ufw-allow: add page (#23299)

pages/linux/ufw-allow.md

@@ -0,0 +1,28 @@
+# ufw allow
+
+> Allow traffic through the firewall.
+> More information: <https://manned.org/ufw>.
+
+- Allow all traffic on a port:
+
+`ufw allow {{port}}`
+
+- Allow traffic for a protocol on a port:
+
+`ufw allow {{port}}/{{protocol}}`
+
+- Allow incoming traffic for a protocol and add a comment for documentation:
+
+`ufw allow in {{protocol}} comment '{{comment}}'`
+
+- Allow all traffic from a source address:
+
+`ufw allow from {{source_address}}`
+
+- Allow TCP traffic from 192.168.1.12 to 192.168.1.100 on port 443:
+
+`ufw allow from 192.168.1.12 to 192.168.1.100 port 443 proto tcp`
+
+- Allow all incoming GRE traffic to 192.168.1.100 on the eth0 interface:
+
+`ufw allow in on eth0 to 192.168.1.100 proto gre`