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#16
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Can't connect to Web
VanguardLH wrote on 5/28/2017 4:11 PM:
Stef wrote: Steve Hayes wrote: This morning I suddenly lost my connection to the web while I was browsing. Mail still worked, news still worked, but the web connection did not. I reset the router, rebooted my computer, but still nothing. I wondered if it was a browser fault (I use Firefox) so tried Internet Explorer. It too could not connect, but offered to run diagnostics. This is what was found: ---- diagnostic report ---- [snip] DNS Client Diagnostic DNS - Not a home user scenario info Using Web Proxy: no info Resolving name ok for (www.microsoft.com): yes No DNS servers DNS failure I haven't read the entire thread, but this is mostly likely your problem. Your default Domain Name Server is down or can't be accessed. When you can't access "The Web" with your browser, but mail, ftp, etc work (they don't use DNS), that's where I'd start the troubleshooting. WRONG. Anytime you use a hostname (host.domain.tld) to specify a host, like for an e-mail or ftp or "etc" server, DNS gets used. Humans like names. Computers demand numbers. How many times have you encountered a user that specifies the IP address address for their e-mail server when configuring an account within their local e-mail client? Look at your own e-mail config in whatever local e-mail client you use. Did you enter a hostname or an IP address? Unless you do the DNS lookup when configuring the e-mail account in your e-mail client, you don't get that info from the e-mail provider as they give you hostnames. How many web pages have you visited where absolute references (non-relative or just a path under the current location) to sources in a web page use IP addresses instead of hostnames? If DNS were unusable to the OP, he wouldn't be doing e-mail or newsgroups. If the OP were having to use IP addresses for everything, he would've mentioned it and maybe how he got those IP addresses. Not 100% true. I believe the Eudora email client uses DNS once to lookup the IP address of the email server(s) when it first accesses them. From then on it uses that stored IP address. There were times when I have ported my domain to new hosting and the browser always finds the web site once it is back up. But the email program seems to continue to access the old servers until I do something to make to do a DNS lookup again (like restart it). -- Rick C |
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#17
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Can't connect to Web
On 28/5/2017 18:53, Steve Hayes wrote:
On Sun, 28 May 2017 17:16:01 +0000 (UTC), Stef wrote: Google's web site is hardly ever down. It's a good place to test if your DNS is down using its IP addresses. You may get some kind of error notice, but as long the number IP address you entered is replaced with a URL with "google" in it, it's working even if typing in www.google.com doesn't. pinging both the domain name of a site and its IP address will test the DNS, too. Having read the replies to your post, I think the DNS thing is unlikely, but last week Google appeared to be down quite a bit, but only in some places. I had to resort to Bing for searches, and was quite surprised at how quickly it appeared, much faster than Google, probably because it has less traffic. Sites that connect to Google were also much slower to load -- they seemed to hang until the Google connection timed out. Perhaps, the problem is something other than DNS, but since "it" failed, it's a good place to start. Google is a huge, busy site and I'm sure gets lots of DoS attacks, but it's up the vast majority of the time and good to test if DNS is down or it's something else. I used to use Yahoo, but it's regularly slow responding and times out or I get tired of waiting. At least where I am -- Southwestern US. I've abandoned Google for searches and now use duckduckgo.com. Fast, seems up all the time and doesn't profile searchers. I don't and NEVER will use Bing: Part of my many personal protests against Microsoft and its business practices. I only use Windows when I have no other choices. Stef |
#18
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Can't connect to Web
On 28/5/2017 13:11, VanguardLH wrote:
