Introduce:

• Plan the physical and logical structure of the network
• Assign IP addresses
• Install the network hardware
• Set up each host to configure network interfaces at boot time
• Set up routing daemons and static routes

Designing and installing a physical network  will discuss in Chapter 15. Network Hardware.

This Section talk about non-hardware network setup topic:

• IP address
• ifconfig command
• route command
• routed daemon
• gated daemon

• IP addresses
• must be unique
• assigned by InterNIC Registration Services
• how to get IP address
• ftp or email get form
• InterNIC guaranteed unique
• subdivide address space assigned to you
• subnet address
• responsible for assigning a host number to each machine on your network.

• Addresses are assigned to network interface, not machines.
• if machine more than one interface, it will more than one address
• mapping the address and machine's name into the /etc/hosts file, or DNS.
• allow user to refer it by hostname
• for example:
• 130.85.100.125  everest.cs.umbc.edu everest.cs everest
          127.0.0.1       localhost         loopback
class B address, on the 100 subnet known name as everest.cs.pdx.edu
• disadvantage: /etc/hosts file must be replicated on every machine.
• Chapter 18 Sharing System Files will discuss it.
• DNS is also a good method to manage the mapping, it allows users to refer machines by their hostnames.
• Chapter 16 will describe it more detail

• ifconfig command:
• ifconfig [-v] interface | -a [family] [ dest_addr ] [ up ] [ down ] option [ netmask mask ] [ metric n ] [broadcast]
• interface identifies the hardware interface could be find with command netstat -i
• Name Mtu   Network         Address            Ipkts Ierrs    Opkts Oerrs  Coll

ec0  1500  130.85.100      everest.cs.umbc. 42385380    42 37721674   257 17000333
                            clifford.cs.umbc.
lo0  32992 loopback        localhost.umbc. 42676431     0 42676431     0     0
• family argument tell which protocal layer you want to configure with, in real life, it always deal with IP configuration, so set family to inet
• default value is inet for some systems, except HP-UX and BSDI require rexplicitly value
• address parameter
• two format: traditional Internet dot notation
• or hostname: discovered by looking up the name in /etc/hosts or DNS
• recommend the number address
• loopback interface is ususlly called lo0, it is fictitious hardware, through which packets bound for the local host can be routed to itself
• ifconfig other parameter
• -a          Apply the commands to all interfaces in  the system.
• -ad        Apply the commands to  all  ``down''  interfaces in the system.

-au        Apply the commands to  all ``up''  interfaces in the system.
• arp        Enable the use of the  Address  Resolution Protocol  in mapping between network level addresses   and   link   level   addresses( Ethernet).   This is currently implementent for mapping between TCP/IP  addresses  and Ethernet addresses.
• -arp       Disable the use of the Address Resolution Protocol.
• auto-revarp    Use the Reverse Address Resolution  Protocol  (RARP)  to  automatically  translate Ethernet address to IP address for this interface.
• metric n          Set the routing metric of the interface to n,  default 0.   metrics 16 means infinite routing.
• netmask mask    The option sets the subnet mask for the interface.  The mask contains 1's for  the  bit  positions  in  the 32-bit address which are to be used for the network and subnet  parts, and  0's  for  the  host  part.

A `+' (plus sign) is given for the netmask value,  the mask is looked up in the netmasks database using the interface network number as  the key.
• broadcast addr   The option sets the IP broadcast address for the interface. The default broadcast address is the address with a host part of all 1's.

A + (plus sign) given for the broadcast  value causes  the  broadcast address to be reset to a default appropriate based on netmask and so on.
• ifconfig -a netmask + broadcast +   and

ifconfig -a broadcast + netmask +
may  result  in  different  values  for  the  interfaces'  broadcast addresses.arguments of ifconfig are interpreted left
to right

A example of Routing tables

Internet:
Destination                  Gateway                Netmask        Flags      Refs     Use       Interface
default                        130.85.100.1                               UGS        19   129178       ec0
127.0.0.1                   127.0.0.1                                     UH          10    46635         lo0
130.85.100                link#1                     0xffffff00        UC           0        0              ec0
130.85.100.125         127.0.0.1                                     UGHS      1     1934           lo0
130.85.101                130.85.100.150     0xffffff00        UG           0     2306           ec0
224                             link#1                    0xf0000000   UCS         0        0              ec0
255.255.255.255       130.85.100.255                           UGHS      0        0              ec0

 G      Gateway address. Destination requires forwarding by intermediary
 H       Host entry (net otherwise)
 U       route is up, usable
 S       Manually added route
 C      Generate new routes on use

• route - manually manipulate the routing tables, define static routes.
• Routing is performed at IP layer. when a packet for other host arrived the router
• compare the destination IP address with the routes in the routing table
• if IP match, forward the packet to the 'next gateway' assicated with the route
• if host is a directly-connected network with the route, the 'next gateway' is the host interface, the packet is directly to its destination. ifconfig add it when configure an interface
• otherwise, if a default route exist, forward the packet to that gateway,

if not ,    the router return an ICMP back to sender
• route command
• example:
• route add host 127.0.0.1   0  #for loopback

route add default 128.138.242.1   1   # gateway
• add       Add a route.
• flush     Remove all 'gateway' routes.
• delete    Delete a specific route.
• change  Change aspects of a route (such as its gateway).
• get         Lookup and display the route for a destination.
• net and host  The optional modifiers net and host force the destination to be interpreted as a network or a host..  Otherwise, if the destination has a ``local address part'' of INADDR_ANY , or if the destination is the symbolic name of a network, then the route is assumed to be to a network; otherwise, it is presumed to be a route to a host.

For example, 128.32 is interpreted as       -host 128.0.0.32  ;
                     128.32.130 is interpreted as -host 128.32.0.130;
           -net    128.32 is interpreted as             128.32.0.0;     ( means net )
    and -net     128.32.130 is interpreted as     128.32.130.0. ( means net )

routed was a standard UNIX routing daemon

• it is simplicity
• it is gradually replaced by gated daemon
• routed only support RIP
• RIP is a simple interior routing protocol.
• every 30 seconds, routing server check the network information of routes that it know
• then update routing table
• routed includes two modes
• server mode (-s)
• quite mode (-q)
• both modes listen for broadcast, but only server mode distribute their own information
• By dafault, the (-q) quite mode run with one interface, the (-s) server mode run with several interface
• routed -t
• use for debug routing
• no require configuration if no gateway to Internet or other AS ( autonomous systems )
• single gateway, just run routed with -g flag ( -g: global )
• more gateways, describe them in file /etc/gateways, the routed will reference it when starts up.
• gateways file defines entries like route command
• gateways file also defines gateway as active or passive
• active gateways will be cancled if no speak RIP
• passive gateways will still exist

• gated support different protocol
• Interior Routing Protocol: RIP, OSPF
• Exterior Routing Protocol: EGP, BGP
• Old Protocol: HELLO
• with gated you can use multiple protocol at same time, and gated can translate routing metrics between them

A example of configure file:

RIP yes ( yes means to be a RIP serevr mode if there is more than one interface, otherwise a passive listener -- quite mode)
EGP no
HELLO no

defaultgateway 128.138.243.120 rip passive. This line sets the default route for the local machine.
 

• Old systems, the network was configured by editing /etc/rc and directly changing the ifconfig and route commands.
• The newer scripts reuse configuration information from other system files or define they own configuration files.