IP packet filter firewall

You might need to change packet filter rules to allow Universal Connection traffic to flow through your firewall to IBM.

An Internet Protocol (IP) packet filter firewall allows you to create a set of rules that either discard or accept traffic over a network connection. The firewall itself does not affect this traffic. Because a packet filter can only discard traffic that is sent to it, the device with the packet filter must either perform IP routing or be the destination for the traffic.

A packet filter has a set of rules with accept or deny actions. When the packet filter receives a packet of information, the filter compares the packet to your preconfigured rule set. At the first match, the packet filter either accepts or denies the packet of information. Most packet filters have an implicit deny all rule at the bottom of the rules file.

Packet filters usually permit or deny network traffic based on the following information:

Source and destination IP addresses
Protocol, such as Transmission Control Protocol (TCP), User Datagram Protocol (UDP), or Internet Control Message Protocol (ICMP)
Source and destination ports, ICMP types, and codes
Flags in the TCP header, such as whether the packet is a connect request
Direction (inbound or outbound)
Which physical interface the packet is traversing

All packet filters have a common problem: the trust is based on IP addresses. Although this security type is not sufficient for an entire network, this type of security is acceptable on a component level.

Most IP packet filters are stateless, which means that they do not remember anything about the packets they previously process. A packet filter with state can keep some information about previous traffic, which gives you the ability to configure that only replies to requests from the internal network are allowed from the Internet. Stateless packet filters are vulnerable to spoofing because the source IP address and ACK bit in the packet's header can be easily forged by attackers.

IBM® i allows you to specify packet filter rules on interfaces and remote access service profiles. If you are using either an external packet filter firewall or packet filter rules on the system and your Universal Connection information passes through these filters, you must change the filter rules to allow the connection to the IBM virtual private network (VPN) Gateway as follows:

Table 1. IP filter rules change: Packet filters
IP filter rules	IP filter values
UDP inbound traffic filter rule	Allow port 4500 for VPN gateway addresses
UDP inbound traffic filter rule	Allow port 500 for VPN gateway addresses
UDP outbound traffic filter rule	Allow port 4500 for VPN gateway IP addresses
UDP outbound traffic filter rule	Allow port 500 for VPN gateway IP addresses
Encapsulated Security Payload (ESP) inbound traffic filter rule	Allow ESP protocol (X'32') for VPN gateway IP addresses
ESP outbound traffic filter rule	Allow ESP protocol (X'32') for VPN gateway IP addresses

For those Universal Connection applications that use Hypertext Transfer Protocol (HTTP) and Hypertext Transfer Protocol Secure (HTTPS) for a transport, you must change the filter rules to allow connections to the IBM service destinations as follows:

Table 2. IP filter rules change: HTTP and HTTPS
IP filter rules	IP filter values
TCP inbound traffic filter rule	Allow port 80 for all service destination addresses
TCP inbound traffic filter rule	Allow port 443 for all service destination addresses
TCP outbound traffic filter rule	Allow port 80 for all service destination addresses
TCP outbound traffic filter rule	Allow port 443 for all service destination addresses

To change the filter rules, you need to specify an actual IBM VPN gateway address. In addition, for HTTP and HTTPS traffic, to change the filter rules, you might need to specify actual service destination addresses.