Using nslookup to help diagnose DNS resolving issue

If you are having issues to resolve your servers to the designated name servers, you may want to use these 3 tools (nslookup, dig, host) which can help to diagnose the DNS resolution. This entry mentions only nslookup.

Utility 1: nslookup
nslookup is one useful tools to assist in diagnosing problems with your resolving. Unfortunately, this niffy tools is already deprecated or in other words not actively maintained.

# nslookup -debug yournameserver.com

(-debug =  Turn on or off the display of the full response packet and any intermediate response packets when searching.)

# nslookup -debug -d2 yournameserver.com

(-d2 = Turn debugging mode on or off. This displays more about what nslookup is doing.)

Sample output on d2

lock_lookup dighost.c:3173
main parsing yournameserver.com
addlookup()
make_empty_lookup()
looking up starfruit.spms.ntu.edu.sg
setup_system()
create_search_list()
ndots is 1.
........
....... 
success
flush_server_list()
freeing commctx
freeing socketmgr
freeing timermgr
destroy DST lib
detach from entropy
unlock_lookup dighost.c:3219

Resources:

1. Tracking "Server Failed" Error from DNS