Case 1: Are DNS servers working?
  • dig returns results right away => defined dns servers are working
  • dig returns results with a 2+ seconds delay or timeout => defined dns servers are NOT working

Recommendations:

  1. Test configuring client to use a different DNS server 
    dig @dnsServer1.kimconnect.com ldapServerName
  2. Verify that routing and firewall rules are passing traffic from client to DNS servers
  3. Cleanup invalid DNS records in AD
Case 2: Is localhost able to cache hardware address?
  • apr -a command returns results right away, and the ldap server IP mac address is present => ARP is working fine
  • apr -a command takes awhile to populate => indication that localhost arp table is having issues, so it’s not caching mac to ip for fast lookups

Recommendations:

a. Add a static arp entry into localhost

Command:

arp -s ip-address-of-ldap-server hardware-address-of-ldap-server
# Example:
sudo arp -s 10.10.10.10 aa:11:bb:22:cc:44

# How to reverse the change:
sudo arp --delete 10.10.10.10

# How to check the ARP Table:
sudo arp -avn # more verbose
sudo arp -n # simple view

b. Clear ARP cash & DNS cache

ip -s -s neigh flush all
arp -n
service nscd restart
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