Exam JN0-349 topic 1 question 16 discussion (2024)

FAQs

Which OSPF area type receives only the default route from the backbone? ›

Stub Area The stub area is an area that does not receive external routes except the default route, but does receive inter-area routes.

GRE adds two headers to each packet: the GRE header, which is 4 bytes long, and an IP header, which is 20 bytes long. The GRE header indicates the protocol type used by the encapsulated packet. The IP header encapsulates the original packet's header and payload.

Backbone Areas

An OSPF backbone area consists of all networks in area ID 0.0. 0.0, their attached routing devices, and all ABRs. The backbone itself does not have any ABRs. The backbone distributes routing information between areas.

In order for OSPF to generate a default route, you must use the default-information originate command. There are two ways to advertise a default route into a normal area. The first is to advertise 0.0. 0.0 into the OSPF domain, provided the advertising router already has a default route.

Examples of tunnels include PPTP, IPSec, L2TP etc. Tunneling increases overhead, because it needs an extra set of IP headers. Typically this is 20 bytes per packet, so if the normal packet size (MTU) on a network is 1500 bytes, a packet that is sent through a tunnel can only be 1480 bytes big.

GRE is a tunneling protocol which is used to transport multicast, broadcast and non-IP packets like IPX etc. IPSec is an encryption protocol. IPSec can only transport unicast packets not multicast & broadcast. Hence we wrap it GRE first and then into IPSec which is called as GRE over IPSec.

mGRE is a similar protocol with a single endpoint at one side of the tunnel connected to multiple endpoints at the other side of the tunnel. MPLS is a widely deployed VPN internet architecture. MPLS requires that all core routers in the network support MPLS.

Backbone: The area with ID 0 (or 0.0. 0.0) is reserved for the OSPF network backbone, which forms the core of an OSPF network—all other areas are connected to it. Normal: A normal or regular area has a unique ID ranging from 1 (or 0.0. 0.1) to 4,294,967,295 (or 255.255.

Default. The preference is 10 for OSPF internal routes and 150 for OSPF external routes (ASE routes).

Broadcast—By default, OSPF considers the network type as broadcast.

What is the default OSPF external route? ›

By default, OSPF uses the Type 2 external metric. Both Type 1 and Type 2 external metrics can be present in the AS at the same time. In that event, Type 1 external metrics always takes the precedence. Type 1 external paths are always preferred over Type 2 external paths.