Comments inline: Howard C. Berkowitz wrote: > > At 5:00 PM +0000 12/3/02, p b wrote: > >One of the cisco press books indicates one should use > >type 1 externals when the route is being advertised by > >>1 ASBR and type 2 externals when there's a single > >ASBR. > > This is just plain wrong. The reason you have E1 and E2 is to > have > different routing policies. > > E1 enforces a closest-exit policy which gives a degree of load > sharing. > > E2 enforces a best-exit policy. For example, you might have > one fast > link to an ISP and one dial backup link, or a primary and a > backup > provider. In both cases, you want an E2 because you always > want to > go to a specific exit UNLESS there is a failure.
See ACRC (Chappel), page 217. Under E1 explanation "...Use this packet type when you have multiple ASBRs advertising a route to the same AS" Under E2 explanation "... use this packet type if only one router is advertising a route to the AS..." > > > > >Are there any issues if one uses type 1 external even > >when the route is being advertised by a single ASBR? It > >would seem useful, given the cost to the external is > >compatible with the costing used in the OSPF network, to > >use type 1 externals even if the route originates from a > >single ASBR. The benefit being able to get a meaningful > >cost value to the external. > > Why? If there's only one connection to the outside, does the > internal > cost really matter if you have to go there? Is there no benefit to knowing the cumulative cost? Is there a benefit to knowing an E2 cost which has no cost meaning within the OSPF AS? As mentioned, there is only a single ASBR advertising this route, but there may be many paths to this ABSR. So if there's no overhead with using a type 1 here, why not use it and get the cost information? > > > > >Is there any unexpected issues which might arise when > >doing this? Flooding of LSAs or SPF aren't imapcted > >if a route is an E1 or E2, right? > > > >Thanks > > Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=58469&t=58454 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
