Sip.conf file

Asterisk Asterisk General
1

Is there anyone who can answer the following configuration is the best?

[general]
port=5060
bindaddr=0.0.0.0
srvlookup=yes
defaultexpirey=1800
disallow=all
allow=ulaw
allow=alaw
allow=g726
allow=ilbc
allow=gsm
musicclass=default
language=da
relaxdtmf=yes
rtpiholdtimeout=300
rtptimeout=60
useragent=Asterisk
nat=yes
dtmfmode=auto
registerattempts=0
localnet=192.168.0.0/255.255.0.0
localnet=10.0.0.0/255.0.0.0
localnet=172.16.0.0/12
localnet=169.254.0.0/255.255.0.0
externip=

2

why

nat=yes
?

3

I do not know, should I choose no?

Are there other things to be corrected, removed or added?

4

you should almost never use nat=yes. Simply remove the line. The rest looks okay with the exception of inconsistent specifications for localnet CIDR vs subnet