Question:
  Should I leave my router switched on all the time  ?  I have been
  turning it off at night when I turn off the computer, but  this
  morning I forgot it and spent ages trying to get on line before
  I realised.  Do you leave yours on all the time.

Answer:	(By Julian H. Stacey http://www.berklix.com/~jhs/cv/ )
  Some people have DSL as a card plugged into PC, so no choice for them.

  My router is in 2 parts: A 220V ADSL modem, connected via an
  ethernet cable (no hub) to a full function PC (old mini tower).
  That mini tower is a firewall gateway router proxy that connects
  my internal ethernet host to internet.
  
  The DSL modem:
    The modem stays turned on for months. Though in summer I think
    about that, as theres so much that stays on all night & its one
    more office heat source.  Powered up continuously it will of course
    be warmer & the electrolytic capacitors will dry out & die sooner.
    On the other hand, my main tower's main board died last
    week, cos the BIOS ROM chip died. Not that I wouldnt expect a ROM
    to die quicker if left on (as it usually is for weeks), but on the
    other hand I didnt need that BIOS till I turned on. Does one want to
    increase the chances of problems next morning at power up ?
    
    An administrator friend once said he had so much kit, whenever he
    turned it all on (eg after Xmas)  something always failed to start.
    
    My ADSL modem takes maybe 20+ seconds to synchronise when powered
    up or re-connected on the phone line side.
  
  My gateway router-PC:
    Usually stays on for weeks, except in hot weather overnight.
  
    The firewall runs on the gateway = router PC, not on all the internal
    hosts.  I wrote the firewall router rules myself.  Being paranoid,
    I dont trust my own rules, & if I Know I won't be using the net for
    a while I unplug the ethernet cable between gateway/router & DSL
    modem.
    
  What should you do ?
    I'd suggest turn off.  Being paranoid as I feel I'm trained to
    be, I'd ask: while powering up, does Microsoft & the raft of other
    stuff initially lock itself tight, then install firewall rules
    to progressively unlock bits, or does it start open, & later
    lock bits up ? Is there a window of opportunity each time the
    machine boots ? (automatic intrusion takes a few seconds, &
    Microsoft machines are scanned & attacked extremely quickly if
    you have right software to see it - I have seen it). If you
    leave yourself connected for long periods, & are you sure your
    firewall rules are correct & appropriate (*) ? Unplugging gives
    absolute security :-)
    
    If default firewall rules are too difficult the manufacturer
    will get many complaints, particularly from unskilled people,
    costing extra support salaries.  if firewall rules are too easy
    some people will be broken into, & subset will notice, a smaller
    subset will complain to firewall manufacturer, & some of those
    will be fobbed off or blamed for changing something, of the
    remainder, some will probably be bought off with a free software
    upgrade, virtually none will see a cash damages payment.

    So if you were a firewall vendor, what would you do ?  & if a
    cautious user what would you do ? (Answer turn off everything,
    & only very cautiously turn on a minimum of what's essential).
    Firewalls are a pain. So are locked doors & gate security/porters.
    But just like one bolts a door at times in case the lock is
    picked, why not power down or physically unplug the DSL modem
    when you know you don't need it. ?

PS
http://www.berklix.com/~jhs/txt/ip/