Secondary DNS ? :s

Hope someone can help;

What do I use as my secondary DNS?

If ive got it right, I use my Routers Address for the Primary DNS but what about the secondary, it won't allow me to use the same....

I'm trying to get my computer set to a fixed IP as to Windows automatically allocating the address...

You can specify the address of an alternate DNS server to be used if the first is unavailable. A lot of people use Google's DNS servers - 8.8.8.8 and 8.8.4.4 - mainly because the IP addresses are easy to remember.

I think I need to read up on this as I tried those values earlier today and then I had no internet access.

I think I will have to look at the manual on my Routers CD, as I think I may need to change something within the router.

What confuses me, is that I have set my Sky+ and PS3 to use a fixed IP without these problems but then again, these are connected via cable. Obviously WiFi must be different.

If you can advise further I would be grateful but you are probably confused by what I have written LoL

Thanks again....

In reply to a post by shaneosborne:

If ive got it right, I use my Routers Address for the Primary DNS

You are talking about the settings on your PC?

You should let that "Obtain DNS Auto" and set the DNSs in your router to those of your ISP or Google or OpenDNS as suggested.

If you like you could set these in all your PCs but I find it simpler to just set them in router.

What fixed IPs are you talking of? Do you mean IPs within your local network like 192.168.x.y? Or are you meaning static IPs allocated by your ISP?

Anyway these have nowt to do with the DNS.

In relation to my home network. 192.168.1.*** etc.

It wont allow me to select 'Obtain DNS Server Address Automatically' when I 'Use The Following IP Address' for my PC....

In reply to a post by shaneosborne:

What confuses me, is that I have set my Sky+ and PS3 to use a fixed IP without these problems but then again, these are connected via cable. Obviously WiFi must be different.

Wi-Fi isn't different as regards how DNS works, but there are different use cases.

1) If this is a portable thing such as a laptop or mobile, that you intend to use in other locations:

You are unlikely to want manual IP settings on the wireless interface as you would always have to change that setting when connecting to a different Wi-Fi network. This includes not setting manual DNS settings (even public DNS) on the wireless interface as that is not necessarily suitable on every network.

2) If this is a device that is going to stay put:

Even then it's better to leave network settings on auto unless you know why you need to change something. DHCP gives out more than just IP addresses.

If you want to set DNS by hand, as has been said just set DNS to point to the IP of the local router that connects to the internet. On the router make sure the (WAN) DNS settings are valid for the ISP it connects to, or use public DNS.

3) Note that on most devices, setting a secondary DNS is not mandatory. What happens if you leave it blank?

4) By default home routers provide DNS settings to DHCP clients. Most routers work as a DNS forwarder so they give out their own address.

Some routers will also provide a local DNS service (device names collected from DHCP clients) that can make it easier for devices to find each other within your home network.

They can also provide DHCP Reservations (a table of fixed IPs to MAC Addresses),
other info such as MTU and a time service (NTP); so that these settings are held in one place rather than all over the shop.

5) If the device also has a wired network interface, make sure you aren't changing the settings for that instead - surprisingly easy to do. I say this because not everyone realises IPs are not per device but more per network interface (or even several per interface).

Leave the wired interface settings on auto. Definitely do not try to set the same IP address there, nor a gateway (router) address.

6) If you are using Chrome as your web browser, it tries to be smart about looking up DNS names. But if it has already decided it can't resolve a DNS name to an IP address it might not try again after you change the settings, You can try CTRL-R to refresh but sometimes you have to close and reopen the browser.

The PC has a local cache of DNS responses that can also show the same kind of behaviour. After changing DNS settings, you can do
(in Windows) in a Command Prompt
ipconfig /flushdns

Some versions of Windows require you to open Command Prompt using Run As Administrator for certain command.

7) If you do set your IP addresses by hand, it is up to you to make sure there is no duplication, nor that any manual IPs clash with any auto IPs. Mobiles or tablets (or other guests) on Wi-Fi will still need DHCP unless you enjoy doing it the hard way!
In this case you will need to adjust the router's DHCP settings to leave space for the fixed ones.

For example if the router is on 192.168.1.1 and gives out 192.168.1.2-254 youil have clashes.
You can divide it up however you want. An arbitrary example for 192.168.1.x
x =1: router (default)
x=2-9: keep free - routers / switches etc
x=10-99 fixed IPs
x= 100-199: DHCP range
x=200-249: more fixed IPs
x=250-254: keep free - routers / switches etc

I think many people who tweak like to come up with their own numbering plan.

Note that most home routers are either at .1 or .254, and that .0 and .255 have special meanings.

This is a rather formal example but does show why DHCP reservations are easier as this is in one place on the router rather than in your head or on bits of paper.

