With
Cisco IOS Gateways, dial peers are used to match phone numbers, and the
destination can be a SIP Proxy Server, DNS SRV, or IP address. The following
example shows a Cisco IOS Gateway configuration to send calls to a SIP Proxy
Server using the SIP Proxy's IP address.
sip-ua
sip-server ipv4:10.4.1.100:5060
dial-peer voice 1000 voip
session target sip-server
...
The
sip-server
command on the dial peer tells the Cisco IOS Gateway to use the globally
defined SIP Server that is configured under the
sip-ua
settings. In order to configure multiple SIP Proxies for redundancy, you can
change the IP address to a DNS SRV record, as shown in the following example.
The DNS SRV record allows a single DNS name to be mapped to multiple Reporting
Servers.
sip-ua
sip-server dns:cvp.cisco.com
dial-peer voice 1000 voip
session target sip-server
...
Alternatively, you can configure multiple dial peers to point
directly at multiple SIP Proxy Servers, as shown in the following example. This
configuration allows you to specify IP addresses instead of relying on DNS.
dial-peer voice 1000 voip
session target ipv4:10.4.1.100
preference 1
...
dial-peer voice 1000 voip
session target ipv4:10.4.1.101
preference 1
...
In the
preceding examples, the calls are sent to the SIP Proxy Server for dial plan
resolution and call routing. If there are multiple Unified CVP Call Servers,
the SIP Proxy Server would be configured with multiple routes for load
balancing and redundancy. It is possible for Cisco IOS Gateways to provide load
balancing and redundancy without a SIP Proxy Server. The following example
shows a Cisco IOS Gateway configuration with multiple dial peers so that the
calls are load balanced across three Unified CVP Call Servers.
dial-peer voice 1001 voip
session target ipv4:10.4.33.131
preference 1
...
dial-peer voice 1002 voip
session target ipv4:10.4.33.132
preference 1
...
dial-peer voice 1003 voip
session target ipv4:10.4.33.133
preference 1
...
DNS SRV
records allow an administrator to configure redundancy and load balancing with
finer granularity than with DNS round-robin redundancy and load balancing. A
DNS SRV record allows you to define which hosts should be used for a particular
service (the service in this case is SIP), and it allows you to define the load
balancing characteristics among those hosts. In the following example, the
redundancy provided by the three dial peers configured above is replaced with a
single dial peer using a DNS SRV record. Note that a DNS server is required in
order to do the DNS lookups.
ip name-server 10.4.33.200
dial-peer voice 1000 voip
session target dns:cvp.cisco.com
With
Cisco IOS Gateways, it is possible to define DNS SRV records statically,
similar to static host records. This capability allows you to simplify the dial
peer configuration while also providing DNS SRV load balancing and redundancy.
The disadvantage of this method is that if the SRV record needs to be changed,
it must be changed on each gateway instead of on a centralized DNS Server. The
following example shows the configuration of static SRV records for SIP
services handled by cvp.cisco.com, and the SIP SRV records for cvp.cisco.com
are configured to load balance across three servers:
ip host cvp4cc2.cisco.com 10.4.33.132
ip host cvp4cc3.cisco.com 10.4.33.133
ip host cvp4cc1.cisco.com 10.4.33.131
(SRV records for
SIP/TCP)
ip host _sip._tcp.cvp.cisco.com srv 1 50 5060 cvp4cc3.cisco.com
ip host _sip._tcp.cvp.cisco.com srv 1 50 5060 cvp4cc2.cisco.com
ip host _sip._tcp.cvp.cisco.com srv 1 50 5060 cvp4cc1.cisco.com
(SRV records for
SIP/UDP)
ip host _sip._udp.cvp.cisco.com srv 1 50 5060 cvp4cc3.cisco.com
ip host _sip._udp.cvp.cisco.com srv 1 50 5060 cvp4cc2.cisco.com
ip host _sip._udp.cvp.cisco.com srv 1 50 5060 cvp4cc1.cisco.com