Want to protect your cyber security and still get fast solutions? Ask a secure question today.Go Premium

x
?
Solved

OSPF area summary command - Summarizing when two supernet is in two different areas.

Posted on 2016-10-18
1
Medium Priority
?
138 Views
Last Modified: 2016-10-26
See photo:

I found this command in my network:

C1: Core switch 1
C2: Core switch 2
R1: Router 1
R2: Router 2
Block1: Distro block 1
Block2: Distro block 2

Core 1:
 area 100 range 10.148.0.0 255.255.128.0

Core 2:
 area 100 range 10.148.0.0 255.255.128.0

Both distribution blocks use subnets that fall under 10.148.0.0/17, but block 1 is in area 100, and block two is in area 102.

How big of an issue is summarizing if a subnet of the network is that is being summarized is in a different OSPF area?  There are no duplications anywhere, and the network is up and running.
Note101816.pdf
0
Comment
Question by:PeraHoman
1 Comment
 
LVL 32

Accepted Solution

by:
Predrag earned 2000 total points
ID: 41849096
Core 1:
 
area 100 range 10.148.0.0 255.255.128.0

Core 2:
 area 100 range 10.148.0.0 255.255.128.0
Since those two are summarizing the same area it is not problem since both advertise the same network range for area 100. However you need to be aware that qual cost path routing in OSPF can have unexpected results. Please read - How does OSPF use two Multilink paths to transfer packets?
On the drawing area 102 have 10.148.0.0/22 and area 100 have 10.148.0.0/17 in that case if ranges in areas 100 and 102 do not overlap (area 102 have IP address range 10.148.0.0/22 and area 100 do not have IP addresses from that IP address range) it is OK since IP address range (or summary) for area 102 is more specific than summarization for area 100.
When packet is compared to entries in routing table - the most specific route available will be selected.

According to your picture packets with IP destination address:
10.148.0.1 - 10.148.3.254 - will always be forwarded to area 102
10.148.4.0 - 10.148.127.254 - will always be forwarded to area 100
If IP routes are advertised correctly outside of areas (there is no reason not to be).
So, by itself it is not a problem since more specific route is always preferred.
0

Featured Post

Concerto Cloud for Software Providers & ISVs

Can Concerto Cloud Services help you focus on evolving your application offerings, while delivering the best cloud experience to your customers? From DevOps to revenue models and customer support, the answer is yes!

Learn how Concerto can help you.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

During and after that shift to cloud, one area that still poses a struggle for many organizations is what to do with their department file shares.
On Feb. 28, Amazon’s Simple Storage Service (S3) went down after an employee issued the wrong command during a debugging exercise. Among those affected were big names like Netflix, Spotify and Expedia.
As a trusted technology advisor to your customers you are likely getting the daily question of, ‘should I put this in the cloud?’ As customer demands for cloud services increases, companies will see a shift from traditional buying patterns to new…
Both in life and business – not all partnerships are created equal. Spend 30 short minutes with us to learn:   • Key questions to ask when considering a partnership to accelerate your business into the cloud • Pitfalls and mistakes other partners…

580 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question