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My ISP says that it can provide an optic fiber connection with a pool of 4 static IP addresses (subnet 255.255.255.248 i think).
My question is that if I get that connection,
1 ip will be used for network
1 for default gateway
1 for broadcast.
So I will get only 1 usable ip address, while other internet plan have only 1 static ip address and cost less. So what is the benefit of pool of 4 ip?
EDIT
netmask would be 255.255.255.252
This depends on exactly how the ISP provides them to you. You may have "4 DHCP addresses", a "routed" /30, or a "connected" /29.
For example, Time Warner Cable (business class) allows 4 devices to use DHCP to get an address. (similar to residential service that's limited to one)
"routed" is what you'd see where you have a WAN side and LAN side. This is the traditional "lease line" model where the T1/DS3/etc. ISP side has an independent address to which the static address block is routed; from there they can be assigned as a LAN or NAT'd individually (the firewall situation Bulki mentions.)
"connected" would be where the ISP provides your LAN (i.e. a data center, or the "routed" example where you don't control the router)
subnet 255.255.255.248
which gives you 8 addresses, 1 for network, 1 for broadcast, 1 for default gateway => you can use up to 5 addresses. Sometimes (mostly in datacenter environment) more addresses are reserved for FHRP.
example: 8.8.8.0/29, 8.8.8.0 is network address, 8.8.8.7 is broadcast address 8.8.8.6 is default gateway address you can use 8.8.8.[1-5] as host ip addresses.
If, however, your ISP gives you a subnet with 4 addresses at all, which is /30 (netmask 255.255.255.252), you can still use one address as host address (the rest are broadcast, network, and default gateway addresses). This option gives you no advantage over "other internet plan" speaking in terms of address count.
TL;DR: subnet 255.255.255.248 gives you up to 5 usable ip addresses, subnet 255.255.255.252 gives you one.
Normally a /30 is used for 2 addresses. That is correct. However on firewalls this is often again divided in /32's so you can use them seperately. It's like an ISP gets a range from it's provider (ex: RIPE) and then divides these adresses via subnetting to their customers. The same principle can be applied to this /30 by yourself.
