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The DNS (Domain Name System) group object contains a list of DNS servers used to resolve SIP NAPTR, SRV and A-record look-ups. The DNS server group is contained in an Address Context and is referenced by Zones and SIP Trunk Groups in that Address Context.

The following diagram depicts the DNS server group configuration.

Figure : DNS Server Group Configuration

 

 

Creating and Configuring DNS Servers

You may create up to eight DNS servers. The DNS Client sends the query to the server with highest priority (lower value) first, and in case of a timeout, the query is resent to the server with the next highest priority. For servers with the same priority, the selection is distributed based on the weight value. Priority and weight values are configurable. You can also configure recursion preference (recursion involves assistance from other DNS servers to help resolve the query).

When a DNS group is configured at the Address Context level for an interface, it must also be configured at the Zone level in that Address Context.

To assign a DNS group to a zone, refer to Zone - DNS Group - CLI page.

Note

The SBC Core supports up to eight DNS servers per DNS group. The SBC 5000/7000 series platforms support up to 2,048 DNS Groups system-wide. SBC SWe supports up to 128 DNS Groups. See SBC Provisioning Limits for additional provisioning limitations.

Info

The SBC 52x0 and SBC 7000 systems support creating IP Interface Groups containing sets of IP interfaces that are not "processor friendly" (i.e. carried on physical Ethernet ports served by separate processors). However, restrictions exist regarding the usage of such Interface Groups.

(This ability does not apply to the SBC 51x0 and SBC 5400 systems which have only two physical media ports. IP interfaces from the two physical ports may be configured within the same IP Interface Groups without restriction.)

For complete details, refer to Configuring IP Interface Groups and Interfaces.

Note

Before deleting a DNS group, first delete the DNS local record names and DNS server in that group. 

Command Syntax

The DSN Group CLI syntax is shown below:

% set addressContext <addressContext name> dnsGroup <dnsGroup name>
	ednsSupport <disabled | enabled>
	interface <interface name> 
	localRecord <record name> 
		data <#> 
		hostName <name> 
		order <centralized-roundrobin | priority | roundrobin> 
		state <disabled | enabled> 
	server <DSN server name> 
		ipAddress <ip address> 
		priority <0-100> 
		recordOrder <centralized-roundrobin | priority | roundrobin>
		recursionDesired <false | true> 
		state <disabled | enabled>
		tcpFallback <disabled | enabled>
		transportProtocol <tcp | udp>
		weight <0-100> 
	type <ip | mgmt | none>
	useConfiguredDnsServer <disabled | enabled>

 

CLI syntax to configure the type of IP interfaces to be used for this DNS Group:

% set addressContext <addressContext name> dnsGroup <dnsGroup name> type <ip | mgmt | none>

 

CLI syntax to configure the local DNS resource record:

% set addressContext <addressContext name> dnsGroup <dnsGroup name> localRecord <record_name> 
	data <index#> 
		ipAddress <ip address> 
		priority <0-100> 
		state <disabled | enabled> 
		type <a | aaaa> 
	hostName <host_Name> 
	order <centralized-roundrobin | priority | roundrobin> 
	state <enabled | disabled>

 

CLI syntax to configure the DNS server for this address context:

% set addressContext <addressContext name> dnsGroup <dnsGroup name> server <DNS server name> 
	ipAddress <DNS_ipAddress> 
	priority <0-100> 
	recordOrder <centralized-roundrobin | priority | roundrobin>
	recursionDesired <false | true> 
	state <disabled | enabled>
	tcpFallback <disabled | enabled>
	transportProtocol <tcp | udp> 
	weight <0-100>

 

CLI syntax to configure and display the type of IP interfaces to be used for this DNS Group:

% set addressContext <addressContext_name> dnsGroup <dnsGroup_name> type ip
-OR-
% set addressContext <addressContext_name> dnsGroup <dnsGroup_name> type mgmt interface mgmtGroup

% show addressContext <addressContext_name> dnsGroup <dnsGroup_name> type

Command Parameters

Table : DNS Group Parameters

 

Parameter

Description

Mandatory parameters:

ednsSupport

Enable flag to support Extension mechanisms for Domain Name Systems (EDNS) for statically configured and dynamically learned DNS servers.

