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Author Topic: DHCP Pool and subnetting  (Read 3572 times)

K5TTT

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DHCP Pool and subnetting
« on: March 20, 2015, 10:37:46 PM »

OK, so I'm on hold with support now.  It's been over an hour and I'm on my way to level 3 support.  The first two levels haven't a clue how the netmask relates to a subnet, so they can't begin to understand my question about the DHCP pool.  They keep telling me to set it back to the default settings.  Ugh!  Maybe someone here can answer my question.

My Router IP is 172.30.100.1
Subnet mask is 255.255.252.0 or in slash notation, that's a /22 subnet containing 1024 addresses.

The configuration page contains two boxes and defaults to look like this...
DHCP IP Address Range : 100 to 199 (addresses within the LAN subnet)

So, my question is does that 2nd number (199) represent 172.30.100.199 or 172.30.103.199?

They only give us the last octet to work with, so this is a fault of the design team.  It could have been made a whole lot easier to understand.  They could easily calculate the first three octets from the netmask and preface each box with those.   The statement in parenthesis just makes it more confusing.  Surely that really means the last part of the subnet and not the first, otherwise, you could define a /22 subnet but only be able to dole out 254 addresses out of the 1024 addresses in the subnet.
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K5TTT

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Re: DHCP Pool and subnetting
« Reply #1 on: March 20, 2015, 10:49:15 PM »

I'm still interested in some confirmation.  Support told me they took it to the lab.  The answer to my question was NEITHER.  They told me the first number is the first IP address at the beginning of the subnet, as expected.  The 2nd number is not an IP address.  It is the maximum number of addresses to assign!  So, to assign the maximum number of addresses left in the subnet, you can put a number up to 999 in the 2nd box.  Total design fail for those who wrote the configuration pages.

Make sense to anyone else?
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FurryNutz

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Re: DHCP Pool and subnetting
« Reply #2 on: March 23, 2015, 07:50:09 AM »

Link>Welcome!

  • What Hardware version is your router? Look at sticker under the router case.
  • Link>What Firmware version is currently loaded? Found on the routers web page under status.
  • What region are you located?

Is this for home or a business?
The DIR series class of routers are home class routers. Thus there isn't a lot of advanced features or abilities for these routers to do a lot of advanced networking or configurations like in corporate or business environments so such features are not available on these routers. Generally the IP address range seen on these routers is from ###.###.0.2 up to .254 in the last octet. D-Link sets aside a default Dymamic DHCP Pool ranges between .100 and .199 for all of there routers. Leaving the rest for static configurations or adjustment of the DHCP Pool. Also most home users don't have 999 devices connected to the router at one time. Yes the quantity of devices at home is growing now days, however the DIR series routers an handle them with little or no configurations.

The configuration your using is probably not supported on home class routers as we don't see this kind of need for the average home users. Just saying.  :-\
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PacketTracer

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Re: DHCP Pool and subnetting
« Reply #3 on: March 23, 2015, 01:44:24 PM »

Hi,

you could bring some light into the dark by analyzing what kind of DHCP server packets the router sends if configured to use a LAN address range 172.30.100.0/22. Start a sniffer (e.g. Wireshark) on some PC that already has an IPv4 address. Starting a second PC or device will solicit the router's DHCP server to broadcast DHCP offers which you can see with the sniffer on the first PC. Do these DHCP server broadcast packets contain a subnet mask option (option number 1, see RFC2132) of 255.255.252.0 (/22) or 255.255.255.0 (/24)?

I suppose the last case is true (255.255.255.0) and hence DIR-860L will only provide addresses out of range 172.30.100.0/24.

By the way, the manual clearly states on page 53:
Quote
DHCP IP Address Range: Enter the starting and ending IP addresses for the DHCP server’s IP assignment.
Hence, D-Link's support information (The 2nd number is not an IP address.  It is the maximum number of addresses to assign!) seems to be nonsense.

PT
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Kakashi::.

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Re: DHCP Pool and subnetting
« Reply #4 on: March 23, 2015, 05:14:11 PM »

OK, so I'm on hold with support now.  It's been over an hour and I'm on my way to level 3 support.  The first two levels haven't a clue how the netmask relates to a subnet, so they can't begin to understand my question about the DHCP pool.  They keep telling me to set it back to the default settings.  Ugh!  Maybe someone here can answer my question......

Did support provided you with a support case #  or reference number at all?
I agree with PacketTracer regarding the DHCP settings. D-Link has not done DHCP differently in years. If I remember correctly the last consumer router that was able to identify the local network size by using it's subnet mask values, was the DI-604 (a very old model #)


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PacketTracer

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Re: DHCP Pool and subnetting
« Reply #5 on: March 24, 2015, 12:05:07 AM »

... even more simple (instead of using a sniffer): Just look at a DHCP client (e.g. using command "ipconfig /all" inside a command prompt of a Windows PC), if it got a subnet mask of 255.255.252.0 or 255.255.255.0 from your DHCP server.

If DHCP clients have a different view than your router what their network is (172.30.100.0/24 versus 172.30.100.0/22), problems will arise. For example, 172.30.100.255 will be considered a normal unicast address for your router while it is a broadcast address for DHCP clients.

PT
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FurryNutz

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Re: DHCP Pool and subnetting
« Reply #6 on: March 24, 2015, 06:52:15 AM »

Please provide us with screen shot of your Setup/Networking configuration on the 860L.
Adding Screenshots In A Post

OK, so I'm on hold with support now.  It's been over an hour and I'm on my way to level 3 support.  The first two levels haven't a clue how the netmask relates to a subnet, so they can't begin to understand my question about the DHCP pool.  They keep telling me to set it back to the default settings.  Ugh!  Maybe someone here can answer my question.

My Router IP is 172.30.100.1
Subnet mask is 255.255.252.0 or in slash notation, that's a /22 subnet containing 1024 addresses.

The configuration page contains two boxes and defaults to look like this...
DHCP IP Address Range : 100 to 199 (addresses within the LAN subnet)

So, my question is does that 2nd number (199) represent 172.30.100.199 or 172.30.103.199?

They only give us the last octet to work with, so this is a fault of the design team.  It could have been made a whole lot easier to understand.  They could easily calculate the first three octets from the netmask and preface each box with those.   The statement in parenthesis just makes it more confusing.  Surely that really means the last part of the subnet and not the first, otherwise, you could define a /22 subnet but only be able to dole out 254 addresses out of the 1024 addresses in the subnet.
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"Nothing Funny about It...." We are not here to Impress anyone! You have a be a COMPETENT user first to under stand COMPETENT help!

FurryNutz

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Re: DHCP Pool and subnetting
« Reply #7 on: March 30, 2015, 09:12:35 AM »

Any status on this?  ???

I'm still interested in some confirmation.  Support told me they took it to the lab.  The answer to my question was NEITHER.  They told me the first number is the first IP address at the beginning of the subnet, as expected.  The 2nd number is not an IP address.  It is the maximum number of addresses to assign!  So, to assign the maximum number of addresses left in the subnet, you can put a number up to 999 in the 2nd box.  Total design fail for those who wrote the configuration pages.

Make sense to anyone else?
Logged
"Nothing Funny about It...." We are not here to Impress anyone! You have a be a COMPETENT user first to under stand COMPETENT help!