OSPF

Página 1

ospf construye rutas:

Neighbors

data base exchange

agregando la mejor ruta

OSPF neighbors are routers that both use OSPF and both sit on the same data link. (misma subred)

the routers send OSPF Hello messages, introducing themselves to the neighbor.

show ip ospf neighbors

OSPF Hello mediante el cual se crean relaciones con los vecinos.

Router ID (RID),

IOS chooses its OSPF RID based on an interface IPv4 address, because those are some nearby convenient 32-bit numbers as well. However, the OSPF RID can be directly configured

The Hello messages themselves have the following features: • The Hello message follows the IP packet header, with IP protocol type 89. • Hello packets are sent to multicast IP address 224.0.0.5, a multicast IP address intended for all OSPF-speaking routers. • OSPF routers listen for packets sent to IP multicast address 224.0.0.5, in part hoping to receive Hello packets and learn about new neighbors.

8Classful routing protocols do not send masks in the routing

update messages.

OSPF, and the other uses EIGRP, on at least one router, both

OSPF and EIGRP must be used. Then,

that router can take routes learned by OSPF and advertise

them into EIGRP, and vice versa, through a

process called route redistribution.

Si el router

aprende rutas por diferentes protocolos de enrutamiento

to the same subnet,

because each routing protocol’s metric is based on different information, IOS

cannot compare the metrics.

Distancia

administrative denota que tan credible es un protocol de enrutamiento entero en un solo router. El numero mas bajo, el

major, o el protocol de enrutamiento mas creible .

For example, RIP has a default administrative distance of

120, OSPF uses a default

of 110, and EIGRP defaults to 90. When using OSPF and EIGRP,

the router will believe the EIGRP

route instead of the OSPF route (at least by default).

link-state

advertisement (LSA)

In OSPF, the name of the data structure that resides inside

the LSDB and describes in detail the

various components in a network, including routers and links

(subnets).

link-state database

(LSDB) : en OSPF la estructura de datos en

In OSPF, the data structure in RAM of a router that holds

the various LSAs, with the collective

LSAs representing the entire topology of the network.

Each

LSA is a data structure with some specific information about the network

topology; the LSDB is

simply the collection of all the LSAs known to a router.

se configura diferentes areas para evitar una LSDB grande lo cual generaria gran consumo de performance:

por area se recomiendan solo 50 routers, aunque esto depende es del diseño, la cantidad de ram, cpu etc.

Area Border Router (ABR): un router que usa ospf y tiene interfaces en multples areas OSPF.

router ospf id_proceso

network red mascara wilcard area num

show ip protocols

Por defecto, los routers escogeran unadir ip de una interfaz para usar como RID (router ID).

show ip ospf neighbor:

enumera los ID de router más reconocibles.

To find its RID, a Cisco router uses the following process when the router reloads and brings up the OSPF process. Note that when one of these steps identifies the RID, the process stops. 1. If the router-id rid OSPF subcommand is configured, this value is used as the RID. 2. If any loopback interfaces have an IP address configured, and the interface has an interface status of up, the router picks the highest numeric IP address among these loopback interfaces. 3. The router picks the highest numeric IP address from all other interfaces whose interface status code (first status code) is up. (In other words, an interface in up/down state will be included by OSPF when choosing its router ID.)

clear ip ospf process

show ip ospf

interfaces pasivas ospf

interfaces en las cuales el router no necesita establecer vecindad y por ende enviar paquetes hello.

Quit sending OSPF Hellos on the interface

Ignore received Hellos on the interface

Do not form neighbor relationships over the interface

show ip ospf interface brief command lists all interfaces on which OSPF is enabled, including passive interfaces. The show ip ospf interface command lists a single line that mentions that the interface is passive

default-information originate: propagar la ruta por defecto

metrica: unidad de medida usada por los algoritmos de protocolos de enrutamiento para determinar la mejor ruta para trafico a usar para alcanzar un destino particular.

ospf

configuracion

comandos