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Category: Dynamic Host Configuration Protocol (DHCP)

Configure Multiple DHCP Option 66 Settings

Recently ran into an issue where a company wanted to use multiple types of VoIP phones that required seperate settings to download their configuration with a vendor – this is usually done in a homogeneous environment via DHCP option 66 settings. (Option 66 is part of IETF RFC 2132 which states that this option uses FQDN or IP address to point to a TFTP server.) In this particular setup only one VoIP phone vendor at a time could be specified in the option 66, so custom settings were going to be needed to make all the other vendors phones work properly. Found that this could be done via DHCP reservation on either their Windows Server 2012 R2 Standard or on their Cisco 871w router, but I am sure their are ways to do it on other vendors equipment (which is outside the scope of this article). So here is how to configure the

Windows Server DHCP Option 66 Reservation

  1. Turn the phone on its back and record the MAC address of the device.
  2. Start the DHCP administrative tool on the server.
  3. Expand the tree into the IPv4 then into the Scope needing the reservation.
  4. Right Click on Reservations and choose “New Reservation…”
    Windows Server DHCP Administrative Tool
  5. Give the new reservation a name, specify IP address and MAC address previously recorded.
    Windows Server DHCP Administrative Tool - New Reservation
  6. Right click on the new reservation and choose Configure Options.
  7. In the Reservation options scroll down to 066 Boot Server Host Name and enter the URL or IP of the vendors configuration server.
    Windows Server DHCP Administrative Tool - Reservation Options
  8. Make sure the vendor has reset the authorization token and factory reset the phone to pull the new reservation and configuration files.

Cisco 800 Series DHCP Option 66 Reservation Setup

Something to remember is that each reservation is treated as its own DHCP pool by the router. (I recommend exporting the configuration file to a local workstation and manually editting if there are more than a couple edits to make.)

  1. Login to router and enter configuration terminal mode:

    Router#configure terminal

  2. Enter the name of the DHCP pool as follows:

    Router(config)#ip dhcp pool Pool_Name

  3. Enter the IP address of the device:

    Router(dhcp-config)#host 192.168.1.100 255.255.255.0

  4. Enter the MAC address of the device:

    Router(dhcp-config)# hardware-address AABB.CCDD.EEFF

  5. Enter Option 66 information:

    Router(dhcp-config)#option 66 ascii http://vendor.url/configuration.xml

  6. Enter Default Gateway:

    Router(dhcp-config)#default-router 192.168.1.1

  7. Enter DNS servers:

    Router(dhcp-config)#dns-server 8.8.8.8 8.8.4.4

  8. Make sure to copy the running configuration to startup configuration:

    Router(dhcp-config)#end
    Router#copy running-config startup-config

  9. Clear the current DHCP bindings to make sure the phone will grab the correct address:

    Router#clear ip dhcp binding *

  10. Make sure the vendor has reset the authorization token and factory reset the phone to pull the new reservation and configuration files.

That is all there is to it. Enjoy a multi-vendor VoIP environment. If you need help configuring your Windows Server or Cisco IOS based router please contact us for support.

Configure Server 2012 VPN Connections

Here are the basics to configure Server 2012 VPN connections to the local network. This is preferred by Farmhouse Networking over a third party vendor software or router based solution because of its native functionality and integration with domain credentials – think Single Sign On (SSO) or one password to access it all.

Install the Routing & Remote Access Service (RRAS) Role

1. Start the Server Manager
2. Click Add Roles and Features from the Manage Menu
3. On Add Roles and Features wizard begins and click Next
4. Select the Role-based or feature-based installation option and click Next
5. If you have more than one server managed via the server manager console, then select the desired server you’d like to install Routing and Remote Access on
6. From the Roles lists select Remote Access, click Add Features on the popup window
7. Click Next
8. Click Next as no additional features are needed
9. Select DirectAccess and VPN (RAS), click Next
10. Click Next
11. Accept default selections and click Next
12. Click Install
13. When installation is completed, click Close

Initial Server 2012 VPN Configuration

1. From the Server Manager screen, click on the warning sign and click ‘Open the Getting Started Wizard’
2. On Configure Remote Access, click Deploy VPN Only.
3. From the Routing and Remote Access MMC, right-click on the server and click ‘Configure and Enable Routing and Remote Access’
4. Click Next on the wizard
5. Select Custom Configuration
6. Select VPN access
7. On completion, click Finish
8. Click Start service to start the RRAS, then wait for the service to startup.

