Accepted Solutions
Outtake from this document. Explain Cisco IOS and IOS XE Call Routing
Number String Dial-Peer Hunting
Number String Preference:
Much like URI's have a specific order of operations for evaluating matches, there is also a set of rules used when evaluating a numeric digit-string. The default dial-peer hunt scheme for a Cisco gateway is set to 0. This means the gateway searches for a pattern with the longest match (most specific). If there are two dial-peers with the same match length, the gateway looks at the explicitly defined dial-peer preference. Lastly, if both of those are the same, it chooses one in a random order.
There are other dial-peer hunt schemes available for configuration; however, most deploymens keep the default of 0.
Gateway(config)# dial-peer hunt ? <0-7> Dial-peer hunting choices, listed in hunting order within each choice: 0 - Longest match in phone number, explicit preference, random selection. 1 - Longest match in phone number, explicit preference, least recent use. 2 - Explicit preference, longest match in phone number, random selection. 3 - Explicit preference, longest match in phone number, least recent use. 4 - Least recent use, longest match in phone number, explicit preference. 5 - Least recent use, explicit preference, longest match in phone number. 6 - Random selection. 7 - Least recent use.
The longest match number string dial-peer algorithm finds the dial-peer with the most numbers in a sequence that exactly match a sequence of numbers in a number string. This concept is clarified in the subsequent scenario.
Scenario: Eligible dial-peers have been configured with these possible matches, and the gateway is evaluating a digit-string of 2001. Dial-peer 1 can match any number 2000 through 2999 while dial-peer 2 can match 2000 through 2009. Dial-Peer 2 would be matched for this call as it is the longest match (most specific) for the digit string 2001 when the default dial-peer hunting mechanisms is employed (dial-peer hunt 0). In other words, the sequence of numbers 200 is the largest sequence that exactly matches a sequence of number in the number string 2001.
!
dial-peer voice 1 voip
destination-pattern 2...
!
dial-peer voice 2 voip
destination-pattern 200.
!
Preference is defined as the administrator defined weight for each dial-peer. Administrators can configure a preference so the call always uses a specific dial-peer before others. By default, all dial-peers are preference 0. A dial-peer with preference 0 is matched before another dial-peer with preference 1 through 10. Most administrators setup multiple dial-peers to send a call to a specific CUCM subscriber with a backup subscriber or another call agent being configured using another dial-peer with a lower preference (which is configured with a higher number).
Scenario: Two dial-peers are configured with the same match length for the digit string of 2001. The administrator defines an explicit preference. The gateway evaluates both dial-peers the same since their match length is the same. However, the administrator sets dial-peer 1 with a higher preference so that dial-peer is chosen as the first dial-peer used in routing the call. Dial-Peer 2 would remain as a secondary option can a failure occur on the first dial-peer.
!
dial-peer voice 1 voip
destination-pattern 2...
preference 1
!
dial-peer voice 2 voip
destination-pattern 2...
preference 2
!
A Cisco gateway only attempts to route a call via one eligible outbound dial-peer at a time. If a failure condition is observed on the first selected dial-peer, then the gateway attempts to route the call out the next eligible dial-peer. This continues until the call either succeeds or fails because there are no more eligible dial-peers left to try. A common symptom of dial-peer hunting and failure is a noticeable delay in ringback while making calls. Debugs are usually needed to verify exactly why the call is failing on a given dial-peer. The command huntstop can be employed on a dial-peer if an administrator does not want a gateway to look for another dial-peer when a failure condition is observed.
Scenario: Two dial-peers are configured with the same match length for the digit string of 2001. The administrator has defined an explicit preference and does not want to match dial-peer 2 for this particular call. Since there are two dial-peers with the same match-length, the preference is used to determine the dial-peer. Dial-Peer 1 has the lowest configured preference number, so it is used to route the call. If a failure condition occurs on the outbound call leg using dial-peer 1, then the gateway immediately stops dial-peer hunting since the huntstop command is configured. In this scenario, dial-peer 2 is never utilized for outbound routing.
! dial-peer voice 1 voip destination-pattern 2... preference 1 huntstop ! dial-peer voice 2 voip destination-pattern 2... preference 2 !
