- Minumum amount of
information needed
to connect a host/node (computer)
on the Internet:
- The host must be given a
(unique) IP address
- The host must have a minimum (smallest possible) routing table (in order to forward IP packets !!!)
- The host must be given a
(unique) IP address
- Booting:
- Booting =
loading/starting an
Operating System into a
computer.
(= Turn on a computer)
- Booting =
loading/starting an
Operating System into a
computer.
- Information
available to
a computer
at boot time:
- The
Ethernet address
of its
network card
Because:
- The Ethernet address is enbedded inside the Ethernet card
(A computer can read the Ethernet address from an Ethernet card)
And nothing else...
- The
Ethernet address
of its
network card
- In general:
- Setting up a computer
in general
involves entering a
lot
of information
into the
routing table
- Setting up a computer on the
Internet
in general
is not easy
This process must be done manually by humans
(That's why there are good paying jobs like network administrators)
- Setting up a computer on the
Internet
in general
is not easy
- Setting up a computer
in general
involves entering a
lot
of information
into the
routing table
- The most common
configuration
of an Internet host is:
- A user's
desktop workstation/laptop
that is
connected to
one physical (Ethernet/Wireless)
network
- A user's
desktop workstation/laptop
that is
connected to
one physical (Ethernet/Wireless)
network
- IP configuration setup
for such
an IP host (computer):
- Level 2 forwarding table and
level 3 routing table for
such a
host/node:
This configuration will:
- Forward IP packets with
same network ID as
yourself:
- Onto your own IP network directly to the destination (according to the <level 2 forwarding table)
- Forward all other IP packets
to:
- The default router
- Level 2 forwarding table and
level 3 routing table for
such a
host/node:
- Example:
output of netstat -r -n
on W303
cheung@W303> netstat -r -n Kernel IP routing table Destination Gateway Genmask Flags MSS Window irtt Iface =================================================================================== 170.140.150.0/23 0.0.0.0 255.255.254.0 U 0 0 0 eth0 169.254.0.0/16 0.0.0.0 255.255.0.0 U 0 0 0 eth0 0.0.0.0 170.140.150.254 0.0.0.0 UG 0 0 0 eth0
How to read the information:
- The entry:
170.140.150.0/23 0.0.0.0 255.255.254.0 U 0 0 0 eth0
functions as an entry in the forwarding table
(The forwarding table is a text book concept --- how it is implemented depends on the software vendor)
- The default entry in
routing table is:
0.0.0.0 170.140.150.254 0.0.0.0 UG 0 0 0 eth0
- The 169.254.0.0/16 entry
is the
"zero configuration" route put in to the
routing table by the
start up procedure
- By default, the
zeroconf route (169.254.0.0)
is enabled when the
system boots.
See: click here
(Looks like our System Administrator left it on)
- By default, the
zeroconf route (169.254.0.0)
is enabled when the
system boots.
- The entry: