getting errors in ospf cost

[sivared0001]

                   

task1- i am supposed to ping from R1 to R8 the route should go R1-R2-R4-R3-R5-R6-R8

but it was going like this R1-R2-R4-R6-R8

task2- i am supposed to ping from R2 to R7 the route should go R2-R1-R3-R5-R6-R8-R7

but it was going like this R2-R1-R3-R5-R7

All ip addresses in this topology is /27

loopback 0 is the router id

example

R1-loopback0 1.1.1.1

R2-loopback0 2.2.2.2 and so on...

even if i you give the correct ospf costing it is not going like the above. I think it choosing the least hop count to travel

please help me on this .

[MHM Cisco World]

This second post same issue i reply with answer for your previous post, check my answer.

My answer is same you need transit capability.

[sivared0001]

i am not able to understand the link that you provided its kind of difficult , is there any ther way?

can i get the configuration commands and also on what routers do i have to use

there are two commands i knew

1.no capability transit 

2. capability transit

if these are the commands then on what routers do i have to use based on the error that i am getting in the topology

[MHM Cisco World]

https://ccieblog.co.uk/ospf/ospf-capability-transit

it little complicated but try look to link this example explain why we need this capability.

[MHM Cisco World]

no capability transit 

in each R5 & R6

task1  R1-R2-R4-R3-R5-R6-R8
R1-R3 cost 1000
R3-R5 cost = R5-R6 cost  = R4-R6 cost "SAME COST of R3-R4 COST"

task2 R2-R1-R3-R5-R6-R8-R7
R2-R4 cost 1000
R3-R5 cost = R5-R6 cost  = R4-R6 cost "SAME COST of R3-R4 COST"

that it how you can solve this issue.

[David Ruess]

@MHM Cisco World I believe that will help for the first task but not the second. Maybe I don't understand it but in the OP post he said task 2 was this:

task2- i am supposed to ping from R2 to R7 the route should go R2-R1-R3-R5-R6-R8-R7

but it was going like this R2-R1-R3-R5-R7

Lets look at the bottom half of the diagram (R5-R8) He wants the ping to go from R5-R6-R8-R7, but since R5 is directly connected to R7 its not learned through OSPF. Its a directly connected route. So modifying anything in OSPF (cost or transit area) wont have an affect. Further more the rules of OSPF state that it will use INTRA Area route before it uses INTRA area route as its first criterial. Since R5 is a part of R7s INTRA Area it will choose that path and not go through R6 which would be an INTR Area for the R7 route learned from R6.

So no matter the transit path of Area 100, weather it be through the Virtual links or shortest path the end state wont be reached because the last leg of the routes are directly connected or INTRA Area which Nulls any OSPF configuration past that.

Does this sound correct or did I miss something?

-David

[MHM Cisco World]

Hi @David Ruess 
OK I see prefer path through R6, 
same as mention above just make R5-R7 high cost with 1000

for first task it OK, do you check it?

[David Ruess]

@MHM Cisco World that's what I was trying to say. The cost to R5->R7 is not taken into account because even though its advertised into OSPF R5 sees it as directly connected with an AD of 0. OSPF is not used between this link since it has a higher AD.

As far as the first task I cant reproduce the OPs route (still trying). With or without the "transit capability" command.

[Georg Pauwen]

Hello,

post the full running configurations (sh run) of all eight routers. Put descriptions on the connecting interfaces so we know what is connected to what.

[sivared0001]

i am sending you the configuration txt file 

[paul driver]

Hello
Based on your topology, the problem you have is ONLY R3-R4 will advertise and more importantly process summary LSA's as these are the only ABRs that have full connection to the backbone area 0
To make R5 -R6 R7-R8 process summary LSAs for their respective areas they need a connection into area 0 (use a loopback x ) but this will still now allow R3-R4 to process the other ABRs summary's they will still be ignored, The alternative would to be to create VLs between those areas

[sivared0001]

i already gave r3 to r5 virtual link and vice versa, 

r4 to r6 virtual link and vice versa

still getting error as mentioned in the question

[paul driver]

Hello

VL
R3<>area100<>R7
R4<>area100<>R8

Remove any static routing

[sivared0001]

still not working and i did not give any static route 

even if i give

VL
R3<>area100<>R7
R4<>area100<>R8

it still going through R7 to R8 instead of R5-R6-R8 when i traceroute from R1 to R8

[paul driver]

Hello

This makes no sense - 

if r1 prefers r2 then why should r2 prefer r1

R1

R1-R2-R4-R3-R5-R6-R8

R2

R2-R1-R3-R5-R6-R8-R7