206 Chapter 5: Designing Static Dial Plans for Large VoIP Networks
Note that the WesternGK has been conﬁgured with 2 dial-peers. The preference command
assigns the dial-peer order. This command is generally used for failover purposes when you
have the same destination pattern assigned to multiple dial peers.
Dial peer 1 ﬁrst sends an ARQ message to the WesternGK to determine if it knows the
called number’s terminating gateway address. If the WesternGK does not know this, the
WesternGK will send an ARJ message to the gateway. The second dial peer will then
append a 2# technology preﬁx to the called number and again try an ARQ message to the
WesternGK. This time, the 2# matches the gw-type-preﬁx 2# command to hop off to the
DGK. The DGK also recognizes the 2# and matches its gw-type-preﬁx 2# command to hop
off to the hopoffGK. Note that the 2# gets propagated with the called number.
You can enter the hopoff keyword and gatekeeper ID multiple times in the same command
to deﬁne a group of gatekeepers that will service a given technology preﬁx. Only one of the
gatekeepers in the hopoff list can be local.
If the technology preﬁx does not have any forced zone attribute, the gatekeeper uses zone
preﬁx matching to determine the zone. If the matching zone preﬁx is associated with a
remote zone, an LRQ message is sent to the remote gatekeeper. The LRQ message contains
the entire called number, including the previously stripped technology preﬁx. If the
matching preﬁx is for a local zone, that zone is used to satisfy the request.
If no zone preﬁx match is found, the default behavior is to attempt to use a local zone for
hopoff rather than to fail the call. However, this might not be the desired behavior. You
might prefer that an ARJ message be returned to the gateway so that it can fall through to
an alternate dial peer (for example, one that speciﬁes that the next hop is through a special-
rate PSTN). To override the default behavior, use the arq reject-unknown-preﬁx
Example: Use of Translation Rules, Technology
Preﬁxes, and Dial-Peer Failover
This example demonstrates the use of Cisco IOS tools and features to provide better call
routing control with hierarchical design and to minimize dial-peer conﬁguration.
Figure 5-16 illustrates the topology of the example network.