On 7/25/19 6:48 AM, rainer at ultra-secure.de wrote:> Am 2019-07-25 15:41, schrieb hw: >> On 7/25/19 2:53 PM, rainer at ultra-secure.de wrote: >>> Am 2019-07-25 14:51, schrieb hw: >>>> Hi, >>>> >>>> how can DNS reliability, as experienced by clients on the LAN who are >>>> sending queries, be increased? >>>> >>>> Would I have to set up some sort of cluster consisting of several >>>> servers all providing DNS services which is reachable under a single >>>> IP address known to the clients? >>>> >>>> Just setting up several name servers and making them known to the >>>> clients >>>> for the clients to automatically switch isn't a good solution because >>>> the clients take their timeouts and users lacking even the most basic >>>> knowledge inevitably panic when the first name server does not answer >>>> queries. >>> >>> Run a local cache (unbound) and enter all your local resolvers as >>> upstreams. >> >> That can fail just as well --- or be even worse when the clients >> can't switch >> over anymore.? I have that and am avoiding to use it for some clients >> because >> it takes a while for the cache to get updated when I make changes. >> >> However, if that cache fails, chances are that the internet >> connection is also >> down in which case it can be troublesome to even get local host names >> resolved. >> When that happens, trouble is to be expected. > > > Anything else is - IMHO - much more work, much more complicated and > much more likely to fail, in a more spectacular way. > Especially all those keepalive "solutions". > > I have found that I need to restart unbound if all upstreams had failed.Configure all dns servers as primary slaves (plus 1 primary master) for your own domains.? I have never seen problems with resolution of local dns domains when the Internet was down. Depending on the size of your network, you can run a caching server on each host (configured as a primary slave for your own domains) and? then configure that local server to use forwarders.? When you use multiple forwarders the local server does not have to wait for timeouts before querying another server.? Then you just run 2 or more servers to use for forwarding.? Use forward-only to force all local servers to use only forwarding (for security and caching reasons).? Much simpler than using keepalived.? In recent years I *have not had any* problems with bind9 or powerdns crashing. As far as using the ISC server vs powerdns, you may want to check on peoples recent experiences.? There was a time when many thought powerdns had much better performance and fewer security issues.? For various reasons? I've seen some people including myself, switch back to ISC bind9.? I switched about 1.5 years ago because I was getting better performance from bind9.? You may want to check out other peoples experience before switching to powerdns. Nataraj
On 7/25/19 8:14 AM, Nataraj wrote:> On 7/25/19 6:48 AM, rainer at ultra-secure.de wrote: >> Am 2019-07-25 15:41, schrieb hw: >>> On 7/25/19 2:53 PM, rainer at ultra-secure.de wrote: >>>> Am 2019-07-25 14:51, schrieb hw: >>>>> Hi, >>>>> >>>>> how can DNS reliability, as experienced by clients on the LAN who are >>>>> sending queries, be increased? >>>>> >>>>> Would I have to set up some sort of cluster consisting of several >>>>> servers all providing DNS services which is reachable under a single >>>>> IP address known to the clients? >>>>> >>>>> Just setting up several name servers and making them known to the >>>>> clients >>>>> for the clients to automatically switch isn't a good solution because >>>>> the clients take their timeouts and users lacking even the most basic >>>>> knowledge inevitably panic when the first name server does not answer >>>>> queries. >>>> Run a local cache (unbound) and enter all your local resolvers as >>>> upstreams. >>> That can fail just as well --- or be even worse when the clients >>> can't switch >>> over anymore.? I have that and am avoiding to use it for some clients >>> because >>> it takes a while for the cache to get updated when I make changes. >>> >>> However, if that cache fails, chances are that the internet >>> connection is also >>> down in which case it can be troublesome to even get local host names >>> resolved. >>> When that happens, trouble is to be expected. >> >> Anything else is - IMHO - much more work, much more complicated and >> much more likely to fail, in a more spectacular way. >> Especially all those keepalive "solutions". >> >> I have found that I need to restart unbound if all upstreams had failed. > > Configure all dns servers as primary slaves (plus 1 primary master) for > your own domains.? I have never seen problems with resolution of local > dns domains when the Internet was down.I meant to say: Configure all dns servers as secondary/slaves (one should be the primary master) for your own domains. Thos means that all of your servers are authoritative for your own domains, so they cannot fail on local dns lookups due to Internet problems.> > Depending on the size of your network, you can run a caching server on > each host (configured as a primary slave for your own domains) and? then > configure that local server to use forwarders.? When you use multiple > forwarders the local server does not have to wait for timeouts before > querying another server.? Then you just run 2 or more servers to use for > forwarding.? Use forward-only to force all local servers to use only > forwarding (for security and caching reasons).? Much simpler than using > keepalived.? In recent years I *have not had any* problems with bind9 or > powerdns crashing. > > As far as using the ISC server vs powerdns, you may want to check on > peoples recent experiences.? There was a time when many thought powerdns > had much better performance and fewer security issues.? For various > reasons? I've seen some people including myself, switch back to ISC > bind9.? I switched about 1.5 years ago because I was getting better > performance from bind9.? You may want to check out other peoples > experience before switching to powerdns. > > > Nataraj > > > _______________________________________________ > CentOS mailing list > CentOS at centos.org > https://lists.centos.org/mailman/listinfo/centos
