Tag Archives: 3.6a

3.6.a Describe packet types

3.6.a [ii] Route types [N1, N2, E1, E2]

There are several types of OSPF routes:

● Intra-Area—In a multi-area 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.

● Inter-Area—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.

● External Type-2 or External Type-1—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.

● NSSA external type 2 or NSSA external type 1—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 show ip route command output.

Adam, Paul (2014-07-12). All-in-One CCIE V5 Written Exam Guide (Kindle Locations 3355-3371).  . Kindle Edition.

packetlife.net/blog/2008/jun/24/ospf-area-types/

3.6.a Describe packet types

  • 3.6.a [i] LSA types [1, 2, 3, 4, 5, 7, 9]

LSA type 1

Router LSA:  the router advertises its presence along with the links to other routers or networks and their metrics within the same area. Type 1 LSAs are flooded only in their own area. The originating router provides the link state id for type 1 link state advertisements.

LSA type 2

Network LSA: the DR of a broadcast segment lists the routers joined by the segment. Type 2LSAs are flooded only in their own area. the link state id is the ip interface address of the DR.

LSA type 3

Summary Network LSA: originated from an ABR to advertise the subnets in an area to routers outside that area. When an ABR receives a Type1 or 2 LSA, it generates a Type 3 LSA for the networks learned from the Type 1 or 2 LSA to other areas. the link state id is the ip  address of the subnet/s being advertised.

LSA type 4

Summary ASBR LSA: similar to type 3, however, it advertises a host route used to reach the ASBR. the link state id is the RID of the ASBR. not flooded to stub areas.

LSA TYPE 5

External: as the name implies, type 5 LSA’s contain information about other routing processes being imported to OSPF. the link state id is the external network number. not flooded to stub areas.

LSA type 7

NSSA:  creates a special type of link-state advertisement, which can only exist in an NSSA area. An NSSA ASBR generates this LSA and an NSSA ABR translates it into a type 5 LSA, which gets propagated into the OSPF domain.

LSA type 9

Link-local Opaque: for OSPFv2, and  Intra-Area-Prefix LSA for OSPFv3. It is the OSPFv3 LSA that contains prefixes for stub and transit networks in the link-state ID.

3.6.a Describe packet types

3.6.a [i] LSA types [1, 2, 3, 4, 5, 7, 9]

this is a great article…

OSPF route calculation overview

1) Routers establish adjacencies to flood topological information. The flooding process in OSPF is pretty complicated, and ensures the LSAs are delivered to all routers in a single area. As mentioned, topological information is carried in the form of LSAs and cannot be filtered, which it is essential to the OSPF algorithm. The only thing that limits LSA propagation is the flooding domain associated with the particular LSA type. Using the topological information learned, all routers within an area build the consistent graph of the network connections.

the rest is here:

http://blog.ine.com/2009/08/17/ospf-route-filtering-demystified/

3.6.a Describe packet types

3.6.a [i] LSA types [1, 2, 3, 4, 5, 7, 9]

type 6 mospf

type 8 external attributes

opaque’s:

http://tools.ietf.org/rfc/rfc2370.txt

 Opaque
   LSAs provide a generalized mechanism to allow for the future
   extensibility of OSPF. The information contained in Opaque LSAs may
   be used directly by OSPF or indirectly by some application wishing to
   distribute information throughout the OSPF domain.
3.0 The Opaque LSA

   Opaque LSAs are types 9, 10 and 11 link-state advertisements.  Opaque
   LSAs consist of a standard LSA header followed by a 32-bit aligned
   application-specific information field.  Standard link-state database
   flooding mechanisms are used for distribution of Opaque LSAs.  The
   range of topological distribution (i.e., the flooding scope) of an
   Opaque LSA is identified by its link-state type.  This section
   documents the flooding of Opaque LSAs.

   The flooding scope associated with each Opaque link-state type is
   defined as follows.

     o Link-state type 9 denotes a link-local scope. Type-9 Opaque
       LSAs are not flooded beyond the local (sub)network.

     o Link-state type 10 denotes an area-local scope. Type-10 Opaque
       LSAs are not flooded beyond the borders of their associated area.

     o Link-state type 11 denotes that the LSA is flooded throughout
       the Autonomous System (AS). The flooding scope of type-11
       LSAs are equivalent to the flooding scope of AS-external (type-5)
       LSAs.  Specifically type-11 Opaque LSAs are 1) flooded throughout
       all transit areas, 2) not flooded into stub areas from the
       backbone and 3) not originated by routers into their connected
       stub areas.  As with type-5 LSAs, if a type-11 Opaque LSA is
       received in a stub area from a neighboring router within the
       stub area the LSA is rejected.