  • disabled (default)
  • enabled

Refer to the following pages for additional details:

interface

<IP or Mgmt Interface group name> – Use this parameter to specify the name of the IP or Management Interface group.

Note

This parameter displays only after type parameter is specified.

localRecord

<name> – The local DNS resource record name. Configuration options:

  • data <index>– The DNS record index number for this DNS record.
    • ipAddress – Specifies the IPv4 or IPv6 address of the local name service record data.
    • priority – The local name service record data priority. (range: 0-100 / default = 0).
    • state– Administrative state of the local name service record data.
      • disabled (default)
      • enabled
    • type <a | aaaa> – Specifies the local name service record data type.
  • hostName – A unique host name of this local name service record. The host name must be unique across all records.
  • order– Specifies the lookup order of this local name service record. Options are:
    • centralized-roundrobin – (recommended) This option uses the round-robin technique with respect to the whole system.
    • priority – Lookup order is based on the order in which entries returned in DNS response.
    • roundrobin Use this option to share and distribute local records among internal SBC processes in a round-robin fashion. Over a large number of calls, a fair amount of distribution occur across all DNS records.
  • state – The state of this local name service record.
    • disabled (default)
    • enabled

Note

Ensure the DNS local record name (not the FQDN to be resolved) is globally unique. 


server

The DNS server to be configured within the DNS group.

  • ipAddress  The IPv4 or IPv6 address of this DNS Server.
  • priority  The DNS server priority. (range: 0-100 / default = 0).
  • recordOrder The lookup order of local name service records associated with the specified DNS server.
    • centralized-roundrobin – (recommended) This option uses the round-robin technique with respect to the whole system.
    • priority (default) – Lookup order is based on the order in which entries returned in DNS response.
    • roundrobin Use this option to share and distribute local records among internal SBC processes in a round-robin fashion. Over a large number of calls, a fair amount of distribution occur across all DNS records.
  • recursionDesired– Enable to use recursion for this DNS Server.
    • false
    • true (default)
  • stateThe Administrative state of DNS Server configuration.
    • disabled (default)
    • enabled
  • tcpFallback – Enable flag (per DNS server) to support TCP fallback when transport protocol is configured as UDP.
    • disabled (default)
    • enabled
  • transportProtocol– Use this parameter to choose the transport protocol to use for DNS queries for this DNS server.
    • tcp
    • udp (default)
  • weight The load-sharing weight of this DNS Server. (range: 0-100) default = 0.

type

The type of IP interfaces to be used for this DNS Group.

  • ip
  • mgmt
    • interface mgmtGroup – management interface group name.
  • none (default)

interface

Specifies the name of the Management Interface group when using the management interfaces.

Note

This parameter displays after type parameter is specified.

useConfiguredDnsServer

With the flag disabled, the SBC stores the Authoritative NS records received in Domain Name System (DNS) query response and uses it for locating a closer DNS server for subsequent DNS queries. There are cases where “Authoritative” servers, which are used for the previous queries may not be directly reachable from SBC, or query responses are blocked by IP ACL rules configured on the SBC. This causes DNS queries to fail and subsequent call failures. With the flag enabled, the SBC supports using the configured DNS for external DNS queries within that DNS group. It sends the DNS queries to the DNS server in the DNS group and ignores the Authoritative servers.

  • disabled (default)
  • enabled

Note

The SBC supports, by default, 1300 Maximum Transmission Unit (MTU) bytes, and the MTU size used by the SBC is configurable. If the initial INVITE message size exceeds the default MTU value, the SBC sends the data over the TCP transport protocol. The TCP transport protocol is used if it is allowed by the transport profile, irrespective of its preference order.

Command Examples

Refer to Configuring DNS Groups for example DNS configurations.

 


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