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DNS issue and DHCP DNS settings

adept2
Novice

DNS issue and DHCP DNS settings

I am having a problem with a DGND3700v2 running V1.1.00.23.

Every so often it stops responding to DNS queries. If a client on the LAN changes its DNS setting to point directly to a DNS server on the internet the client works fine, but DNS queries sent to the modem time out until the modem is rebooted.

I have tried setting the router to use the ISP assigned DNS, or manually setting the DNS servers, but neither setting fixes the issue. The problem isn't with the upstream DNS server, as clients on the LAN can use the same DNS server successfully.

Also, according to the manual when you assign DNS servers in the modem Web-GUI, the modem is supposed to pass those DNS servers to clients when they connect via DHCP. What we are seeing is the router always assigns it's own address as the DNS server, no matter the DNS configuration on the modem.

This is very frustrating and I am about to junk the router and buy another one..

Has anyone seen this issue, and is there a fix? Should we downgrade to an earlier firmware?

Message 1 of 20
Babylon5
NETGEAR Employee Retired

Re: DNS issue and DHCP DNS settings

Is there any information in the router log relating to DNS?

If you run a packet capture program on a PC, e.g. Microsoft Network Monitor or Wireshark, this should show you the DNS request going out and the response (or lack of).

Have you tried a factory reset?
____________________________
Working on behalf of Netgear
My name is Andy
Message 2 of 20
adept2
Novice

Re: DNS issue and DHCP DNS settings

I tried a factory reset, but after a couple of days DNS dies again.

Here are the packet captures you requested

The first the first shows the unanswered DNS queries.

The second shows the DHCP packets specifying the router as the resolver, and not the primary and secondary DNS servers specified on the router.


