[NTLUG:Discuss] NAT question

[Terry]

I've seen mention of the fact that it's not good to have more than one
NAT device on a network.  Is that so?  And if so, why?

Is it just that each NAT device or system just adds more overhead or
slows the network down, and it slows the network down twice as much if
you have two?  Or three times as much if you have 3, etc.   Or... ?

One more question.  Should a firewall be rebooted regularly?  Say once
a month or once a week or... not at all? Or what?