From: Xiao Li (lixiao00@hotmail.com)
Date: Thu Nov 01 2007 - 07:46:48 ART
Hi, I was doing core work book lab 6 this afternoon and the redistribution really got me hard. I thought of using distance to limit route feed back is convenient and reliable.. it proves me wrong. OSPF, RIP , EIGRP are mutually redistributed on R3, R4 and R5.. so I apply the golden rules: from lower ad to higher ad, no worries, routes will never get feed back to the lower ad domain because the higher ad route will not get in the routing table at the other redistribution point... checked from higher ad to lower ad, use distances command to lower down the ad for the redistributed routes.. checked I thought that should more or less has done the magic automatically.. but I keep getting routing loops for routes coming from the rip domain.. after some time i realized that whenever a route is added in the rip domain, the route is looping between r3, r4, r5.. further i realized that the route propagation in RIP is much slower than redistributing from rip->eigrp100->eig!
rp200->rip.. so when the route is ready to be redistributed from eigrp200->rip at R4, the higher ad rip route (as compared to eigrp external) did not reach R4 yet to stop it.. and I was careless enough to put "redistribute eigrp 200 metric 1" under rip, which make it a prefer rip route from R3 since metric is low. The solution guide does use metric 10 on R4 and R5, but on R3, it uses metric 1 also. I am thinking that this can also cause a problem when bb2 advertise new rip routes or reload, as r5->rip->ospf->eigrp200->eigrp100->r3 could still go faster than R5->rip->R3. I did not have a time to test this out though.. will try that later..
Changing the metric to a higher value when redistributing to rip will work around this issue, but it does not seem to be a complete solution. The fact is: for a short period of time, the routes are feed back to rip domain where is originates. Another problem is: the rip metric can't really go too high.
I can't think of a way to use tag either.. tags are overridden, and in this lab there is so many point of redistribution. Is there a way to append the tag like the AS path does in bgp? Or any other way to better address this problem? Thanks for the advise.
Best regards,
Li Xiao
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