From: David Lonnie (david.lonnie@gmail.com)
Date: Sun Jun 01 2008 - 23:51:56 ART
Hi,Paul.
It's a very excellent lecture.
I lab it according to your description.
Without filtering,there will be really some problems.
I think filtering routes learned from ospf is enough, when restributing
eigrp to ospf domain.
There won't be loop whithin eigrp domain,because of AD of intenal(90) < AD
of external (170).
Is it?
On Mon, Jun 2, 2008 at 5:45 AM, Paul Cosgrove <paul.cosgrove@heanet.ie>
wrote:
> If OSPF learns external prefixes from another domain with a higher AD, then
> you can see problems occuring around mutual redistribution, whether or not
> it is from EIGRP.
> Consider three OSPF routers A, B and C. A connects directly to both B and
> C.
> - each router has a loopback in ospf
> - A also runs RIP and redistributes RIP learned routes (e.g. 1.1.1.0/24)
> into OSPF. - B & C perform mutual redistribution into the same EIGRP domain.
>
> C's link to the rest of the OSPF network goes down
> - C still has a path to the RIP domain via EIGRP to B, then OSPF from B to
> A.
> - C redistributes these EIGRP routes back into its OSPF process.
>
> C's link to the rest of the OSPF network is restored.
> - C is sourcing an OSPF E2 route for 1.1.1.0/24
> - A is also sourcing an OSPF E2 route for 1.1.1.0/24
> AD does not help in this case, as both OSPF routers learn the same prefixes
> from protocols with higher ADs, so both generate the same type of LSA.
>
> OSPF routers will select one of these as the best route, but if C's route
> is selected a permanent routing loop will be created. The order of
> configuration, topology changes, or simply clearing the OSPF process can all
> trigger this problem. You can prevent it by making sure the originating
> protocol on A has a lower AD than OSPF for its own routes, or by using
> filtering (such as with tags).
>
> Paul.
>
>
> adedayo ademuyiwa wrote:
>
>> HI Bill,
>>
>> I agreed with your answer. when redistributing between ospf and eigrp, you
>> do not need to tag any route becuase eigrp has inbuilt mechanism to
>> prevent
>> loop. that is the eigrp external AD is higher that ospf AD.
>>
>> so routes going from ospf to eigrp domain will be 170 therefore it will
>> not
>> fall back to ospf domain.
>>
>>
>> On 6/1/08, Bill Eyer <beyer@optonline.net> wrote:
>>
>>
>>> There is no need to tag when mutually redistributing routes from
>>> EIGRP<->OSPF on two routers even with a loop. That's because EIGRP uses
>>> a
>>> different admin distance for external routes, so the OSPF routes aren't
>>> fed
>>> back into EIGRP automatically. Better to not tag and see what works
>>> right
>>> and what doesn't than just tag everything all over the place. That way
>>> if
>>> you get a lab that doesn't allow you to tag, you have a clearer
>>> understanding of how it works.
>>>
>>> Good luck,
>>>
>>> Bill
>>>
>>> Dale Kling wrote:
>>>
>>>
>>>
>>>> Yes, tagging is the easiest to prevent route feedback, for me anyway,
>>>> it's
>>>> not always needed though. Administrative distance plays an important
>>>> factor
>>>> in route feedback as well as other routing path decisions. Sounds like
>>>> the
>>>> concept of how administrative distance effects redistribution on a
>>>> router
>>>> would payoff greatly for you. The IE Blogs on redistribution are
>>>> excellent
>>>> for your questions and I would highly read and study all 3 parts for a
>>>> great
>>>> understanding. I've read them 3 times each myself.
>>>>
>>>> regards,
>>>>
>>>> Dale
>>>>
>>>> On Sun, Jun 1, 2008 at 12:29 PM, Usama Pervaiz <chaudri@gmail.com>
>>>> wrote:
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>> The reason I asked the question was because I was doing one of IE labs
>>>>> (lab 1 actually). Even though mutual redistribution was being done on
>>>>> two routers, no route tags were defined and nothing was being blocked.
>>>>> This is what I did:
>>>>>
>>>>> ON R3:
>>>>>
>>>>> router eigrp 100
>>>>> redistribute ospf 1 metric 1500 1 255 1 1500 route-map RED-OSPF
>>>>> network 183.5.123.0 0.0.0.255
>>>>> no auto-summary
>>>>> !
>>>>> router ospf 1
>>>>> router-id 3.3.3.3
>>>>> log-adjacency-changes
>>>>> redistribute eigrp 100 subnets route-map RED-EIGRP
>>>>> network 150.5.3.3 0.0.0.0 area 0
>>>>> network 183.5.0.3 0.0.0.0 area 0
>>>>>
>>>>> route-map RED-EIGRP deny 10
>>>>> match tag 110
>>>>> !
>>>>> route-map RED-EIGRP permit 20
>>>>> set tag 170
>>>>> !
>>>>> route-map RED-OSPF deny 10
>>>>> match tag 170
>>>>> !
