Hi All, In V1, L3, 3.8 we are asked to ensure that Cat1 takes specific backup links to reach the STP root, Cat4. Cat1 has two equal-cost (FE) paths to Cat3, and two equal-cost FE paths to Cat2, plus the Gig link to Cat2. Cat1 must prefer the "higher-numbered" port on Cat3, then the "higher-numbered" port on Cat2 if the links to Cat4 go down. I took that to mean the Fa0/24 link to Cat2. The restriction is that we can use only one interface command on Cat1.
I solved it by tweaking port-priorities on both Cat2 and Cat3 to make Cat1 prefer the higher ports, and then in order to ensure the port-priority was used in the port selection for the Cat1-Cat2 link, I used my one interface command on Cat1 to make the cost of the Gig link equal to the FE links (200000, this was MST). At that point I had to come up with another way to make Cat3 the first preferred path, so I sweetened the interface cost on Cat3's links to Cat4. This worked as desired when both of Cat1's links to Cat4 were dropped and then *both* links to Cat3 were dropped. Now, I missed the fact that the Cat2 link should be used only if that higher port on Cat3 goes down, not both links on Cat3. So OK, I missed that one. But in the DSG they use the one interface command on Cat1 to tweak the port cost on the preferred link from Cat1 to Cat3, preferring it and leaving the others default. They then did the same priority tweak on Cat2 I did. OK, I see how that accomplishes the goal, *IF* you ignore the fact that the Gig link from Cat1-Cat2 would win next due to lower cost with no consideration for port priority. In the DSG they seem to complete ignore the fact that the Gig link bandwidth between Cat1-Cat2 had to have the cost fixed. Their output for Cat1's 'sh spann' shows: Fa0/1 Desg FWD 200000 Gi0/2 Desg FWD 200000 Fa0/4 Desg FWD 200000 Which is kinda wacky because the Gig links should be listed last and the Cat1-Cat2 link is Gig0/1, not Gi0/2. It seems they doctored the output here and labeled Fa0/2 as Gi0/2 and the DSG makes no mention of Gi0/1. Anyone have any guidance on this? It's really very frustrating to see that the DSG's solutions aren't even feasible within the constraints they dictate without ignoring or "pre-fixing" part of the lab topology. _______________________________________________ For more information regarding industry leading CCIE Lab training, please visit www.ipexpert.com Are you a CCNP or CCIE and looking for a job? Check out www.PlatinumPlacement.com
