1. How Corporate Firewalls Works
● About the kind of the fire wall
● What is Firewall Work
● What is Bastion Host?
● The bastion hosts and the access router

2. About the kind of the fire wall
● Packet filtering
The packet filtering chooses the right or wrong of the passage by the
contents of the IP packet.
● Circuit level gateway
Because a gateway has a virtual connection course with inside host
between a foreign host, the circuit level gateway enables access. From
the outside, it seems to have access from the outside of the gateway.
● Application level gateway
It start a program corresponding to the service on a gateway with the
application level gateway, and there is a thing doing a client program for
broadcast system correspondence by the access to the foreign host
relays this program from inside host, and performing it that a change is
necessary for an access procedure.

3. What is Firewalls Work
● The firewall chiefly has the following two.
● Static Packet Filter
The communication can be controlled on the condition of
setting it and the reception, the refusal, and abandonment be
controlled. However, it takes time and the protection is not
perfect.
● Dynamic Packet Filter
The control of the communication can be changed according
to the IP packet.

4. What is Bastion Host?
● The bastion host is a
special purpose
computer on the
network and
configured to
withstand attacks.
● There are two
common network
configurations that
include bastion hosts
and their placement.

5. The bastion hosts and the access router
● The host protect a corporate network.
• Its function is block off all access from intruder in
the firewall.
● The exterior screening router(called an access
router)
• Its works is monitoring the all for indivdual packets.

6. References
● http://www0.ise.osaka-sandai.ac.jp/~nakano/files/fw.html
● Wikipedia
http://ja.wikipedia.org/wiki/