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Resolving Cisco Switch & Router ‘DHCP Server Pool Exhausted-Empty’ Error – Client IP Assignment Failure

Posted in Cisco Switches - Catalyst Switch Configuration

Resolving Cisco Switch & Router ‘DHCP Server Pool Exhausted-Empty’ Error – Client IP Assignment Failure - 5.0 out of 5 based on 1 vote

cisco-switch-router-dhcp-server-conflicts-1In previous articles, we showed how it is possible to configure a Cisco router or Catalyst switch to provide DHCP server services to network clients. Everything usually works without a problem, however there are times when the Cisco DHCP server stops assigning IP addresses and we need to look into the issue and resolve it as quickly as possible. System messages such as ‘POOL EXHAUSTED’, ‘ASSIGNMENT FAILURE’ & ‘address pool Guest-VLAN is empty’ provide some basic information, however further investigation is required to identify the real cause.

Small-sized networks usually have DHCP services configured on their Cisco router, while large-sized networks (with multiple VLANs) assign DHCP services to their backbone layer-3 switch (Catalyst 6500, 4500, 3750 etc). The good news is that configuration and debugging commands are identical for both Cisco Catalyst switches and Cisco routers.


Debugging DHCP Server on Cisco Catalyst Switch & Cisco Router

The first symptoms of DHCP server issues are users nagging that they cannot connect to the network because they haven’t got an IP address, and that’s where the fun begins.

Assuming no configuration changes have been made to the Cisco DHCP server, the best way to troubleshoot the problem is to enable debugging on the dhcp server.  The debug ip dhcp events & debug ip dhcp server packets are useful debugging commands that will help us identify what is happening:

How To Stop CallManager (CUCM) 7, 8, 9, 10.5 with MGCP / H.323 Voice Gateway From Rejecting Anonymous (Hidden Caller-ID) Calls

Posted in Cisco VoIP/CCME - CallManager - Unity Express

How To Stop CallManager (CUCM) 7, 8, 9, 10.5 with MGCP / H.323 Voice Gateway From Rejecting Anonymous (Hidden Caller-ID) Calls - 5.0 out of 5 based on 2 votes

cucm-rejecting-anonymous-caller-id-workaround-1Cisco Unified CallManager (CUCM) and its Voice Gateway relies on the telecommunication provider (telco) to send the correct call details for every incoming call, to allow the system to correctly process it and route it.

One problem many engineers stumble upon is the routing of incoming calls which have their caller-id blocked.  In these cases, quite a few telcos send Anonymous instead of N/A as the Calling Party Number (the number that is calling us), instead of the typical N/A string:

Jan 30 07:42:16.892: ISDN Se0/1/0:15 Q931: RX <- SETUP pd = 8  callref = 0x1075
 Sending Complete      
 Bearer Capability i = 0x8090A3
                Standard = CCITT
                Transfer Capability = Speech 
                Transfer Mode = Circuit
                Transfer Rate = 64 kbit/s
        Channel ID i = 0xA98381
                Exclusive, Channel 1
        Calling Party Number i = 0x0180, 'anonymous'
                Plan:ISDN, Type:Unknown
        Called Party Number i = 0x81, '0298889994'
                Plan:ISDN, Type:Unknown
Jan 30 07:42:16.900: ISDN Se0/1/0:15 Q931: TX -> CALL_PROC pd = 8  callref = 0x9075
        Channel ID i = 0xA98381
                Exclusive, Channel 1
Jan 30 07:42:16.904: ISDN Se0/1/0:15 Q931: TX -> DISCONNECT pd = 8  callref = 0x9075
        Cause i = 0x8095 - Call rejected
Jan 30 07:42:16.912: ISDN Se0/1/0:15 Q931: RX <- RELEASE pd = 8  callref = 0x1075
Jan 30 07:42:16.944: ISDN Se0/1/0:15 Q931: TX -> RELEASE_COMP pd = 8  callref = 0x9075
The problem becomes more difficult to solve when the Voice Gateway is configured to use MGCP (Media Gateway Control Protocol) as the control protocol with CUCM. With MGCP, there is no control in manipulating the Calling Party Number (as opposed to H.323). Despite the fallback, most engineers use MGCP as it dramatically simplifies the configuration on both CUCM and the Voice Gateway.

By default, all CUCM versions from version 6 and above will automatically reject calls when Calling Party Number set to Anonymous, making it impossible for callers with hidden ID to successfully call the company.

Solutions to Stop CUCM From Rejecting Anonymous Caller-IDs

Free Hyper-V eBook - Create, Manage and Troubleshoot Your Hyper-V VMs. Free PowerShell Scripts Included!

