By the use of OSPF authentication you can prevent unwanted routing updates from being received and processed by the routers. If authentication is configured on a router, it will authenticate the source of each OSPF packet by using a password, which is known by both routers. 

External routes in OSPF are carried by type 5 LSA (external LSAs). Type 5 LSAs are generated by ASBR (Autonomous System Boundary Router), that’s why external route summarization must be configured on ASBR. Stub area do not allow ASBR because they don’t allow type 5 LSAs.

OSPF does not support auto summarization, only manual. OSPF route summarization can be of two types:

1. Internal route summarization;
2. External route summarization.

 In this article we will work with OSPF internal route summarization on Cisco routers.

Using a default route will save router’s resources because there is no need to run SPF algorithm each time when external network changes occur. In this lab we will examine how to propagate a default route in an OSPF standard area.

By default EIGRP has auto summarization enabled. This means that it will summarize to classfull addresses at network boundaries. Leaving auto summarization enabled could cause a lot of troubles in our network. EIGRP has the ability to create summary routes at arbitrary boundaries by using manual summarization.