02-05-2014 12:58 AM - edited 03-07-2019 06:00 PM
Hi all,
I have
The network 192.168.0.0 is directly connected to Router A and B. Router A and B are redistributing the network in the ospf area 0.
Router A,B,C,D belong to the same OSPF Area.
Router C is DR. The cost of the link is indicated in the draw.
Question:
Router D (and router C) is using as next hop the Router A for reaching the network 192.168.0.0.
Why the router D is not using the router B as next hop due to the fact that all the possible paths are equal cost?
Thanks.
Solved! Go to Solution.
02-05-2014 03:32 AM
Fabio,
if the Forwarding Address is not 0.0.0.0, the next hop will be calculated by evaluating the OSPF internal path to the FA.
Useful link: The Effects of the Forwarding Address on Type 5 LSA Path Selection
Otherwise you'll have to look for the components of the costs: Cost to ASBR + Seed cost (E2; default: 20) or external cost (E1).
HTH
Rolf
02-05-2014 02:41 AM
Fabio
Are C and D not seeing equal cost paths ?
Jon
02-05-2014 03:18 AM
Every interface of every router inside the mentioned ospf process is seeing the cost ,emtioned in the draw (1)
02-05-2014 03:20 AM
Fabio
So do C and D have two equal cost paths in the IP routing table to that network ?
Jon
02-05-2014 03:22 AM
Hi Jon,
no. Router B and C have only one entry in the routing table and both are using as next hop router A.
02-05-2014 03:22 AM
Fabio,
Jon,
I hope you allow me to join.
Could you please post the output of
- show ip ospf border-routers
- show ip ospf database external 192.168.0.0
from Router D?
Points to focus on:
- metric-type E1/E2
- seed-metric (E2) / external metric (E1)
- costs to ASBRs A and B
- non-zero Forwarding Addresses in Type-5 LSAs
Regards
Rolf
02-05-2014 03:26 AM
Can you paste the output of show ip protocols and show ip ospf database router x.x.x.x where x.x.x.x is the RID of Router A and B, C and D.
Daniel Dib
CCIE #37149
Please rate helpful posts.
02-05-2014 03:28 AM
Hi All,
I got all your point. No output possible.
I will analise th answer of Rolf.
I just need an indication of what can be.
02-05-2014 03:32 AM
Fabio,
if the Forwarding Address is not 0.0.0.0, the next hop will be calculated by evaluating the OSPF internal path to the FA.
Useful link: The Effects of the Forwarding Address on Type 5 LSA Path Selection
Otherwise you'll have to look for the components of the costs: Cost to ASBR + Seed cost (E2; default: 20) or external cost (E1).
HTH
Rolf
02-05-2014 05:06 AM
Let me check, I am really curiosi to figure out this point and of course I will let you know.
Thanks all.
Cheers,
Fabio.
02-17-2014 08:50 AM
Hi,
At the end the information provided by Rolf fit in my case.
Playing with the cost to reach the ASBR and the metric of the external route I was able to figure out why the router A is the50
preferred exit point: during the redistribution router A is modifying the metric value, in this way C and D are using A as
Thanks all!!!
02-05-2014 03:27 AM
Rolf
Always welcome
Jon
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