Articles in the Networking category

Blow Away Your Cisco Catalyst Configuration

Posted on June 14, 2007 in Networking

If you've ever needed to reset a Cisco Catalyst switch to it's factory default (locked out, perhaps?), you've probably spent some time digging around on Cisco's web site. The Catalyst password recovery procedure starts off by reseting the Catalyst to it's original factory settings. Below, I'm going to give you …
Configure DHCP Option 82 on Cisco Catalyst Switches Safely

Posted on June 13, 2007 in Networking

Configure Cisco Catalyst DHCP snooping and Option 82 safely with a small pilot VLAN, explicit trusted uplinks, verification commands, and a rollback plan.
The Annoyance of 'show config'

Posted on June 11, 2007 in Networking
How many times has this happened to you?
```
SLAP#write memory
startup-config file open failed (Device or resource busy)
```
If you work in an environment where multiple users have enable access on Cisco devices, you've probably seen it more than once. This particular error is caused when another user has …
How Do You Want Your DS3? Scrambled?

Posted on May 28, 2007 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 Reasons You Should Be Using Rapid Spanning Tree (802.1w)

Posted on May 25, 2007 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 …
Controlling Peer-to-Peer (P2P) Traffic with Cisco NBAR

Posted on May 22, 2007 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 …
Top 10 Protocols on a Residential Broadband Network

Posted on May 19, 2007 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 …
T1 / T3 Alarms

Posted on May 18, 2007 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 …
Using ACLs to Block NetBIOS Traffic on Cisco Catalyst Switches

Posted on May 13, 2007 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 …
Using Cisco NBAR to Monitor Traffic Protocols on Your Network

Posted on May 12, 2007 in Networking

Many network administrators already know how to use tools like Cacti or MRTG to monitor the usage on their network links. (If you don't, let me know and I'll show you how.) Unfortunately, those tools only reveal part of the story. They show you how much traffic is traversing a …
What is NetBIOS?

Posted on May 09, 2007 in Networking
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<table class="protocol_basics" align="right">
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<th colspan="2">
```
Protocol Basics
```
</th>
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</tr>
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Layer:
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Session
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Transport:
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<acronym title="Transmission Control Protocol">TCP</acronym>, <acronym title="User Datagram Protocol">UDP</acronym>
```
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Port(s):
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137, 138 …
Choosing Between RADIUS And TACACS+

Posted on April 24, 2007 in Networking

Deciding whether to use <acronym title="Remote Authentication Dial-In User Service">RADIUS</acronym> or <acronym title="Terminal Access Controller Access Control System Plus">TACACS+</acronym> for <acronym title="Authentication, Authorization, Accounting">AAA</acronym> functionality on a Cisco-based network seems straight-forward. After all, if the network uses Cisco, shouldn't the AAA …
UDLD In Radio-Based Metro Ethernet Rings

Posted on April 17, 2007 in Networking

<acronym title="UniDirectional Link Detection">UDLD</acronym> is a Cisco protocol designed to detect and disable unidirectional links in Ethernet (fiber or twisted-pair). In the case of a radio-based Metro Ethernet ring, UDLD goes the extra mile in preventing Spanning-Tree loops and user service interruption.

In this simple network of …
Implement a Sensible Naming Policy in Cisco IOS

Posted on April 10, 2007 in Networking

Network configuration names are not decoration. They are operational metadata. When something is broken at 2:00 a.m., the difference between ACL-EDGE-IN and access-list is not aesthetic. It is the difference between narrowing the blast radius quickly and spelunking through hundreds or thousands of lines of Cisco IOS configuration …

Articles in the Networking category

Loss of Signal (LOS)