Archive for Brad Hedlund

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Brad Hedlund is a Systems Engineer at Cisco Systems in the U.S. Enterprise Sales Organization and is the editor of Internetwork Expert.ORG. Brad has 12 years experience in Enterprise IT networking and has been CCIE certified for 8 years - CCIE #5530 (Routing and Switching). In August 2007, Brad received recognition as a "Top Engineer" at Cisco.

Re-certified

July 4th, 2008 • Brad Hedlund • 0 comments • Related • Filed Under

I passed the 350-001 Routing & Switching Exam to re-certify my CCIE status.  This was the new 3.1 version of the test with 105 questions.  I can tell you that this test is no walk in the park, they have definitely cranked up the difficulty here.  Word of advice:  Know your OSPF cold!

I have uploaded some of my study notes here:

OSPF

Spanning Tree

Multicast

EIGRP

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Cisco Nexus 5000 announced Today

April 8th, 2008 • Brad Hedlund • 6 comments • Related • Filed Under

What is the new Cisco Nexus 5000? — The industry first switch to deliver unified server I/O, providing Fiber Channel and IP traffic over a single 10G Ethernet port to the server.  Nexus 5000 delivers very low latency wire speed lossless Ethernet service to the server.

A few words about Nexus 7000

March 30th, 2008 • Brad Hedlund • 8 comments • Related • Filed Under

If you are not familiar with the innovation in Cisco Nexus 7000 it’s easy to just dismiss it as “Cisco’s answer to Force10″. The reality is, the Nexus 7000 is much more than just a “me too” 10-gig switch to compete with likes of Force10, Foundry, Extreme, and others — Nexus is a complete technology leap beyond what any other switch vendor has to offer today.

Let’s hit on some of the many points that make Nexus 7000 unique and why this switch is in a league of its own…

CCIE R&S Written Test Study Notes - Part 1

January 6th, 2008 • Brad Hedlund • 1 comment • Related • Filed Under

Well, it’s that time again. Time to re-certify my CCIE R&S certification by passing the written test. To prepare for the re-certification test I am reading from the book CCIE Routing and Switching Exam Guide Volume 3 (a very good book!).

The bottom line is this: The CCIE Routing and Switching written exam is a TOUGH TEST not be taken lightly. Even a veteran CCIE like myself can fail it miserably if you are not careful.

As I read through the book I will take some notes and post them here.
Here is Part 1…

Two routing protocols, Same administrative distance?

December 31st, 2007 • Brad Hedlund • 3 comments • Related • Filed Under

What happens when a router has two routing protocols running and is receiving similar routes from each routing protocol?

Easy question, right? The routing protocol with the lower administrative distance has its routes installed in the routing table (routing information base - RIB).

However, an interesting question that comes up from time to time is this:

What if I configure the administrative distance to be the same for two routing protocols? Will the router install routes from each routing protocol and allow me to load balance traffic?

Outage Story with VTP

December 2nd, 2007 • Brad Hedlund • 4 comments • Related • Filed Under

One of my accounts had an unfortunate network outage that lasted about an hour. This outage was caused by human error with VTP but not in the classic revision number way we have heard about before.

Here is what happened…

Switchport Configurations Explained

November 27th, 2007 • Brad Hedlund • 0 comments • Related • Filed Under

It always helps me to think of the English translation when trying to memorize and understand some the Cisco IOS settings I think are important.

Here are some Cisco IOS switchport configurations translated into English:

‘switchport mode trunk‘ says: “Always trunk on this end, and I will send DTP to attempt to negotiate a trunk on the other end.”

‘switchport nonegotiate‘ says: “Do not send or respond to DTP from this end. Disable all DTP on this port.” (Best used on user access ports, when trunking to non-Cisco switches, when trunking to a router1, or if you are paranoid about fast convergence2)

VLAN Trunking using IEEE 802.1Q

November 27th, 2007 • Brad Hedlund • 0 comments • Related • Filed Under

IEEE 802.1Q (sometimes referred to as 1Q or DOT1Q) is a industry standards based implementation of carring traffic for multiple VLANs on a single trunking interface between two Ethernet switches. 802.1Q is for Ethernet networks only.

Unlike ISL , 802.1Q does not encapsulate the original Ethernet frame.

For Ethernet V2 frames, 802.1Q inserts a new 4-byte field between the SA and TYPE fields of the original Ethernet frame. Since the addition of this new DOT1Q field changes the original frame, 802.1Q also recomputes and rewrites the original 4-byte FCS at the end of the frame.
802.1Q Header Insertion into Ethernet II frame (click image to enlarge)
802.1Q header

VLAN Trunking using ISL

November 26th, 2007 • Brad Hedlund • 3 comments • Related • Filed Under

Inter-Switch Link (ISL) is a Cisco specific implementation of trunking multiple VLANs between two Cisco switches where a single interface will carry traffic for more than one VLAN. ISL was designed to work with Ethernet, FDDI, Token Ring, and ATM.

ISL completely encapsulates the original Ethernet frame by adding a new 26 byte header and new 4 byte FCS trailer. The new ISL header contains a VLAN ID field and QoS priority information (among other things).

ISL Header (click image to enlarge)

ISL HEADER

Things to know about VTP

November 21st, 2007 • Brad Hedlund • 0 comments • Related • Filed Under

Some notes about VTP (VLAN Trunking Protocol):

  • Cisco switches running Cisco IOS store VTP and VLAN information in a separate database stored in Flash, in file called vlan.dat.
  • Cisco switches running CatOS store VTP and VLAN information in the main switch configuration file, stored in NVRAM.
  • VTP information is only transmitted over trunk ports.
  • A VTP client does not need a VTP domain name to be configured to learn VLANs. If the domain name is left blank it will configure itself with the domain name learned from the first advertisement from the VTP server.
  • A VTP advertisement contains the VLANs configured in the domain that are allowed on the trunk, the VTP domain name, and the VTP configuration revision number.
  • If the revision number received in a VTP advertisement is greater than the current stored revision number, the switch will accept the new configuration and overwrite its existing vlan.dat file with the newly received VLAN configuration.
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