Posted in Windows 2012 Server

Free Hyper-V eBook - Create, Manage and Troubleshoot Your Hyper-V VMs. Free PowerShell Scripts Included! - 5.0 out of 5 based on 1 vote

hyper-v-altaro-cookbook-1With the introduction of Hyper-V on the Windows Server platform, virtualization has quickly become the de facto standard for all companies seeking to consolidate their server infrastructure. While we've covered a number of virtualization topics, including Hyper-V installation, Management-Configuration, Hyper-V Backups, Best Practices and much more, this e-Book offered by Altaro is all about getting the most out of your Hyper-V infrastructure.

The Altaro PowerShell Hyper-V Cookbook has been written by Jeffery Hicks - a well known PowerShell MVP, covers a number of very important topics that are guaranteed to help you discover more about your Hyper-V server(s) and help you make the most out of what they can offer.

Topics covered include:

  • Hyper-V Cmdlets - Understand what they are, how to use them and create a Hyper-V virtual machine
  • Discover and display information about your VMs and Hyper-V host
  • Easily Identify VHD/VHDX files
  • Mount ISO files
  • Delete obsolete snapshots and query Hyper-V event logs
  • and much more!

 Don't miss this opportunity and grab your free copy for a limited time!

 BONUS: All PowerShell scripts are included FREE in a separate ZIP file!

Continued: Protecting Enterprise & SMB Networks From Exploits, Hacking & Attacks - Automate System Patching Process - Part 2

Posted in Security Articles

Continued: Protecting Enterprise & SMB Networks From Exploits, Hacking & Attacks - Automate System Patching Process - Part 2 - 4.7 out of 5 based on 6 votes

protecting-enterprise-smb-by-patching-systems-part-2-1In our previous article Protecting Enterprise & SMB Networks From Exploits, Hacking & Attacks By Correctly Patching Systems - Part 1, we analysed the implications of unpatched systems and how hackers use these weaknesses to gain access to data and sensitive financial information. Included in the analysis were two major companies, eBay and a number of famous P.F. Chang's chain of restaurants. We then provided some rules IT Departments, Managers and Administrators should follow in order to secure their systems at the best possible level.

This article continues with a number of important tips to further enhance the security of your company systems and how tools such as GFI's LanGuard can be used to scan, identify, patch and automate the whole process of protecting your systems.

Tips To Enhance The System Security Patching Process (Continued)

Set Your Priorities

Not all computers in the organization need to be patched at the same time. Some computers are more likely to be attacked because they are interface facing. Systems handling e-commerce such as point-of-sales machines and servers holding the customer database are usually more vulnerable to attack. Therefore, prioritize the patching process so that the most critical systems are serviced before others are.

Standardize Your Configurations

If you use many tools and software programs, you will need to track and install several patches. Standardizing your configuration allows all systems to use the same operating system and tools. That results in easier maintenance and tracking of patches and service pack levels. If possible, lock down the configuration - this can easily be achieved in a Windows environment with the usage of Active Directory Group Policies. Enforcing Group Policies ensures users are not able to make any system configuration changes and all security polices are enforced correctly.

Plan Your Patches

How to Install and Configure Windows 2012 DNS Server Role

Posted in Windows 2012 Server

How to Install and Configure Windows 2012 DNS Server Role - 5.0 out of 5 based on 1 vote

Our previous article covered introduction to the Domain Name System (DNS) and explained the importance of the DNS Server role within the network infrastructure, especially when Active Directory is involved. This article will cover the installation of the DNS server role in Windows 2012 Server and will include all necessary information for the successful deployment and configuration of the DNS service. Users interested can also read our DNS articles covering the Linux operating system or analysis of the DNS Protocol under our Network Protocols section.

The DNS Server can be installed during the deployment of Active Directory Services or as a stand-alone service on any Windows server. We'll be covering both options in this article.

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DNS Server Installation via Active Directory Services Deployment

Administrators who are in the process deploying Active Directory Services will be prompted to install the DNS server role during the AD installation process, as shown in the figure 1 below:

windows-2012-dns-server-installation-configuration-1Figure 1. DNS Installation via Active Directory Services Deployment

Alternatively Administrators can select to install DNS server role later on or even on a different server, as shown next. We decided to install the DNS Server role on the Active Directory Domain Controller Server.


DNS Server Installation on Domain Controller or Stand Alone Server

To begin the installation, open Server Manger and click Add Roles and Features. Click Next on Before you begin page. Now choose Role-based or feature-based installation and click Next:


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