Shulou(Shulou.com)06/01 Report--

1. Backbone area: It plays the role of letting other non-backbone areas know the network situation of other areas. In other words, all routing information for non-backbone areas flows through the backbone area.

2. Virtual link: A link that passes through a non-backbone area to a backbone area.

Purpose of use:

Connect a non-backbone area to a backbone area via a non-backbone area

connecting two separate backbone sections by a non-backbone section

Rules:

Must be configured between two ABRs

The area through which the virtual link passes must have complete routing information as a transmission area.

The intermediate transport area cannot be a stub area

2 Operations, basic concepts

1. Advantages of OSPF's hierarchical topology:

1) Reduce SPF calculation frequency

2) Reduce routing table

3) Reduce LSU update overhead

2. OSPF router types

1) Internal routers: routers with all interfaces in the same AREA

2) Backbone router AREA0: A router with at least one interface connected to AREA0.

3) Area border router ABR: A router that connects multiple areas

ASBR: A router that has at least one interface to an external network.

3. Area Type of OSPF

1) Standard area: can receive link state updates and summaries.

2) Backbone area: AREA0, to which other areas must be connected to exchange routing information.

3) End zone: does not receive link state updates for TYPE 5.

4) Complete stub area: does not receive link state updates for TYPE 3 4 5

5) Secondary stub area: Receive link state update of TYPE 7, and summarize LSA of TYPE 7 in ABR.

4. LSA types for OSPF

1) TYPE 1: Each router generates for the area to which it belongs, describes the link state of the area, and only performs FLOODING in a specific AREA.

2) TYPE 2: In multi-access networks, generated by DR.

3) TYPE 3: Generated by ABR, describes the link between ABR and the internal router of a local area, these entries are flooded to the external ABR through AREA0.

TYPE 4: Generated by ABR, describes reachability to ASBR.

5) TYPE 5: Generated by ASBR, describes routes to destinations outside the AS, and is FLOODING to the entire AS except for the "stub area." E1: Use Internal Overhead + External Overhead E2(default): Use External Overhead

6) TYPE 6: MOSPF: Routers enhance OSPF functionality by using their Link State Database to establish multicast distribution trees for forwarding multicast traffic.

7) TYPE 7: generated by ASBR connected to NSSA, LSA of TYPE 7 FLOODING throughout NSSA, LSA of TYPE 7 can be converted to LSA of TYPE 5 by ABR. (ABR can summarize LSA of TYPE 7)

5. The process of LSA FLOODING (route discovery process)

1) Before routing occurs first within an AREA and starts sending aggregated LSAs to other AREAs, the entire area must be synchronized. (See Single Area OSPF Routing Operations)

2) The ABR checks the Link State Database within the AREA and generates a summarized LSA using TYPE 3 4. and send it to other networks.

3) Summarized LSAs are placed in an LSU and forwarded out over the ABR interface. (There are three exceptions: (1) The connected router is in a state below EXCHANGE.) (2) The connection is the complete terminal area. (3) The summarized LSA includes routes for TYPE 5 and connects stub areas.

4) ABR/ASBR receives aggregated LSAs, adds them to its own Link State Database, and FLOODING them to the local zone.

6. Update routing tables (maintain routes)

1) All routers first compute paths to destinations within the zone and add them to the routing table. TYPE 1 2 (see Route Maintenance in Single Area OSFP Operations)

2) All routers compute paths to other areas. TYPE 3 4

3) All routers except those in the stub area compute routes to the outside of the AS.

7. opaque LSA

1) TYPE 9----flooding only to local network 3. Area Type of OSPF

1) Standard area: can receive link state updates and summaries.

2) Backbone area: AREA0, to which other areas must be connected to exchange routing information.

3) End zone: does not receive link state updates for TYPE 5.

4) Complete stub area: does not receive link state updates for TYPE 3 4 5

5) Secondary stub area: Receive link state update of TYPE 7, and summarize LSA of TYPE 7 in ABR.

4. LSA types for OSPF

1) TYPE 1: Each router generates for the area to which it belongs, describes the link state of the area, and only performs FLOODING in a specific AREA.

2) TYPE 2: In multi-access networks, generated by DR.

3) TYPE 3: Generated by ABR, describes the link between ABR and the internal router of a local area, these entries are flooded to the external ABR through AREA0.

TYPE 4: Generated by ABR, describes reachability to ASBR.

5) TYPE 5: Generated by ASBR, describes routes to destinations outside the AS, and is FLOODING to the entire AS except for the "stub area." E1: Use Internal Overhead + External Overhead E2(default): Use External Overhead

6) TYPE 6: MOSPF: Routers enhance OSPF functionality by using their Link State Database to establish multicast distribution trees for forwarding multicast traffic.

7) TYPE 7: generated by ASBR connected to NSSA, LSA of TYPE 7 FLOODING throughout NSSA, LSA of TYPE 7 can be converted to LSA of TYPE 5 by ABR. (ABR can summarize LSA of TYPE 7)

5. The process of LSA FLOODING (route discovery process)

1) Before routing occurs first within an AREA and starts sending aggregated LSAs to other AREAs, the entire area must be synchronized. (See Single Area OSPF Routing Operations)

2) ABR checks the Link State Database within AREA and generates a summarized LSA using TYPE 3 4. and send it to other networks.

3) Summarized LSAs are placed in an LSU and forwarded out over the ABR interface. (There are three exceptions: (1) The connected router is in a state below EXCHANGE.) (2) The connection is the complete terminal area. (3) The summarized LSA includes routes for TYPE 5 and connects stub areas.

4) ABR/ASBR receives aggregated LSAs, adds them to its own Link State Database, and FLOODING them to the local zone.

6. Update routing tables (maintain routes)

1) All routers first compute paths to destinations within the area and add them to the routing table. TYPE 1 2 (see Route Maintenance in Single Area OSFP Operations)

2) All routers compute paths to other areas. TYPE 3 4

3) All routers except those in the stub area compute routes to the outside of the AS.

7. opaque LSA

TYPE 9----flooding only to local network

TYPE 10----flooding only in relevant AREAS

TYPE 11---Flooding throughout AS.

TYPE 10----flooding only in relevant AREAS

TYPE 11----Flooding throughout AS.

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