Stef wrote: Steve Hayes wrote: This morning I suddenly lost my connection to the web while I was browsing. Mail still worked, news still worked, but the web connection did not. I reset the router, rebooted my computer, but still nothing. I wondered if it was a browser fault (I use Firefox) so tried Internet Explorer. It too could not connect, but offered to run diagnostics. This is what was found: ---- diagnostic report ---- [snip] DNS Client Diagnostic DNS - Not a home user scenario info Using Web Proxy: no info Resolving name ok for (www.microsoft.com): yes No DNS servers DNS failure I haven't read the entire thread, but this is mostly likely your problem. Your default Domain Name Server is down or can't be accessed. When you can't access "The Web" with your browser, but mail, ftp, etc work (they don't use DNS), that's where I'd start the troubleshooting. WRONG. Anytime you use a hostname (host.domain.tld) to specify a host, like for an e-mail or ftp or "etc" server, DNS gets used. Humans like names. Computers demand numbers. How many times have you encountered a user that specifies the IP address address for their e-mail server when configuring an account within their local e-mail client? Look at your own e-mail config in whatever local e-mail client you use. Did you enter a hostname or an IP address? Unless you do the DNS lookup when configuring the e-mail account in your e-mail client, you don't get that info from the e-mail provider as they give you hostnames. How many web pages have you visited where absolute references (non-relative or just a path under the current location) to sources in a web page use IP addresses instead of hostnames? If DNS were unusable to the OP, he wouldn't be doing e-mail or newsgroups. If the OP were having to use IP addresses for everything, he would've mentioned it and maybe how he got those IP addresses. NOT ALWAYS. I'm old school. I use traditional, dedicated email, ftp, usenet clients instead of a browser for all that. And those clients work just fine even when my DNSes are not reachable which is very, very rare. FWIW, Even when I enter the server names like mail.mymailprovider.com in the configs, they still work without a DNS. I think the client gets the IP and stores and uses it after that. I never bothered to check and all have been working fine for almost 5 years without any problems. With the usenet client I enter the actual IP addresses. PS. Linux is my primary system and Internet access. Windows runs in a VM on that machine for those times I need it. Here's a couple articles https://www.lifewire.com/find-the-ip...eb-site-818155 Requires DNS be working. Yes, but the article also includes some IPs for testing. https://www.lifewire.com/what-is-the...-google-818153 Requires DNS be working. Yes, but the article also includes some IPs for testing. Also, if DNS was unusable, how would the OP get to the lifewire site? You didn't give him the IP address for that site. I was going to include it for testing purposes, but when I tested it myself to be sure it worked, it didn't. Don't know why. Didn't check why. either. Other IPs for the articles I tested did work though. Stef |
#19
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Can't connect to Web
On 28/5/2017 10:48, Bert wrote:
In news but mail, ftp, etc work (they don't use DNS), Unless the IP addresses for the servers are hard-coded into the client, they certanly do. I enter IP addresses sometimes. Just enter and save them. But even when I enter the server "name," I think my email and ftp clients lookup the IP address on first access and store them for future use, so it doesn't have to look it up each time. The reason I say this is even when my DNSes are "down" those clients (and usenet clent, too) still work. I don't use a web browser for those tasks. Stef |
#20
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Can't connect to Web
In news
But even when I enter the server "name," I think my email and ftp clients lookup the IP address on first access and store them for future use, so it doesn't have to look it up each time If they do, it's a bad idea. Many large-scale systems (and some small ones) have multiple IP addresses and rotate the way they appear to DNS requests in order to balance user load. They'll also take addresses out of rotation if systems are down. -- St. Paul, MN |
#21
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Can't connect to Web
Steve Hayes wrote:
Having read the replies to your post, I think the DNS thing is unlikely, but last week Google appeared to be down quite a bit, but only in some places. I had to resort to Bing for searches, and was quite surprised at how quickly it appeared, much faster than Google, probably because it has less traffic. Sites that connect to Google were also much slower to load -- they seemed to hang until the Google connection timed out. From people I asked, it seemed that Google's servers in the east of South Africa and in New Zealand were down, but not in the UK or USA. You might also trying to find out if the route you happen to get is actually usable to you. Routing is not dynamic: when you can't get through one route to a target, you don't automatically get assigned a different route to try. Hosts (nodes in a route) go down, become unresponsive, or get too busy so they are excessively slow and clients will timeout. Updating the routing tables (once the problem has been reported and after someone takes action) can take about 4 hours (that's usually how long I wait for routing