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OSPF stub area and route external to AS

Stub area is an area that does not accept information about routes external to the autonomous system.

Does the "external routes" must be from non-OSPF (RIP, IGRP, EIGRP) always with different AS, or it can be from another OSPF but with different AS ?

5 REPLIES
Cisco Employee

Re: OSPF stub area and route external to AS

OSPF routes redistributed from one process to another will also be seen as external routes and will therefore not be flooded to stubby areas.

Hope this helps,

Harold Ritter
Sr. Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México
Paseo de la Reforma 222
Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México
New Member

Re: OSPF stub area and route external to AS

Why cisco book says about external route as :"non-ospf"-------> that means cisco book specifys external route with non-ospf only!!!

And as you mentioned that external route can be form another ospf process

Cisco Employee

Re: OSPF stub area and route external to AS

Any route redistributed into OSPF will be seen as an external route no matter if it is from OSPF or any other source. Redistribution of OSPF routes from one process to another is kind of a corner case and this is probably why is was omitted in the book.

Hope this helps,

Harold Ritter
Sr. Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México
Paseo de la Reforma 222
Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México
New Member

Re: OSPF stub area and route external to AS

Thanks hritter for this clarification.

One more think you said : "from OSPF or any other source".

I want you to comment this also please :

http://www.riverstonenet.com/support/ospf/ospf-areas.htm

"A router that redistributes prefixes from other sources into OSPF is an ASBR. Routes from non-OSPF sources are referred to as External routes---etc".

Cisco Employee

Re: OSPF stub area and route external to AS

Again, I think that this quote refers to external routes as non-ospf routes because one would usually redistribute from one different protocol to OSPF. Nevertheless, the corner case of OSPF routes being redistributed from one process to another, which is not even possible for some vendors, will cause these OSPF routes to be seen as external in the OSPF process in which these routes are being redistributed.

Hope this helps,

Harold Ritter
Sr. Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México
Paseo de la Reforma 222
Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México
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