From: Fahad Khan (fahad.khan@gmail.com)
Date: Tue Oct 21 2008 - 05:52:53 ARST
yes no doubt about cef, but the question restricts. did u try through
modifying AD?
On 10/21/08, Ahsan Mohiuddin <ahsan.mohiuddin@gmail.com> wrote:
>
> the dreaded routing loop.. clichi, isn't it :)
>
> Point is, you mustn't change the pre-config i.e. the loop should remain in
> place. Steps 1-8 are part of the pre-config; we have to find solution to
the
> "TASK".
>
> Interesting thing is that if you disable CEF and enable process switching
> on R3, you will have 100% reachability to 6.6.1.0/24; one packet will go
> directly out R3's s1/1, the next will go out s1/0.35 but eventually will
> follow the path out R3 itself, that is after looping thru R6 then R4
> (R3--->R5--->R6--->R4--->R3--->R1). Although not ideal but it works
> perfectly well. However, the task asks not to disable CEF on R3.
>
>
>
> On Tue, Oct 21, 2008 at 11:25 AM, Fahad Khan <fahad.khan@gmail.com> wrote:
>
>> The routing loop is being occured in between R3 and R5
>>
>> R3 : D EX 6.6.1.0 [170/2425856] via *6.6.35.5*, 00:01:37,
>> Serial1/0.35 -----> next hop is R5
>> [170/2425856] via 6.6.13.1, 00:01:37, Serial1/1
>>
>>
>> R5 : D EX 6.6.1.0 [170/2937856] via *6.6.35.3*, 00:01:23,
>> Serial1/0.53 ------> next hop is R3
>>
>> The problems like routing loops and route feedback are handled by
>>
>> 1- Tagging
>> 2- Modifying AD
>> 3- Modifying Metric
>>
>> Ist solution:
>>
>> On R4, set a tag when redistribution is done from EIGRP to OSPF and On R5
>> , configure NOT to send the tagged routes back to R3.
>>
>> 2nd solution: (modifying AD seems not possible in this case; since In
>> eigrp we cant modify specific external routes)
>>
>> well,
>>
>> On R3 , see if you can modify the AD of the route coming from R5 (distance
>> 180 x.x.x.x 0.0.0.0 <acl>)
>>
>> (lab it n tell us)
>>
>> HTH
>>
>> best regards,
>> On 10/21/08, Ahsan Mohiuddin <ahsan.mohiuddin@gmail.com> wrote:
>>
>>> Here's the topology:
>>>
>>> R1---R3----R4
>>> | |
>>> R5----R6
>>>
>>> All links are frame-relay P2P, except R1-R3 which is HDLC serial.
>>>
>>> (1) R1 is advertising its Lo0 int (6.6.1.1/24) in RIP. R1 is also
>>> running
>>> EIGRP 100 and redistributing RIP into EIGRP 100.
>>> (2) R1 & R3 are EIGRP neighbors over serial link (6.6.13.0/24).
>>>
>>> (3) R3 is learning the route to 6.6.1.0/24 via 6.6.13.1:
>>>
>>> D EX 6.6.1.0 [170/2425856] via 6.6.13.1, 00:00:02, Serial1/1
>>>
>>> R3 is able to ping destination 6.6.1.1:
>>>
>>> Sending 5, 100-byte ICMP Echos to 6.6.1.1, timeout is 2 seconds:
>>> !!!!!
>>> Success rate is 100 percent (5/5), round-trip min/avg/max = 4/12/32 ms
>>>
>>> (4) R3 is advertising this route to its EIGRP 100 neighbors R4 & R5.
>>>
>>> At R4:
>>> D EX 6.6.1.0 [170/2937856] via 6.6.34.3, 00:07:26, Serial1/0.43
>>> At R5:
>>> D EX 6.6.1.0 [170/2937856] via 6.6.35.3, 00:01:23, Serial1/0.53
>>>
>>> (5) R4, R5, R6 are running in OSPF Area 0. Note that R4 & R5 do not have
>>> a
>>> direct link, and both these routers are OSPF neighbors to R6.
>>> (6) Now on R4, we configure redistribution of EIGRP 100 into OSPF. As a
>>> result, R6 learns the route 6.6.1.0/24:
>>>
>>> O E2 6.6.1.0 [110/20] via 6.6.46.4, 00:03:06, Serial1/0.64
>>>
>>> (7) R6 advertises this route to R5. As a result, R5 removes it original
>>> route (distance 170) and installs O E2 (distance 90) route:
>>>
>>> O E2 6.6.1.0 [110/20] via 6.6.56.6, 00:00:01, Serial1/0.56
>>>
>>> (8) We configure R5 to redistribute OSPF into EIGRP 100. This causes R3
>>> to
>>> learn an additional path to 6.6.1.0/24:
>>>
>>> At R3:
>>> D EX 6.6.1.0 [170/2425856] via 6.6.35.5, 00:01:37, Serial1/0.35
>>> [170/2425856] via 6.6.13.1, 00:01:37, Serial1/1
>>>
>>> (9) Now at R3, if we ping 6.6.1.1..
>>>
>>> Sending 5, 100-byte ICMP Echos to 6.6.1.1, timeout is 2 seconds:
>>> .....
>>> Success rate is 0 percent (0/5)
>>>
>>> *TASK*
>>> Ensure that R3 can reach 6.6.1.0/24. Do not disable CEF on R3. Do not
>>> create
>>> any tunnels. You are allowed to change IP Addressing on a single link
>>> (subnet) in the topology.
>>>
>>>
>>>
>>> Blogs and organic groups at http://www.ccie.net
>>>
>>> _______________________________________________________________________
>>> Subscription information may be found at:
>>> http://www.groupstudy.com/list/CCIELab.html
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>
>>
>> --
>> Fahad Khan
>
>
>
-- Fahad KhanBlogs and organic groups at http://www.ccie.net
This archive was generated by hypermail 2.1.4 : Sat Nov 01 2008 - 15:35:21 ARST