UDP Port Blocked?

Linode Staff

Are certain UDP ports blocked by Linode? For example, when I set my application to listen on port 1194/udp, my client can connect. However, when I try something else like port 55555, my client can't connect.

I've tried multiple distributions (Arch, Ubuntu, CentOS) and the issue is the same. I've also cleared my firewall rules, no change:

[root@localhost ~]# iptables --policy OUTPUT ACCEPT
[root@localhost ~]# iptables --policy INPUT ACCEPT
[root@localhost ~]# iptables --policy FORWARD ACCEPT

3 Replies

I would start by using ss to examine UDP on your Linode more closely:


By default, we don't block any UDP traffic. You may also want to try specifically opening these ports through iptables, like so:

iptables -A INPUT -p tcp --dport 55555 -j ACCEPT
iptables -A OUTPUT -p tcp --dport 55555 -j ACCEPT

Then re-try. If you still have issues, try providing more details about your application stack here.

well after some other trial and errors i have found out that my isp is blocking me to access my linode on certain udp ports (the clinet could connect using a different isp) , however the client is able to connect to my other server (not linode) trough 55555 by my own isp too

i mean does my isp blocks certain udp ports only to linode?!

@realone_amm writes:

i mean does my isp blocks certain udp ports only to linode?!

Only your ISP knows that… You should ask them.

-- sw


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