Link Layer Discovery Protocol (LLDP)

In a previous post, we examined CDP in great detail as it relates to the CCIE written and lab exam. In this post, we will do the same, but for LLDP.

Fibre Channel Port Types

Link Layer Discovery Protocol (LLDP), standardized by the IEEE as part of 802.1ab, enables discovery of nodes, which in turn facilitates future applications of standard management tools such as Simple Network Management Protocol (SNMP) in multivendor networks. Discovery information includes device identifiers, port identifiers, versions, and other details.

LLDP is unidirectional, operating only in an advertising mode. LLDP does not solicit information or monitor state changes between LLDP nodes. LLDP periodically sends advertisements to a constrained multicast address. Devices supporting LLDP can send information about themselves while they receive and record information about their neighbors. Additionally, devices can choose to turn off the send or receive functions independently. Advertisements are sent out and received on every active and enabled interface, allowing any device in a network to learn about all devices to which it is connected. LLDP and Cisco Discovery Protocol can operate on the same interface.

To enable LLDP globally on your Cisco device, use the global configuration command:

lldp run

To disable LLDP on a specific interface, use the interface command:

no lldp {med-tlv-select tlv receive | transmit

Hold time is the duration that a receiving device should maintain LLDP neighbor information before aging it. Perform this task to define a hold time for an LLDP-enabled device in global configuration mode:

lldp holdtime seconds 

Perform this task in global configuration mode to specify an interval at which the Cisco software sends LLDP updates to neighboring devices:

lldp timer rate 

Understanding the Windows 10 Boot Process

Windows 10 Boot Process

In order to properly troubleshoot Windows 10 startup problems (as you are required to do in exam MD-100 from Microsoft), it is critical that you understand the various phases of the boot process and the components involved. This post provides that information below:

Phase 1 – Preboot

In this phase, the PC’s firmware is in charge and initiates a POST and loads the firmware settings. Once all this works (hopefully), the system identifies a valid system disk and reads the MBR. The system then starts the Windows Boot Manager. This is located here: %SystemDrive%\bootmgr

Phase 2 – Windows Boot Manager

It is the job of the Windows Boot Manager to find and start the Windows loader (Winload.exe). This is located on the Windows boot partition – %SystemRoot%\system32\winload.exe

Phase 3 – Windows Operating System Loader

In this phase, essential drivers required to start the Windows kernel are loaded and the kernel starts to run. The key file here is %SystemRoot%\system32\ntoskrnl.exe

Phase 4 – Windows NT OS Kernel

The kernel loads the system registry hive into memory and loads the drivers that are marked as BOOT_START. The kernel then passes control to the session manager process (Smss.exe).

You can identify the phase you are in visually by what your computer is displaying and the LEDs that are on the system. I will follow up with additional posts on this subject so that you can easily tell what phase you are stuck at – and what you can do to fix things.

Thanks for reading, and be sure to check out my new MD-100 Windows 10 training at CBT Nuggets!