Avi Load Balancer DNS supports name server (NS) records as part of the static DNS records (Avi Load Balancer GSLB does not support NS records).
A DNS Name Server (NS) record specifies the domain name of the name server servicing a particular domain. For instance, an NS record with a time-to-live (TTL) of 1100 seconds, and for the com domain serviced by the name server a.gtld-servers.net, will be defined as below:
com. 1100 IN NS a.gtld-servers.net.
For the NS records, the Avi Load Balancer DNS can behave both as an authoritative and non-authoritative server. An NS record can be configured on Avi Load Balancer DNS for two modes of the DNS domain, delegated and non-delegated.
Delegated Domains or Zone Cuts
If the desired behavior is to have the Avi Load Balancer DNS act as a non-authoritative server for the domain of the NS record, then the NS record must be configured with the option of delegation set to True. The delegation indicates that the domain name for the NS record is delegated to another authoritative name server. That is, the domain name for the NS record is a zone cut, with the domains within this domain being owned by another name server.
For instance, xyz.avi.com is a zone cut for the domain avi.com, whereby domains within xyz.avi.com (aka *.xyz.avi.com) is managed by another name server than the one managing xyz.avi.com).
When a domain name is configured to be a zone cut, it is mandatory to configure the IP address of the corresponding name servers in the NS record associated with this domain name. The IP address is mandatory when the name server’s domain can result in a recursive DNS query to this domain name:
DNS query for NS record for domain: avi.com
Response contains name server: ns1.avi.com
Since domain name ns1.avi.com must be resolved, it results in an A query for ns1.avi.com, resulting in a response with NS record for ns1.foo.com (but no A record, thereby leading to NS request for ns1.avi.com again and again), leading to an indefinite recursion.
To avoid this recursion, the FQDN for the name server in the NS record is also configured with the A record (the IP address). This A record is called the glue record for the NS record. For instance,
static_dns_records {
fqdn: "avi.com"
type: DNS_RECORD_NS
delegated: true
wildcard_match: true
ttl: 1100
ns {
nsname: "ns1.avi.com"
ip_address {
addr: "192.5.6.30"
type: V4
}
}
ns {
nsname: "ns2.avi.net"
}
}
The above configuration for a static NS record is for the domain “avi.com,” which has NS records pointing to two name servers. Thus, any DNS query with the subdomain “avi.com” that comes to this server will be served the NS records in the AUTHORITY SECTION of the DNS response. This response will cause a recursive name resolver to direct the DNS query to either of the two name servers. Thus, a query for A record for www.avi.com will get a response of two NS records in the DNS response along with the glue record for ns1.avi.com in the ADDITIONAL SECTION of the response. The recursive resolver will then send the same DNS query to the name server ns1.avi.com or ns2.avi.net.
If the desired behavior is to catch all queries for domain names containing “avi.com” as a subdomain, then you must set the wildcard match field to True, otherwise, only queries for “avi.com” will get directed to the name servers. When wildcard matching is set for “avi.com” any query of the form *.avi.com, for instnace, foo.avi.com, abc.xyz.avi.com, and so on) will get directed to the configured name servers. When wildcard matching is not set, then query to domains of the form *.avi.com may or may not succeed depending on whether these FQDNs are configured or not in the DNS virtual service.
Shown below is a dig request for:
A record (A, AAAA, CNAME, SRV, and so on)
To a domain containing the delegated domain “com” as a subdomain
With wildcard matching set, 13 name servers (from
a.gtld-servers.nettom.gtld-servers.net)Corresponding glue records.
The requested domain sales.avi.com has "com" as a subdomain.