Edited by prlzx (Wed 29-Feb-12 16:25:53)

192.168.1.99 for network ip (99 can be anything between 2 and 254)
255.255.255.0 subnet
192.168.1.1 default gateway (your router address)

Primary DNS: 87.86.189.16
Secondary DNS: 87.86.189.17 SKY DNS servers

To check : windows key+R CMD [enter] ipconfig /all [enter]
If the dns servers are different in there use them.

In reply to a post by shaneosborne:

It wont allow me to select 'Obtain DNS Server Address Automatically' when I 'Use The Following IP Address' for my PC....

Then leave them both on Auto on the PCs and use Address Reservation by MAC in the DHCP of the router to fix the local IP addys.

Brilliant, many thanks.

It's for a fixed PC and the reason I wanted to change all of my equipment to fixed IP was due to always getting conflict errors, two devices being allocated the same IP Address.

I will probably leave it as it is as all seems to be fine now. I have set my PS3 to a fixed IP as I am using the QoS Option on my Router and also a fixed IP for my Sky+HD box. Both of these devices are connected to my router by cable and all seems to be okay now.

I thought it would be easier and make things simpler if I set all of my devices on the network with a fixed IP. Instead I have just done it with the wired devices, I hope I don't get any more problems...

I couldn't leave the DNS blank as it said invalid entry, I even tried 0.0.0.0 but it showed invalid and it wouldn't allow me to set it to automaticallyy set DNS.

All seems fine now, so I will leave before I mess something up.

The whole purpose was for the QoS feature....

Thanks again for your time and help...

No worries

The reasons for IP conflicts:

• part (7) of my other post. As soon as even one device has an IP set by hand, the router doesn't know you have done that, so you have some extra work to stop it giving out that IP to something else.
  
• More than one DHCP server in the network. This is not actually forbidden and the protocols provide for a device to pick one from multiple answers. However a "losing" DHCP server won't know what IP address was picked so you have to set their ranges (scopes) not to overlap.
  
• Malfunctioning or misconfigured DHCP server (rarely).
  
• A device connected to the same network by both wired and wireless interfaces. If the same IP address is set on both interfaces it will conflict with itself
  

Out of interest for future reference, what operating system was running on the PC that required both 2 DNS settings filling in? Any I have seen are happy with primary DNS set and secondary blank.

Edited by prlzx (Wed 29-Feb-12 17:25:01)

So, do I just change the DHCP START and END range to exclude the fixed IP Addresses/Devices I have set or is this for something completely different?

I've noticed on this page of the Router Control Panel it shows 'Use Router as DNS Server'.

I assume to get the Primary and Secondary DNS to work on as I first mentioned then I would have to uncheck this and enter the Google DNS Server Addresses for the setup to work and allow internet access?

I think it's best left as it is, do you think it is worth changing the IP Range to exclude the two fixed IP/Devices which are both wired to exclude those two IP's?

Sorry if im making this confusing :/

In reply to a post by shaneosborne:

So, do I just change the DHCP START and END range to exclude the fixed IP Addresses/Devices I have set or is this for something completely different?

Exactly. So if your fixed IPs are at the lower end, make the DHCP Start address something larger than the last fixed address you want to use. Plenty of room so you can leave big gaps!

In reply to a post by shaneosborne:

I've noticed on this page of the Router Control Panel it shows 'Use Router as DNS Server'.

I assume to get the Primary and Secondary DNS to work on as I first mentioned then I would have to uncheck this and enter the Google DNS Server Addresses for the setup to work and allow internet access?

Not quite. This page is to do with what the router gives out to the local network. You leave Use Router as DNS Server ticked.

Devices whose network settings are "Auto" will receive a DNS setting telling them to ask the router, the router then "asks the internet".

How the router knows who to ask (ISP or public DNS) is a different page, the settings for internet (WAN) side of things, often on or near the page that deals with ADSL or Cable connection settings but varies by model.

Edit: if you have a Draytek, I'm afraid (from experience) some versions of their firmware had a confusing layout for DNS settings which mixed up local and external settings. It is worth updating to the latest firmware from their website.

In reply to a post by shaneosborne:

I think it's best left as it is, do you think it is worth changing the IP Range to exclude the two fixed IP/Devices which are both wired to exclude those two IP's?

By those two IPs you mean the fixed IPs such as the games console - yes. If you don't exclude them from the range, the router will give them out at some random point in the future (imagine the router is a person giving out printed cards with numbers on, it doesn't know you are also giving out your own handwritten cards unless you tell it so it can exclude them from its set).

