<SNIP>
Yes. I think the netmask should be 255.255.255.255
1/ but why they are using this netmask setting? save ip address?
then does the router handle many routes in this setting?
</SNIP>
I have no idea the only way you can have a /32 is with a ppp that doesnt
use arps to talk to each end of the tunnel.
I would assume they have /24's and are giving out /32 via dhcp to customers
and the customers should see 255.255.255.0 with a gateway of eg, .1 etc..
<SNIP>
2/ What is this advantage for the hosting company?
</SNIP>
If the company is setup the way i think it is the only reason for this is:
1, they have no clue what they are doing
2, they offer a very cheap hosting service and have no managed switches, and
dont understand how to subnet and use vlan's.
<SNIP>
3/ If I need more ip in the same server, how it works?
</SNIP>
I would of thought if you have 2 x servers you wanted to co-locate the
hosting company would offer you a /29 with 1 gateway 1 broadcast and 4
useable on a vlan, so local traffic only sits on the vlan and the servers
can talk to each other via the local vlan.
I guess if the machines have more then 1 nic you can connect the 2 machines
via a local 'backnet' network it can be useful if you have a cross-over
cable between the 2 x machines and its a 1GB port. This also saves using the
switches, in some cases hosting companies may count all traffic that goes
over the interface (if they dont use net flow) and you could end up paying
for traffic which you really shouldnt have to pay for.
If you are using the additional ports for high amounts of data eg, backup's
images etc, you can really tweak tcp settings so you can send JUMBO frames
and squeeze some speed out of it.
<SNIP>
4/ Why you said the hosting company is cheap to use this configuration?
</SNIP>
Yes its alot cheaper to have say a common-gateway that all traffic will
route over and then connect a bunch of switches to this common router and
manage it via dhcp, its very messy and also very noisy i can only imagine
after you connect a few servers that over time you will see arp storms and
all traffic on the network will cease to flow.
As mentioned in my other posts how it should be done, clearly you need to
buy layer 3 switches and layer 2 switches and a nice core router to deal
with your bgp, you also need to make sure your using devices that can handle
high packets per second.
As i am writing this i feel as if im doing someone homework for them... 
Thank you again.
<SNIP>
2/ lf the network card in server has problem and need change another
one, will my ip address change to another ip address also?
</SNIP>
Yeah well thats how dhcp works, via ma caddy, i guess you can always spoof
your old mac address.
<SNIP>
3/ why hosting company is using /32 and dhcp? what is advantage? ls it
easy for administration?
</SNIP>
Im guessing because the users are to stupid to understand what a subnet
mask/gateway is its just easier to get the mac address and assign it to a
user then let the user assign a ip.
Normally in a co-location setup its not like this, inless its very cheap
hosting.
My co-location has the following setup, and this is how MOST networks
should
