MobiLink IP
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MobilinkIP_Usermanual-sw1.2.21_revGen.doc
Page 63 of 188
Apply
immediately applies the new rules, but they are not yet saved. „
Save
” saves them, but only in
the temporary memory. The rules do not become persistent, unless you press the „Commit” button.
This is very useful when testing new rules: you edit them and press Apply, than watch for the effect.
If you do not like how the firewall performs, you just reboot the MobiLink IP equipment, and the
recent changes will be lost, so you can start again editing the IP tables!
Definition
IP Tables is a user space application program that allows a system administrator to configure the
tables provided by the firewall of the Linux kernel (implemented as different Netfilter modules) and
the chains and rules it stores. Different kernel modules and programs are currently used for different
protocols, the iptables apply only to IPv4.
A firewall using iptables this way is said to be a
stateful
firewall versus the older, stateless firewall,
which was not fully aware of the context from which a data. Therefore, the iptables firewall can make
better decisions on the fate of packets and connections.,
There are five predefined chains, though a table may not have all chains. Predefined chains have a
policy, for example ACCEPT, which is applied to the packet if it reaches the end of the chain. The
system administrator can create as many other chains as desired. These chains have no policy; if a
packet reaches the end of the chain it is returned to the chain which called it. A chain may be empty.
PREROUTING:
before effective routing, packets will enter this chain, as soon as they are received by
an interface, before a routing decision is made.
POSTROUTING
: after the local routing is performed, but before
leaving
an interface
INPUT:
Right before they are sent a local process, the rules apply to external packets that are sent to
the equipment.
OUTPUT:
Right after they are generated by a local process, rules apply to packets that get out of the
MobiLink IP equipment.
FORWARD
: transfer operations, the data packets are coming in through one interface and getting out
via another interface. All packets that have been routed and were not for local delivery will traverse
this chain.
After you perform changes, you will see the completion time / date for the changed rules:
Or:
Don’t forget to click the Save button and then “Commit” to make the changes you performed
permanent.
