Bandwidth Optimization; Security - Enterasys Security Router X-PeditionTM User Manual

reference point represents the customer premises' wiring. S/T is a point-to-multipoint wiring
configuration, that is, the NTI can be connected to as many as eight TEs that contend for the two B
channels. Most XSR applications are critical and require point-to-point connections with the ISDN
service to ensure that the B channels are available in a timely fashion. International users are
limited to ordering the S/T NIM as it is the only approved device for connection to the network.
North American users can order U or S/T NIMs depending on wiring premises' requirements.

Bandwidth Optimization

The XSR offers features which reduce call connection time and prevent network overhead from
triggering ISDN calls.
• Dial-on-Demand (DoD) processes data calls strictly as needed, when interesting packets must
be passed to specific destinations.
• Bandwidth-on-Demand (BoD) allocates ISDN bandwidth as efficiently as possible to
accommodate varying traffic loads. The first element of this feature set is short-hold mode,
which prevents links from forming in the absence of data traffic, while simulating continuous
connections.
For instance, suppose a remote workstation was connected to the corporate LAN via ISDN, but no
data was being sent because a user's PC was idle. With short-hold mode, in the absence of any
data traffic the ISDN call would be brought down, although from the user's perspective the link/
route would still be active, since any data transfer would automatically (and transparently) bring
up an ISDN call.
The second element of BoD directs that as traffic requirements increase or decrease, B-channels
can be added or subtracted to best accommodate the load. This dynamic form of channel
aggregation is often used by Multilink PPP which aggregates channels across multiple B channels
of one or more BRI/PRI ports. The XSR implements this element of BoD with the
load-threshold
To further make BoD work properly, the XSR also implements filtering and protocol spoofing in
order to prevent network overhead such as RIP updates from needlessly bringing up the ISDN
link. Although some of these frames can be discarded without any negative consequences, most
are required to keep workstations and servers across the entire enterprise network synchronized
with one another.
The XSR filters unnecessary overhead by the use of Access Control Lists specifying interesting
packets, and by spoofing protocol overhead packets to maintain the routes while keeping ISDN
connection costs under control.
The XSR performs LAN spoofing where on demand calls spoof RIP or OSPF updates - RIP
updates are sent over the WAN only when changes to the network occur and are piggy-backed with
data traffic. The

Security

Security is another important element of dial-up data communications, and ISDN can support the
security features of protocols running through it, as well as its own unique mechanisms. ISDN, in
addition to supporting the standard authentication schemes of protocols riding on it (e.g. PPP's
PAP/CHAP protocols), enhances the security of dial-up connections with call number ID.
With support for call number identification invoked by the
XSR enables the comparison of incoming callers' phone numbers with a list of acceptable
numbers. Calls can then be restricted to pre-screened locations, a definite advantage especially
when PAP/CHAP authentication is unavailable.
, multilink min-links
dialer map command
, and bap set of commands.
is used to enable spoofing.
isdn calling-number
Understanding ISDN
multilink
command, the
XSR User's Guide 11-5