Question on auto-summarization in routing protocols

1.  When auto-summarization is on in EIGRP, I notice it summarizes to the classful boundary (ie: 192.168.3.0/24).  Is this just how IGP's work with auto-summarization on?  They will always summarize to a classful boundary correct?  /8  /16  /24 ?

If I turn off auto-summarization ,  I notice I see the REAL subnet mask. (thanks donjohnston for this info)

2.  Is auto-summarization usually used in production enviornments?  What if you have an internal network that spans several sites.  Each router is running EIGRP. Would you use auto summarization there?  I imagine yes if the networks are contiguous?

Thanks
dissolvedAsked:
Who is Participating?
I wear a lot of hats...

"The solutions and answers provided on Experts Exchange have been extremely helpful to me over the last few years. I wear a lot of hats - Developer, Database Administrator, Help Desk, etc., so I know a lot of things but not a lot about one thing. Experts Exchange gives me answers from people who do know a lot about one thing, in a easy to use platform." -Todd S.

JFrederick29Commented:
1.  Yes, it summarizes to the classful boundary.

2.  I never use auto-summary.  I always disable it and summarize manually.  This gives you the control over which routes are summarized.
0

Experts Exchange Solution brought to you by

Your issues matter to us.

Facing a tech roadblock? Get the help and guidance you need from experienced professionals who care. Ask your question anytime, anywhere, with no hassle.

Start your 7-day free trial
dissolvedAuthor Commented:
When you say summarize manually...what do you mean?

Do you mean you just diable auto-summarization and let the routing protocol advertise the real mask.
Or is there an actual "manual process" that lets you summarize manually?

Thanks J
0
Don JohnstonInstructorCommented:
It's manually process.

If you have a number of networks on one side of your router like

172.16.16.0
172.16.17.0
172.16.18.0
172.16.19.0

You could manually summerize these as 172.16.16.0/22

With auto summerization, the router would advertise 172.16.0.0

-Don
0
Ultimate Tool Kit for Technology Solution Provider

Broken down into practical pointers and step-by-step instructions, the IT Service Excellence Tool Kit delivers expert advice for technology solution providers. Get your free copy now.

dissolvedAuthor Commented:
Hi Don,
Ok, so the 172.16.16.0/22 is a supernet address correct?

2. Auto summarization (from a routing protocol such as ripv2 or eigrp) would advertise the route as 172.16.0.0/16 correct?
0
Don JohnstonInstructorCommented:
No. It's a subnet of the 172.16.0.0/16 network.

-Don
0
dissolvedAuthor Commented:
ok, thanks man.

what about my other question.  WIth auto summarization the route would be advertised as 172.16.0.0/16 by the routing protocols that support VLSM? Right?
0
JFrederick29Commented:
Yes, that is correct.  With auto summarization enabled (default), EIGRP or RIPv2 is going to advertise the route using the classful mask, which, could lead to problems if using discontiguous subnets.

To manually summarize using EIGRP:

interface s0/0
ip summary-address eigrp <as> 172.16.16.0 255.255.252.0
0
dissolvedAuthor Commented:
thanks guys
0
It's more than this solution.Get answers and train to solve all your tech problems - anytime, anywhere.Try it for free Edge Out The Competitionfor your dream job with proven skills and certifications.Get started today Stand Outas the employee with proven skills.Start learning today for free Move Your Career Forwardwith certification training in the latest technologies.Start your trial today
Routers

From novice to tech pro — start learning today.

Question has a verified solution.

Are you are experiencing a similar issue? Get a personalized answer when you ask a related question.

Have a better answer? Share it in a comment.