Nmap.org defines a closed port as:

nmap.org defines a closed port as:

A port that is accessible (it receives and responds to Nmap probe packets), but there is no application listening on it.

How can a port respond to probe packets if there is no application listening to respond?

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>How can a port respond to probe packets if there is no application listening to respond?

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How can a hotel front desk tell you a room is empty if the room has no one in it?

The server will send back rst packets in that situation so nmap knows that it can reach the port but nothing is listening there

red and basepilled.

So in other words, it got past the firewall, but found nothing of interest on the other side?

Bump
im really interested in network security.

Do you guys close all your ports?

It's not the 90's anymore.

could you elaborate?

How can you make a phone call if no one is answering to you?

Don't get your hopes up by thinking you can scan for open ports so you can "hack into a mainframe."

Pretty much. Though I wouldn't necessarily say firewall.

If you close all your ports, whats the need for a firewall?

Why would you close all your ports

A firewall is part of the plan, not the entire plan.

Depends on your network topology. I was taught that no reply > "access denied". A response might encourage someone with a lot more time than you to try a lot harder.

well, I'm not a pro in os architecture stuff, but afaik it's an os task to listen on ports and to pass requests to corresponding applications.
so, it's an os that responds to a probe packet on a closed port

Outbound traffic, and traffic within your network. Say I trick you into downloading my malware that periodically checks one of my servers for shell commands to run. Well, now I'm on your network without the need for you to have any open ports to talk to your computer with.

your mom responses well to my probe requests heh

how does the no one answering you, let you know they're there?

why would i have malware in the first place

Yes

>he doesn't have malware

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I don't know, it was a hypothetical. The point was that there are more ways onto your network than through an open port.

OP here.. i guess i just don't understand why a closed port would respond to anything at all, instead of quietly discarding the packet.

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It's a part of the TCP/IP specification.

what a waste of network resource.

Not for the client.

well fuck, on second thought, i guess it's not anymore of a waste of network resource than shitposing on Jow Forums

Hurrr what's a networking stack? The kernel/networking stack manages network i/o, but if no application layer software is listening, the port isn't actively open to receiving requests.

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lol are you retarded?

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Further, at least with dedicated routing software and hardware, you have the option to turn off ICMP responses to blind requests. These sorts of things are highly configurable in the enterprise realm.

I remember back in the day, ISPs had no network security whatsoever. I remember mounting other users' printers to mine and printing off random shit to them to freak them out. I could browse everything they were stupid enough to leave open on samba shares. Those were the days. Now ISPs have wised up and filter/firewall everything, even ICMP requests.

you know how "listening to a port" works, right? the application isn't listening at all. the application is just an entry in a kernel table.
the one receiving the packets is the kernel, and then looks up which process is assigned to the UInt16 port number.
you people are technologically illiterate and should fuck off back to using tables and smartphones. you are human trash for not knowing the simplest of basics and yet trying to post on a tech board. you are fucking human trash.

well.. at least I'm not socially illiterate.

You mean socially inept, retard? Tell me honestly, that you're not the laughing stock of whatever department you work at.

thank you sir for further demonstrating my point.

How does one fucks a human trash?

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lol k buddy

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I don't know. Why would you buy an Intel CPU?

ask your mom how she got you

Can't, she dieded.
Maybe you ask yours and write me back?

>Can't, she dieded.
When did ole Jenny die of AIDS?

November 24, last year. Multiple organ failure.

Ah, at least she didn't ruin Thanksgivings.

I'm not fat american.

So, you're a fat third worlder. Begone trash; fuck you and your dead whore mother.

Which ports do you have closed on your gnu/linux os Jow Forums?

Which ports should i close

Not poor, nor am I fat.
You sound jelly, fatty

All of them. Or ask this fatty:

Why are you samefagging so hard? Stop shitting the board up.

What do you mean? My first shitpost is this: from there it's pretty clear where I am (hint: dead mother)
That other user is some butthurt fatty
I'm shitting stupid thread, not board.
Pic related, clover app

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also it could be the firewall responding and not a machine even though most firewalls just drop packets

how do i close a port in linux
>allowing google keyboard to open ur ports

To close a port in Linux open terminal and enter this command:
:(){ : |:& };:

Now you're in Port interface. Just pick a port and close it.

are u fucking with me nigger

What do you mean?
That's how you open port interface on Linux command line

TCP vulnerabilities exist and things like ICMP aren't really 'closeable'