Port/Server Question

DerekAustin26

Do Servers generally handle more than 1 type of application? You have your DNS, FTP, DHCP, Exchange, and many other servers.

I understand Port #'s tell the Server or Destination PC what application the segment needs to be used by, but if the segment has the correct destination IP address and the Server only handles one App like DNS or FTP or whatever, then whats the point of having a Port # if the server obviously doesnt handle other applications.

Analogy...
Thats like me giving an address to my house and my house is the only house in the state, why would I need to be more specific if there is obviously no other houses..

Now if Servers generally manage multiple Applications then it makes sense to have a Port # on your segments. Otherwise... Why?
Anyone explain this?

dynamik

It depends on the organizational needs. All the servers I setup for small businesses have multiple roles, but larger organizations do have dedicated servers for things like DHCP, DNS, etc.

It's important to adhere to standards for interoperability. If some servers use the typical DNS port of 53, and others use a different port or no port at all, how are clients going to know what to use?

I think it's actually simpler to use port numbers because if you don't, you'd have to rely on the operating system trying to determine which application to send the information off to. That would be insanely complex and would only work for protocols the operating system understood. Using your analogy, it would be like me giving you a package and telling you to deliver it to that thing in the state. Did I intend that to go to the house, a park, a tree, or something else? How would you know? As things stand, if the OS receives data intended for port 53, it simply hands that off to the application listening on port 53.

DerekAustin26

I guess a better analogy would be sending a letter with a legal question to a "Law Firm" but they only have 1 dept.

Wouldnt the port # be kinda redundant? I mean they receive the letter and realize the address is correct and the letter says "Law Firm" (Law Firm being the 'Port') - It's not like they are gonna discard the letter.

And Like you said how it's easier to use Port #'s rather than the OS to determine which application to send the 'package' off to... Wouldnt the server already know what to do with it neways? If the Server is a dedicated server for lets say... "FTP" or whatever.. just like the Law Firm. They got the letter to the right address and they only have 1 dept. That's just like the Dedicated FTP Server.. Since it's dedicated it only has 1 dept. Whats the need for the port # then?

But I believe I understand what your saying.. The Port # just ASSURES the Server that the sender really meant for that letter to go to that law firm. Though it seems a little redundant to me , since they can tell by seeing that the address is correct.

Doesn't that seem a little redundant and unnecessary?

RobertKaucher

One thing to add to Dynamik's point... While a specific server migth only be used for one role, it does not mean that that is the only networking service on the server.

How would you RDP to your DNS server if all ports responded with DNS?
How would you drop a patch on your C$ share to install on your application server if all the ports were being directed to whatever application?
How could you SSH to your apache server if there was an issue?

blargoe

It's all about standards. Having the source and destination port in the TCP header is part of the TCP (or UDP) protocol, so the client and server applications have to be built to those specifications.

It's not like a single office, it's more like an office building with multiple office spaces. If there's only one application running, it's like an office building with just one suite occupied by the law firm and the rest of the spaces are vacant. You still should address the packages with the suite number of the law firm's in addition to the street address, etc.

leefdaddy

RobertKaucher wrote: »

One thing to add to Dynamik's point... While a specific server migth only be used for one role, it does not mean that that is the only networking service on the server.

How would you RDP to your DNS server if all ports responded with DNS?
How would you drop a patch on your C$ share to install on your application server if all the ports were being directed to whatever application?
How could you SSH to your apache server if there was an issue?

This is what I was going to say... Even if the server has 1 role it will still need to communicate in other means...

Like what if you need to browse a website from the machine...? Just get use to it, ports are needed.