>>>>> route-map RED-OSPF permit 20
>>>>> set tag 110
>>>>>
>>>>>
>>>>> ON R5:
>>>>>
>>>>> router eigrp 100
>>>>> redistribute ospf 1 metric 1500 1 255 1 1500 route-map RED-OSPF
>>>>> network 183.5.105.0 0.0.0.255
>>>>> distance eigrp 120 170
>>>>> no auto-summary
>>>>> !
>>>>> router ospf 1
>>>>> router-id 5.5.5.5
>>>>> log-adjacency-changes
>>>>> redistribute eigrp 100 subnets route-map RED-EIGRP
>>>>> network 150.5.5.5 0.0.0.0 area 0
>>>>> network 183.5.0.5 0.0.0.0 area 0
>>>>> network 183.5.45.5 0.0.0.0 area 45
>>>>> neighbor 183.5.45.4
>>>>>
>>>>> route-map RED-EIGRP deny 10
>>>>> match tag 110
>>>>> !
>>>>> route-map RED-EIGRP permit 20
>>>>> set tag 170
>>>>> !
>>>>> route-map RED-OSPF deny 10
>>>>> match tag 170
>>>>> !
>>>>> route-map RED-OSPF permit 20
>>>>> set tag 110
>>>>>
>>>>>
>>>>> Is this the proper way of blocking the routes from redistributing into
>>>>> their original routing domain? Is this a "best practice"? Is this what
>>>>> is expected in the lab?
>>>>>
>>>>> Any and all help will be appreciated!
>>>>>
>>>>> Thanks,
>>>>> Usama
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>> On Sun, Jun 1, 2008 at 2:19 AM, attia mohamed <ahmattia78@yahoo.com>
>>>>> wrote:
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>> hi
>>>>>> i asked that question to a ccie certified person so he told me that
>>>>>> there
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>> is a differnce between loop prevention and mutual redistibution as
>>>>> redistribution on one router donot make loop but on two routers may
>>>>> make
>>>>> loop .
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>> so making tag on the same router that mean mutal redistribution making
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>> tagging with two routers is loop prevention ( same routing protocol)
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>> --- On Sat, 5/31/08, John <jgarrison1@austin.rr.com> wrote:
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>> From: John <jgarrison1@austin.rr.com>
>>>>>>> Subject: Re: Route redistribution question
>>>>>>> To: "Usama Pervaiz" <chaudri@gmail.com>, "Cisco certification" <
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>> ccielab@groupstudy.com>
>>>>>>
>>>>>>
>>>>>
>>>>>
>>>>>> Date: Saturday, May 31, 2008, 5:35 PM
>>>>>>
>>>>>>
>>>>>>> This is a good article on the subject
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>
>>>>> http://blog.internetworkexpert.com/category/ccie-routing-switching/interior-gateway-routing/
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>> ----- Original Message -----
>>>>>>
>>>>>>
>>>>>>> From: "Usama Pervaiz" <chaudri@gmail.com>
>>>>>>> To: "Cisco certification"
>>>>>>> <ccielab@groupstudy.com>
>>>>>>> Sent: Saturday, May 31, 2008 2:49 PM
>>>>>>> Subject: Route redistribution question
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>> Hello all,
>>>>>>>>
>>>>>>>> I have a quick question on redistribution. I apologize
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>> if this has
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>> been asked already.
>>>>>>>>
>>>>>>>> I have two routers lets say R1 and R2 both with two
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>> interface fa0/0
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>> and fa0/1 (for simplicity). R1 fa0/0 and R2 fa0/0 are
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>> both in OSPF and
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>> are in area 0 (there are other routers in the middle)
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>> that would make
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>> both R1 and R2 ASBR's. R1 fa0/1 and R2 fa0/1 are
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>> both in EIGRP AS 100.
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>> At this point all connectivity is there and everything
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>> is well within
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>> the area and AS.
>>>>>>>>
>>>>>>>> Now if I do mutual redistribution on both R1 and R2 do
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>> I have to tag
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>> the routes and block them on the other router? i.e. I
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>> redistributed
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>> EIGRP into OSPF on R2 do I tag these routes with 90
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>> (for simplicity)
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>> and on R1 block these routes from re-redistributing
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>> into EIGRP on R1?
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>> Will it even redistribute these routes into EIGRP
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>> again even if I
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>> don't?
>>>>>>>>
>>>>>>>> Any and all help would be appreciated and sorry for
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>> being so long winded!
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>> Thanks,
>>>>>>>> Usama
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>
>>>>>>> _______________________________________________________________________
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
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>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>
>>>>>>> _______________________________________________________________________
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>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>> --
>>>>> -----------------------------------------------------
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>>>>> Shake your fist at the gates saying,
>>>>> "I have come home now!"
>>>>>
>>>>> Fetch me the spirit, the son and the father,
>>>>> Tell them their pillar of faith has ascended.
>>>>>
>>>>> "It's time now!
>>>>> My time now!
>>>>> Give me my
>>>>> Give me my own wings!"...
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>>>>>
>>>>>
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>>>>>
>>>>>
>>>>>
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