In the docs I've read (and I think this was posted on this list as well), one might use E2s when you've got one exit point that is always prefered over the other(s). This might happen if you've got 2 ISPs and one configured as a backup only. The primary exit point is always prefered, regardless of the internal cost to get to it.
E1s are useful when one might want to load share traffic to the exit points. Each router computes the internal cost to each exit, and takes the path to the closest based on internal cost. ericbrouwers wrote: > > Hi, > > Why is an E1 route preferred over an E2 route for the same destination? > > The cost of an E1 route is the sum of the external reported cost and the > internal cost used to reach that destination. > The cost of an E2 route is always the external cost, irrespective of the > internal cost to reach that route. > > This implies that the path with the higher cost is preferred.... Is it maybe > because E1 routes are reflecting the real cost? They are not hiding the > internal costs.....But if this is the reasoning behind it, why has Cisco made > E2 the default instead of E1???? > > Anyone an idea? > > Eric Brouwers > > By the way, CCNP Routing Exam Certification Guide seems to be wrong on page > 294, chapter 6. The E2 definition is not right: > "... > The routes discovered by OSPF in this way can have the cost of the path > calculated in one of two ways: > . E1-The cost of the path to the ASBR is added to the external cost to the > next-hop router outside the AS. > . E2-The cost of the path to the ASBR is all that is considered in the > calculation. This is the default configuration. This is used when there is > only one router advertising the route and no selection is required. If both > an > E1 and an E2 path are offered to the remote network, the E1 path will be > used. > ..." Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=61629&t=61619 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
