Cabletron Systems Netlink FRX8000, User Manual

Page: 139 / 468

Configuring X.25 9-21
Configuring X.25 Address Translation Templates
The FRX8000's X.25 address translation feature provides automatic translation of
selected fields within a Call Request packet, according to a previously defined “tem-
plate.” You can change the called address, calling address, user data, and/or facilities
fields of a Call Request packet as it passes into or out of the node.
There are various uses for this feature; for example:
●
For security reasons, a translation of the calling address might enable routing of
all Call Request packets with certain addresses, while all others are cleared.
●
Translation of user data can allow rerouting of all packets with the same called
address, with all those containing one type of information going to one location,
while those with another type go elsewhere.
The translation template has two parts: the template ID and the translation formula.
The Call Request packet can be modified (using the translation formula) to replace
parts of it with characters specified by the formula and/or with parts of the template
ID.
Each port has two sets of translation templates associated with it, one for incoming
packets and one for outgoing packets. When an incoming packet enters the node, it is
immediately checked against any incoming template defined for that port. If the
packet matches the template, a translation is carried out and the packet continues
toward its destination, using the routing tables defined by the SVC records. If the
packet does not match the template, it is not accepted.
An outgoing packet is checked just before it leaves the node. If it matches the tem-
plate, a translation is carried out; if it does not match, it continues unchanged.
The “hunt group” routing path function is performed within the routing table process,
so to handle outbound packets, a port that is part of a hunt group needs a set of tem-
plates that is specific to that port. This allows a different set of outbound translations
for each port.
Address translation is especially useful in providing backup routing via a public data
network (PDN), as represented in the following example.