Secondary Subnet

[Jeremy Bullock]

We are experiencing a 100% DHCP use on one of our subnets/VLANs. If I add a secondary subnet to that VLAN, will the client attempt to get a primary address, fail and then use the secondary subnet for an IP?

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[Darrin Green]

The short answer is no. What DHCP Subnet?

Post by Jeremy Bullock
We are experiencing a 100% DHCP use on one of our subnets/VLANs. If I
add a secondary subnet to that VLAN, will the client attempt to get a
primary address, fail and then use the secondary subnet for an IP?

--
Darrin E. Green
Senior Technical Support Specialist
Dallas Area Rapid Transit
1401 Pacific Avenue
Dallas, Texas 75202
Ph 214-749-3173
Fax [phone]
Email ***@dart.org

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[Shuttlesworth, James]

It can - but its actually a question of how your DHCP server is setup rather than the VLAN issue the two subnets need to be linked for that behavior - different DHCP servers use different terms for that behavior. What is the DHCP server?


------------------------------
James Shuttlesworth
Ursinus College
Information Technology
***@ursinus.edu

From: Jeremy Bullock [mailto:***@uca.edu]
Sent: Wednesday, August 21, 2013 10:44 AM
To: Enterasys Customer Mailing List
Subject: [enterasys] Secondary Subnet

We are experiencing a 100% DHCP use on one of our subnets/VLANs. If I add a secondary subnet to that VLAN, will the client attempt to get a primary address, fail and then use the secondary subnet for an IP?

* --To unsubscribe from enterasys, send email to ***@unc.edu<mailto:***@unc.edu> with the body: unsubscribe enterasys ***@ursinus.edu<mailto:***@ursinus.edu>

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[Markus Kaiser]

This might help in case of Win DHCP:

http://technet.microsoft.com/en-us/library/dd759168.aspx

Kind regards,

Markus


___________________________

On 21.08.2013, at 16:47, "Shuttlesworth, James" <***@ursinus.edu> wrote:

It can – but its actually a question of how your DHCP server is setup
rather than the VLAN issue the two subnets need to be linked for that
behavior – different DHCP servers use different terms for that behavior.
What is the DHCP server?





------------------------------

James Shuttlesworth

Ursinus College

Information Technology

***@ursinus.edu



*From:* Jeremy Bullock [mailto:***@uca.edu <***@uca.edu>]
*Sent:* Wednesday, August 21, 2013 10:44 AM
*To:* Enterasys Customer Mailing List
*Subject:* [enterasys] Secondary Subnet



We are experiencing a 100% DHCP use on one of our subnets/VLANs. If I add
a secondary subnet to that VLAN, will the client attempt to get a primary
address, fail and then use the secondary subnet for an IP?

- --To unsubscribe from enterasys, send email to ***@unc.edu with
the body: unsubscribe enterasys ***@ursinus.edu


- --To unsubscribe from enterasys, send email to ***@unc.edu with
the body: unsubscribe enterasys ***@enterasys.com

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[d***@fhsu.edu]

I do this by creating a superscope in my Winders (sic) DHCP server. First
add the secondary address to your vlan interface, then create your DHCP
scope & merge into a superscope. Bam, you're good to go... assuming any
explicit permit ACLs have also been modified as well...

Derek Johnson | Data Communications Coordinator
FORT HAYS STATE UNIVERSITY
415 Lyman Dr. TH 101, Hays, KS 67601
(785) 628 - 5688 | ***@fhsu.edu





From: "Jeremy Bullock" <***@uca.edu>
To: "Enterasys Customer Mailing List" <***@listserv.unc.edu>
Date: 08/21/2013 09:44 AM
Subject: [enterasys] Secondary Subnet



We are experiencing a 100% DHCP use on one of our subnets/VLANs. If I add
a secondary subnet to that VLAN, will the client attempt to get a primary
address, fail and then use the secondary subnet for an IP?
--To unsubscribe from enterasys, send email to ***@unc.edu with the
body: unsubscribe enterasys ***@fhsu.edu

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[Stephen Loeckle]

I've fixed this issue at a number of customers by doing one of two things, depending on the installation. You can create a new vlan on the network with a new set of IP addresses, then create a new scope on your DHCP server then setup ip helpers in your layer 3 switch so DHCP requests get forwarded to your single DHCP server.

interface vlan.0.370
ip address 10.1.7.1 255.255.255.0 primary
no shutdown
exit
interface vlan.0.380
ip address 10.1.8.1 255.255.255.0 primary
ip helper-address 10.1.7.10
ip helper-address 10.1.7.11
no shutdown
exit

Or, the easier method IMHO, especially if you don't have a layer 3 switch, is to just change the subnet mask on the network. For example, if you are using 255.255.255.0, you can change it to 255.255.254.0 to double your ip address space or 255.255.252.0 to quadruple your ip address space. Do calculations before you do this so you know what new IP addresses are available to you. For example, if you're using 192.168.1.0 as your network and you expand the subnet mask from 255.255.255.0 to 255.255.254.0, you must use 192.168.0.0, not 192.168.2.0. In CIDR terms, 192.168.1.0/24 expanded to /23 becomes 192.168.0.0/23. Does this make sense? I'll be happy to help if you need clarification or calculations.

Stephen Loeckle
Lucid Networks

From: Jeremy Bullock <***@uca.edu<mailto:***@uca.edu>>
Reply-To: "***@listserv.unc.edu<mailto:***@listserv.unc.edu>" <***@listserv.unc.edu<mailto:***@listserv.unc.edu>>
Date: Wednesday, August 21, 2013 9:44 AM
To: Enterasys Customer Mailing List <***@listserv.unc.edu<mailto:***@listserv.unc.edu>>
Subject: [enterasys] Secondary Subnet

We are experiencing a 100% DHCP use on one of our subnets/VLANs. If I add a secondary subnet to that VLAN, will the client attempt to get a primary address, fail and then use the secondary subnet for an IP?

* --To unsubscribe from enterasys, send email to ***@unc.edu<mailto:***@unc.edu> with the body: unsubscribe enterasys ***@lucidnetworks.net<mailto:***@lucidnetworks.net>

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