Toillustrate how to specify disallowed R2R shortcuts using protocol addresses and
masks, consider the following network diagram:
Example 1: An entry with

address=9.9.9.1 mask=255.255.255.255

would cause
the NHS to send a NAK to the sender of a Next Hop Resolution
Request with destination protocol address 9.9.9.1 (HOST1). Since
9.9.9.1 is not directly attached to one of the device subnets, but is
reached by another router, the router checks the Disallowed R2R
Shortcuts List.
Example 2: An entry with

address=9.9.9.0 mask=255.255.255.0

would cause the
router to send a NAK for any destination address 9.9.9.1 through
9.9.9.255. HOST1, HOST2, and ROUTER2 could not be reached
using shortcuts to the router but devices on the other subnets serviced
by ROUTER2 could be reached.
Example 3: An entry with

address=1.1.1.5 mask=255.255.255.255

would cause
the router to respond negatively for any destination whose next-hop
router is 1.1.1.5, ROUTER1. The router would respond negatively for
any address on subnet 9.9.9 and for any address on the other IP
subnets reached via router 9.9.9.3 because next hop is 1.1.1.5.
Example 4: An entry with

address=anything mask=0.0.0.0

would disable R2R
shortcuts for all addresses.
Protocol Access Control Usage
This parameter determines if the protocol layer access controls will be checked and,
if so, how these controls will be applied to NHRP packets.
If this configuration parameter is set to its default value of

none

, the protocol layer
access controls are not checked.
With the value of

source and destination

, when the NHRP requester is not a router,
the NHRP client’s IP address is assumed to be the source of all IP packets that will
be transmitted by that client using the NHRP shortcut route. The router denies
NHRP shortcut requests from a non-router NHRP client if any IP packets are being
filtered for that IP destination/source address pair, where the source is the NHRP
client’s address.
ATM nhs
1.1.1.4 1.1.1.5 9.9.9.5 9.9.9.3
host1
9.9.9.1
Other
IP
sub-
nets
host2
9.9.9.2
Router1 Router21.1.1 9.9.9
Figure 34. Using Disallowed Router-to-RouterShortcuts
Using NHRP
356 MRS V3.2 Protocol Config Ref Vol2