If you post the output from debug voip ccapi inout put in a text file we can check what’s going on.
Outtake from this document. Explain Cisco IOS and IOS XE Call Routing
Number String Dial-Peer Hunting
Number String Preference:
Much like URI's have a specific order of operations for evaluating matches, there is also a set of rules used when evaluating a numeric digit-string. The default dial-peer hunt scheme for a Cisco gateway is set to 0. This means the gateway searches for a pattern with the longest match (most specific). If there are two dial-peers with the same match length, the gateway looks at the explicitly defined dial-peer preference. Lastly, if both of those are the same, it chooses one in a random order.
There are other dial-peer hunt schemes available for configuration; however, most deploymens keep the default of 0.
Gateway(config)# dial-peer hunt ? <0-7> Dial-peer hunting choices, listed in hunting order within each choice: 0 - Longest match in phone number, explicit preference, random selection. 1 - Longest match in phone number, explicit preference, least recent use. 2 - Explicit preference, longest match in phone number, random selection. 3 - Explicit preference, longest match in phone number, least recent use. 4 - Least recent use, longest match in phone number, explicit preference. 5 - Least recent use, explicit preference, longest match in phone number. 6 - Random selection. 7 - Least recent use.
The longest match number string dial-peer algorithm finds the dial-peer with the most numbers in a sequence that exactly match a sequence of numbers in a number string. This concept is clarified in the subsequent scenario.
Scenario: Eligible dial-peers have been configured with these possible matches, and the gateway is evaluating a digit-string of 2001. Dial-peer 1 can match any number 2000 through 2999 while dial-peer 2 can match 2000 through 2009. Dial-Peer 2 would be matched for this call as it is the longest match (most specific) for the digit string 2001 when the default dial-peer hunting mechanisms is employed (dial-peer hunt 0). In other words, the sequence of numbers 200 is the largest sequence that exactly matches a sequence of number in the number string 2001.
!
dial-peer voice 1 voip
destination-pattern 2...
!
dial-peer voice 2 voip
destination-pattern 200.
!
Preference is defined as the administrator defined weight for each dial-peer. Administrators can configure a preference so the call always uses a specific dial-peer before others. By default, all dial-peers are preference 0. A dial-peer with preference 0 is matched before another dial-peer with preference 1 through 10. Most administrators setup multiple dial-peers to send a call to a specific CUCM subscriber with a backup subscriber or another call agent being configured using another dial-peer with a lower preference (which is configured with a higher number).
Scenario: Two dial-peers are configured with the same match length for the digit string of 2001. The administrator defines an explicit preference. The gateway evaluates both dial-peers the same since their match length is the same. However, the administrator sets dial-peer 1 with a higher preference so that dial-peer is chosen as the first dial-peer used in routing the call. Dial-Peer 2 would remain as a secondary option can a failure occur on the first dial-peer.
!
dial-peer voice 1 voip
destination-pattern 2...
preference 1
!
dial-peer voice 2 voip
destination-pattern 2...
preference 2
!
A Cisco gateway only attempts to route a call via one eligible outbound dial-peer at a time. If a failure condition is observed on the first selected dial-peer, then the gateway attempts to route the call out the next eligible dial-peer. This continues until the call either succeeds or fails because there are no more eligible dial-peers left to try. A common symptom of dial-peer hunting and failure is a noticeable delay in ringback while making calls. Debugs are usually needed to verify exactly why the call is failing on a given dial-peer. The command huntstop can be employed on a dial-peer if an administrator does not want a gateway to look for another dial-peer when a failure condition is observed.
Scenario: Two dial-peers are configured with the same match length for the digit string of 2001. The administrator has defined an explicit preference and does not want to match dial-peer 2 for this particular call. Since there are two dial-peers with the same match-length, the preference is used to determine the dial-peer. Dial-Peer 1 has the lowest configured preference number, so it is used to route the call. If a failure condition occurs on the outbound call leg using dial-peer 1, then the gateway immediately stops dial-peer hunting since the huntstop command is configured. In this scenario, dial-peer 2 is never utilized for outbound routing.
! dial-peer voice 1 voip destination-pattern 2... preference 1 huntstop ! dial-peer voice 2 voip destination-pattern 2... preference 2 !
