Information Technology Reference
In-Depth Information
The organization shown in Figure 6-12 prefers to use the IP WAN as its primary communi-
cation path between Arizona and Texas. However, if the IP WAN should fail, calls be-
tween the offices should use the PSTN as their communication path.
One of the benefits of using VoIP is the merging of voice networks into one, seamless
communication path. Because calls are traveling over the IP WAN, users in the Arizona of-
fice can dial the users in the Texas office using their four-digit (6XXX) extension. Like-
wise, users in the Texas office can dial the users in the Arizona office using their four-digit
(5XXX) extension. It would be inconvenient to require all the users in the Arizona office
to dial the Texas office using the PSTN DID range rather than the four-digit extension
(and vice versa).
Using a combination of the preference and prefix commands, you can allow this failover
transformation to occur dynamically, as shown in Example 6-17.
Example 6-17
Dynamic WAN to PSTN Failover Implementation
Key
To p i c
Arizona(config)#
dial-peer voice 10 voip
Arizona(config-dial-peer)#
destination-pattern 6...
Arizona(config-dial-peer)#
session target ipv4:10.1.1.2
Arizona(config-dial-peer)#
preference 0
Arizona(config-dial-peer)#
exit
Arizona(config)# dial-peer voice 11 pots
Arizona(config-dial-peer)#
destination-pattern 6...
Arizona(config-dial-peer)#
port 1/0:1
Arizona(config-dial-peer)#
preference 1
Arizona(config-dial-peer)#
no digit-strip
Arizona(config-dial-peer)#
prefix 1512555
Texas(config)#
dial-peer voice 10 voip
Texas(config-dial-peer)#
destination-pattern 5...
Texas(config-dial-peer)#
session target ipv4:10.1.1.1
Texas(config-dial-peer)#
preference 0
Texas(config-dial-peer)#
exit
Texas(config)#
dial-peer voice 11 pots
Texas(config-dial-peer)#
destination-pattern 5...
Texas(config-dial-peer)#
port 1/0:1
Texas(config-dial-peer)#
preference 1
Texas(config-dial-peer)#
no digit-strip
Texas(config-dial-peer)#
prefix 1480555
The
preference
command allows the router to determine which dial peer it should use in
the case where the destination patterns are identical. It might seem counterintuitive, but
the router considers lower preferences to be better than higher preferences (the preference
value can be any number from 0-10). The default preference for a dial peer is 0. Thus, the
preference 0
command in Example 6-17 under dial peer 10 on both routers is redundant.
