Google DNS vs ISP DNS

[bekdik]

Okay well obviously the very first user to lookup something new that isn't cached is going to do the full lookup, but everyone else will then be server locally not so?

And doesn't this really account for just about any DNS server? I mean even the ISP's official servers don't specially sync every single entry all the time so at some point you'll do a full lookup to root servers if need be.

Your local machine OS also has a dns cache.

 

[Tinuva]

Okay well obviously the very first user to lookup something new that isn't cached is going to do the full lookup, but everyone else will then be server locally not so?

And doesn't this really account for just about any DNS server? I mean even the ISP's official servers don't specially sync every single entry all the time so at some point you'll do a full lookup to root servers if need be.

Your reasoning is correct, but to be technically correct, it behaves more like a proxy than a server that stores entries statically. DNS servers never store any data on disk, with the exception of the ips to the root dns servers. Everything is temporary cached into memory only. I am excluding badly configured servers which will make use of swap memory.

 

[SauRoNZA]

Your reasoning is correct, but to be technically correct, it behaves more like a proxy than a server that stores entries statically. DNS servers never store any data on disk, with the exception of the ips to the root dns servers. Everything is temporary cached into memory only. I am excluding badly configured servers which will make use of swap memory.

I always assumed it's like a proxy, but assumed the entries as stored more permanently.

Presumably so that bad entries/changes are constantly updated?

Is this where the 24h propagation delay comes in?

Would a stored approach work much better with only changes "pushed" to other servers?

 

[SauRoNZA]

Your local machine OS also has a dns cache.

Yes but this is meaningless if I'm doing a lookup for the first time.

In which case referring an upstream server that has already done the lookup recently makes more sense.

 

[Tinuva]

I always assumed it's like a proxy, but assumed the entries as stored more permanently.

Definitely not stored permanently. Only authoritative server store entries manually.

Presumably so that bad entries/changes are constantly updated?

I wouldn't know, the thing is, storing trillions of dns records that change every so few seconds is pointless. Can you imagine the IOPS you would need on your storage system? Back in the day SSDs didn't exist and memory was the only option. So by design I believe that is the reason why only cached to memory.

Is this where the 24h propagation delay comes in?

No. 24h propagation delay is because TLD (top level domain) servers, the ones hosted by .co.za for example, who do store entries manually, usually have a very high TTL. Thus this only affects domain owners when they change the DNS (authoritative) servers for their domain.

Would a stored approach work much better with only changes "pushed" to other servers?

I doubt it. The only time stored contents would help, is when the DNS server reboots, and need to rebuild it's cache. However rebuilding the cache by doing actual lookups goes plenty fast enough, much faster than you can imagine, that it really would be a pointless exercise writing this piece of code into recursive DNS server software. Technically you could, practically it would be a pointless exercise.

 

[ranger]

If it's a cache server then there's no reason for it to do any lookups beyond itself.

How does ir populate the cache? What happens when the cache is out of date?

IOW, it depends on the TTL of the records. Many CDNs and large volume sites have low TTLs on the records that matter most.

 

[ranger]

So I saw a few posts here on mybroadband about using 8.8.8.8 and 8.8.4.4 as your DNS since IS and now Telkom has a local mirror for it.

You may want to do a traceroute to these IPs ...

How would this affect day to day internet should you choose to use google's DNS.

I am not aware of a decent study on this or useful tools. dnsbench test the response times of caching dns servers, bht this is useless, as outside the U.S. it us the latency to the result that is much more important than the latency *of* tge result.

The DNS is mirrored locally now that is good because it will shorten response time but in terms of youtube and akamai servers.

Note that Google DNS is just caching DNS on IP Anycast, Google's authoritative DNS isn't local.

Akamai should serve you from the best deployment if you use your ISPs DNS, I don't think they can make the best decision if you use Google DNS (but it is non-trivial to test).

Would you still be served by local cache servers like the ISP's DNS or will it cause problems and serve content from international servers?

If you use Google DNS, you should get the right Youtube servers (just as if you use your ISPs dns), but you may get the wrong servers for any othet CDN.

 

[ranger]

It is actually interesting.

Since I posted I did some tests. IS and Telkom pings it as a local server with +- 29ms from Richards Bay aka Durban IPC. Afrihost adsl and MTN LTE reports pings of 250ms+ so they are not peering with the server or they are simply directing the traffic straight to Europe.

AFAIK MTN isn't at NAPAfrica.

That said how can one compare the speed now with Telkom since SAIX server does not reply to ping requests...

Test that which actually matters, how long they take to respond to DNS requests.

