> > Got it. I think i just read about a similar thing EIGRP does that for loop > prevention it inserts it's router-id with external routes. Makes sense. > > So normally you would use the distance command with the ip address you are > getting the routes from (say a neighbor) and manipulate the distance (to > prevent routes getting into the routing table), but when working with > external routes you have to refer to the router-id. > > Thanks Derek. > On Jul 27, 2011, at 7:19 PM, Mills, Derek wrote: > >> It's kind of deceiving on which IP you specify in the distance command using >> an ACL with OSPF. It is not based on the next-hop but rather what the ID of >> the router that injected that route into the area. So, on R5 distance is >> applied to R6 router-id, and vice versa on R6. If on R5 you issue show route >> 10.0.0.35 R6's ID should show up (not as next-hop but I forget exactly how >> it is listed). That is how I figure out what IP to use in these type of >> distance commands. >> >> So therefore, the fact that it is coming through R2 doesn't matter...it is >> all about which router is injecting the route into the area. >> >> As you stated, the whole thing could have been avoided by not redistributing >> on R5. I read somewhere that this is a major trap on CCIE lab. Purposefully >> designed to let the student create their own problems when it was not >> necessary, as per the task, to redistribute on both R5 and R6. >> >> Derek >> >> >> -----Original Message----- >> From: Alef [mailto:[email protected]] >> Sent: Wednesday, July 27, 2011 1:03 PM >> To: Mills, Derek >> Subject: Re: [OSL | CCIE_RS] Vol2, Lab8, Task 3.9 - Conflicting LSAID and >> distance manipulation >> >> Hey Derek, >> No, you're right on target. Thanks, that explains it. >> I still don't understand why the distance is applied on R5 for R6 and vice >> versa. Also, should it not be applied to R2 on both R5 and R6 as well ? >> >> Alef >> On Jul 27, 2011, at 6:47 PM, Mills, Derek wrote: >> >>> First of all I am not sure why the DSG shows redistribution from EIGRP on >>> both R6 and R5 since the task states "Redistribute as needed..." without a >>> requirement that if R5 or R6 goes down all IGP routes must still be >>> available. Perhaps such a requirement is stated somewhere else. >>> >>> But, onto your question... >>> >>> I assume the 10.0.0.35, 10.0.0.36, and 10.0.0.38 routes are redistributed >>> into EIGRP AS 1 somewhere south of R6 since they are AS 170 at R6. If you >>> follow the redistribution upstream taking the route R6 EIGRP --> R5 EIGRP >>> --> R2 OSPF these routes end back at R6 as -- yes E2 routes but more >>> importantly as AD 110. When R6 hears these routes advertised as OSPF AD 110 >>> it removes the EIGRP routes with 170 from the routing table. Since those >>> routes are not in the routing table any more, R6 tells R5 to withdraw those >>> routes via EIGRP. So now R5 does not redistribute into OSPF. So now R6 no >>> longer gets an OSPF route for the 10.0.0.x routes and removes the OSPF >>> routes. As such, R6 notices that it has EIGRP routes with AD 170 in the >>> EIGRP topology table and adds them to the routing table. Wow, new EIGRP >>> routes in the routing table so R6 advertises them to R5 and the whole thing >>> starts over. >>> >>> The key takeaway here is that with EIGRP, unlike OSPF, if the route is not >>> in the routing table it will not be advertised to EIGRP neighbors. Same >>> with RIP. >>> >>> Maybe I was way off on your question but hopefully this helps. >>> >>> >>> Derek >>> >>> >>> -----Original Message----- >>> From: [email protected] >>> [mailto:[email protected]] On Behalf Of Alef >>> Sent: Wednesday, July 27, 2011 7:07 AM >>> To: [email protected] IE >>> Subject: [OSL | CCIE_RS] Vol2, Lab8, Task 3.9 - Conflicting LSAID and >>> distance manipulation >>> >>> 3.9 >>> >>> I wondered if the following message from OSPF on Cat4 had anything to do >>> with the /31 mask on the link between R6 and R9 and if it was merely a >>> informational message or actually botched up something. >>> >>> Jul 27 10:13:11.407: %OSPF-4-CONFLICTING_LSAID: LSA origination prevented >>> by existing LSA with same LSID but a different mask >>> Existing Type 5 LSA: LSID 172.30.96.0/31 >>> New Destination: 172.30.96.0/32 >>> >>> But the biggest issue i have is that i don't understand why we have to >>> apply the distance command. When RIP routes are being redistributed into >>> OSPF on R2, they are OSPF E2 external. Fine. When OSPF from Area 124 is >>> being redistributed into EIGRP AS 1 they are being external routes 170. >>> Also fine. Then EIGRP is being redistributed into R6 again, making these >>> also OSPF E2 routes. Why do we need to manipulate anything, as the routes >>> clearly comes from different distribution points (i.e route sources). For >>> some reason they all are originated from R2. I can clearly see it works, i >>> just don't understand how. >>> >>> Not working and without applied distance on R6: >>> IPeR6(config-router)#do sh ip route | i 10.0.0.3[586] >>> O E2 10.0.0.35/32 [110/20] via 172.30.100.2, 00:00:08, Serial0/1/0 >>> O E2 10.0.0.38/32 [110/20] via 172.30.100.2, 00:00:08, Serial0/1/0 >>> O E2 10.0.0.36/32 [110/20] via 172.30.100.2, 00:00:08, Serial0/1/0 >>> IPeR6(config-router)#distance 171 10.0.0.5 0.0.0.0 2 >>> >>> Working and with applied distance 171 to neighbor R5: >>> IPeR6(config-router)#do sh ip route | i 10.0.0.3[586] >>> D EX 10.0.0.35/32 [170/3417088] via 172.30.96.1, 00:00:02, Multilink1 >>> D EX 10.0.0.38/32 [170/3417088] via 172.30.96.1, 00:00:02, Multilink1 >>> D EX 10.0.0.36/32 [170/3417088] via 172.30.96.1, 00:00:02, Multilink1 >>> >>> Any help would be greatly appreciated in making me understand this. >>> Regards, >>> Alef >>> _______________________________________________ >>> 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 >> >
_______________________________________________ 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
