For the past couple of weeks I've been whacking out various CCIE practice labs. I've also been suffering various degrees of euphoria and depression, depending upon how badly I was suckered by the redistribution problems.
After a particularly long and frustrating day with the Cisco ASET Lab #1, it suddenly occurred to me that there are many ways to do things, and for some reason, I've been overlooking what may be the best way to deal with redistribution. Those of you who have worked these practice labs know how it goes. You read through the lab, then you start configuring. Step 1 - set up OSPF Step 2 - set up RIP Step 3 - redistribute between OSPF and RIP Step 4 - set up EIGRP Step 5 - redistribute between EIGRP and RIP Step 6 - set up IS-IS Step 7 - redistribute between IS-IS and OSPF Step 8 - scream in anguish as you discover that your routing tables have turned to trash and half your network becomes unreachable. ASET #1 was particularly nasty in how it accomplished Step 8 Which brings me to the topic of this post. CCIE's and folks who've been through the Lab without success - what do you think of this approach: 1) do NOT do any redistribution anyplace until all routing protocols have been configured everywhere. Yes, I know that typically you have a section with several steps, one of which is redistribution. But mark your place and return after the IGPs are up and running and all routes for a particular IGP are where they should be. 2) return to the first redistribution task. Before configuring anything, refer to your diagram ( you DO write out a nice diagram, don't you? ) and ask yourself: "after I do one way redistribution, what routes will appear where?" 2a) Consider how administrative distance might change things 2b) Follow the redistribution to it's extreme. For example, if you redistribute EIGRP into OSPF, what routers will these routes end up on? Will there be any implications to the routing tables? 3) repeat step 2 for every redistribution point, each time considering the totality of the contents of the redistributed routes. So if you have redistributed IS-IS into OSPF, how do those redistributed routes flow through the OSPF domain? 4) Keep an eye out for things like split horizon 5) every step along the way, consider what routers need to see what routes. Watch for situations where necessary routes do not appear. ( you have probably trashed it because of overzealous filtering. ) 5) If problems occur, such as a routing loop, trace back where the problem route came from, and see what can be done to evade the problem. Summary routes work wonders sometimes. So do route-maps and distribute lists. Re-reading this, I see that this topic does not lend itself well to text. I can say with certainty that I now have a very clear vision of redistribution methodology. I've tested it three times now with different labs, and I believe I am solving the redistribution problems more quickly than ever. I hope that I have painted enough of a picture that some of you can fill in the rest. Chuck -- TANSTAAFL "there ain't no such thing as a free lunch" Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=66306&t=66306 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
