Aug 18, 2014

dns resolver behavior

i had an occasion to have to look up windows client behavior when it came to dns. specifically, i wanted to know how the client behaves when the primary name server is offline. before i had to fire up packet trace and check for myself, i stumbled on a couple of useful articles that spell it out.

UPDATE: had a conversation with a talented linux dns guy and discovered a few more useful things to note.

dns client resolver behavior
dns client resolution timeouts
dns forwarders and conditional forwarders resolution timeouts

in summary, it works as follows:

  • dns query sent to preferred
  • if no response within 1 second, dns query sent to alternate
  • if no response within 1 second, dns query sent to preferred again
  • if no response within 2 seconds, dns query sent to preferred and alternate
  • if no response within 4 seconds, dns query sent to preferred and alternate again
  • if no response within 7 seconds, process times out


something to note for linux systems, these appear to be default values:

  • timeout:n
    sets the amount of time the resolver will wait for a response from a remote name server before retrying the query via a different name server.  Measured in seconds, the default is RES_TIMEOUT (currently 5, see <resolv.h>).  The value for this option is silently capped to 30.
  • attempts:n
    sets the number of times the resolver will send a query to its name servers before giving up and returning an error to the calling application.  The default is RES_DFLRETRY (currently 2, see <resolv.h>).  The value for this option is silently capped to 5.
  • rotate
    sets RES_ROTATE in _res.options, which causes round-robin selection of name servers from among those listed.  This has the effect of spreading the query load among all listed servers, rather than having all clients try the first listed server first every time.
  • search
    Resolver queries having fewer than ndots dots default is 1) in them will be attempted using each component of the search path in turn until a match is found.
  • ndots:n
    sets a threshold for the number of dots which must appear in a name given to res_query(3) (see resolver(3)) before an initial absolute query will be made.  The default for n is 1, meaning that if there are any dots in a name, the name will be tried first as an absolute name before any search list elements are appended to it.  The value for this option is silently capped to 15.

in summary, the timeout value indicates how long the client will wait until it tries the next server in the search list. the number of queries attempted per server is dependent on how ndots is configured. once the server list is exhausted, the attempts value indicates if the client should try the list again.

additional settings can be found here:

Aug 12, 2014

troubleshooting wmi…

this exhaustive series on troubleshooting wmi from the ask the performance team blog is too good to pass up. use of wmi is pervasive, guaranteeing that just about all of us have run into wmi issues at some point or another. if you haven’t yet, it’s only a matter of time. might as well do your homework.

here are the topics the series will be covering:

  • WMI: Common Symptoms and Errors
  • WMI: Repository Corruption, or Not?
  • WMI: Missing or Failing WMI Providers or Invalid WMI Class
  • WMI: High Memory Usage by WMI Service or Wmiprvse.exe
  • WMI: How to troubleshoot High CPU Usage by WMI Components
  • WMI: How to Troubleshoot WMI High Handle Count


i’ve blogged a few times about wmi myself:

Jul 24, 2014

misc: flying with cortana

if you’re a windows phone 8.1 user, you’re probably in love with cortana already. she is a fantastic organizer! despite all that, sometimes, she fails to understand your flight itinerary, especially on multi-leg flights. she might capture just one leg of the flight. so how do you fix?

i looked for a way to do this but wasn’t able to find any well-documented procedures, so here’s my shot at it.

  • have cortana search for the flight information. in my test, i’m using aa1947 as an example.
  • click the Show AA 1947 updates link. this will add it to your itinerary.


if the date isn’t right, don’t worry. you can change it.

  • switch over to the interests section.
  • under travel, you should be able to find your flight information. click on it.


  • under the Flight date section, simply choose which date you’re interested in.

now cortana will track that flight for you.

Jul 23, 2014

misc: cool things about onenote

onenote has been my constant companion for many years now. between onenote and outlook, i can’t think of very many things that can’t be effectively managed, tasked, or tracked -- at least from a day-to-day perspective. i found some pretty cool things about onenote recently that i thought i’d share: subpages and onetastic.



Snagit screen capturefor those of that don’t know, i’m an avid pool player. naturally, since i use onenote, i’m a pool player that likes to keep a lot of notes about billiards as you can see in the screenshot.

the first thing i want to point out is onenote allows the use of subpages. i went for far too long without knowing that. if you look at #1, you can see how onenote looks when you collapse subpages. #2 is the expanded view.

once you collect your pages as subpages, it makes managing them easier since you can work with them in bulk (move, copy, delete, cut, etc.)

to create a subpage, right-click the page tab and choose make subpage. the shortcut trick to make or promote a subpage is to drag the page tab left or right with your mouse as shown below.

Snagit screen capture



i stumbled on this gem while i was looking for a tool to apply styles like you can in pretty much every other office product. enter onetastic. onetastic for microsoft onenote is an amazing collection of tools Snagit screen capturethat integrate directly with onenote. since most of the tools are macros, it’s as extensible as you want to make it. so far, i’ve found that their collection of macros is more than enough for me.

if you’re a heavy onenote user, it’s definitely worth checking. i found all kinds of other cool macros like sorting pages, creating a table of content, search & highlight, etc.




onenote 2013 keyboard shortcuts