Hi. One of our customers has recently started having strange DNS issues when trying to browse the internet (email and AV updates are working fine). They use a Cisco 877 integrated device as their default gateway, service provider is BT (UK). I can ping the internet OK but cannot browse to most sites e.g. www.microsoft.com and www.symantec.com are OK but www.google.co.uk, www.bbc.co.uk are not (in fact, microsoft and symantec are the only ones I've managed to connect to so far).
I've checked with BT that our public DNS server IPs are correct. I've also tried using Firefox to no avail.
I've only encountered this problem once before (on a Netgear router) and this required a firmware upgrade. However, my Cisco logon doesn't give me access to download upgrades so I'm hoping thats not the problem this time. IOS version is 12.4(6)T6
Has anyone encountered this problem before? Any ideas on how I can resolve? Any help/pointers would be greatly appreciated.