In this section:
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 following diagram shows a typical DNS server group configuration.
DNS Server Group Configuration
Note
The SBC supports associating a DNS group with a zone belonging to a different Address Context than that of the DNS group. The DNS query is resolved using the DNS group configured. Refer to Configuring DNS Groups for a configuration example.
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 5xx0/5400/7000 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.
Note
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
You must configure Cluster Admin for intra-cluster node communication before configuring a D-SBC signaling port, Load balancing service and DNS group parameters.
Refer to Cluster Admin - CLI for configuration details.
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> transport <tcp | udp> 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
DNS Group Parameters
Parameter | Description |
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ednsSupport | Enable flag to support Extension mechanisms for Domain Name Systems (EDNS) for statically configured and dynamically learned DNS servers.
NOTE: Refer to the following pages for additional details:
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NOTE: This parameter displays only after |
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| The DNS server to be configured within the DNS group.
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transport | The transport protocol to use to communicate with DNS servers.
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| The type of IP interfaces to be used for this DNS Group.
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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.
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Note
The SBC supports, by default, 1,300 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
Go to Configuring DNS Groups page for example DNS configurations.
Overview
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