; <<>> DiG 9.10.3-P4-Ubuntu <<>> @10.90.91.62 sales.avi.com A ; (1 server found) ;; global options: +cmd ;; Got answer: ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 57472 ;; flags: qr aa rd; QUERY: 1, ANSWER: 0, AUTHORITY: 13, ADDITIONAL: 13 ;; WARNING: recursion requested but not available ;; QUESTION SECTION: ;sales.avi.com. IN A ;; AUTHORITY SECTION: com. 1100 IN NS a.gtld-servers.net. com. 1100 IN NS b.gtld-servers.net. com. 1100 IN NS c.gtld-servers.net. com. 1100 IN NS d.gtld-servers.net. com. 1100 IN NS e.gtld-servers.net. com. 1100 IN NS f.gtld-servers.net. com. 1100 IN NS g.gtld-servers.net. com. 1100 IN NS h.gtld-servers.net. com. 1100 IN NS i.gtld-servers.net. com. 1100 IN NS j.gtld-servers.net. com. 1100 IN NS k.gtld-servers.net. com. 1100 IN NS l.gtld-servers.net. com. 1100 IN NS m.gtld-servers.net. ;; ADDITIONAL SECTION: a.gtld-servers.net. 1100 IN A 192.5.6.30 b.gtld-servers.net. 1100 IN A 192.33.14.30 c.gtld-servers.net. 1100 IN A 192.26.92.30 d.gtld-servers.net. 1100 IN A 192.31.80.30 e.gtld-servers.net. 1100 IN A 192.12.94.30 f.gtld-servers.net. 1100 IN A 192.35.51.30 g.gtld-servers.net. 1100 IN A 192.42.93.30 h.gtld-servers.net. 1100 IN A 192.54.112.30 i.gtld-servers.net. 1100 IN A 192.43.172.30 j.gtld-servers.net. 1100 IN A 192.48.79.30 k.gtld-servers.net. 1100 IN A 192.52.178.30 l.gtld-servers.net. 1100 IN A 192.41.162.30 m.gtld-servers.net. 1100 IN A 192.42.93.30 ;; Query time: 0 msec ;; SERVER: 10.90.91.62#53(10.90.91.62) ;; WHEN: Fri May 26 14:55:20 PDT 2017 ;; MSG SIZE rcvd: 469
Non-delegated Domains
If the desired behavior is to have the Avi Load Balancer DNS act as an authoritative server for the NS record, then the NS record must not be configured with the option of delegation set to True. The delegation indicates that the domain name for the NS record is delegated to another authoritative name server. For instance,
static_dns_records {
fqdn: "google.com"
type: DNS_RECORD_NS
wildcard_match: true
ttl: 1100
ns {
nsname: "ns1.google.com"
ip_address {
addr: "192.5.6.30"
type: V4
}
}
ns {
nsname: "ns2.google.com"
ip_address {
addr: "192.33.14.30"
type: V4
}
}
ns {
nsname: "ns3.google.com"
ip_address {
addr: "192.26.92.30"
type: V4
}
}
ns {
nsname: "ns4.google.com"
ip_address {
addr: "192.31.80.30"
type: V4
}
}
}
The above configuration for a static NS record is for the domain “google.com,” which has NS records pointing to four name servers. For these NS records, Avi Load Balancer DNS is an authoritative name server. Thus, any DNS NS query with the domain “google.com” that comes to this server will be served the NS records in the ANSWER SECTION of the DNS response, and the A records for the name server IP addresses are served in the ADDITIONAL SECTION.
If the wildcard match field is set to True, but the domain is not delegated, then any DNS query which matches the non-delegated domain will get an NXDOMAIN response.
Shown below is a dig query request:
Of any type (A, NS, CNAME, SRV, and so on.)
To the domain “google.com,”
With wildcard matching on, and
Four name servers (from
ns1.google.comtons4.google.com)
; <<>> DiG 9.10.3-P4-Ubuntu <<>> @10.90.91.63 google.com A ; (1 server found) ;; global options: +cmd ;; Got answer: ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 39235 ;; flags: qr aa rd; QUERY: 1, ANSWER: 4, AUTHORITY: 0, ADDITIONAL: 4 ;; WARNING: recursion requested but not available ;; QUESTION SECTION: ;google.com. IN A ;; ANSWER SECTION: google.com. 1100 IN NS ns1.google.com. google.com. 1100 IN NS ns2.google.com. google.com. 1100 IN NS ns3.google.com. google.com. 1100 IN NS ns4.google.com. ;; ADDITIONAL SECTION: ns1.google.com. 1100 IN A 192.5.6.30 ns2.google.com. 1100 IN A 192.33.14.30 ns3.google.com. 1100 IN A 192.26.92.30 ns4.google.com. 1100 IN A 192.31.80.30 ;; Query time: 0 msec ;; SERVER: 10.90.91.63#53(10.90.91.63) ;; WHEN: Fri May 26 15:49:35 PDT 2017 ;; MSG SIZE rcvd: 164
A dig query request of any type (A, NS, CNAME, SRV, and so on.) to a domain containing the domain “google.com”, with wildcard matching on, four name servers (from ns1.google.com to ns2.google.com) and corresponding A records will always elicit an NXDOMAIN response:
; <<>> DiG 9.10.3-P4-Ubuntu <<>> @10.90.91.63 mail.google.com A ; (1 server found) ;; global options: +cmd ;; Got answer: ;; ->>HEADER<<- opcode: QUERY, status: NXDOMAIN, id: 42986 ;; flags: qr aa rd; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 0 ;; WARNING: recursion requested but not available ;; QUESTION SECTION: ;mail.google.com. IN A ;; Query time: 0 msec ;; SERVER: 10.90.91.63#53(10.90.91.63) ;; WHEN: Fri May 26 16:56:25 PDT 2017 ;; MSG SIZE rcvd: 33
