network cisco ccna gns3 certification arteq

network cisco ccna gns3 certification arteq
a network runs through it

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Monday, July 30, 2012

intra v inter...

intra means inside or within

inter means between or among

from stretch at

There are two points at which OSPF routes can be filtered: within an area, or between areas on an area border router (ABR).

                                           intra                         inter


OSPF Router Types

Internal Router: Responsible for maintaining a current and accurate database of subnets within the area. Forwards data to other networks using the shortest path.

Backbone Router: Has an interface connected to the backbone (Area 0).

Area Border Router (ABR): Has interfaces in multiple areas with at lest one interface in area 0. Connects other areas  to the backbone and maintains routing information for each connected area.

Autonomous System Boundary Router (ASBR): Router located between OSPF autonomous system and a non-OSPF network. Used to redistribute routing information between networks. Must reside in a non-stub area. Also, a router becomes an ASBR when OSPF is redistributing from other routing protocols, including static routes, and it may reside in a pure OSPF network.


Type 1: Router link advertisements generated by each router for each area it belongs to. Flooded to a single area only (intra-area route). In a multiarea OSPF network, routes, originated within an area, are known by the routers in the same area as Intra-Area routes. These routes are flagged as O in the “show ip route” command output.

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 (intra-area route). When a route crosses an OSPF Area Border Router (ABR), the route is known as an OSPF Inter-Area route. These routes are flagged as O IA in the “show ip route” command output.

Both Intra and Inter-Area routes are also called OSPF Internal routes, as they are generated by OSPF itself, when an interface is covered with the OSPF network command.

Type 3/4: Summary link advertisements generated by ABRs describing inter-area routes. Type 3 describes routes to networks and is used for summarization. The "default-information originate" is also Type 3. Type 4 describes routes to the ASBR (interarea summary route).

Type 5: Generated by the ASBR and describes links external to the Autonomous System (AS). These are the redistributed (from other routing protocols including static routes) routes. Flooded to all areas except stub areas (external route). Routes which were redistributed into OSPF, such as Connected, Static, or other Routing Protocol, are known as External Type-2 or External Type-1. These routes are flagged as O E2 or O E1 in the “show ip route” command output.

Type 6: Group membership link entry generated by multicast OSPF routers.

Type 7: NSSA external routes generated by ASBR. Only flooded to the NSSA. External routes injected internally by ASBRs within each POP (Areas other than Area 0) are LSAs of type 7. The ABR between will translate LASs type 7 to LSAs type 5 from each POP/Area to Area 0 (external route). When an area is configured as a Not-So-Stub Area (NSSA), and routes are redistributed into OSPF, the routes are known as NSSA external type 2 or NSSA external type 1. These routes are flagged as O N2 or O N1 in the “how ip route” command output.

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