On 7/25/19 5:14 PM, Nataraj wrote:> On 7/25/19 6:48 AM, rainer at ultra-secure.de wrote: >> Am 2019-07-25 15:41, schrieb hw: >>> On 7/25/19 2:53 PM, rainer at ultra-secure.de wrote: >>>> Am 2019-07-25 14:51, schrieb hw: >>>>> Hi, >>>>> >>>>> how can DNS reliability, as experienced by clients on the LAN who are >>>>> sending queries, be increased? >>>>> >>>>> Would I have to set up some sort of cluster consisting of several >>>>> servers all providing DNS services which is reachable under a single >>>>> IP address known to the clients? >>>>> >>>>> Just setting up several name servers and making them known to the >>>>> clients >>>>> for the clients to automatically switch isn't a good solution because >>>>> the clients take their timeouts and users lacking even the most basic >>>>> knowledge inevitably panic when the first name server does not answer >>>>> queries. >>>> >>>> Run a local cache (unbound) and enter all your local resolvers as >>>> upstreams. >>> >>> That can fail just as well --- or be even worse when the clients >>> can't switch >>> over anymore.? I have that and am avoiding to use it for some clients >>> because >>> it takes a while for the cache to get updated when I make changes. >>> >>> However, if that cache fails, chances are that the internet >>> connection is also >>> down in which case it can be troublesome to even get local host names >>> resolved. >>> When that happens, trouble is to be expected. >> >> >> Anything else is - IMHO - much more work, much more complicated and >> much more likely to fail, in a more spectacular way. >> Especially all those keepalive "solutions". >> >> I have found that I need to restart unbound if all upstreams had failed. > > > Configure all dns servers as primary slaves (plus 1 primary master) for > your own domains.? I have never seen problems with resolution of local > dns domains when the Internet was down.It seemed to have to do with the TTL for the local names being too short and DNS being designed to generally query root servers rather than sticking to their local information.> Depending on the size of your network, you can run a caching server on > each host (configured as a primary slave for your own domains) and? then > configure that local server to use forwarders.? When you use multiple > forwarders the local server does not have to wait for timeouts before > querying another server.? Then you just run 2 or more servers to use for > forwarding.? Use forward-only to force all local servers to use only > forwarding (for security and caching reasons).? Much simpler than using > keepalived.Hm. I thought about something like that, but without the separation into local slaves using forwarders and the forwarders. I will probably do that; it seems like the most reasonable solution, and I should have at least one forwarder anyway so as not to leak information to the internet-only VLANs. It would be an improvement in several ways and give better reliability. It doesn't really help those clients I can not run name servers on, though. > In recent years I *have not had any* problems with bind9 or> powerdns crashing. > > As far as using the ISC server vs powerdns, you may want to check on > peoples recent experiences.? There was a time when many thought powerdns > had much better performance and fewer security issues.? For various > reasons? I've seen some people including myself, switch back to ISC > bind9.? I switched about 1.5 years ago because I was getting better > performance from bind9.? You may want to check out other peoples > experience before switching to powerdns.Bind has been around for ages, and I've never had any issues with it for the last 25 years or so. Just set it up and let it do its thing, and it does. If there were performance problems, I imagine they would be more likely due to insufficient internet bandwidth. Perhaps it would take all the DNS queries that come up during a week or even a month to arrive within a second before any performance considerations become relevant ...
On 7/25/19 7:10 PM, Nataraj wrote:> [...] > > I meant to say: > > Configure all dns servers as secondary/slaves (one should be the primary master) for your own domains. Thos means that all of your servers are authoritative for your own domains, so they cannot fail on local dns lookups due to Internet problems.Ah!? When I had it happen a couple years ago and wondered why even local names couldn't be resolved (which didn't make sense to me because the server would always know about them from the zone files), I was told that nothing could be done about it because DNS is designed to do lookups no matter what. However, that was a server acting as both a local master and as a forwarder. If what you say is true, I would now understand this much better --- and I'd need to change my setup.
