Assumption is a dangerous thing..especially in the world of systems administration.
As I write this,I still laugh at myself because I was troubleshooting a box only on one level till it finally kicked in on what to see at all levels.
Basically,long story short-box was a linux server and it was a Windows environment pre-dominantly(essential service like DHCP was by Windows box).DNS was still linux service.
I swapped out the NIC that was the culprit from the box and rebuilt the box using the in-built NIC,box was built and I was very happy till…I realised that host file on master DNS needed to be changed as the MAC that was referred too was no longer in use,so I changed the MAC on master DNS hostfile.
As per normal practise,tried pinging the box…. no reply.Cross checked the connections from box to switch where it was terminated,all was ok.Tried swapping the port where it was terminated,still no go.
Fun continues…DNS resolution was now fine which meant that host entry on master was no longer stale still the beloved box was not replying to pings..either from LAN or WAN(note-always test connectivity from multiple subnets so that you can sleep well at night).
I was a bit annoyed…until light bulb kicked in…there was a DHCP server on network which had the reservation for this box and reservation was tied to the old MAC address of the box. D’OH!
Changed the reservation entry for the box in Windows DHCP scope to reflect the new MAC address and bounced the box.
Hallelujah! Successful ICMP reply from the sweet thing and boy was I happy.
Moral of story :
Always think about multiple services while troubleshooting any thing that is on network.
Never assume any device will work once plugged in,always be prepared to troubleshoot on all levels.
This will save a lot of time when troubleshooting-guaranteed.