13:44:52.427483 IP 192.168.0.50.53543 > 192.168.0.1.53: 58168+ A? d.dropbox.com. (31)
13:44:53.224035 IP 192.168.0.50.58761 > 192.168.0.1.53: 23974+ A? ssl.gstatic.com. (33)
13:44:54.575041 IP 192.168.0.1.53715 > 255.255.255.255.7423: UDP, length 173
13:44:56.304650 IP 192.168.0.50.58761 > 192.168.0.1.53: 23974+ A? ssl.gstatic.com. (33)
13:44:57.545639 IP 192.168.0.1.53715 > 255.255.255.255.7423: UDP, length 173
13:44:59.674669 IP 192.168.0.50.52921 > 192.168.0.1.53: 4820+ A? clients6.google.com. (37)
13:45:00.521497 IP 192.168.0.1.53715 > 255.255.255.255.7423: UDP, length 173
13:45:03.586250 IP 192.168.0.1.53715 > 255.255.255.255.7423: UDP, length 173
13:45:05.322884 IP 192.168.0.50.58761 > 192.168.0.1.53: 23974+ A? ssl.gstatic.com. (33)
13:45:05.486670 IP 192.168.0.50 > 192.168.0.1: ICMP echo request, id 379, seq 0, length 64
13:45:05.489026 IP 192.168.0.1 > 192.168.0.50: ICMP echo reply, id 379, seq 0, length 64
13:45:06.316149 IP 192.168.0.50.56777 > 192.168.0.1.53: 18720+ A? www3.l.google.com. (35)
13:45:06.487419 IP 192.168.0.50 > 192.168.0.1: ICMP echo request, id 379, seq 1, length 64
13:45:06.488983 IP 192.168.0.1 > 192.168.0.50: ICMP echo reply, id 379, seq 1, length 64
13:45:06.539016 IP 192.168.0.1.53715 > 255.255.255.255.7423: UDP, length 173
13:45:07.487884 IP 192.168.0.50 > 192.168.0.1: ICMP echo request, id 379, seq 2, length 64
13:45:07.489998 IP 192.168.0.1 > 192.168.0.50: ICMP echo reply, id 379, seq 2, length 64
13:45:08.489005 IP 192.168.0.50 > 192.168.0.1: ICMP echo request, id 379, seq 3, length 64
13:45:08.491074 IP 192.168.0.1 > 192.168.0.50: ICMP echo reply, id 379, seq 3, length 64
13:45:09.489322 IP 192.168.0.50 > 192.168.0.1: ICMP echo request, id 379, seq 4, length 64
13:45:09.490898 IP 192.168.0.1 > 192.168.0.50: ICMP echo reply, id 379, seq 4, length 64
13:45:09.544986 IP 192.168.0.1.53715 > 255.255.255.255.7423: UDP, length 173
13:45:10.489576 IP 192.168.0.50 > 192.168.0.1: ICMP echo request, id 379, seq 5, length 64
13:45:10.491282 ARP, Request who-has 192.168.0.50 tell 192.168.0.1, length 28
13:45:10.491297 ARP, Reply 192.168.0.50 is-at 9c:f3:87:b4:8b:c6, length 28
13:45:10.491973 IP 192.168.0.1 > 192.168.0.50: ICMP echo reply, id 379, seq 5, length 64
13:45:12.596608 IP 192.168.0.1.53715 > 255.255.255.255.7423: UDP, length 173
13:45:15.556980 IP 192.168.0.1.53715 > 255.255.255.255.7423: UDP, length 173
13:45:18.638564 IP 192.168.0.1.53715 > 255.255.255.255.7423: UDP, length 173
13:45:20.758982 IP 192.168.0.50.53628 > 192.168.0.1.53: 54154+ A? www.abc.net.au. (32)
13:45:21.568968 IP 192.168.0.1.53715 > 255.255.255.255.7423: UDP, length 173
13:45:24.577698 IP 192.168.0.1.53715 > 255.255.255.255.7423: UDP, length 173
13:45:25.758154 IP 192.168.0.50.53628 > 192.168.0.1.53: 54154+ A? www.abc.net.au. (32)
13:45:27.580772 IP 192.168.0.1.53715 > 255.255.255.255.7423: UDP, length 173
13:45:30.619196 IP 192.168.0.1.53715 > 255.255.255.255.7423: UDP, length 173
13:45:30.758493 IP 192.168.0.50.53628 > 192.168.0.1.53: 54154+ A? www.abc.net.au. (32)
13:45:33.690943 IP 192.168.0.1.53715 > 255.255.255.255.7423: UDP, length 173
13:45:36.598435 IP 192.168.0.1.53715 > 255.255.255.255.7423: UDP, length 173


DHCP


PAD Option 0, length 0, occurs 26
13:56:08.194197 IP (tos 0x0, ttl 255, id 39994, offset 0, flags [none], proto UDP (17), length 328)
0.0.0.0.68 > 255.255.255.255.67: [udp sum ok] BOOTP/DHCP, Request from 9c:f3:87:b4:8b:c6, length 300, xid 0xb9065a44, Flags [none] (0x0000)
Client-Ethernet-Address 9c:f3:87:b4:8b:c6
Vendor-rfc1048 Extensions
Magic Cookie 0x63825363
DHCP-Message Option 53, length 1: Discover
Parameter-Request Option 55, length 9:
Subnet-Mask, Default-Gateway, Domain-Name-Server, Domain-Name
Option 119, LDAP, Option 252, Netbios-Name-Server
Netbios-Node
MSZ Option 57, length 2: 1500
Client-ID Option 61, length 7: ether 9c:f3:87:b4:8b:c6
Lease-Time Option 51, length 4: 7776000
Hostname Option 12, length 9: "OwenAir-2"
END Option 255, length 0
PAD Option 0, length 0, occurs 15
13:56:08.290723 ARP, Ethernet (len 6), IPv4 (len 4), Request who-has 192.168.0.50 tell 192.168.0.1, length 46
13:56:08.389741 ARP, Ethernet (len 6), IPv4 (len 4), Request who-has 192.168.0.65 tell 192.168.0.32, length 46
13:56:08.492557 IP (tos 0x0, ttl 64, id 43105, offset 0, flags [none], proto UDP (17), length 116)
192.168.0.55.61188 > 192.168.0.255.19540: [udp sum ok] UDP, length 88
13:56:08.802977 IP (tos 0x0, ttl 64, id 0, offset 0, flags [none], proto UDP (17), length 328)
192.168.0.1.67 > 192.168.0.50.68: [udp sum ok] BOOTP/DHCP, Reply, length 300, xid 0xb9065a44, Flags [none] (0x0000)
Your-IP 192.168.0.50
Client-Ethernet-Address 9c:f3:87:b4:8b:c6
Vendor-rfc1048 Extensions
Magic Cookie 0x63825363
DHCP-Message Option 53, length 1: Offer
Server-ID Option 54, length 4: 192.168.0.1
Lease-Time Option 51, length 4: 86400
Subnet-Mask Option 1, length 4: 255.255.255.0
Default-Gateway Option 3, length 4: 192.168.0.1
Domain-Name-Server Option 6, length 4: 192.168.0.1
END Option 255, length 0
PAD Option 0, length 0, occurs 26
Message 3 of 20
Babylon5
NETGEAR Employee Retired

