Articles in the Networking category

  1. What is DHCP Option 82?

    Posted on in Networking

    Light bulb 2 (Photo by brokenarts)To put it simply, DHCP Option 82 is the "DHCP Relay Agent Information Option". Wasn't that easy?

    Option 82 was designed to allow a DHCP Relay Agent to insert circuit specific information into a request that is being forwarded to a DHCP server. Specifically the option works by setting two …

  2. How Do You Want Your DS3? Scrambled?

    Posted on in Networking

    DS3 (also known as T3) scrambling is not an issue that comes up very often. It's something every network administrator should know about, though. After all, it just might save your bacon.

    Some physical layer protocols depend on the transition from 1 to 0 in a frame to maintain clocking …

  3. 3 Reasons You Should Be Using Rapid Spanning Tree (802.1w)

    Posted on in Networking

    Most network administrators should be familiar with Spanning Tree Protocol (STP; IEEE 802.1D). <acronym title="Spanning Tree Protocol">STP</acronym> is tasked with ensuring there are no loops in a bridged network. Unfortunately, STP is an older protocol and doesn't quite mesh with today's high speed networks. Here are …

  4. Controlling Peer-to-Peer (P2P) Traffic with Cisco NBAR

    Posted on in Networking

    Is your network bandwidth being consumed by Peer-to-Peer (P2P) traffic? (Hint: If you don't know, it's time to fire up NBAR and do a little investigating.) One way to stop P2P traffic is to use an access-list to block traffic on the well-know P2P ports. Unfortunately, many P2P technologies no …

  5. Top 10 Protocols on a Residential Broadband Network

    Posted on in Networking

    I recently wrote about using Cisco's NBAR to investigate what protocols were in use on your network. I thought it might be interesting to take a look at the top 10 protocols on a residential broadband network. If you're running a large network, or planning a large network, perhaps this …

  6. T1/T3 Alarms

    Posted on in Networking

    The following is a list of alarms you may receive on your T1 or T3 (or E1/E3) interface. Where applicable, troubleshooting hints are included.

    Loss of Signal (LOS)

    A Loss of Signal (LOS) alarm indicates that the interface is not receiving a valid T1 or T3 signal. This is …

  7. Using ACLs to Block NetBIOS Traffic on Cisco Catalyst Switches

    Posted on in Networking

    In a Metro Ethernet network, the possibility exists for a lot of NetBIOS broadcasts if your users are connecting directly to the ring rather than through a firewall. My first assumption was that most users would have a firewall, but this is really only guaranteed in the case of business-class …

  8. What is NetBIOS?

    Posted on in Networking

    <table class="protocol_basics" align="right">
    
    <tr>
    
    <th colspan="2">
    

    Protocol Basics

    </th>
    
    </tr>
    
    <tr>
    
    <td>
    

    Layer:

    </td>
    
    <td>
    

    Session

    </td>
    
    </tr>
    
    <tr>
    
    <td>
    

    Transport:

    </td>
    
    <td>
    

    <acronym title="Transmission Control Protocol">TCP</acronym>, <acronym title="User Datagram Protocol">UDP</acronym>

    </td>
    
    </tr>
    
    <tr>
    
    <td>
    

    Port(s):

    </td>
    
    <td>
    

    137, 138 …

  9. Cisco Announces Flash Defects

    Posted on in Networking

    Cisco Systems, Inc.Cisco released several field notices today regarding manufacturing defects which reduce the reliability of certain Compact Flash and ATA Flash disks.The flash disks, manufactured between May 2005 and October 2006, may fail, preventing systems that rely on IOS images stored on them from rebooting.

    A ROMMON upgrade resolves the …

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