool (firewall)

iputils: arping, clockdiff, ping, tracepath

Legacy tools

net-tools: configuration tools for Linux networking (arp, ifconfig, ipmaddr, iptunnel, mii-tool, nameif, netstat, plipconfig, rarp, route, slattach)

iptables: Linux kernel packet control tool (firewall)

Network Application Programs

Most common network application programs are collected in the inetutils package: dnsdomainname, ftp, ftpd, hostname, ifconfig, ping, rcp, rlogin, rlogind, rsh, rshd, talk, talkd, telnet, telnetd, whois

IPv4 Addresses, an Explanation

Internet Protocol v4 Addresses are composed of 4 bytes (32 bit), each byte is converted to a decimal number (0-255) and bytes are separated by a . (dot), for this reason IPv4 addresses are limits to near 4 billions (2³²). Usually every network interface has its own IP address in a format like this: 192.168.0.5

Subnetting

Addresses in a network have some digits in common, that part is called the network portion of the address, the remaining numbers are called the host portion.

For example:

           -----------------  ---------------
           Host Address       192.168.0.23
           Network Portion    192.168.0.
           Host portion                .23
           -----------------  ---------------
           Network Address    192.168.0.0
           Broadcast Address  192.168.0.255
           -----------------  ---------------

Subnetting is a way to subdivide an TCP/IP network. The Classless Inter-Domain Routing (CIDR) is the current method for defining subnet, the IP address is followed by a prefix number between 0 and 32 that shows how many bits represent the network.

192.168.0.23/24 => network 192.168.0.0 - 192.168.0.255
192.168.0.23/16 => network 192.168.0.0 - 192.168.255.255

This method replace the obsolete classful network addressing architecture.

The maximum number of addresses of a network may be calculated as 2^{32 − prefix number}

CIDR	Classful network mask	Number of Hosts	Typical use
/8	255.0.0.0	16777214 = 224 - 2	Largest IANA block allocation
/9	255.128.0.0	8388608 = 223
/10	255.192.0.0	4194304 = 222
/11	255.224.0.0	2097152 = 221
/12	255.240.0.0	1048576 = 220
/13	255.248.0.0	524288 = 219
/14	255.252.0.0	262144 = 218
/15	255.254.0.0	131072 = 217
/16	255.255.0.0	65536 = 216
/17	255.255.128.0	32768 = 215	ISP / large business
/18	255.255.192.0	16384 = 214	ISP / large business
/19	255.255.224.0	8192 = 213	ISP / large business
/20	255.255.240.0	4096 = 212	Small ISP / large business
/21	255.255.248.0	2048 = 211	Small ISP / large business
/22	255.255.252.0	1024 = 210
/23	255.255.254.0	512 = 29
/24	255.255.255.0	256 = 28	Large LAN
/25	255.255.255.128	128 = 27	Large LAN
/26	255.255.255.192	64 = 26	Small LAN
/27	255.255.255.224	32 = 25	Small LAN
/28	255.255.255.240	16 = 24	Small LAN
/29	255.255.255.248	8 = 2³	The smallest multi-host network
/30	255.255.255.252	4 = 2²	Point-to-point links (glue network)
/31	255.255.255.254	2 = 21	Point-to-point network (RFC 3021)
/32	255.255.255.255	1 = 20	Single host

Traffic between subnets is guaranteed by routers.

Bibliography

Linux Networking HOWTO