Add IPv4 IP Address Range

1. From the Routing and Remote Access MMC, right-click on the server and click ‘Properties’
2. Under properties screen click IPv4 tab, select Static address pool, click Add and enter the desired IP address range on the windows popup
3. Click OK to close

Open Ports on Network Firewall

For compatibility, here are the ports to open for both Point-to-Point Tunneling Protocol (PPTP) and Layer 2 Tunneling Protocol (L2TP) on the network firewall:

500, 1701, 1723 & 4500

Need to open IP Protocol 47 also on the router to allow PPTP Passthrough.

(Note: On SonicWall routers, you will need to create address objects for internal / external IP addresses, service group containing all the above ports, NAT rule for PPTP traffic and firewall rule allowing the service group from the external to the internal IP address.)

Enable Remote Access for users

Open the properties of a domain user account via Active Directory Users and Computer MMC. Click on Dail-in, under Network Access Permission click Allow access

If your company is in need of a robust and simple to use Windows Server 2012 VPN connection to your LAN resources, then contact us for assistance.

Command Line Configuring TCP/IP Addressing

Recently had an issue where a client needed to have their IP address statically assigned and the thought came to mind that my Remote Monitoring software was able to give me command line access, so I thought I would try configuring TCP/IP addressing via the command line interface and not have to interrupt the end users work. Here is how to get it done:

netsh interface ip set address name="Local Area Connection" static [static IP] [subnet mask] [default gateway] 1

That gets the IP address, subnet mask and default gateway – so what about static DNS? Here is the next step:

netsh interface ip add dns name="Local Area Connection" addr=[DNS address #1]

netsh interface ip add dns name="Local Area Connection" addr=[DNS address #2] index=2

If your company need remote assistance or help planning / maintaining / configuring TCP/IP addressing in your network infrastructure, then contact us for assistance.

Dynamic Host Configuration Protocol Rebuild – DHCP Repair

Had a school that reported that several computers were unable to get new IP addresses and therefore unable to logon to the domain. Their DHCP was handled by their local domain controllers with each server handling half of the /23 address space which equates to 510 total usable address for local devices on that subnet. Checked DHCP on the primary domain controller and found that their were 450+ BAD ADDRESS items in the scopes lease, so deleted these to free up space. Checked on the secondary domain controller and found that the DHCP server had a blue exclamation point on it which meant that the scopes leases were exhausted. Tried to look at the lease list and it had a red X on it and no entries listed. So how to fix this? Here is a method that I found to perform a DHCP repair / rebuild in this kind of situation:

How to Perform DHCP Repair / Rebuild

1. On the Windows DHCP server open a command prompt with administrative privileges
2. Type the following command to backup all the DHCP configurations settings:

netsh DHCP server dump>DHCPdump.txt

3. Stop the DHCP server service
4. Delete the contents of the c:\Windows\System32\DHCP folder including all subfolders.
5. Start the DHCP server.
6. In the same administrative command prompt type to restore the DHCP configuration settings:

netsh exec DHCPdump.txt

7. Then in the administrative command prompt type to run diagnostics on the DHCP scope:

netsh DHCP server initiate reconcile

8. Open up the DHCP administrator tool and check that all of the options are intact and the Reservations are present.
9. In the same administrative command prompt type to export all DHCP information to a file:

netsh DHCP server export DHCP.txt all

10. Copy this file and the DHCPdump.txt file somewhere else as a backup.

This DHCP repair worked immediately and client workstations started to register for DHCP leases again.
If your company is using Windows DHCP Servers or need help with a DHCP repair / rebuild, then contact us for assistance.

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