On 7/25/19 1:10 PM, hw wrote:>> >> Configure all dns servers as primary slaves (plus 1 primary master) for >> your own domains.? I have never seen problems with resolution of local >> dns domains when the Internet was down. > > It seemed to have to do with the TTL for the local names being too > short and DNS being designed to generally query root servers rather > than sticking to their local information.It has nothing to do with the ttl. The TTL does cause expiration in an authoritative server.? TTLs only affect? caching servers.? The primary master gets changed when you edit the local zone database.? The secondary slave gets updated when the serial number in the SOA record on the primary master gets bumped.?? You must either do that manually or use a zone database management tool that does it for you. If a dns server is configured as a primary master or a secondary slave for a domain, then it is authoritative for that domain and does not require queries to any other server on your network or on the Internet.? The difference between a primary master and a secondary slave is the primary master is where you edit the zone records and the secondary slave replicates the zone database from the primary master.? Even if the primary master goes down, the secondary slave still has a copy of the zone files in it's disk files (or other database format that you configure) and will server them flawlessly. One way to see if a server is properly configured as authoritative for a domain is: nataraj at pygeum:~$ dig mydomain.com. soa @127.0.0.1 ; <<>> DiG 9.11.3-1ubuntu1.8-Ubuntu <<>> mydomain.com. soa at 127.0.0.1 ;; global options: +cmd ;; Got answer: ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 52104 ;; flags: qr *aa* rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 3, ADDITIONAL: 4 ;; OPT PSEUDOSECTION: ; EDNS: version: 0, flags:; udp: 4096 ; COOKIE: 64f402c0c22d57aa2bbb10fc5d3a340d8c19377b924d01c2 (good) ;; QUESTION SECTION: ;mydomain.com.??? ??? ??? IN??? SOA ;; ANSWER SECTION: Mydomain.Com.??? ??? 14400??? IN??? SOA??? ns1.mydomain.com. postmaster.Mydomain.COM. 2019072505 1200 600 15552000 14400 ;; AUTHORITY SECTION: Mydomain.Com.??? ??? 14400??? IN??? NS??? ns1.Mydomain.Com. Mydomain.Com.??? ??? 14400??? IN??? NS??? ns2.Mydomain.Com. Mydomain.Com.??? ??? 14400??? IN??? NS??? ns3.Mydomain.com. ;; ADDITIONAL SECTION: ns1.mydomain.com.??? ??? 14400??? IN??? A??? 8.8.8.8 ;; Query time: 1 msec ;; SERVER: 127.0.0.1#53(127.0.0.1) ;; WHEN: Thu Jul 25 15:58:21 PDT 2019 ;; MSG SIZE? rcvd: 243 The AA flag in the flags section tells you that you have queried a dns server that is authoritative for the domain that you queried.? If it doesn't have the AA flag then you have not properly set up the primary master or secondary slave for that domain. If your masters and slaves are all configured correctly for a domain then they will all have the same serial number? in the SOA record (and same results for any query in that domain).? If they don't then something is wrong and your zone transfers are not occuring properly.> >> Depending on the size of your network, you can run a caching server on >> each host (configured as a primary slave for your own domains) and? then >> configure that local server to use forwarders.? When you use multiple >> forwarders the local server does not have to wait for timeouts before >> querying another server.? Then you just run 2 or more servers to use for >> forwarding.? Use forward-only to force all local servers to use only >> forwarding (for security and caching reasons).? Much simpler than using >> keepalived. > > Hm.? I thought about something like that, but without the separation > into local slaves using forwarders and the forwarders.? I will > probably do that; it seems like the most reasonable solution, and I > should have at least one forwarder anyway so as not to leak > information to the internet-only VLANs.? It would be an improvement in > several ways and give better reliability.The local server can have forward-only either on or off.? If off, It will go out directly to the Internet if it does not receive a response from a forwarder.? Using forward only and putting your forwarders on a seperate network away from your inside network means if there is a security hole in the nameserver, your inside hosts are less likely to be compromised.? ? You could also configure your ISP's or google or other public recursive name servers as forwarders if you don't want to run your own.> > It doesn't really help those clients I can not run name servers on, > though. > > > In recent years I *have not had any* problems with bind9 or >> powerdns crashing. >> >> As far as using the ISC server vs powerdns, you may want to check on >> peoples recent experiences.? There was a time when many thought powerdns >> had much better performance and fewer security issues.? For various >> reasons? I've seen some people including myself, switch back to ISC >> bind9.? I switched about 1.5 years ago because I was getting better >> performance from bind9.? You may want to check out other peoples >> experience before switching to powerdns. > > Bind has been around for ages, and I've never had any issues with it > for the last 25 years or so.? Just set it up and let it do its thing, > and it does. > > If there were performance problems, I imagine they would be more > likely due to insufficient internet bandwidth.? Perhaps it would take > all the DNS queries that come up during a week or even a month to > arrive within a second before any performance considerations become > relevant ...Exactly, a simple bind9 configuration is adequate unless you run an application with huge numbers of DNS queries.> _______________________________________________ > CentOS mailing list > CentOS at centos.org > https://lists.centos.org/mailman/listinfo/centos