moving right along

My wife took the baby with her to another baby shower today. She left me alone so that I could get some studying done. I dunno what happened, but I’m going to call today a wash. I struggled to focus on anything, and stay with it. I made it through another BGP video, and listened to the IPv6 video while I cleaned the apartment up a bit. All in all, I really didn’t get very far.

This next week should be pretty relaxed at work. We’re still holding our breath for some upcoming information, and all of our projects are on hold. On top of that, my boss may be going out of town on a family emergency, and my co-worker is leaving to see his mother off to London for a two year mission. Maria has told me she’s going to allow me every evening this week to study (save for thursday night, when she takes the 8 year old to see the doodle bops).

I am going to get through all of the BGP chapters in the authorized self study guide and videos on Monday. Tuesday will be spent focusing on IPv6/OPSFv3, and Wednesday on Multicast. Thursday will be review and some additional lab work just to solidify everything. I’ll make the decision to take the test this week by Wednesday. Because of the work related stuff, I MAY put it off until early the following week (which would give me one more weekend to study), but we’ll see.

In the meantime, my notes from the BGP section today:
There are two main classes of attributes in BGP: well known and optional.
Within these two classes, there are two sub-classes each:

well known: mandatory and discretionary
optional: transitive and non-transitive

well known mandatory attributes are as_path, origin, and next hop
well known discretionary attributes are local preference and atomic aggregate
optional transitive attributes are aggregator and community
optional non-transitive attributes are MED (multi-exit discriminator)

optional attributes aren’t necessarily understood by all BGP speakers. If a BGP speaker sees an optional transitive attribute that it doesn’t understand, it just forwards that information onto the next peer. Attributes that are optional non-transitive are dropped by BGP speakers that don’t understand them. Chris Bryant mentioned the partial bit for optional transitive attributes. I’d like to see the behavior for all of the above. I just don’t know how likely it is with all cisco gear.

BGP best path selection:
1. use the path with the highest weight (weight is a cisco proprietary attribute)
2. use the path with the highest local preference (this is 100 by default and is the same throughout the AS. can be assigned through the bgp default local-pref # router configuration command, or done on a per-route basis with route maps. route maps are preferred)
3. use the path that was originated locally
4. use the path with the shortest as_path
5. use the path with the best origin code (IGP is preferred over EGP is preferred over ?/incomplete)
6. use the path with the lowest MED (I think I read somewhere that Cisco uses this attribute the exact opposite of the RFC standard. I want to say the command to correct this is bgp bestpath med missing-as-worst.)
7. use eBGP path over iBGP path.
8. use the lowest IGP metric to the BGP next hop
9. use the most recent path
10. use the lowest BGP Router-ID.

I have additional notes, but They work better with diagrams and sample configs. Since I don’t have visio on my laptop yet, I’ll hold off on the diagrams for now. Besides… It’s time to get in the shower and get ready to go out tonight. This was the stipulation set on me getting to study today.

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