Edited by prlzx (Wed 29-Feb-12 17:46:51)

Brilliant - Will change the ranges now

Many thanks for all of your help and time, very much appreciated sir. Thankyou

In reply to a post by prlzx:

As soon as even one device has an IP set by hand, the router doesn't know you have done that, so you have some extra work to stop it giving out that IP to something else.

Thus it is simpler to just reserve the fixed IPs in the router's DHCP rather than on the individual devices. Then the router will know they have been used and you don't need to mess about defining IP ranges to keep free.

In reply to a post by shaneosborne:

Hope someone can help;

What do I use as my secondary DNS?

If ive got it right, I use my Routers Address for the Primary DNS but what about the secondary, it won't allow me to use the same....

I'm trying to get my computer set to a fixed IP as to Windows automatically allocating the address...

Hi, I use static IP addresses for my network and for the Windows PC settings I leave the Secondary DNS: blank. The static IP address must not be within the range of the router DHCP server settings.

Follow the instructions on the link (Static IP address set-up and converting from a DHCP based LAN configuration) (made easy!)

http://www.homenethelp.com/web/howto/static-ip-addre...

Slightly unrelated but if you are getting IP conflicts on your network when using DHCP, perhaps it is time to throw whatever is acting as the DHCP server in the bin, perhaps your router? and get a quality device.

I think people are going round in circles by not reading the whole thread as the OP is pretty such sorted ...

I already explained what causes IP conflicts (commonly setting 1 or more IPs by hand and not realising the router will still give out those IPs from time to time unless you tell DHCP not to).

A faulty DHCP server is not impossible but these days really it is almost never the cause in real setups.
People also forget things like releasing leases on PCs if they do stuff like swap out the DHCP server (for a new one with no leases stored yet) and then assume the new server is faulty.

I lose track of the offices I have visited where all PCs were setup manually (including laptops) and the significant administrative burden with the comment being "well we tried changing (a few) things back to automatic but we get conflicts" and you can see that is faulty reasoning rather than faulty router.

Or, some PCs fail to get an IP address (because a connecting switch was unplugged). So someone sets a manual IP (because "it stops Windows popping up that yellow triangle thingy" - so that must have fixed it). The PC now has a supposedly "valid" IP address, the symptom has been hidden but it hasn't actually fixed the cause.

I (and XRaySpeX and others) also stated that DHCP reservations are the tidy way to deal with this.

To avoid complications I would always suggest either letting DHCP manage all (end) devices or (but only as a last resort for small networks) manually setting everything but not a mixture of the two. I say (end) devices because in a big network there may be things like servers or wireless bridges that you prefer to set manually.

That said, if someone is determined to tinker manually it is important to have an approach that will still work.

Back to the OP who is trying to get from where they are now (seems to be working for now) to a reliable setup in the least number of steps - and changing the Range Start IP (and rebooting the end devices) will likely keep things working - plus learning more about DHCP works in the process which is to be encouraged ...

---

Now no doubt someone will be thinking, doesn't DHCP use ARP (or PING) to check if an IP is in use before actually allocating it?
Well, it can but have a think about real networks where not all devices are turned on all the time.

A device with a manual IP might be off because Bob isn't at work today (Thursday).
Ann turns on her computer and gets an DHCP supplied address. Her lease is valid for days (or even weeks). No problems today.

Now it's Friday and Bob is back at work. He turns on his computer. Ann and Bob both get an IP conflct. Because Bob decided to set a manual IP and didn't tell anyone. Then Bob says "oh theses automatic IPs don't work - they cause conflicts".

I know I'm having a soapbox moment here but we've had DHCP for nearly 20 years because someone put in the effort to design a protocol so that we could spend more time using networks rather than configuring them, I'm looking forward to IPv6 when maybe people will decide memorising IP addresses is no longer fun!

And yet we still see people proposing doing things the hard way, often for the wrong reasons or to fix a different problem (such as wanting to port forward to a single computer to play a game) that DHCP (and NAT) already provide settings for.

Edited by prlzx (Fri 02-Mar-12 02:37:15)

You missed:
Device allocated an address, router rebooted, new device conected to the network and router allocates same address again as the reservation table has no persietence.

Seen that too many times....

In reply to a post by ionic:

router rebooted

You mean factory reset? That's rare and exceptional. All DHCP settings, incl. reservations, held thro' reboot.

I think this thread got onto enterprise networks when as I understand it the OP was a home user.

All these problems mentioned regarding corporate and enterprise networks, well, quite simply the network team should just be sacked for incompetence -- assuming they are claiming to be an IT professional -- if they do not know how to recover from a DHCP server failure or how to configure a mix, everything mentioned here should be known by anyone worth their salt who is a network admin in either networking hardware or the windows field.

Edited by Pipexer (Fri 02-Mar-12 17:22:24)