Moxa Technologies UC-7110 User Manual
Page 38
UC-7110 Series User’s Manual
Configuring UC-7110
4-6
NOTE
IPTABLES plays the role of packet filtering or NAT. Take care when setting up the IPTABLES
rules. If the rules are not correct, remote hosts that connect via a LAN or PPP may be denied
access. We recommend using the Serial Console to set up the IPTABLES.
Click on the following links for more information about iptables.
Since the IPTABLES command is very complex, to illustrate the IPTABLES syntax we have
divided our discussion of the various rules into three categories: Observe and erase chain rules,
Define policy rules, and Append or delete rules.
Observe and erase chain rules
Usage:
# iptables [-t tables] [-L] [-n]
-t tables:
Table to manipulate (default: ‘filter’); example: nat or filter.
-L [chain]: List List all rules in selected chains. If no chain is selected, all chains are listed.
-n:
Numeric output of addresses and ports.
# iptables [-t tables] [-FXZ]
-F: Flush the selected chain (all the chains in the table if none is listed).
-X: Delete the specified user-defined chain.
-Z: Set the packet and byte counters in all chains to zero.
Examples:
# iptables -L -n
In this example, since we do not use the -t parameter, the system uses the default ‘filter’ table.
Three chains are included: INPUT, OUTPUT, and FORWARD. INPUT chains are accepted
automatically, and all connections are accepted without being filtered.
#iptables –F
#iptables –X
#iptables -Z
Define policy for chain rules
Usage:
# iptables [-t tables] [-P] [INPUT, OUTPUT, FORWARD, PREROUTING, OUTPUT, POSTROUTING]
[ACCEPT, DROP]
-P:
Set the policy for the chain to the given target.
INPUT:
For packets coming into the UC-7110.
OUTPUT: For
locally-generated packets.
FORWARD:
For packets routed out through the UC-7110.
PREROUTING:
To alter packets as soon as they come in.
POSTROUTING:
To alter packets as they are about to be sent out.
Examples:
#iptables –P INPUT DROP
#iptables –P OUTPUT ACCEPT
#iptables –P FORWARD ACCEPT
#iptables –t nat –P PREROUTING ACCEPT
#iptables –t nat –P OUTPUT ACCEPT
#iptables -t nat –P POSTROUTING ACCEPT
In this example, the policy accepts outgoing packets and denies incoming packets.