Bootcamp with Narbik – Day 5 Comments

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The first part of the morning, we worked on labs. Narbik wanted us to do BGP labs, but there was one big area I wanted to work on while Narbik was on-hand to ask questions: NAT. I’m not too bad with NAT, but I’m not great, either. NAT is one of those topics that I’ve never spent focused time with, and one Narbik’s workbooks includes 13 NAT labs. Here’s a little thing I ran into dealing with the “extendable” keyword.

  • The “extendable” keyword in an IP NAT statement allows you to build multiple NATs to the same inside destination. The Doc CD doesn’t explain this.

    R1(config)#ip nat inside source static 10.1.1.1 200.2.2.2
    R1(config)#ip nat inside source static 10.1.1.1 200.3.3.3
    % 10.1.1.1 already mapped (10.1.1.1 -> 200.2.2.2)
    R1(config)#ip nat inside source static 10.1.1.1 200.3.3.3 extendable
    % 10.1.1.1 already mapped (10.1.1.1 -> 200.2.2.2)
    R1(config)#ip nat inside source static 10.1.1.1 200.2.2.2 extendable
    R1(config)#ip nat inside source static 10.1.1.1 200.3.3.3 extendable
    R1(config)#do show ip nat trans
    Pro Inside global Inside local Outside local Outside global
    — 200.2.2.2 10.1.1.1 — —
    — 200.3.3.3 10.1.1.1 — —

    R1(config)#

  • There were several other NAT labs, including one I need to go back to called “NAT on a Stick”.  I couldn’t get that one working, but I was totally fried when I tried it later in the day.  Plus, there was a lot of us talking and telling stories at that point, late on Friday.  We were all getting pretty burnt.

After a couple of hours in the morning to do labs, Narbik lectured on QoS, focused mostly on the router queueing techniques.  He had discussed SRR and WRR ingress and egress queues on the 3550/3560 platform earlier in the week.  His lecture was a ground-up review of the ToS byte, including IP precedence, Class Selector, Assured Forwarding, and Express Forwarding.  As with his other lectures, he explained the history and evolution of the QoS process, so you kind of understood how the different queueing paradigms came to be.  After dissecting the ToS byte down to the bit level and explaining marking, he broke down priority queueing, custom queueing, CBWFQ, WRED, FRTS (both legacy and MQC), shaping, and policing.  He got right into the nitty-gritty of FRTS, shaping, and policing as well, touching on how to arrive at Bc and Tc values, as well as the various token bucket models.

I’m no dummy when it comes to QoS, but I have to admit to having a much better understanding of the traffic-shaping & policing processes now.  Narbik can really break it down.

I just got home after traveling for most of the last 12 hours.  I’m planning to blog a couple of more articles about the bootcamp later today:  one to cover day 6, and one to cover more general comments about the overall bootcamp experience.

1 comment

  • You rock Ethan!

    I thought I needed another dose of NMC’s QoS lecture but Narbik did a wonderful job on the topic and I no longer felt like I needed a trip to see my friends at NMC afterwards. NMC did something Narbik did not though. They have some great practical examples demonstrating the practical application of QoS with the CLI and verification commands.

    While I loved the commands with verification, I have yet to sit a lab where I had a chance to create use them in the lab. I guess I’m a slow poke.

    Excellent commentary and you are a great class-mate.

By Ethan Banks

Ethan Banks is a podcaster and writer with a BSCS and 20+ years in enterprise IT. He's operated data centers with a special focus on infrastructure — especially networking. He's been a CNE, MCSE, CEH, CCNA, CCNP, CCSP, and CCIE R&S #20655. He's the co-founder of Packet Pushers Interactive, LLC where he creates content for humans in the hot aisle.

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