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WRVS4400N periodically blocking outgoing DNS from LAN

I have a WRVS4400N, periodically it stops forwarding DNS requests to outside DNS servers.  I have statically assigned my DNS servers with the same DNS servers the router has configured as well as assigned known working DNS servers the router is not configured for.  Both result in the same problem.  Approximately every couple of days the router seems to start blocking DNS requests.  Running nslookup I get no response from DNS servers.  After rebooting the router everything starts working again.  I have updated to the latest firmware revision and it still does the same thing. Any ideas?


I put a RV-120W online last week, and I am seeing the same behavior.

Internet comes up 85% of the time, and occassionally I get "Page cannot be displayed" errors.

NSLOOKUP cannot find DNS server time to time.

We have a T1 line with Static IP.

Replacing a netgear unit which had no issues.

Hello Jason --Thanks for posting in the Support Community.

The RV 120W Engineering Team is reviewing your issue. Would you be kind enough to share your configuration file? This will help us troubleshoot.


Stephanie Reaves

Small Business Technology Group


Stephanie Reaves

Small Business Technology Group

So... What about getting some support on the orignal post too?



Sorry, take the lead on the thread.  I will use a seperate thread for my issue.

Just as an FYI, I reviewed my server and router settings last week.  I finally factory reset the RV120W and rebuilt my settings late Friday afternoon.

The results have been fairly promising.  I am still vey upset that I have to go through any of this "extra" effort.

This morning was the first test with my LAN at full capacity.  For the most part, I am seeing much better DNS resolution.  However, I still getl periodic behavior where the the RV120W is blocking DNS resolution.  I get "cannot be displayed" errors on both main web sites (even google) and on some web content such as ads imbedded in sites.  For the most part though, the connection is much more stable and at least operational.  Emails and Downloads are coming through again without corruption and streaming data is stable.

Again, what's strange on my end is I get stable download and upload speeds, pings and latency are all in good range, and I get resolution 95% of the time.  But I am concerned because I am still seeing the odd behavior and DNS blocks.

NSLOOKUP gives me the same behavior.  Most of the time I see my servers, but every so often it times out.

Can I ask who your ISP is?  I have a T1 from One Communications utilizing Verizon infrastructure.

I have a Windows 2003 server handling DHCP.  DNS on server.  TCP/IP settings on server have a static IP, and DNS points to server address and alternate ISP DNS address.  DNS has forwarders setup pointing to three DNS address as given to me by my ISP.

If I statically assign IP / Gateway / DNS on a workstation I see same behavior.

What was really strange was the WAP functionally worked perfectly last week.  When Wi-Fi was used on systems I had no DNS or corrupt files last week, or DNS issues.

Let me know what you see on your end.



Made a change to Firewall settings late yesterday.  Turned off "Block UDP Flood".

So far I see positive results:

VPN tunnels had much better performance last night.  Painting and refreshing was much better.  No disconnections.

This morning, LAN seems stable.

Simple tests from my machine show the following:

     DNS lookup / tracert commands all successful.  No time outs.

     Pings have been stable.  Very minor lost packets.  Much better

     Speed test all stable.  Latency consistant.

     A primitive test (opening 20 browser windows) work perfectly.  Not one error.  Previously I would have 20% error rate ("page not found").

     Have 2 tunnels now into LAN and no performance loss.

     Streaming on all computers has been stable this morning.  No stutters or loss of data stream yet.

Fingers are crossed.

Employee David Hornstein
Currently Being Moderated
25. Aug 24, 2010 7:38 AM in response to: Jason Mack
Re: RV120W ROUTER/FIREWALL "cannot display the webpage"

Hi Jason et al..

i believe the technician are now aware of a UDP issue on the Rv120W.

The internal discussions on the issue from R&D and development  seems to be;

1.       By default on RV120W there is a UDP Flood attack check which limits 25 UDP Connections Per Client in one instance, i.e at a particular time instance a PC behind this router can establish only 25 UDP Transactions, if we exceed router drops UDP Packets.

2.       We have a script that sends dns lookup queries at a very high rate than the router clears the UDP entries, this way we build up the UDP entry table in the router(i.e 25 entries)

3.       Once 25 limit is reached we are unable to resolve further DNS queries, using the script or using the browser.

4.       In the real world scenarios there might be one PC behind the router and open a website where all the items on the webpage are linked to different website, if you open this kind of website it may have links to more that 25 different website and clog the routers UDP table for that particular PC and user might not be able to resolve further DNS queries and unable to browse any new websites. This unability to browse happens until the UDP entries on the router time outs  and are cleared.

5.       This limit of 25 is because of the feature called Block UDP flood on the router which is enabled by default.

6.       Once we disable the block UDP Flood, router does not check for 25 UDP Connections limit and dns resolution is continuous without a break.

This is what a customers in the field might be seeing interruptions in DNS resolutions and website browse failed.

Some customers explicitly talked about DNS failures.

Jason I can see you have placed a service call, so hopefully CCORAL who posted on the 15 August should be helping you.

So Folks, If the Technician  deem the problem not a hardware issue requiring RMA, the technician will escalate the call to our Level 2 folks in Irvine, probably CCORAL.  You will get assistance to resolve this issue.

The Small Business Support center, should be aware of the problem. Please feel free to show them this posting, i am willing to chat with them to get the ball rolling.

So again, if you have not done so already,  please contact the SBSC  and place a service request and keep a copy of that number they give you as a reference (you may need it). My appologies for the inconvenience you have all had.


Dave Hornstein

Small Business, Channel Systems Engineer

Cisco  - Research Triangle Park.  USA