DNS issues - is it my isp or my network

Hi

I am not convinced Vodafone isn't having problems with their infrastructure.

This is because every time the internet stops working, it's only the DNS portion that doesn't work. I can still ping 8.8.8.8 which is googles dns server.

I'm using my trusty billion 8800nl instead of their [censored] router and it says the second dns is 90.255.255.255.

Isn't that address reserved for broadcasting?

thats like me putting my router's ip as 192.168.1.255

Edited by deleted (Mon 21-Oct-19 14:36:24)

That IP does seem correct for Voda DNS. If you have changed your primary to google then what reason did you not change the secondary to google secondary?

In reply to a post by picky_user:

Isn't that address reserved for broadcasting?

If part of a local LAN, generally yes...

but this is allocated to a service so you can technically use .0 or .255 if you want. Similar to that some broadband connections can be assigned .0 and .255 address. All perfectly valid.

Matt

Depending on the size of the netblock the network has been allocated from an IP address ending in .255 is potentially valid. Basically anything bigger than a /24 will have one valid .255 and .0 in it.

So for example 15.0.255.255 is a valid IP address somewhere inside the large block that HP has. Though depending on how they have carved their IP address range up internally it might not be valid.

That said 90.255.255.255 is not valid.

In reply to a post by jabuzzard:

That said 90.255.255.255 is not valid.

I don't believe you are correct. Broadcast addresses are only used within LANs. As this is a public Internet address it would not be used for broadcasting over the WAN and therefore is a perfectly valid address to use. I can't find anything solid to back this up but given this address works and can be pinged over the Internet I believe my understanding is correct.

Depends on the subnet size which depend on the subnet mask, if its set to a 255.255.255.0 mask it will only contains one 0 and one 255 in the range and they are both reserved but when the mask is set to 255.255.254.0 you get 2 x 255 (510) IP addresses so there are two 0 and two 255 in the range but only the first and last are reserved. you can increase the subnet size up and up by changing the subnet mask but there are issues with larger subnets. You can also reduced the size of the subnet down below 255 by changing the subnet mask e.g. 255.255.255.128 this will affect the reserved addresses.

In reply to a post by dect:

Depends on the subnet size which depend on the subnet mask, if its set to a 255.255.255.0 mask it will only contains one 0 and one 255 in the range and they are both reserved but when the mask is set to 255.255.254.0 you get 2 x 255 (510) IP addresses so there are two 0 and two 255 in the range but only the first and last are reserved. you can increase the subnet size up and up by changing the subnet mask but there are issues with larger subnets. You can also reduced the size of the subnet down below 255 by changing the subnet mask e.g. 255.255.255.128 this will affect the reserved addresses.

Ah ok. hahah A little rusty on calculating subnet masks and all that.
I never need to do it.

Am I correct in assuming it's vodafone being rubbish. Yes I have a rather complicated network with 3 vlans because I can and I am a nerd.


I am convinced it's them because when this happens I reset the modem then it works again but it's only been like this for a few days. I switched to Vodafone back in JULY!! Not had any problems apart from the usual initial teething issues.

When the DNS stops working again, Is there a way I can see where the dns request ends up? A bit like a traceroute but for dns?


If it does indeed end up as far as the modem then it's Vodafone's responsibility is it not?

I would try just using the VF router out of the box for a few days, in default config mode. There is not widespread vodafone users reporting no internet due to DNS issues, no.

Why do you need multiple VLANs? It sounds as though you are over-complicating your network despite not fully understanding how broadcast addresses work in relation to subnet masks, nor how DNS works.

Personally I wouldn't trust Vodafone DNS servers. Out of all the available public DNS servers you are probably best with 1.1.1.1 as they are less likely to be snooping on you compared to Google or Quad9.

It would be very easy to prove if it is the DNS side which is going wrong by opening nslookup in command prompt

then type
server <primary DNS server IP>
www.google.com
see if it resolves

then type <secondary DNS server IP>
www.google.com
see if it resolves

then type server 1.1.1.1
www.google.com
see if it resolves

For example:

Text

1 23 45 67 89 1011 1213 1415 1617 1819 2021 2223 2425 2627 2829 3031 3233

C:\Users\Admin>nslookup Default Server:  dns1.aa.net.ukAddress:  2001:8b0::2020  > server 2001:8b0::2020 Default Server:  dns1.aa.net.ukAddress:  2001:8b0::2020  > www.google.com Server:  dns1.aa.net.ukAddress:  2001:8b0::2020  Non-authoritative answer: Name:    www.google.comAddresses:  2a00:1450:4009:814::2004           216.58.210.228  > server 1.1.1.1Default Server:  one.one.one.one Address:  1.1.1.1  > www.google.comServer:  one.one.one.one Address:  1.1.1.1  Non-authoritative answer:Name:    www.google.com Addresses:  2a00:1450:4009:81c::2004          216.58.210.36  > exit  C:\Users\Admin>

Depending on what results you get from those 3 tests should point you in the direction of whether your ISP DNS servers are problematic or you have a wider connection issues.

Bear in mind 98% of Vodafone customers are probably using the provided [censored] routers or whatever so if their DNS service kept going down they would have their entire customer base complaining. So it is unlikely the issue is with their DNS servers if it is occurring frequently.

Try this, should list all the DNS: https://ipleak.net/