Comments on: Advanced Route Redistribution Scenario (IEWB-RS v4.1 Vol II Lab 2 Task 4.11)

By: jay

jay — Wed, 02 Feb 2011 06:11:21 +0000

Hi Brian,

I just looked at this briefly, regarding that redistribution problem of BGP > EIGRP > OSPF @R5. why cant we just change the AD of BGP routes >OSPF @ R5 redistribution point (e.g. AD 100)? or I am missing something.

This way EIGRP > OSPF routes will be less attractive to other ASBR in Area 0 OSPF.

Will appreciate some answer.

Thanks
Jay

By: sovanvichet

sovanvichet — Mon, 17 May 2010 15:44:23 +0000

awesome explaination, i understand alot more about redistribution.

super brian

By: Audyn Espinoza

Audyn Espinoza — Tue, 07 Apr 2009 17:28:45 +0000

Adrian, to answer your question, it seems to me (i could be wrong) that it should always advertise. If we were to expect the eigrp to advertise only if it was put in RT, then this could cause flapping, because once the eigrp would get added to RT, the router would lose its ospf route from RT and therefore stop redistributing (according to the rule of thumb that says redistribute only routes in RT). it would cause the router to flap endlessly. Also, notice what it says in your output:
Advertised by eigrp 10 metric 10000 1 255 1 1500

By: Audyn Espinoza

Audyn Espinoza — Tue, 07 Apr 2009 17:14:41 +0000

Let’s say we redistribute a rip (AD 120) route into ospf (AD 90). My question is: what tells the router not to use the redistributed route since it has a better AD of 110-ospf, than the original rip route with AD of 120. i know it obviously doesn’t use the ospf route in this case, but just curious as to how the router come to this conclusion.

By: Adrian

Adrian — Sat, 28 Feb 2009 19:17:12 +0000

Something doesn’t quite make sense to me regarding this. I am trying to lab this scenario now and kind of stumbled upon a similar fix to what Brian outlines here.

However Brian suggests “When EIGRP goes to send an update to it’s neighbors it selects the routes from the IP routing table and not the EIGRP topology table”

However when you look at R3′s route for R6′s external EIGRP route, you see the following:

R3#sh ip route 132.1.6.0
Routing entry for 132.1.6.0/24
Known via “ospf 1″, distance 110, metric 20, type extern 2, forward metric 64
Redistributing via eigrp 10
Advertised by eigrp 10 metric 10000 1 255 1 1500
Last update from 132.1.0.2 on Serial0/0, 00:04:13 ago
Routing Descriptor Blocks:
* 132.1.0.2, from 150.1.2.2, 00:04:13 ago, via Serial0/0
Route metric is 20, traffic share count is 1

So following on from what Brian suggests, R5 (whose only neighbour is R3 and only talks EIGRP with him), should therefore have no route to R6. But it does!

R5#sh ip route 132.1.6.0
Routing entry for 132.1.6.0/24
Known via “eigrp 10″, distance 170, metric 2170112, type external
Redistributing via eigrp 10
Last update from 132.1.35.3 on Serial0/0.1, 00:05:10 ago
Routing Descriptor Blocks:
* 132.1.35.3, from 132.1.35.3, 00:05:10 ago, via Serial0/0.1
Route metric is 2170112, traffic share count is 1
Total delay is 20010 microseconds, minimum bandwidth is 1544 Kbit
Reliability 255/255, minimum MTU 1500 bytes
Loading 1/255, Hops 1

R5 has learnt of this prefix seemingly via R;3 EIGRP topology table. Can someone shed light on why this is happening in this case?

By: Jains

Jains — Sat, 14 Feb 2009 16:17:42 +0000

I have abstracted from Mr. Dennis and Mr. Lapukhov articles. hth
Goal #1 Determine the minimum redistribution necessary to obtain full IP reachability as a “safety net”.
Goal #2 Determine what the problems will be. Routing loops must always be fixed. Subotimal, backup routes etc. may not matter.
Goal #3 Verify full IP reachability and save configs.
Goal #4 If there is time try meet the full requirements for the redistribution task. Go back to the safety net (Goal#1-3) if time runs out.

Rule #1 Always prefer Internal Routing Info over External.
Rule #2 Never redistribute a prefix injected from Domain A into Domain B back into Domain A.
Rule #3 A routing protocol selects only routes that are in its routing table as that routing protocol and directly connected routes when it redistributes.

Tool#1 Administrative Distance
Tool#2 Filtering
Tool#3 Summartiztion
Tool#4 Forward/Backward Chaining to determine where a route is lost or changed.
Tool#5 TCL script to verify reahability.

By: parveen jindgar

parveen jindgar — Fri, 05 Dec 2008 17:38:19 +0000

hi Mr Brian it is very nice explanation.But still i need clarification how R1 is learning RIP native routes from R3.

Regards
parveen jindgar

By: BINISHTIMENET

BINISHTIMENET — Wed, 19 Nov 2008 06:40:53 +0000

ROUTE REDISTRIBUTION HAS BEEN MADE SIMPLE.BASIC CONCEPTS HAS BEEN THROUGLY DEFINED

By: BINISH

BINISH — Wed, 19 Nov 2008 06:38:42 +0000

IT WAS REALLY HELPUL.IT NOW IT IS SOMEWHAT CLEAR

By: Implementing Redistribution and Controlling Routing Updates | Defending against lameness since 2008

Thu, 04 Sep 2008 16:57:07 +0000

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