UDP Client - Open Ports?

TCP and UDP are just two examples of transport layer implementations. Both of them are using term 'port' to determine which app should receive incoming packet, but they could be routed/filtered differently by routers/switches/firewalls/etc.

TCP and UDP are just two examples of transport layer implementations. Both of them are using term 'port' to determine which app should receive incoming packet, but they could be routed/filtered differently by routers/switches/firewalls/etc. So the answer is no. You will have similar problems with opening ports.

Just except 'TCP port xxx should be opened' you have to demand 'UDP port xxx should be opened'. In most home networks firewall rules allow outgoing packets (requests) to any remote port (on your server for example, where this port should be opened). And when such a packet goes through a router - it creates temporary rule to allow answers come back to the local port from which request packet.

So, normal scenario is like that: Packet originated from home computer with IP 5.5.5.5. Lets say it has source UDP port 55555, source IP address 5.5.5.5 and destination port 8888. Packet reaches home router.

As it is going from inside - router allows it to pass through and creates rule say for 2 minutes to allow packets targeted to 5.5.5.5 to UDP port 55555. Packet reaches corporate router before your server.It has rule to pass packets for port 8888 so packet is allowed to go. Your server receives the packet and processes it.

In response it creates packet for IP 5.5.5.5 and UDP port 55555. Corporate router allows response to go. Home router allows response to go according to temporary rule.

Your computer receives the response. Corporate computers and routers often more restrictive to ensure security, so second point could restrict packet if your user (IP 5.5.5.5) is in corporate network. It is very simplified as in reality there's almost always things like NAT and rules are more complex... But in general it gives the idea how it works internally.

Because that client is a game client. IOS app. I don't want that any user that would wanna play in the game will have to open ports.

– Eli Jul 9 at 10:53 @Eli - reread this answer, and then reread it again until you either understand what it says or have a specific question about it. You've just restated the Ivan's answer in the form of a question which makes me think you didn't give it enough attention. – msw Jul 9 at 11:01 See my response update.

Your game server's administrator is the only one who need to open ports most of the time. And yes - most users use router firewalls. It is just the default rule even on the simplest home routers - to allow outgoing packets and to block incoming except those came as an answer to previous outgoing packet.

– Ivan Danilov Jul 9 at 11:03 @msw I updated my answer just after Eli had posted his comment.So it is ok :) – Ivan Danilov Jul 9 at 11:03 OK - so I've got it. Just checking - In most of the users, they will not have opening ports problem, right? – Eli Jul 9 at 11:05.

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