Re: DNS issue and DHCP DNS settings

Thanks, I’ll take a closer look when I get home from work this evening (about 10 hours from now).

The router acts as a DNS Relay, it does not pass the DNS server address(s) to the clients. When a DNS request is sent to the router from a client, the router forwards the request to the DNS server(s).

I can see pings to the router (192.168.0.1) from 192.168.0.50, but DNS queries seem to be directed to 192.168.0.53? Can you point out the lines where you believe the DNS query is directed to the router please?
____________________________
Working on behalf of Netgear
My name is Andy
Message 4 of 20
adept2
Novice

Re: DNS issue and DHCP DNS settings

Babylon5 wrote:

The router acts as a DNS Relay, it does not pass the DNS server address(s) to the clients. When a DNS request is sent to the router from a client, the router forwards the request to the DNS server(s).


I thought I had read that DHCP was supposed to return the primary and secondary DNS servers if set, but the latest manual says it will always return the router's IP address. By being unable to influence this behaviour of DHCP we can't bypass the buggy DNS server on the router.



I can see pings to the router (192.168.0.1) from 192.168.0.50, but DNS queries seem to be directed to 192.168.0.53? Can you point out the lines where you believe the DNS query is directed to the router please?


As in the following example

13:45:06.316149 IP 192.168.0.50.56777 > 192.168.0.1.53: 18720+ A? www3.l.google.com. (35)

and IP packet is sent from port 56777 on host 192.168.0.50 to port 53 (DNS) on 192.168.0.1 (the router) but with no response. Rebooting the router fixes this for a random period of time between 10 minutes and 2 days.
Message 5 of 20
adept2
Novice

Re: DNS issue and DHCP DNS settings

I found the manual reference.

If you click on the link ""Documentation" on the bottom left of the genie scree, it takes you to
* http://docs.netgear.com/dgnd3700v2/enu/202-10642-03/
Which has a link "user manual (pdf)"
* http://docs.netgear.com/dgnd3700v2/enu/202-10642-03/usermanual.pdf

This document is dated March 2012. On page 52 it says (emphasis added)


The wireless modem router delivers the following parameters to any LAN device that
requests DHCP:
• An IP address from the range you have defined
• Subnet mask
• Gateway IP address (the wireless modem router’s LAN IP address)
Primary DNS server (if you entered a primary DNS address in the Internet Basic Settings
screen; otherwise, the wireless modem router’s LAN IP address)
• Secondary DNS server (if you entered a secondary DNS address in the Internet Basic
Settings screen)



This would be great if it actually did this.

