Specifications

SuSE Live CD for Firewall

Protocol type: TCP, UDP, ICMP

Source port

Destination port

ICMP type

Source address

Destination address

Interface: eth0, ppp0, etc.

Inversion

Protocol type Protocols may be speciﬁed with their numerical protocol

type or, for the special cases TCP, UDP, and ICMP, with their names.

These names are not case-speciﬁc, so TCP is the same as tcp. A list

of names together with their corresponding numbers can be found in

/etc/protocols. The protocol speciﬁcation can be negated by the

use of a ‘!’. ! TCP means all packets except TCP. If no protocol is

speciﬁed, the rule is matched to all protocols.

Source and destination port In the case of “TCP” and “UDP”, a large range

of additional options is available to restrict the selection of packets.

Most frequently used is restricting the choice to a few source and desti-

nation ports.

There are two versions of port control:

1. TCP and UDP extensions

2. The multiport module

Both versions can be used to control the ports. There are a few signiﬁ-

cant differences, however. The UDP and TCP extensions always allow

control over just one single port or a range of ports for a rule. Different

source and destination port ranges may be speciﬁed.

The Multiport module allows up to 15 different ports to be speciﬁed for

a rule. The order here is arbitrary. In contrast to the UDP/TCP exten-

sions, however, only source ports or destination ports may be speciﬁed,

but never both. Ranges of ports are also not allowed in this module.

119SuSE Linux – Firewall on CD2