VPN Causes DNS Failures

VPN Causes DNS Failures

VPN Causes DNS Failures
VPN Causes DNS Failures
2024-07-29 18:31:19 - last edited 2024-07-30 01:58:41
Model: ER605 (TL-R605)  
Hardware Version: V2
Firmware Version: 2.2.5

(I have an er605 in which I have 2 Wan and 2 lan.

Lan 1: Everything by default

Lan 2: On this lan I have VPN(OPENVPN) that spans all Vlan

The omada server is on lan 1)

 

I have observed that DNS 8.8.8.8 sometimes responds and sometimes does not.

Because of this, perform ping and traceroute from different points on the network

 

Ping and traceroute from lan 1: pings respond (30ms on average) and traceroute seems to be all ok. But sometimes it stops responding on the entire LAN leaving devices that use said DNS offline

Lan 1

 

Ping and traceroute from OMADA (Network Check): *here it gets fun* The ping gives me an average of 250ms and when measuring the tarceroute I realize that it gives me that latency because the DNS 8.8.8.8 is jumping through the lan 2 vpn. Only that DNS jumps to the LAN 2 VPN, I do the ping and traceroute but DNS 8.8.4.4 gives me everything correct and without jumping to the LAN 2 VPN

networkcheck

nc2

 

Ping and traceroute from the terminal: I ping at 8.8.8.8 and it comes out 100% packet loss and the tracert only jumps at 169.254.11.21 and there it stays

ts1

ts2

Who is to blame for all these failures?

-------The VPN------

The vpn assigns me 2 dns, the first is the vpn gateway and the 2 is 8.8.8.8

When the VPN assigns me 8.8.8.8, it is seen that the ER605 begins to have failures with said DNS


The last thing was to ping -t and see how it came out since 8.8.8.8 could not be accessed and the moment I turned off the vpn of lan 2 the dns 8.8.8.8 began to respond correctly at all points.  I turned the VPN back on and the fault came back

 

(I think this bug could also affect the DNS cache since the router would not be able to access the DNS 8.8.8.8 the DNS cache would also fall)

I clarify that I have not verified the latter but it fits very well with failures that I have had with the DNS cache*

 

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6 Reply
Re:VPN Causes DNS Failures
2024-07-30 01:57:28

Hi @Josvell 

Thanks for posting in our business forum.

It is not a problem with the router at all. Same thing for me. I got 8.8.8.8 in 8ms from my computer. Well, in theory, the server should be located in the USA and I am supposed to get pings larger than 10 due to the physical distance. I am getting a business fiber and a dedicated line to the global Internet. It will definitely not get me 8ms. 

But it is not getting that latency. This is not a problem with the router at all. It could be the cache or the redirection on your local network/ISP.

 

The DNS is simple as it means but the background and the depth of it is more than that and most people cannot figure them out.

 

 

If natively in your country, you cannot access the 8.8.8.8, then if you need to access it, you need to configure the VPN. And the result of 200ms latency to the 8.8.8.8 is normal from the local computer, which could be the cache or something. I have not digged into this part but I am pretty certain it is not a problem with the router but a mechanism of the DNS.

 

169.254.11.22 is explained on the forum. You might search for this or find it by the label KB. I have written an article about it.

 

If you need to discuss this furter and more to add, please attach a diagram along with the description.

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Re:VPN Causes DNS Failures
2024-07-30 05:21:08

  @Clive_A I understand what your saying to me. But is it normal that when I activate the VPN (VpnJapon) the DNS 8.8.8.8, which is the DNS that said VPN uses by default, stops working on the entire network? Even if it is not the network that has the VPN? And according to the routing table it tells me that it is sending 8.8.8.8 to the VpnJapon interface?  

Hgii

The DNS responds well from all points and with normal latency. It is the precise moment that I activate the VPN, the DNS drops and does not respond again until I turn off the VPN 

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Re:VPN Causes DNS Failures
2024-07-30 05:47:13

Hi @Josvell 

Thanks for posting in our business forum.

I have several questions:

1. Do you have access to the 8.8.8.8? What's the tracert like on the PC?

2. What's the OVPN tunnel mode? Now, the VPN forces 8.8.8.8 to route over the VPN tunnel, it seems to be a setting on the VPN server. Do you host the server or it is third-party?

 

Josvell wrote

  @Clive_A I understand what your saying to me. But is it normal that when I activate the VPN (VpnJapon) the DNS 8.8.8.8, which is the DNS that said VPN uses by default, stops working on the entire network? Even if it is not the network that has the VPN? And according to the routing table it tells me that it is sending 8.8.8.8 to the VpnJapon interface?  

Hgii

The DNS responds well from all points and with normal latency. It is the precise moment that I activate the VPN, the DNS drops and does not respond again until I turn off the VPN 

It should not stop the entire network's Internet access.

Unless you are using the full tunnel mode. And the server is misconfigured causing the traffic to stop.

 

What do you expect to achieve with this VPN server? Might be wrong for the use case?

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Re:VPN Causes DNS Failures
2024-07-31 04:25:43

  @Clive_A

 1- When I activate the Vpn. in all Vlans they lose access 8.8.8.8. But when the VPN is off, the DNS responds correctly anywhere on the network.

2-

The VPN is in Client-to-Site mode, and if it is correct. The Vpn is forcing 8.8.8.8 to go through said Vpn

3-

It is a third-party Vpn. It's from VPNgate. It is the first on the list and is free to use  

 

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Re:VPN Causes DNS Failures
2024-07-31 05:47:50

Hi @Josvell 

Thanks for posting in our business forum.

Josvell wrote

  @Clive_A

 1- When I activate the Vpn. in all Vlans they lose access 8.8.8.8. But when the VPN is off, the DNS responds correctly anywhere on the network.

2-

The VPN is in Client-to-Site mode, and if it is correct. The Vpn is forcing 8.8.8.8 to go through said Vpn

3-

It is a third-party Vpn. It's from VPNgate. It is the first on the list and is free to use  

 

I think it is the server issue. When you use it, do you get all traffic forwarded through the tunnel?

Best Regards! If you are new to the forum, please read: Howto - A Guide to Use Forum Effectively. Read Before You Post. Look for a model? Search your model NOW Official and Beta firmware. NEW features! Subscribe for the latest update!Download Beta Here☚ ☛ ★ Configuration Guide ★ ☚ ☛ ★ Knowledge Base ★ ☚ ☛ ★ Troubleshooting ★ ☚ ● Be kind and nice. ● Stay on the topic. ● Post details. ● Search first. ● Please don't take it for granted. ● No email confidentiality should be violated. ● S/N, MAC, and your true public IP should be mosaiced.
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#6
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Re:VPN Causes DNS Failures
2024-08-01 19:49:20

  @Clive_A In Vlan2 where the VPN is applied, I do get latency from the 8.8.8.8 that passes through the VPN. But on Vlan1 8.8.8.8 just stops responding (stops responding when Vlan2's vpn is enabled.

 

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#7
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