Nexus OSPF

[hs08]

Hello,

I have cisco ISR and Nexus 7707 with ospf enabled. Nexus use 40Gbps for reference bandwidth and ISR use 100Mbps.

From R1 perspective cost to reach 10.103.248.1 is 41, and i have though that 40 is cost from R1 to R2 (40 div 1), and 1 is cost from R2 to the host. 

My question is, why the cost is not 80 (R1-R2 is 40 and R2-host=40)? Since from R1 to R2 and R2 to the host same using 40Gbps for the bandwidth reference?

[hs08]

Hello,

here cost to 10.103.245.9

[Giuseppe Larosa]

Hello @hs08 ,

this is from the router LSA you have posted

Link connected to: a Stub Network
(Link ID) Network/subnet number: 10.103.248.0        --> This host subnet
(Link Data) Network Mask: 255.255.255.0
Number of MTID metrics: 0
>>>>>>>>>>>>>>>>>>>>>>>>>>>> TOS 0 Metrics: 40 !

as you see the cost is 40 then from R1 point of view is 41 as explained by anyone in this thread

You can see by yourself. There is no need to make a lab for this.

Hope to help

Giuseppe

[MHM Cisco World]

previous example I show you how we calculate the cost 
below is I think explain the issue you face 
R1-R2 link, 
both R1 and R2 send LSA1 for this link, R1 use it LSA1 not what R2 advertise 
so I in lab I change cost in R2 to be 40 for link R1-R2 and R1 config default (which is one)
so R1 use it LSA1 cost which is 1 instead of 40 
and hence the total cost is
R1-R2 = 1
R2-SW = 10
total cost 11

NOTE:- cisco not recommend mismatch cost in link, this lead to asymmetric

so return to your network  

for 10.103.245.9 there are two LSA1 
check LSA1 advertise by R1 not R2 

MHM 

[MHM Cisco World]

@hs08 any update for this case ?

Also

Router use cost different than NSK for same link interconnect both

Check if you use refrence bandwidth in NSK this can lead to this issue.

MHM

[hs08]

Hi @MHM Cisco World 

Still trying to understand, will update soon.

[MHM Cisco World]

What is not clear to you?

You have issue that why you see different cost in lsa1 for same prefix

Mostly router abd NSK use different refrence bandwidth that make NSK use 40 and router use 1 cost for same link.

It common issue. 

MHM

[hs08]

Hi @MHM Cisco World 

Currently my nexus is replaced to catalyst 9500 and this make me can't investigate further.

[MHM Cisco World · Accepted solution]

Even if you change platform' if you use wrong refrence BW then issue will appear again

I will try share more detail later today 

MHM

[hs08]

Hi,

Yes, so in my current topology now all link have same reference BW. Thanks