CODEWITHSUNDEEP
httpbrowserdnsipport
ashu
ashu

Reputation: 1357

How browser access internet when ports are blocked

I was having a doubt on how browser gets the data from website. I read these two links:

how can an application use port 80/HTTP without conflicting with browsers?

and

Port 80 blocked on my ISP so how my browser still works?

With this I understand that browser opens a local random source port and connect to port 80 of website. Now our system firewall have opened all outbound connection and blocked all incoming connection as default configuration. So how does it get back the response. Similarly how response comes back when our home routers and ISP have ports blocked.

So now, I am assuming that connection is somewhat different from response. And there must be some sort of header/information that is sent along which helps in recognizing it as response? And this helps in bypassing the ports?

My humble apologies in case I am messing up all terminologies and thanks for patience. I am beginner in this stuff. Any link towards guide will be very useful.

Upvotes: 1

Views: 742

Answers (1)

Malt
Malt

Reputation: 30295

So how does it get back the response

Assuming you're talking about a firewall or NAT, these devices track outgoing connections, and allow replies to pass through. Connections are typically identified using Source IP + Destination IP + Source Port + Destination Port + Protocol (TCP/UDP). These connection identifiers are stored in a table in the NAT/Firewall.

Upvotes: 1

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