Cisco Cisco Expressway Maintenance Manual
■
A record for
expressway.example.com
returns the IPv4 address of the Expressway
■
AAAA record for
expressway.example.com
returns the IPv6 address of the Expressway
How you add the DNS records depends on the type of DNS server you are using. Instructions for setting up two
common DNS servers are given in the DNS configuration section.
common DNS servers are given in the DNS configuration section.
SIP endpoints always register with an AOR in the form of a URI, so no special configuration is required.
Several mechanisms could have been used to locate the Expressway. You may want to enable calls placed to
user@<IP_address>
to be routed to an existing registration for
user@example.com
. In this case you would configure a
example.com
.
URI Dialing and Firewall Traversal
If URI dialing via DNS is being used in conjunction with firewall traversal, DNS zones should be configured on the
Expressway-E and any Expressways on the public network only. Expressways behind the firewall should not have any
DNS zones configured. This will ensure that any outgoing URI calls made by endpoints registered with the
Expressway will be routed through the Expressway-E.
Expressway-E and any Expressways on the public network only. Expressways behind the firewall should not have any
DNS zones configured. This will ensure that any outgoing URI calls made by endpoints registered with the
Expressway will be routed through the Expressway-E.
In addition, the DNS records for incoming calls should be configured with the address of the Expressway-E as the
authoritative proxy for the enterprise (the DNS configuration section for more information). This ensures that incoming
calls placed using URI dialing enter the enterprise through the Expressway-E, allowing successful traversal of the
firewall.
authoritative proxy for the enterprise (the DNS configuration section for more information). This ensures that incoming
calls placed using URI dialing enter the enterprise through the Expressway-E, allowing successful traversal of the
firewall.
About ENUM Dialing
ENUM dialing allows an endpoint to be contacted by a caller dialing an E.164 number - a telephone number - even if
that endpoint has registered using a different format of alias.
that endpoint has registered using a different format of alias.
Using ENUM dialing, when an E.164 number is dialed it is converted into a URI using information stored in DNS. The
Expressway then attempts to find the endpoint based on the URI that has been returned.
Expressway then attempts to find the endpoint based on the URI that has been returned.
The ENUM dialing facility allows you to retain the flexibility of URI dialing while having the simplicity of being called
using just a number - particularly important if any of your callers are restricted to dialing using a numeric keypad.
using just a number - particularly important if any of your callers are restricted to dialing using a numeric keypad.
The Expressway supports outward ENUM dialing by allowing you to configure ENUM zones on the Expressway. When
an ENUM zone is queried, this triggers the Expressway to transform the E.164 number that was dialed into an ENUM
domain which is then queried for using DNS.
an ENUM zone is queried, this triggers the Expressway to transform the E.164 number that was dialed into an ENUM
domain which is then queried for using DNS.
Note:
ENUM dialing relies on the presence of relevant DNS NAPTR records for the ENUM domain being queried. These
are the responsibility of the administrator of that domain.
ENUM Dialing Process
When the Expressway attempts to locate a destination endpoint using ENUM, the general process is as follows:
1.
The user dials the E.164 number from their endpoint.
2.
The Expressway converts the E.164 number into an ENUM domain as follows:
a.
The digits are reversed and separated by a dot.
b.
The name of the domain that is hosting the NAPTR records for that E.164 number is added as a suffix.
3.
DNS is then queried for the resulting ENUM domain.
4.
If a NAPTR record exists for that ENUM domain, this will advise how the number should be converted into one
(or possibly more) H.323/SIP URIs.
(or possibly more) H.323/SIP URIs.
5.
. Note
that this is considered to be a completely new search, and so pre-search transforms and Call Policy will
therefore apply.
therefore apply.
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Cisco Expressway Administrator Guide
Dial Plan and Call Processing