F5 DNS Resolution Flow
f5bigipDNSzone transferBIND
Decision flow
We configure a listener on BigIP where the query arrives (e.g. 10.1.20.20).
- >Is there any Wide IP / FQDN configured against the query?
- >Is the name in the DNS Express Zone? (AD DNS is configured as primary DNS server and F5 is configured as secondary, where every entry is replicated to.)
- >Checks the F5 DNS cache.
- >Checks the master DNS cache which we assign in F5 DNS. Here, F5 will work as a recursive resolver. But if the resolving cache is not configured...
- >Is there any pool attached to the listener?
- >Pool: we do not set up any secondary servers; rather, when a DNS query is received at F5, we configure F5 to direct it to the AD DNS.
- >But if the pool is not configured, then...
- >In F5 DNS, a local BIND DNS can be configured, where it is checked next.
- >Checks if the listener is a Self-IP. If it is, then the query fails; if not, then the query is sent to that IP and the answer is cached.
Zone transfer
Verify if a DNS zone transfer has occurred. To make F5 DNS make a DNS zone transfer request to the already-present primary DNS server, we can simply change the DNS Express zone state to DISABLE and re-ENABLE again.
- >
dnsxdump - >
tail -f "/var/log/ltm"
Resolution order check1/3
After the Wide IP and DNS Express zone checks, what does BIG-IP consult next?