I also did a test with Telkom one on default SAIX DNS and one with Google DNS and both times the video was served by Telkom Google cache server. So Google service will be good but would be interesting to see other services like akamai.

I see that the ISP actually also plays a big role here.

Bigger than which DNS you use.

 

[ranger]

Each ISP defines the IP address location. It sort of overrides any other locations.

No, it is defined by where the ISP or it's transit providers peer with Google. If the ISP itself defined the location, that would be route hijacking and IP address spoofing.

 

[cavedog]

Thanks for all the replies... Very informative.

@ranger so essentially there might not really be a difference between say SAIX DNS and Google's DNS since the servers needs to get their record somewhere and if it is not cached it needs to be looked up so if both SAIX and Google's DNS does not have it and it needs to be looked up the speed would be the same essentially?

Nice to have the tech savvy people on the forums.

 

[giggity]

No, it is defined by where the ISP or it's transit providers peer with Google. If the ISP itself defined the location, that would be route hijacking and IP address spoofing.

But each ISP's routing affects which server it directs to, right?

 

[MGRobinson]

Personally I prefer using Google DNS servers to my ISP's simply because I get a lower ping to them and I think they are more reliable.

 

[SauRoNZA]

How does ir populate the cache? What happens when the cache is out of date?

IOW, it depends on the TTL of the records. Many CDNs and large volume sites have low TTLs on the records that matter most.

No I meant for the next user to make the same request not the very first one.

But it's all been covered now.

 

[SauRoNZA]

Personally I prefer using Google DNS servers to my ISP's simply because I get a lower ping to them and I think they are more reliable.

Same here.

When I'm not using Unotelly I use Google because Mweb's are on the blink half the time.

 

[bekdik]

Google's namebench allows the comparison of DNS servers.

Are you a power-user with 5 minutes to spare? Do you want a faster internet experience?

Try out namebench. It hunts down the fastest DNS servers available for your computer to use. namebench runs a fair and thorough benchmark using your web browser history, tcpdump output, or standardized datasets in order to provide an individualized recommendation. namebench is completely free and does not modify your system in any way. This project began as a 20% project at Google.

namebench runs on Mac OS X, Windows, and UNIX, and is available with a graphical user interface as well as a command-line interface.

 

[PostmanPot]

@ranger or anyone who might know, what are the best DNS servers for Telkom Internet in Cape Town? I use a capped account but performance has been hit and miss for months/years.

 

[ranger]

Google's namebench allows the comparison of DNS servers.

Yes, it started as a Google 'pet project on company time' (this initiative doesn't exist anymore), is hosted on Google Code, and there seems to still be at least one Google employee who has contributed to it, but I wouldn't call it Google's.

Yes, it allows you to test name server performance, but not the quality of the results. For example, it says I should use 'iAfrica', but for a number of high traffic sites that server gives me results in London (170-200ms away), where the correct results (provided by SAIX DNS) are in South Africa (10-45ms away). Your browser or OS will cache the DNS lookup (so you only save the maybe 5ms DNS latency once), but each HTTP request will incur the 150ms latency penalty.

Who cares if a DNS server is 5ms faster on some obscure sites you never visit, but for the sites you visit regularly the content is served with 200ms higher layency. The DNS latency won't have as visible effect as the latency to the service served from the wrong country.

 

[ranger]

@ranger or anyone who might know, what are the best DNS servers for Telkom Internet in Cape Town? I use a capped account but performance has been hit and miss for months/years.

What performance has been hit and miss? Is it attributable to DNS (slow DNS response or directing you to a slower node for the same content?

Note that we had run out of transmission for IPC capacity, and it took Telkom Wholesale months longer than usual to provision more transmission. We believe the Cape Town site has sufficient IPC now, but we may need to allocate more transit.

We give you what we believe are the best DNS servers for your location. Currently we are using SAIX DNS ( you can find the servers listed on a page at http://www.saix.net), but migrating to our own DNS servers is on the to-do list for this year. It might be useful swapping the order of the DNS servers we provide, or you can choose another one in the same region from the SAIX page.

I would advise against normally using a 3rd-party DNS server unless you have a specific problem, in which case only if you have reported the problem and until it is resolved. For users on Telkom Internet, Google (e.g. 8.8.8.8) is probably the best alternative to the DNS we provide for now.

 

[Tinuva]

I must say, since Google made their public dns 8.8.8.8 and 8.8.4.4 local to South Africa (JHB), it became a true and real proper alternative for South Africans.

 

[Hemps]

Is using google DNS still the best option?

Currently on Apple Music I found using the 8.8.8.8 was very sluggish.