Solved

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

Posted on 2016-10-18
1
41 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 26

Accepted Solution

by:
Predrag Jovic earned 500 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

How to run any project with ease

Manage projects of all sizes how you want. Great for personal to-do lists, project milestones, team priorities and launch plans.
- Combine task lists, docs, spreadsheets, and chat in one
- View and edit from mobile/offline
- Cut down on emails

Join & Write a Comment

Suggested Solutions

Hello to you all, I hear of many people congratulate AWS (Amazon Web Services) on how easy it is to spin up and create new EC2 (Elastic Compute Cloud) instances, but then fail and struggle to connect to them using simple tools such as SSH (Secure…
Quality of Service (QoS) options are nearly endless when it comes to networks today. This article is merely one example of how it can be handled in a hub-n-spoke design using a 3-tier configuration.
Viewers will learn how to properly install and use Secure Shell (SSH) to work on projects or homework remotely. Download Secure Shell: Follow basic installation instructions: Open Secure Shell and use "Quick Connect" to enter credentials includi…
After creating this article (http://www.experts-exchange.com/articles/23699/Setup-Mikrotik-routers-with-OSPF.html), I decided to make a video (no audio) to show you how to configure the routers and run some trace routes and pings between the 7 sites…

743 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

Need Help in Real-Time?

Connect with top rated Experts

12 Experts available now in Live!

Get 1:1 Help Now