EA6500 v1 dns suddenly fails [SOLVED]

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emacc
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Joined: 02 Aug 2020
Posts: 3

PostPosted: Wed Apr 14, 2021 20:15    Post subject: EA6500 v1 dns suddenly fails [SOLVED] Reply with quote
Can someone shed some light on this situation?

My router: Cisco (Linksys) EA6500 v1
Firmware release: DD-WRT v3.0-r43904 giga (07/23/20)

I've been using the internet on rock solid connection for a few weeks now, but suddenly the router has stopped resolving names. I use a VPN on a couple of devices, and name resolution works without problems via that.

A reboot has not solved the issue. The internet access is otherwise fine. I have worked around the problem by configuring DNS in each device's network interface. I'd prefer it to be in one place (the router), but at least name resolution works.

This output from dig shows the "SERVFAIL"; the failure is instant, if that offers a clue:

    ; <<>> DiG 9.16.1-Ubuntu <<>> @192.168.1.1 ibm.com
    ; (1 server found)
    ;; global options: +cmd
    ;; Got answer:
    ;; ->>HEADER<<- opcode: QUERY, status: SERVFAIL, id: 12573
    ;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 1

    ;; OPT PSEUDOSECTION:
    ; EDNS: version: 0, flags:; udp: 4096
    ;; QUESTION SECTION:
    ;ibm.com. IN A

    ;; Query time: 783 msec
    ;; SERVER: 192.168.1.1#53(192.168.1.1)
    ;; WHEN: Wed Apr 14 15:44:00 EDT 2021
    ;; MSG SIZE rcvd: 36


From the services page: Screenshot from 2021-04-14 15-59-49.png is attached
From setup page: Screenshot from 2021-04-14 16-04-41.png is attached

If I should include something else here, please let me know.



Screenshot from 2021-04-14 16-04-41.png
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 Viewed:  1150 Time(s)

Screenshot from 2021-04-14 16-04-41.png



Screenshot from 2021-04-14 15-59-49.png
 Description:
 Filesize:  58.04 KB
 Viewed:  1150 Time(s)

Screenshot from 2021-04-14 15-59-49.png


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kernel-panic69
DD-WRT Guru


Joined: 08 May 2018
Posts: 14125
Location: Texas, USA

PostPosted: Wed Apr 14, 2021 20:21    Post subject: Reply with quote
Moved your post to the correct forum as your device is Broadcom.

1) why do you have static dns servers entered and why do you have your ISP gateway IP entered? The gateway can be left quad zero.

2) not sure if there's any missing config info for unbound here

3) is there any reason why you're on a nearly 9-month old build without specific updates?

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emacc
DD-WRT Novice


Joined: 02 Aug 2020
Posts: 3

PostPosted: Thu Apr 15, 2021 17:26    Post subject: EA6500 v1 dns suddenly fails Reply with quote
Hello! Thank you for replying.

On your points:

1. It was set to all zeroes initially; that is an attempt to fix. I will put it back to 0s.

2. Sorry, I don't follow. Particularly since I don't really know what 'unbound' means in this context.

3. I had been having problems with DNS previously, and once they were resolved (an Ubuntu issue), I wanted to leave well enough alone. i.e. if it works, don't "fix" it. Is there a compelling reason to upgrade to another release? I value stability over experimentation.
kernel-panic69
DD-WRT Guru


Joined: 08 May 2018
Posts: 14125
Location: Texas, USA

PostPosted: Thu Apr 15, 2021 18:31    Post subject: Reply with quote
The checkbox for recursive dns resolving (unbound). That is another dns resolver that can work with dnsmasq. I also just noticed that you don't have ntp enabled. Is there any particular reason why?

https://wiki.dd-wrt.com/wiki/index.php/Unbound

You may need to look further into configuring unbound properly. Also, in regards to updating firmware version, there are patches and updates that may improve some stability. The caveat is, nobody seems to be reporting in the build release threads for this device after flashing, and at one point were pidgeon-hole-ing information in the device thread, creating a cumbersome situation that is of no use to the community. This is where I will say for those following, "Flash and report in the build release threads, please."....

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emacc
DD-WRT Novice


Joined: 02 Aug 2020
Posts: 3

PostPosted: Fri Apr 16, 2021 17:19    Post subject: EA6500 v1 dns suddenly fails Reply with quote
I disabled ntp because DNS isn't working and it can't find the time server. It was flooding the syslog.

I'll tinker with the unbound thing and post results soon.

Thank you!

Addendum:
As an experiment, I turned off 'unbound'. and re-enabled ntp, specifying IP per the link you provided...
..and voilà. It works. So, I just need to follow the instructions to configure 'unbound' properly, as you suspected.

Many thanks for your help.

P.P.S.
I edited '/tmp/unbound.conf' to add the forward-addr lines and left the rest as is. Rebooted and ntp is now working successfully.

dig lookups at the router are working, but if I issue:

"nslookup whoami.akamai.net"

at the router, as suggested by the dd-wrt doc you refered to, I get

nslookup: can't resolve '(null)'

From the desktop, the same command gives:

Server: 127.0.0.53
Address: 127.0.0.53#53

The non-authoritative answer references either the VPN external address, or the ISP's depending on VPN state.
In any event, the thing appears stable and usable and I'm calling it resolved.
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