Few questions

EssendonEssendon Member Posts: 4,548 ■■■■■■■■■■
Well, I am gearing to take on the beast soon and quite naturally there are a few doubts here and there compounded by the fact that different sources provide different information. So here goes:

1. The 80/20 rule in DHCP scoping. This is not clear to me because there's conflict between what James said in the Nuggets and what the MS Press book says. Say you have the scope and the first 20 addresses were to be reserved for the ilks of servers and routers. You have to have 2 DHCP servers providing redundancy. Now, to split the scope using the 80/20 rule, should I do 80% of 234 (from 254 - 20) or 80% of 254? James did 80% of 234 while the book did 80% of 254, for the same question. This has got me confused icon_confused.gif

2. Another conflict! To clear out the DNS server cache, can we use the ipconfig/flushdns command? or is this only for the client cache (I know I should have tried this at home first before asking)

3. Page 5-33 of the book explicitly says in a big box " Manually incrementing the Serial Number in the DNS zone properties, forces a zone transfer". I dont think that's true. I have tried that and there were no transfers at all either to the secondary or the subdomain's primary DNS servers. In the Nuggets too he said "Merely incrementing the serial number will not force a zone transfer". Whose right, or am I missing something as zone transfers are triggered when the secondary contacts the primary after the refresh interval expires and checks if the serial number has changed?

4. Page 5-84 Question 5 on the book --
You discover that an administrator has adjusted the default TTL value for your company's primary DNS zone to 5 minutes. Which of the following is the most likely effect of this change?
a. Resource records cached on the primary DNS server expire after 5 minutes.
b. DNS clients have to query the server more frequently to reslove names for which the server is authoritative.
c. Secondary servers initiate a zone transfer every 5 minutes.
d. DNS hosts reregister their records more frequently.

They reckon the answer is b. I think the answer is none of these. Default TTL refers to the cache life of a resource record in non-authoritative servers, which means that these values are irrelevant for the resource records within their authoritative zones. Am I right?

5. If the DHCP log says "Authorisation failed, contoso.com" What does this mean? Can this be because someone has unauthorised it or is it that the server's started for the first time? BTW, the DHCP server on my network always says this when the machine's started. I dont do anything to it and it starts servicing clients by itself. So is that just a MS quirk?

I need help!
NSX, NSX, more NSX..

Blog >> http://virtual10.com


  • astorrsastorrs Member Posts: 3,139 ■■■■■■□□□□
    1. 80% of 234 (from 254 - 20)

    2. from the DNS server "dnscmd /clearcache"

    3. Zone transfers would only happen here if the server was set to notify downstream servers of changes. (the Notify tab). Otherwise it follows the normal update process.

    4. They are being cached on the client computers which will by default use the TTL before dropping them from the cache and querying the DNS server again so B is correct

    5. I assume this is also your domain controller too right? DHCP gets authorized by AD once AD finishes starting up (DHCP is pretty fast to load and the service isn't dependent - nor should it be since you would usually have multiple DCs). You can ignore it.
  • EssendonEssendon Member Posts: 4,548 ■■■■■■■■■■
    Thank you for the quick reply, Andrew. I will modify the memory buffers in my brain accordingly.
    NSX, NSX, more NSX..

    Blog >> http://virtual10.com
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