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ITGround >> Proof of concept building/distribution layer


6/17/10 10:31 AM
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big_slacker
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I posted this on FB but forgot here, and this is the target audience after all. I was teaching a CCNP class this/last week and we were going over some designs. One thing mentioned was understanding how spanning tree despite being good for loop prevention can result in sub-optimal path selection and slow failover in a redundant network with all L2 links to the access layer AND between distribution switches. Especially when its paired with HSRP at the distribution layer.

STP can actually be blocking a port near the access layer causing traffic to hop from there to the distribution switch over to another distribution switch before it gets to the core. This might not be a big deal in low traffic networks since its just switching, but could eventually choke a gig link in higher traffic/oversubscribed situations and certainly when link failure occurs it can result in 30-45 seconds of packet loss before STP reconverges. Thats with regular STP, not RSTP.

Anywho, one design I think is pretty slick is to have L2 redundant links to the access layer and a L3 (routed port) between the distribution switches. This should lead to both L2 links forwarding and assuming HSRP at the distribution layer matches the STP root the best path is always gonna be used. Add in RSTP for fast convergence. Add in HSRP tracking the access layer links with millisecond timers for fast convergence.

The point? Sub second convergence around any link failure in a redundant network. Here is a test output to show that, note that we only lose one packet when the link goes down. I can post configs if anyone cares.

DIST_1(config)#int po2
DIST_1(config-if)#shut
DIST_1(config-if)#
*Mar 1 01:30:33.469: %TRACKING-5-STATE: 1 interface Po2 line-protocol Up->Down
*Mar 1 01:30:33.477: %HSRP-5-STATECHANGE: Vlan50 Grp 1 state Active -> Speak
*Mar 1 01:30:33.502: %LINEPROTO-5-UPDOWN: Line protocol on Interface Port-channel2, changed state to down
*Mar 1 01:30:33.519: %HSRP-5-STATECHANGE: Vlan10 Grp 1 state Active -> Speak
*Mar 1 01:30:33.569: %HSRP-5-STATECHANGE: Vlan30 Grp 1 state Active -> Speak
*Mar 1 01:30:34.257: %HSRP-5-STATECHANGE: Vlan50 Grp 1 state Speak -> Standby
*Mar 1 01:30:34.341: %HSRP-5-STATECHANGE: Vlan10 Grp 1 state Speak -> Standby
*Mar 1 01:30:34.442: %HSRP-5-STATECHANGE: Vlan30 Grp 1 state Speak -> Standby
*Mar 1 01:30:35.423: %LINK-5-CHANGED: Interface FastEthernet0/21, changed state to administratively down
*Mar 1 01:30:35.431: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/21, changed state to down
*Mar 1 01:30:35.440: %LINK-5-CHANGED: Interface FastEthernet0/22, changed state to administratively down
*Mar 1 01:30:35.448: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/22, changed state to down
*Mar 1 01:30:35.473: %LINK-5-CHANGED: Interface Port-channel2, changed state to administratively down
-------------------------------------
R7#ping 10.1.40.8 size 18000 repeat 100000

Type escape sequence to abort.
Sending 100000, 18000-byte ICMP Echos to 10.1.40.8, timeout is 2 seconds:
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!.!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!.
Success rate is 99 percent (937/939), round-trip min/avg/max = 16/17/48 ms
6/20/10 9:51 AM
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JOB
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Hey BS - Did you re-take your CCIE yet?
6/20/10 11:49 AM
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big_slacker
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Thursday is the day!
6/20/10 5:56 PM
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JOB
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Oh! best of luck. I admire your persistence. Fingers crossed for you buddy.
6/20/10 6:46 PM
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big_slacker
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Last week I was hanging out with a triple ccie (R&S, voice, security) who is working on his 4th. He said the secret is knowing your stuff well enough that you belong in the lab and then taking it till you get a test that fits you.

At first it sounded lazy/passive, but knowing this guy he is anything but. He meant you can be super sharp but still get off the wall tasks, get off track troubleshooting something, etc...

I feel better about this attempt and my prep for it than the last 2.
6/20/10 7:52 PM
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JOB
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Yeah man, are you doing it for work - or just to boost your profile? I'm just studying for the CCNA at the moment - Hope to cover it all over this summer before I go back to uni. It doesn't seem too bad - I already have networking theory down before it, so it's just getting used to the IOS config.

Best of luck again man. Hopefully you'll get it this time.
6/21/10 9:59 AM
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big_slacker
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Its a work thing, my employer bills me out based on cert level as well as teaching classes that require the certs. With that said, I've learned a TON I didn't know and the IE on a resume is a big boost as well.

Worth all the hassle and hours? I'm not convinced yet, but I'm past the point of no return anyway. :D
6/21/10 11:33 AM
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JOB
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Fuck it man, go for it :D At least, it would be a great backup plan if you ever lost your job.
6/25/10 1:43 AM
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JOB
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How did you do buddy?
6/25/10 8:13 PM
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big_slacker
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76. Re-read is pending. I triple verified 83 points, I have no idea why I didn't pass this time.
6/26/10 5:16 AM
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JOB
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Hm.. Is it 80% for a pass? When do they get back to you? They don't dick around when it comes to giving that out..
6/26/10 8:04 PM
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big_slacker
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80% is the pass mark. The way the grading works is the next time zone over runs a script. If the script comes up matching you get the score, if not the grader looks at the config and sees if it works or not. Thing is, the grader might not be an expert in all tracks they grade. The re-reads likely go to an expert, or so the theory goes.
6/29/10 1:37 PM
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JOB
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Ah, sorry man :( Isn't this the second time you've come really close to passing?
6/30/10 10:57 AM
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big_slacker
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Yeah, I was closer this time than last. No big deal, its inevitable at this point with where I'm at in terms of prep.

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