Kevin Dorrell, CCIE #20765

14 Feb 2008

NMC Lab 07 Redistribution

Filed under: Redistribution — dorreke @ 22:49

I was reading Ethan’s posting about Lab 07 and his useful work on redistribution, and was gratified to find that there was someone else was taking the same path as me, although I think Ethan’s ideas are a bit further down the path than mine.  I rather like the diagrams in the NMC Answer Key, but I really don’t think I would have time to draw anything so sophisticated in a lab test.

Here is my version of the diagram for lab 7 – compare it with Ethan’s.  The idea I shall steal from Ethan from now on is to mark the AD on each circle, perhaps next to its intersection with a router.

(Not sure I shall get the size right here.)

redis0001.gif

What strikes me about this scenario is there are no redistribution loops, but there are two redistribution “kisses” on R1 and R3.  That makes life easier because we don’t need to think too much about filtering.  But we might need to think about the AD’s of the various alternate routes at R1 and R3.

I think we are OK at R1.  EIGRP has an AD of 90 for internal routes, lower than RIP, while it has an AD of 170 for external routes, higher than RIP.  So R1 will prefer the EIGRP side for native EIGRP routes, and RIP for everything else.  Unfortunately “everthing else” includes the two loopback interfaces that came from EIGRP 103 and EIGRP 106.  Clearly the optimal routing for those is through EIGRP.  So we might have to give EIGRP a distance command just to treat those two prefixes with AD 90 as if they were internal to EIGRP 30.

The other kiss point is R3, which touches both OSPF and EIGRP 30.  (We can ignore EIGRP 103, because that was just a cheap trick to inject a remote external into EIGRP and OSPF.)  R3 will route all native EIGRP 30 prefixes through EIGRP because of the AD 90.  If we want the EIGRP 106 prefix to be optimally routed, we might want to distance that at 90 too.

I have still a way to go on this thought process, and I shall probably post-edit this posting.

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