• Finished IP Forwarding..straightforward
• Read Chapter 7 (EIGRP)
• Labbed INE Vol I EIGRP exercises

As for the last bullet, I didn’t really catch anything “new” to be honest with EIGRP, although I did make a mental note to review any of the little tricky parts with using prefix lists. I was able to successfully configure a few for the scenarios, as well as distribute list and various route filtering in EIGRP, but I feel like there’ s a few “gotchas” that I need to review. Not prior to the written, however.

Tomorrow I’ll begin Chapter 8, OSPF. I’ll be on OSPF most likely the next 2 weeks I think. Depends how things go, but maybe longer. Along with being a long chapter on OSPF, I need a lot of practice labbing OSPF. I’d say I’m a proficient CCNP as it goes with OSPF, but not near a CCIE candidate with it. Most likely somewhere inbetween doing the OSPF reading, I will go back and read/lab some layer 2 topics to stay fresh with those, as I have a tendency to forget all the intricacies!

Night night..it’s 4:30am, nobody can say I’m not dedicated.

STP Root port selection (and tiebreaker) process notes:

• There’s 2 ports per segment..a designated port (closest to the root switch), and a root port. The designated port sends out BPDU’s on the segment as it receives them (in 802.1D)..the root port does not send out any BPDU’s with the exception of TCN BPDU’s..another time, another place.

When a switch is trying to decide between two ports in regards to root port selection, it has a few tiebreakers it tries:

• Lowest Root BID (should be the same)
• Lowest Root Path cost (remember, this is root PATH cost..not just the local configured cost)
• Lowest sending BID (BID = Priority + MAC address, so even if the priorities are the default 32,768, the lowest MAC will win)
• Lowest Port ID..NOT just lowest port number. Port ID is a 16 bit field composed of two subfields, Port priority, and Port number. By default, Port ID would be something such as 0×8001 for Port 1/1. 0×80 in hex = 128 (default port priority). 01 equals 1, which is the last section of the interface number. So, by default, with dual links to the same switch, lowest PORT NUMBER wins, but that’s only a part of the Port ID. The other part is priority, which if configured, will cause a sway in the decision process.

So a general rule of thumb could be developed:

-When two separate paths exist to separate bridges, with the same root path cost..the lowest MAC wins by default. Configuring a lower priority on the non-designated switch (the “loser”) would change this, and cause it to become the designated bridge. If multiple redundant links are in place, this will break down further and not only choose a designated SW with the lowest MAC, it will use the interface with the lowest port number.

-When dual links exist to the same bridge, lowest port number wins. Best way to influence this (IMO) is simply adjust STP port cost on a per-interface basis.

Key point to take away: It’s so important to remember that BPDU’s are sent out the designated port as they are received. Knowing this, you know that a downstream (away from the root) switch is making it’s decisions based on RECEIVED information, with some minor exceptions such as cost (assuming that the locally configured cost affects the root path cost enough to make a difference).

I knocked out chapter 6 of LAN Switching, and part of chapter 7. Once I finish Chapter 7, I’m going to read up on a lot of MSTP, and do some STP labs in the next few days. I’d say that I’ll call STP “done” in about 3-5 days, after which it’ll be onto some IP Addressing review, and then EIGRP. If I can maintain this pace, I think I might be able to bump up my written date, which would give me more time to prep for the lab. We’ll see! Stay posted, I may put some STP notes up tomorrow..

In our scenario, we have two switches, SW4, and SW1, which are directly connected with three fast ethernet links. Here’s how STP would select the root port by the book, then we’ll go over what actually happens, and see how we can influence it.

Root port selection (tie breakers)

1. Lowest sending bridge ID
2. Lowest STP port cost
3. Lowest port-priority
4. Lowest interface number

Lowest Sending Bridge ID

Now, in our scenario, the sending bridge is naturally going to have the same BID, because we have 3 links all to the same switch. Remember, the BID is the priority of the bridge (32768 + VLAN ID if system-id extension is enabled), and the MAC address. That being said, regardless, this won’t matter if the links are all to the same switch…

Lowest STP Port cost

This is referring to the outbound port cost. Remember, STP port cost is associated with an interface, NOT the link itself. So, SW4′s interface is 19 by default, which means, all three interfaces tie.