Going straight to the support page
* http://support.netgear.com/product/dgnd3700v2
The link "User manual" links to
* http://www.downloads.netgear.com/files/GDC/DGND3700V2/DGND3700v2_UM_05June2014.pdf

which is dated June 2014. This says on page 54
The wireless modem router delivers the following parameters to any LAN device that
requests DHCP:
• An IP address from the range that you have defined
• Subnet mask
• Gateway IP address (the wireless modem router’s LAN IP address)
• DNS server IP address (the wireless modem router’s LAN IP address)


On an unrelated note, if the DNS server is not responding to queries, you can still open a TCP connection of 53. I rebooted the router this morning so it is running OK now, but next time it happens I will run the following commands to see if it is just a problem with UCP DNS queries.


dig +tcp www.netgear.com @192.168.0.1
dig notcp www.netgear.com @192.168.0.1

TL;DR
-> There is a bug in V1.1.00.23 where it links to the wrong (old) user manual
-> Netgear have removed functionality that would have allowed us to work around the DNS bug :mad:
Message 6 of 20
Babylon5
NETGEAR Employee Retired

Re: DNS issue and DHCP DNS settings

OK, back at work now so time is short. Can you be sure that where the router does not provide a DNS response, that it has not passed the query on to the ISP DNS server(s), I realise that in post #1 you did state that clients could access the same servers, but I still believe there’s a possibility that the router isn’t getting a response. Can you try setting the router DNS servers to some other DNS server?
____________________________
Working on behalf of Netgear
My name is Andy
Message 7 of 20
adept2
Novice

Re: DNS issue and DHCP DNS settings

I can't be 100% sure the problem isn't upstream from the router, but DNS still stops at random when we have specified primary AND secondary DNS servers, as well as simply taking the ISP's DNS settings. When this happens clients on the LAN can successfully query the primary DNS server on the router, but queries to the router don't come back.

Is there any way of accessing the router diagnostics to see if the DNS proxy process is still alive? Or maybe turning up the log level?


Owen.
Message 8 of 20
Babylon5
NETGEAR Employee Retired

Re: DNS issue and DHCP DNS settings

I can see that from your perspective, it really doesn’t matter what the cause of the issue is as you have no easy long term solution. As you say if the router simply passed on the DNS addresses to clients rather than act as a forwarder that might solve all your problems, even if the issue is downstream. In addition, there have been many posts on these forums in the past where people wanted to use their LAN based DNS server, and such a change would accommodate that also.

So, my purpose in trying to find if the issue may be with the router-DNS server communication is simply to help pin-point the issue before I have discussions with Netgear engineers about this. It’s quite possible that there could be some form of diagnostic firmware that might help to track down the issue, I would have to pass that question on to the engineers.

If you are able to change the DNS servers that the router is currently pointing to, that might help with the diagnostics, and may possibly provide a viable short term work around.
____________________________
Working on behalf of Netgear
My name is Andy
Message 9 of 20
adept2
Novice

Re: DNS issue and DHCP DNS settings

Maybe I wasn't clear.

We have tried both ISP assigned DNS serves, and manually assigning a DNS server to the router. The client on the LAN is able to successfully query the upstream DNS server, but queries the client sends to the router fail, even though the router is configured to use the same DNS server. It is possible that the upstream DNS server is no responding to queries from a router, but is from Windows/McOS/Android/Iphone, but personally I doubt it.

One other test we have run is to change the DNS settings while the router's DNS is crashed in case that restarted the DNS process but no luck.

What I can't tell is if the router is actually forwarding the request, and ignoring the response, or if it is simply not doing anything with the request it receives.

I am well at truly sick of rebooting the router a 2 to 3 times a week when this crashes, and about to simply though it out and by a new one from someone other then NetGear.
Message 10 of 20
adept2
Novice

Re: DNS issue and DHCP DNS settings

Another update. While you can open a tcp connection to port 53, it still doesn't respond.


