Hello,
1) Could we get any issues regarding to "auto summary" feature in following days ? What is the disadvantages of not using this feature ?
If your entire campus runs on 10.x.x.x address exclusively and does not advertise any other addresses in EIGRP then the auto-summary has no effect. The automatic summarization rule states:
If a subnet S of a major network X is to be advertised out an interface that lies in a different major network Y, advertise only network X instead of the subnet S.
The term "major network" refers to the classful network into which a particular address belongs. For example, the major network of the address 10.1.2.3 is 10.0.0.0/8 (class A); the major network of the address 158.193.138.04 is 158.193.0.0/16 (class B); the major network of the IP address 198.51.100.200 is 198.51.100.0/24 (class C). This rule and the overall concept of automatic summarization was valid in times when enterprises have been purchasing complete major networks and were their exclusive owners; however, it is not usable todays as we no longer obtain IP prefixes corresponding to entire classful (major) networks.
So, returning back to your question, if all your networks are from within the 10.0.0.0/8 range, the automatic summarization will not apply because all your subnets and interfaces through which these subnets are advertised are from the same major network 10.0.0.0/8.
As long as you do not intend to carry any other networks in your EIGRP except 10.0.0.0/8 and default route, the setting of the automatic summarization is largely irrelevant. It could, however, start having significance whenever you wanted to advertise any other networks. So during the next maintenance window, it is highly recomended to have the automatic summarization deactivated. In EIGRP, the downtime is relatively short - shouldn't be longer than a second, but every change in the automatic summary setting will cause the EIGRP router to resync with its peer and this is the source of the temporary short-lived outage.
2) When we investigate document, they suggest ; no auto-summary feature with summarize routes and stub zone for dist. locations according to our topology ? Is it right ?
Yes, it is.
Deactivating automatic summarization is considered today to be a routine part of every EIGRP deployment. Some new IOS versions even come with the automatic summarization deactivated by default - check the show ip protocols output carefully to see if your IOS is one of them.
Using EIGRP Stub improves scalability and convergence times especially in large EIGRP networks. Deploying it in your network would certainly be useful and is recommended.
Summarization in EIGRP is strongly called for. It helps keeping routing tables tidy and reasonably small, and it also limits the scope of the EIGRP Query packets which is extremely important for timely convergence and SIA state prevention.
Best regards,
Peter
