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What is the relationship between proxy, NAT and subnet masking?

proxynat subnet subnet mask

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Lately I've been reading about how internet communication and internet security works. I think I generally understand how proxy server, NAT and subnet masking work, but I'm baffled when it comes to understanding the relationship between those and specific purpose of them.


Could someone answer the following questions:


a. Is using a subnet mask obligatory to connect to the Internet?

b. Is using NAT obligatory to connect to the Internet?

c. Why do I need proxy if NAT and subnet mask already hide my IP?

d. I jknow that most 'router' devices have NET in them. Do they also give subnet mask?


Those questions are purely theoretical.


Thanks for advance for answers - and be easy on my rookiness. :)

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The subnet mask is a way of limiting your local area network to a small subset of all possible numbers.  You pretty much have to give your network card a mask when you assign it an address if you do it manually.  If it gets an IP address through DHCP then it will get from the router (or modem) automatically.  Normally a router will assign you an IP address like 192.168.0.x or 192.168.1.x  Where x can be a number between 1 and 254.  The mask in this case is which indicates that only numbers in the fourth position are part of this local area network.  (First three numbers have to stay the same.)  Traffic to another device on the same LAN will go directly to that device.  Any traffic originating on your PC that is designated to go to an address that is not local will usually be sent out the default gateway which is usually your router.  192.168.y.x numbers cannot be used on the Internet so your router must do a NAT on the packet's from address and change it to its own Internet address before forwarding the packet.


Orignally we used a proxy to speed things up back when  Internet connections were a lot slower.  The proxy server would keep uptodate copies of the most popular URLs and when a client asked for a URL it would give them the copy.  This saved the time lost in querying for the page and downloading it (significant if you were on early dialup).  Nowadays the separate proxy server for that purpose is not required because the Internet and your local connection is so much faster.  You generally don't need a proxy unless you are trying to hide your router's IP address or to get around a block like the Chinese firewall that prevents them from going to certain sites.  For paranoid types a proxy can be used to hide their routers Ip address from everyone but the proxy server.  (Your router's IP address is including in any packets the router sends out so if you were trying to hide from someone like the FBI all they have to do is ask your ISP who had that IP address at a certain time and date (IP addresses may be dynamically assigned by the ISP when the router first boots up)).  Some anti-virus software will set up a proxy on your own PC to amke it easy to check all traffic.  Malware will also create a proxy so that they can intercept your traffic or send it to a totally different destination.


Not sure what NET means in your last question but yes a router actually has two subnet masks.  The LAN (the network your computer is on) and the WAN (the link back to your ISP.  When you first connect the router it usually gets assigned an IP address, subnet mask and default route by the ISP.  The LAN address range, and subnet mask and the router's own LAN IP address are usually the same by default on all routers of the same type tho they can be changed by logging on to the router.  When a new PC connects to the router, the router picks out an IP address (usually the next one that is free) from its assigned range then sends that info to the new PC along with the subnet mask and the default route (which is just its own address on the LAN)


Does that help?


Ron (Retired network engineer & CCNP)

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