From: Paul Cosgrove (paul.cosgrove@heanet.ie)
Date: Mon Jun 02 2008 - 05:43:48 ART
Hi David,
You should not have a problem redistributing EIGRP internal routes into
another IGP at two redistribution points, assuming default ADs are used,
but you may have issues if you do the same with EIGRP external routes.
Paul
David Lonnie wrote:
> 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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>>>>>>>>> http://www.groupstudy.com/list/CCIELab.html
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>> _______________________________________________________________________
>>>>>>>> Subscription information may be found at:
>>>>>>>> http://www.groupstudy.com/list/CCIELab.html
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>> --
>>>>>> -----------------------------------------------------
>>>>>> You're the only one who can hold your head up high,
>>>>>> 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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>>>>
>>>>
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>>>
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>
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