Cisco Cisco Expressway
Appendix 3: Cluster Name and DNS SRV Records
Using DNS SRV to convert a domain to an IP address has a number of benefits:
■
The structure of the lookup includes service type and protocol as well as the domain, so that a common domain
can be used to reference multiple different services which are hosted on different machines (e.g. HTTP, SIP,
H.323).
can be used to reference multiple different services which are hosted on different machines (e.g. HTTP, SIP,
H.323).
■
The DNS SRV response includes priority and weighting values which allow the specification of primary,
secondary, tertiary etc groups of servers, and within each priority group, the weighting defines the proportion of
accesses that should use each server.
secondary, tertiary etc groups of servers, and within each priority group, the weighting defines the proportion of
accesses that should use each server.
■
As the DNS SRV response contains details about priorities and weights of multiple servers, the receiving device
can use a single lookup to search for an in-service server (where some servers are inaccessible) without the
need to repeatedly query the DNS server. (This is in contrast to using round robin DNS which does require
repeated lookups into the DNS server if initial servers are found to be inaccessible.)
can use a single lookup to search for an in-service server (where some servers are inaccessible) without the
need to repeatedly query the DNS server. (This is in contrast to using round robin DNS which does require
repeated lookups into the DNS server if initial servers are found to be inaccessible.)
The generic format of a DNS SRV query is:
■
_service._protocol.<fully.qualified.domain>
The DNS SRV response is a set of records in the format:
■
_service._ protocol.<fully.qualified.domain>. TTL Class SRV Priority Weight Port Target
where Target is an A-record defining the destination.
Further details on DNS SRV can be found in
Expressway Administrator Guide and RFC 2782.
DNS SRV Configuration for Mobile and Remote Access
This section summarizes the public (external) and local (internal) DNS requirements. For more information, see the
Cisco Jabber Planning Guide (for your version) on the
Cisco Jabber Planning Guide (for your version) on the
.
Public DNS
The public (external) DNS must be configured with
_collab-edge._tls.<domain>
SRV records so that endpoints can
discover the Expressway-Es to use for mobile and remote access. SIP service records are also required (for general
deployment, not specifically for mobile and remote access). For example, for a cluster of 2 Expressway-E systems:
deployment, not specifically for mobile and remote access). For example, for a cluster of 2 Expressway-E systems:
Domain
Service
Protocol
Priority
Weight
Port
Target host
example.com
collab-edge
tls
10
10
8443
expe1.example.com
example.com
collab-edge
tls
10
10
8443
expe2.example.com
example.com
sips
tcp
10
10
5061
vcse1.example.com
example.com
sips
tcp
10
10
5061
vcse2.example.com
Local DNS
The local (internal) DNS requires
_cisco-uds._tcp.<domain>
SRV records. For example:
Domain
Service
Protocol
Priority
Weight
Port
Target host
example.com
cisco-uds
tcp
10
10
8443
cucmserver1.example.com
example.com
cisco-uds
tcp
10
10
8443
cucmserver2.example.com
Ensure that the
cisco-uds
SRV records are NOT resolvable outside of the internal network, otherwise the Jabber client
will not start mobile and remote access negotiation via the Expressway-E.
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Cisco Expressway Cluster Creation and Maintenance Deployment Guide