Lowest port-priority

This one confuses people. If we configure a low port priority on SW4..it will NOT influence root port selection. Why? Well, BPDU’s are being sent TO us from SW1, listing the port priorities. You can verify this by debugging and seeing that the port priorities for all three ports are included in incoming BPDU’s.

Lowest interface number

Sad, but true, this is the best we can do! It ends up selecting f0/13, instead of f0/14, or f0/15.

How we can influence root port selection on redundant links

• Adjust the STP port cost (outgoing, remember that) on SW4
• Adjust the port priority on SW1′s links to SW4

At the end of the day, because of the order tiebreakers occur, cost will always override the priority. It makes sense, cost is locally configured, priority is configured on the designated port for that segment. It should be noted, however, that if there is say, a ring topology with 4 switches (such as the INE topology), and you have two links, to two different switches, the process is the same, but root path cost comes into play.

Anyway..off to bed..got some solid labbing done tonight.

1. Pick a technology/area to focus on (ie: Switching)
2. Read the chapter from the CCIE exam cert guide
3. Do corresponding InternetworkExpert Volume I labs
4. Re-read if necessary, read supplemental material (ie: LAN Switching from Cisco Press)
5. Run through INE labs again and play with ‘custom’ scenarios, to make sure I have the configuration side down
6. Skim over the section as needed to stay sharp on certain topics

That’s the general idea, which will repeat for every chapter basically. I’ve read most of TCP/IP Vol I, and will probably go back to it once I get to OSPF, but for now, I want to focus, so since switching is at the beginning nof the CCIE cert guide..and a core area, I will be focusing on that for a while.

Tonight’s progress: I’ve read 40+ pages tonight (still reading) from the CCIE Exam cert guide (4th edition). Nothing really has caught me as being “new”, but I’m moving forward and trying to remember little details that could catch me on the written. In the end, though, I’m just trying hard to keep my momentum. I have a tendency to get hung up on something, or get distracted. I need to make sure I take the written for what it is, a test. I need to pass it, and lab, lab, lab. I want to know these technologies, but I also want to be functional, and I can’t get to a CCIE-level of configuration until I pass this written, which is exactly what I intend on doing. Back to reading..if I get any further I may throw up another post later.

Anyway, I’m getting all of the CAT5 cable made. I’m making it all myself, to save money, and to have the cables at the proper lengths. Nothing annoys me more than seeing a rack with 20 ft of extra CAT5 when that’s not necessary. I kind of understand on serial cables..mine are longer than they need to be also, but let’s at least do a LITTLE cable management people. That being said, there’s gotta be a limit, because if you’re anything like me, you move cables around sometimes, and try new things, which is great. We’re not building a permanent rack here, it’s for training purposes- but using that as a reason to not use cable management is kind of a cop out! That aside, to some extent, I expect CCIE racks to be kind of messy, that’s part of the game..just not overly messy

Back to making the CAT5. I haven’t gotten much studying done since I’ve been busy getting the rack up in order to do IEWB Vol I again. I will surely post more once I make some process whether it be on the rack or my personal studies for the written.

I’m essentially trying to start from scratch as far as I’m concerned, to make sure I know everything that will be tested on the RIGHT way, not just through memorization (which I’m guilty of doing for some topics). Hopefully by hitting those topics again I’ll have a deeper understanding of WHY and not just the WHAT.

I had someone ask me when I’d start putting more tech articles like my QOS series up here. I don’t really know. Unfortunately, the only updates I can really provide after reading is where I stand, and that I plan to continue. Until I start labbing again, I really don’t have too much golden info to share..at least none that you can’t find in a book

For what it’s worth, though- I am going to try to get a couple of good articles up in a timely manner once I can either get my lab setup, or get rolling on the rack rentals. I’d like to aim the articles at a subject that a lot of people have trouble with. Any suggestions?