Intermittant DNS Resolution

i have been following 2 other threads on same topic unable resolve issue.

on 11-5-2012 users complained of "internet down" , subsequent investigation pointed @ dns failure. further observation was intermittant without rhyme or reason. affecting different target external sites without exception , starting work again without intervention.

we have swapped routers, isp has swapped interface device problem persist.

network overview cbeyond iad bundled voice/data services (t-1). 5 public ip addresses.

netgear fvs336g2v2 latest firmware assigned xxx.xxx.xxx.106 ip. cbeyond gateway xxx.xxx.xxx.105. lan side 10.0.1.0 router assigned 10.0.1.254. port forwarding set rdc , vnc , 2 ipsec tunnels derived. workstations behind router xp pro sp3 dell t610 raid 1/5 server 2008r2 domain controller , dns active (10.0.1.10). workstations configured point 10.0.1.10 dns. forwarders on dns set cbeyond dns 64.238.96.12 primary , 66.180.96.12 secondary. after reading prior threads ran nslookup , got response of <512 bytes. added l3 dns (4.2.2.2) , elevated first choice , got nslookup results of reply size limit @ least 3048.

still having resolution issues made 4.2.2.2 forwarder , still have intermittant dns resolve/load.

i willing document required assistance in resolving this. please advise test,  inwhat order , how results you.

thanks in advance

kerlegan,

i'll admit - looks deep :)  dns issues, generally, suck - hate when users "the internet's down" @ least it's typically dns.

just clarify you're saying:

your internal clients point local dns server (10.0.1.10).

your local dns has forwarders cbeyond.  added 4.2.2.2, included 4.2.2.2, no improvement.

i'd try , simplify issue.  during episode of "internet down" problem, happens if go 1 of workstations , set 4.2.2.2 dns, attempt access same site that's failing on other internal pc's?  may @ least narrow down issue of local equipment. 

from there, if above works properly, run nslookup on client , check results "known good" result.  change dns on local client next hop toward inside of network - cbeyond if i'm reading post correctly.  repeat, see if fails.  if not, change dns server (10.0.1.10) repeat.

ideally, 1 piece fail, giving place start additional troubleshooting. 

let me know if helps - maybe research somewhere.

good luck.

damian

Windows Server  >  Network Infrastructure Servers