SatLink VSAT User Guide
Publication no. 101557
Copyright © 2009 – STM Group, Inc.
Page 60 (160)
10.1.1 Configuration of Dynamic NAPT
Dynamic NAPT applies for all LAN initiated connections that are to be routed over the DVB satellite
interface. The source address of the outgoing packets will be replaced by the Global Address that is
defined in the NAPT Global Address Table. Port numbers will be mapped to new port numbers that are
automatically generated by the STM SatLink VSAT.
Note that it is required to defined a dedicated global IP address to use NAPT. Using the
DVB interface IP address as global IP address is no longer supported from Release 13
The CLI command
# ip nat global add <gladdr> is used to configure the default global address.
Correspondingly, the user defined global address can be deleted using the CLI command
# ip nat
global del <gladdr>
.
Though the CLI command # ip nat global add <gladdr> allows the user to define more
than one global address, in practice, only the first address in the NAT Global Address table
will be used.
Please note that translation of outbound TCP/UDP fragmented datagrams will fail with NAT enabled. The
reason is that only the first fragment contains the TCP/UDP header that would be necessary to associate
the packet to a session for translation purposes. Subsequent fragments do not contain TCP/UDP port
information, but simply carry the same fragmentation identifier specified in the first fragment.
Consequently the sessions will be corrupted. Whether NAT drops or forwards also an ICMP fragmented
packets depends on a number of things, such as the order in which the NAT router receives the ICMP
fragments and the state of the translation table at that time. Under certain conditions, NAT translates the
ICMP fragments differently, making it impossible for the destination device to reassemble the packet.
To view the currently configured dynamic NAPT entries, type the CLI command:
# ip nat show.
Example:
# ip nat global add 10.10.1.10
# ip nat show
NAT Configuration
-----------------
Network Address Port Translation (NAPT): Enabled
Global Address Table
If IP Address
dvb0 10.10.1.10
NAT Status
----------
Total Sessions 0
Active Sessions 0
Failed Sessions 0
Packet Translations 0
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