problems but they can take a lot longer). Run a traceroute (tracert) to see if you can reach the target host. For example, last night I could not get to boatloadpuzzles.com. The web browser said the site was unresponsive. Not true. A traceroute should I wasn't even getting outside my own ISP's network. Something weird was happening where I kept getting looped back through the same two nodes. I could get to other sites, like yahoo.com, but not to that one site. It wasn't a site problem. It was a routing problem so I wasn't even reaching the site. You can use public proxies to reach a site using different routes. I once couldn't reach creative.com for several days. I could get there okay using a public proxy. Why? The route that I got happened to hit one of their boundary servers (front end) to their web farm that was down. The other routes hit different boundary servers so I could get in. When presented with the various routings (mine that was unusable and others that worked) to show which boundary host was unresponsive, they fixed the problem in a day. Another time I couldn't get to any site on the west coast but I could get elsewhere. Turns out an entire backbone provider (Sprint) had an outage so no one could go either direction across most of the Rockies. I reported the problem but they already knew. That was a short-lived outage but not when you're sitting at your computer wondering why you can't get somewhere. By the way, and back to the DNS topic, there is a possiblity that it will interfere with visiting a site but not because the DNS server is down but because the site might've changed their IP address and you're still trying to use the old lookup from the local DNS client's cache. TTL (time-to-live) entries for successful lookups (positives) last longer in the DNS client's cache than those for failed lookups (negatives). Some users might suggest disabling the DNS Client service but that means your end has to do more DNS lookups. Without the cache, every hostname has to be looked up even if it is the same one. A web page can have hundreds of references requiring a DNS lookup. Having to send a request to a DNS server and get a response takes time. Looking it up in a local cache is much quicker. By default in Windows, the TTLs a positive TTL = 24 hours negative TTL = 5 minutes You can modify those DWORD values in the registry. HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Servic es\DNSCache\Parameters MaxCacheEntryTtlLimit (positive TTL), default = 86400 seconds (24 hours) NegativeCacheTime (negative TTL), default = 300 seconds (5 minutes) (if the entries are absent, the defaults get used) Some folks set the negative TTL to zero to not cache any of the failed DNS lookups. Their intent is to keep requesting new lookups from the DNS server until they happen to get one that works. They're hoping to get to the site as soon as the DNS records get updated. Seems a bit rude but I can see reducing this to one minute. The positive TTL is a bit overly long since it is possible a site has changed their IP address inside of a day. An hour or two seems more appropriate. If you suspect there is a problem with the Windows DNS cache, you can flush it so start over with all new DNS lookups and new cachine. Run: ipconfig /flushdns Note that web clients can incorporate their own internal DNS cache which overrides the defaults defined in the registry. The client uses its own DNS cache instead of relying on the one in Windows. Firefox has its own DNS cache. I suspect that is partly due to Firefox being cross-platform: they want to rely on their own DNS cache instead of hoping there is one (and still functional) back in the OS. I forget why I ran into problems with Firefox's own DNS cache but back then I disabled it to resolve whatever was the problem. I have not disabled the DNS Client in Windows so that DNS caching is available and I don't want (and ran into problems with) Firefox's own internal DNS cache. In about:config, Firefox's TTL setting is at: network.dnsCacheExpiration default = 3600 (1 hour) 0 (zero) disables Firefox's DNS cache Setting to zero means disabling the cache which flushes all currently cached DNS lookups. Apparently Firefox is only caching positive results, not negative ones. You could then reset back to 3600 or a value of your choice or just leave it zero (and rely on the DNS Client in Windows to do both positive and negative DNS caching). There are add-ons for Firefox to flush Firefox's internal DNS cache, like DNS Flusher, but I disabled Firefox's internal DNS cache so I don't need an add-on to fix DNS caching problems within Firefox. In Firefox, I also set network.dns.disablePrefetch = True but that's for a different DNS issue: Firefox populating its internal DNS cache for any resources specified in the currently loaded page. This has Firefox prefetching IP addresses from the DNS server for resources that you may never need, like a hyperlink to another site that you won't be visiting or for ad or tracking sources that can then see your IP address visited them. You might use an adblocker but prefetching in Firefox partially cripples the adblocker from doing its job. See: https://en.wikipedia.org/wiki/Link_p...and_criticisms |
