Sudden blip in internet access

[#1]

From router log
Error Aug 23 09:50:35 FIREWALL replay check (1 of 1): Protocol: ICMP Src ip: 192.168.1.65 Dst ip: 208.67.220.220 Type: Destination Unreachable Code: Port Unreacheable
DNS servers are  Primary 8.8.8.8 Secondary  208.67.220.220 and are set on the PC not the router
So it appears that I couldn't access either DNS server for a short time - any suggestions

[#2]

Considering the source and dest of the icmp packet, I would have thought the log entry means that by the time you received the dns answer, your computer had already given up waiting for it, or the dns cache service had restarted or something like that.