Birmingham mumbai

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The format doesn't really matter; I used 
202008161
, which is simply the year, two-
digit month, two-digit day, and an extra number to cover us if we make more than 
one change in a day (which can sometimes happen). As long as you increment 
the serial number by one every time you modify your 
zone file, you'll be in good 
shape—regardless of what
 format you use. However, the sample format I gave here 
is actually quite common in the field.
These values control how often secondary DNS servers will be instructed to check in 
for updates:
8H ; refresh 
4H ; retry 
4W ; expire 
1D ) ; minimum
With the example refresh value, we're instructing any secondary DNS servers to 
check in every eight hours to see whether or not the zone records were updated. The 
retry field dictates how long the secondary will wait to check in, in case there was an 
error doing so the last time. The last two options in this section, 
expire
 and 
minimum
, 
set the minimum and maximum age of the zone file, respectively. As I mentioned 
though, a full discussion of DNS with 
bind
 could constitute an entire book on its 
own. For now, I would just use these values until you have a reason to need to 
experiment. Here, we identify the name server itself:
IN A 192.168.1.1 
@ IN NS hermes.local.lan. 
In my case, the server is called 
hermes
 and it's located at 
192.168.1.1
.
Next, in our file, we'll have several host entries to allow our resources to be resolved 
on our network by name:
fileserv        IN  A   192.168.1.3 
hermes          IN  A    192.168.1.1 
mailserv        IN  A   192.168.1.5 
mail            IN  CNAME   mailserv. 
web01           IN  A   192.168.1.7 
In that example, I have three hosts: 
fileserv
, 
mailserv
, and 
web01
. In the example, 
these are all address records, which means that any time our server is asked to 
resolve one of these names, it will respond with the corresponding IP address. 
If our DNS server is set as a machine's primary DNS server, it will respond with 
192.168.1.3
 when asked for 
fileserv
 and 
192.168.1.7
 when asked for 
web01
. 

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Chapter 11