#22
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Can't connect to Web
On 31/5/2017 10:51, Bert wrote:
In news But even when I enter the server "name," I think my email and ftp clients lookup the IP address on first access and store them for future use, so it doesn't have to look it up each time If they do, it's a bad idea. Many large-scale systems (and some small ones) have multiple IP addresses and rotate the way they appear to DNS requests in order to balance user load. They'll also take addresses out of rotation if systems are down. I really don't know for sure. I never bother checking. But I do know, the few times the Web didn't work and I knew DNS, or lack thereof, was the problem, I could still get mail, etc. I think the OP is having a configuration problem more than anything else. I used to have a side business troubleshooting such things on Windows machines. Windows has an extraordinary ability to break itself. When the printer or ethernet or wireless, etc. just stop working, particularly when they worked fine before the machine was "turned off" the night before, settings were the first thing I checked. Stef |
#23
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Can't connect to Web
On Wed, 31 May 2017 15:41:21 -0500, VanguardLH wrote:
If you suspect there is a problem with the Windows DNS cache, you can flush it so start over with all new DNS lookups and new cachine. Run: ipconfig /flushdns Note that web clients can incorporate their own internal DNS cache which overrides the defaults defined in the registry. The client uses its own DNS cache instead of relying on the one in Windows. Firefox has its own DNS cache. Thanks for this and lots of other useful information. Since my problem was with the web and not mail or news, and I use Firefox, it was probably not caused by the Windows DNS cache, but with something in Firefox or even in my ISP. It seems to have come right now, not necessarily because of anything I tried. -- Steve Hayes http://www.khanya.org.za/stevesig.htm http://khanya.wordpress.com |
#24
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Can't connect to Web
On Wed, 31 May 2017 17:51:05 -0000 (UTC), Bert wrote:
In news But even when I enter the server "name," I think my email and ftp clients lookup the IP address on first access and store them for future use, so it doesn't have to look it up each time If they do, it's a bad idea. Agreed. Thanks to DNS, if a remote host's IP address needs to change for any reason, DNS will automatically find the new IP. Many large-scale systems (and some small ones) have multiple IP addresses and rotate the way they appear to DNS requests in order to balance user load. Typically referred to as "DNS load balancing", it's a free but very crappy way to make a remote service available. Fortunately, it's pretty rarely used these days. Instead, most publicly accessible organizations use actual load balancers, where a remote FQDN resolves to a single IP address that's configured on the client side of a load balancer. The actual application servers reside behind the load balancer where they can't be accessed directly by the public. They'll also take addresses out of rotation if systems are down. The main problem with DNS load balancing (simply adding additional A or AAAA records for a given FQDN) is that DNS has no way to do application health checks, so regardless of whether a specific server is up or not, DNS will happily hand out its IP address. Real load balancers address that issue by performing periodic application health checks, taking servers out of rotation if they don't respond properly and then adding them back into rotation when they start responding again. |
#25
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Can't connect to Web
On 6/1/2017 1:52 AM, Steve Hayes wrote:
On Wed, 31 May 2017 15:41:21 -0500, VanguardLH wrote: If you suspect there is a problem with the Windows DNS cache, you can flush it so start over with all new DNS lookups and new cachine. Run: ipconfig /flushdns Note that web clients can incorporate their own internal DNS cache which overrides the defaults defined in the registry. The client uses its own DNS cache instead of relying on the one in Windows. Firefox has its own DNS cache. Thanks for this and lots of other useful information. Since my problem was with the web and not mail or news, and I use Firefox, it was probably not caused by the Windows DNS cache, but with something in Firefox or even in my ISP. It seems to have come right now, not necessarily because of anything I tried. |
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