$ dig +tcp www.netgear.com @192.168.0.1 ; dig notcp www.netgear.com @192.168.0.1

; <<>> DiG 9.8.3-P1 <<>> +tcp www.netgear.com @192.168.0.1
;; global options: +cmd
;; connection timed out; no servers could be reached

; <<>> DiG 9.8.3-P1 <<>> notcp www.netgear.com @192.168.0.1
;; global options: +cmd
;; connection timed out; no servers could be reached
;; connection timed out; no servers could be reached

Message 11 of 20
Babylon5
NETGEAR Employee Retired

Re: DNS issue and DHCP DNS settings

Maybe I’m not clear. The DNS setting that I’m referring to is in the router’s Basic Settings, i.e. the IP data that the router picks up from the ISP, in there it’s usually possible to change the ISP’s DNS to another DNS of your choice. LAN clients will still go to the router for DNS, but the router should then pass on the query to the user selected DNS. The purpose of this is to simply see if the router / DNS are talking happily to each other.
____________________________
Working on behalf of Netgear
My name is Andy
Message 12 of 20
adept2
Novice

Re: DNS issue and DHCP DNS settings

It is possible to change the DNS server used by this model of router.

The routes DNS works for a while, and then stops. If we change the DNS settings on the router from ISP assigned to say 61.88.88.88, DNS queries to the router still fail. At the same time, clients on the LAN can use 61.88.88.88 as their DNS server fine.

In other words

$ nslookup www.netgear.com 192.168.0.1

times out but

$ nslookup www.netgear.com 61.88.88.88

works.

If we then reboot the router, the first nslookup starts working for a day or so.
Message 13 of 20
Babylon5
NETGEAR Employee Retired

Re: DNS issue and DHCP DNS settings

OK, well that seems fairly conclusive, I will contact Netgear to see if they have any info relating to this.
____________________________
Working on behalf of Netgear
My name is Andy
Message 14 of 20
nfc911
Aspirant

Re: DNS issue and DHCP DNS settings

Anyone have this issue get any kind of resolution? I've got a D2200 modem/router from frontier that is exhibiting similar behavior.
Message 15 of 20
keenethery
Aspirant

Re: DNS issue and DHCP DNS settings

I have the exact same problem. I've provided the NetGear router with DNS server IPs. I have it enabled as a DHCP host. When a computer connects to it via DHCP and acquires an IP on the NAT, it does not get the DNS IPs, it gets the IP of the router.

 

When that device tries to do a DNS lookup, first going to the NetGear which should relay it upstream to the real DNS servers, that DNS query is unsuccessful.

 

When that device is manually given the same DNS IPs that are configured into NetGear, the DNS lookup is successful.

 

One might say "problem solved, just manually enter the DNS IPs into all your client devices". That solution does not work for devices that do not have a user interface for entering the DNS IPs. Have a Sprint Airave cell phone micro-cell. It has no interface. It expects the DHCP server downstream of it (the NetGear) to provide a DNS IP that works and because that is not working, it is not working.

Model: DM111PSPv2|Broadband ADSL2+ Modem
Message 16 of 20
nfc911
Aspirant

Re: DNS issue and DHCP DNS settings

Any one from Netgear actually monitoring this forum?  I still am having this problem.  Seeing it on an older B90-755044-15 DSL Modem/Router now as well.

Message 17 of 20
DarrenM
Sr. NETGEAR Moderator

Re: DNS issue and DHCP DNS settings

Hello NFC911

 

That is a ISP specific modem you will have to contact your ISP for support on that product.

 

DarrenM

Message 18 of 20
nfc911
Aspirant

Re: DNS issue and DHCP DNS settings

Yes that may be the case but since Netgear still manufacturers and provides the firmware to the ISP isn't it a Netgear issue?  Especially since seen on other Netgear products.  And we all know how intelligent customer support at the ISP is, when the first thing they tell you to do for any issue is to power cycle it.

Message 19 of 20
bwohnoutka
Aspirant

Re: DNS issue and DHCP DNS settings

Having the same problem - DNS queries do not make it out when resolving to 192.168.0.1 aka the Netgear Router.  Please make a suggestion on fixing the issue... I have CenturyLink VDSL and have configured their DNS servers manually, which work when we add them manually devices, overriding the router agrees.  When we reboot everything works for a while, until it does not any more.

Model: D7800|Nighthawk X4S – AC2600 WiFi VDSL/ADSL Modem Router
Message 20 of 20
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