From: lew.pitcher@digitalfreehold.ca   
      
   On Fri, 01 Mar 2024 21:57:02 -0400, Mike Spencer wrote:   
      
   > Lew Pitcher  writes:   
   >   
   >> On Thu, 29 Feb 2024 22:36:59 -0400, Mike Spencer wrote:   
   >>   
   >>> At times, using wicd, I disconnect from the router and reconnect via   
   >>> wi-fi, using a cell phone served by ISP "B" as an access point.  Wicd   
   >>> replaces /etc/resolv.conf with one that references the nameservers of   
   >>> ISP "B".  Apps such as a web browser and Usenet news proceed as   
   >>> expected after the change but sendmail fails to deliver messages to   
   >>> the remote smarthost.   
   >>>   
   >>> Restarting sendmail fixes this.   
   >> [snip]   
   >>   
   >> I think that you are trying to solve the wrong problem. The problem isn't   
   >> that sendmail caches the address of the DNS server, but that you are   
   >> using a DNS server who's address may change over time.   
   >>   
   >> You could just run a caching nameserver on your slackware box, and   
   >> resolve /all/ DNS queries against that server. This way, the DNS   
   >> server maintains a fixed address (perhaps, "localhost", in your case)   
   >> and sendmail doesn't have to fish about for DNS resolution.   
   >   
   > I never thought of that.  The caching nameserver would have to be able   
   > to go to the right remote nameserver to update itself but that might   
   > be handled correctly.   
      
   Unless you configure it incorrectly, a caching nameserver "climbs the   
   tree" of domains for you, starting at the root servers, and working   
   its way up from the TLD to the full hostname. It definitely /would/   
   "go to the right remote nameserver" for any hostname available to   
   a public DNS query.   
      
   >  One more thing to maintain kinda contravenes my preference for   
   > KISS but I'll have a look at that.   
      
   I guess that it depends on your definition of "simple". If "simple"   
   means finding some random hack to sendmail to make it stop caching   
   DNS query results, then, I guess, a sendmail hack satisfies your   
   KISS principle.   
      
   But, if the addition of a single, standard, low maintenance process   
   to your current configuration is simpler than a sendmail hack, then   
   a caching nameserver is the ticket.   
      
   I've run one for years, with no maintenance issues at all.   
      
   But, that's me.  :-)   
      
      
   >> A caching DNS server adds very little to the system overhead, and,   
   >> beyond the initial setup, needs little or no maintenance. It gives   
   >> the added benefit of adding a bit more security to your DNS queries,   
   >> in that your ISP /does not/ handle the queries,  /can't/ log or track   
   >> them, and /can't/ substitute their own sponsored/edited/redirected   
   >> answers.   
   >   
   > A potential problem, yeah.  IIRC, I've only seen it happen twice, once   
   > using somebody's wi-fi where their router did DNS weirdly.  I forget   
   > the details of the other case but it became publicly known and went   
   > away after public protest.   
      
   My GF has cable internet, and her ISP sometimes "redirects" her away   
   from the websites she asks for to sites that the ISP deems more   
   "suitable", using altered DNS reply values. But, then again, that ISP   
   also "injects" its own (sometimes sponsored) HTML into web pages she   
   views. She (thinks that she) has no choice but to tolerate this   
   corporate antisocial behaviour.  :-(   
      
   Luck be with you.   
   --   
   Lew Pitcher   
   "In Skills We Trust"   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)