Networking for GNU/Linux

Ahmed D. Mekkawy AKA linuxawyahmed@linuxawy.org

Part I : TCP/IP overview

Though you should already know TCP/IP, this quick overview Is made to make sure that all course attendees are aligned.

OSI Model Vs. TCP/IP Model

TCP/IP Connection Types

TCP: Connection OrientedInitiating a connection: 3 Way Handshaking

Finalizing a connection.

UDP: Connectionless

ICMP: Error, Control, Information.

Ports

Lower numbered Vs. Higher numbered ports.

Ports can handle multi-connection.

Listening Ports.

TTL

Time To Live.

Decreased by 1 with each router passed.

Designed to forbid packets to flow endlessly because of a mis-configured router or so.

IP

IPv4 Vs. IPv6

Private IPs (eg. 192.168.xxx.xxx , 10.xxx.xxx.xxx)

Localhost (127.xxx.xxx.xxx)

Subnets & netmask.

Network & Broadcast IP.

Gateways

Routing.

Natting.

Port-Forwarding.

Firewalling.

Hub Vs. Switch

Switch Vs. Hub

Switch Vs. Router

Access Points, are they Switches or Hubs?

Main Network Services

DNS

DHCP

Part II: Configure wired NIC

The Native way

ifconfig eth0 10.0.0.1 netmask 255.255.255.0 up

Ifup & ifdown

Multiple Ips on the same NIC: Child interfaces:Ifconfig eth0:0 10.0.0.2 netmask 255.255.255.0 up

Routing:route add default gw 192.168.0.1 eth0

route add -net 10.0.0.1 netmask 255.0.0.0 gw 192.168.0.200 eth0

DHCP client: dhclient eth0

The native way - Contd.

hostname

/etc/resolv.conf

/etc/hosts

The Redhat/Fedora way

/etc/sysconfig/network-scripts/ifcfg-eth0

Or

# File: ifcfg-eth0DEVICE=eth0IPADDR=192.168.1.100NETMASK=255.255.255.0BOOTPROTO=staticONBOOT=yes# The following settings are optionalBROADCAST=192.168.1.255NETWORK=192.168.1.0

# File: ifcfg-eth0DEVICE=eth0BOOTPROTO=dhcpONBOOT=yes

Redhat way - Contd.

/etc/sysconfig/network

Static routes can be added per NIC:

NETWORKING=yesHOSTNAME=bigboyGATEWAY=192.168.1.1

# File /etc/sysconfig/network-scripts/route-wlan0#10.0.0.0/8 via 192.168.1.254

Debian / Ubuntu way

/etc/network/interfaces

# File: /etc/network/interfaces# The loopback network interfaceauto loiface lo inet loopback# The primary network interfaceauto eth1iface eth1 inet static address 216.10.119.240 netmask 255.255.255.224 network 216.10.119.224 broadcast 216.10.119.255 gateway 216.10.119.241 # dns-* options are implemented by the resolvconf dns-nameservers 216.10.119.241 up route add -net 10.0.0.0 netmask 255.0.0.0 gw 216.10.119.225 eth1

Debian / Ubuntu way - Contd.

/etc/network/interfaces Contd

/etc/hostname

auto eth1:1iface eth1:1 inet static address 216.10.119.239 netmask 255.255.255.224

# The secondary network interfaceauto eth0iface eth0 inet dhcp

Part III: Configuring wireless

Wireless Network

ls /sys/classes/net

ls /sys/classes/net/eth1 (look for wireless)

iwlist eth1 scan

Ifconfig eth1 0.0.0.0 up

iwconfig eth1 mode Managed

iwconfig eth1 channel 6

Iwconfig eth1 key restricted s:MyKey # for WEP

Wireless Network - Contd.

If the encryption is WAP:Ifconfig eth1 0.0.0.0 up

Killall wpa_supplicant

wpa_passphrase linksys mysecret > /etc/wpa_supplicant.conf

Iwconfig eth1 mode Managed

Iwconfig eth1 essid linksys

Iwconfig eth1 channel 11

wpa_supplicant -i eth1 -c /etc/wpa_supplicant.conf -d -D wext &

Wireless Network - Contd.

Then get the IP normally through dhcp or through ifconfig command.

dhclient eth1

Reference

http://www.linuxhomenetworking.com

linuxac.org Magazine Jan, 2008

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