From: Anderson Mota Alves (mota_anderson@hotmail.com)
Date: Fri Feb 03 2006 - 08:49:15 GMT-3
Hi everyone,
I'm sending some concepts I was able to catch up along the way of my
study to ccie and I thought it could be very helpful to everybody
studying for the ccie so I'm posting here in case something it's not
right please advise.
OSPF Network Types
--------------------
Point-to-point: Hello Interval: 10 seconds Dead Interval: 40
Broadcast: Hello Interval: 10 seconds Dead Interval: 40
Point-to-Multipoint: Hello Interval 30 Dead Interval: 120
NBMA: Hello Interval 30 Dead Interval: 120
If we have a question where tells us to make an OSPF adjacency between
ospf that have different types
in order to form the adjacency we can either change the type of the ospf
network using the command
ip ospf network type_of_network or if it says you can't use the ip ospf
network command use the
commands ip ospf hello-interval and ip ospf dead-interval in order to
manipulate these values
DR and BDR Election
---------------------
DR/BDR Election: Takes place in Broadcast and Non-Broadcast Network Type
Note: Point-to-Multipoint interface in OSPF is seeing as multiple
point-to-point interfaces
Split-Horizon
---------------
Split-Horizon based on the interface type (Frame-relay)
Split-Horizon is disable on a frame-relay physical ip interface
Split-Horizon is enabled on a frame-relay point-to-point sub ip interface
Split-Horizon is enabled on a frame-relay point-to-multipoint sub ip
interface
But we don't need to worry about split-horizon in OSPF, I think RIP and
EIGRP should be an issue
since they area Distance Vector Routing Protocols
OSPF Mismatches
-----------------
BROADCAST mode if it's connected to an Ethernet Interface
POINT-TO-POINT if it's connected to a point-to-point network
NON_BROADCAST if it's connected to a NBMA network or ATM
Route Types
------------
OSPF
O = Generated by an "Internal Router"
O IA = Represents routes originating from an "Area Border" or "backbone"
router
O E2 = Represents routes originating from an "Autonomous System Border"
Rules of Adjacency in OSPF
---------------------------
Two routers will not become neighbors unless they agree on the following:
Area-id (a way to keep the LSAs inside the your area and must match in
order to form adjacency)
Authentication (if configured the key_id and key configured must match)
Hello and Dead Intervals (tells the interval the LSA is sent and dead
means how much time the router
need to wait before declaring the route dead)
Stub area flag (Bit P) (used to tell the NSSA ABR whether to translate
type 7 to type 5 or not,
If 1 is set in this field it says to translate, 0 means not translate
keeping the route inside the NSSA area
MTU Size (must be equals in the interface of the routers)
OSPF Summarization
--------------------
Inter-Area Route Summarization needs to be configured in ABRs and it
applies to routes from within the AS
it does not apply to external routes injected into OSPF via
redistribution
configured via command: area area_id range ip-address mask
External Route Summarization is specific to external routes that are
injected int OSPF via redistribution.
this command needs to be put in a ASBR. Caution because this command
there is no effect if used in a ABR since the ABR
doesn't redistribute external routes into the area.
configured via command: summary-address ip-address mask
OSPF LSA Types
-----------------
Type 1: Router link advertisements generated by each router
for each area it belongs to. Flooded to a single area only.
Type 2: Network link advertisements generated by designated
routers describing the set of routers attached to a particular
network. Flooded to the area that contains the network.
Type 3/4: Summary link advertisements generated by ABRs
describing inter-area routes. Type 3 describes routes to
networks and is used for summarization. Type 4 describes
routes to the ASBR.
Type 5: Generated by the ASBR and describes links external
to the Autonomous System (AS). Flooded to all areas except
stub areas.
Type 6: Group membership link entry generated by multicast
OSPF routers.
Type 7: NSSA external routes generated by ASBR. Only
flooded to the NSSA. The ABR converts LSA type 7 into LSA
type 5 before flooding them into the backbone (area 0).
Stub and NSSA Areas
----------------------
Stub area: accepts Intra-area, Inter-area and a Default route
(which replaces the external routes)
Totally Stub area: accepts Intra-area and a Default route only
(excluding Inter-area and external routes) and a Default Route is
automatically generated
....................................
NSSA: accepts only type 7 LSA inside the NSSA area that means no type 5
LSA are allowed
(all IGRP are redistributed as type 7, then the type 7 LSA area
translated into type 5 LSAs
by the NSSA ABR and are leaked into the OSPF domain as type 5 LSAs).
Totally NSSA: accepts only type 7 LSA, Intra-area and a Default route
only (excluding Inter-area and external routes)
so not type 3 and type 4 LSAs are allowed in the area and a Default Route
is injected into the NSSA totally
stub area as a type 3 summary LSA.
I hope this helps!!!
This archive was generated by hypermail 2.1.4 : Wed Mar 01 2006 - 11:28:17 GMT-3