No relevant resource is found in the selected language.

This site uses cookies. By continuing to browse the site you are agreeing to our use of cookies. Read our privacy policy>Search

Reminder

To have a better experience, please upgrade your IE browser.

upgrade

ME60 V800R010C10SPC500 Feature Description - WAN Access 01

This is ME60 V800R010C10SPC500 Feature Description - WAN Access
Rate and give feedback:
Huawei uses machine translation combined with human proofreading to translate this document to different languages in order to help you better understand the content of this document. Note: Even the most advanced machine translation cannot match the quality of professional translators. Huawei shall not bear any responsibility for translation accuracy and it is recommended that you refer to the English document (a link for which has been provided).
OSPFv3 Fundamentals

OSPFv3 Fundamentals

Running on IPv6, OSPFv3 is an independent routing protocol that is developed on the basis of OSPFv2.

  • OSPFv3 and OSPFv2 are the same in terms of the working principles of the Hello packet, state machine, link-state database (LSDB), flooding, and route calculation.

  • OSPFv3 packets are encapsulated into IPv6 packets and can be transmitted in unicast or multicast mode.

OSPFv3 Packet Types

Packet Type

Function

Hello packet

Hello packets are sent periodically to discover and maintain OSPFv3 neighbor relationships.

Database Description (DD) packet

DD packets contain the summary of the local LSDB and are exchanged between two OSPFv3 routers to update the LSDBs.

Link State Request (LSR) packet

LSR packets are sent to the neighbor to request the required LSAs.

An OSPFv3 device sends LSR packets to its neighbor only after they exchange DD packets.

Link State Update (LSU) packet

LSU packets carry the LSAs required by neighbors.

Link State Acknowledgment (LSAck) packet

LSAck packets acknowledge the receipt of an LSA.

LSA Types

LSA Type

Description

Router-LSA (Type 1)

Describes the link status and link cost of a router. It is generated by every router and advertised in the area to which the router belongs.

Network-LSA (Type 2)

Describes the link status of all routers on the local network segment. Network-LSAs are generated by a designated router (DR) and advertised in the area to which the DR belongs.

Inter-Area-Prefix-LSA (Type 3)

Describes routes to a specific network segment in an area. Inter-Area-Prefix-LSAs are generated on the Area Border Router (ABR) and sent to related areas.

Inter-Area-Router-LSA (Type 4)

Describes routes to an Autonomous System Boundary Router (ASBR). Inter-Area-Router-LSAs are generated by an ABR and advertised to all related areas except the area to which the ASBR belongs.

AS-external-LSA (Type 5)

Describes routes to a destination outside the AS. AS-external-LSAs are generated by an ASBR and advertised to all areas except stub areas and NSSAs.

NSSA LSA (Type7)

Describes routes to a destination outside the AS. It is generated by an ASBR and advertised in NSSAs only.

Link-LSA (Type 8)

Describes the link-local address and IPv6 address prefix associated with the link and the link option set in the network LSA. Link LSAs are transmitted only on the link.

Intra-Area-Prefix-LSA (Type 9)

Each device or DR generates one or more intra-area prefix LSAs and transmits it in the local area.

  • An intra-area prefix LSA generated by a device describes the IPv6 address prefix associated with the router LSA.
  • An intra-area prefix LSA generated by a DR describes the IPv6 address prefix associated with the network LSA.

Router Types

Figure 7-1 Router types

Table 7-1 Router types and descriptions

Router Type

Description

Internal router

All interfaces on an internal router belong to the same OSPFv3 area.

Area border router (ABR)

An ABR belongs to two or more areas, one of which must be the backbone area.

An ABR is used to connect the backbone area and non-backbone areas. It can be physically or logically connected to the backbone area.

Backbone router

At least one interface on a backbone router belongs to the backbone area.

Internal routers in Area 0 and all ABRs are backbone routers.

AS boundary router (ASBR)

An ASBR exchanges routing information with other ASs.

An ASBR does not necessarily reside on the border of an AS. It can be an internal router or an ABR. An OSPFv3 device that has imported external routing information will become an ASBR.

OSPFv3 Route Types

Inter-area routes and intra-area routes describe the network structure of an AS. External routes describe how to select a route to the destination outside an AS. OSPFv3 classifies the imported AS external routes into Type 1 routes and Type 2 routes.

Table 7-2 lists route types in descending order of priority.

Table 7-2 Types of OSPFv3 routes

Route Type

Description

Intra area route

Indicates routes within an area.

Inter area route

Indicates routes between areas.

Type 1 external route

Type 1 external routes have high reliability.

Cost of a Type 1 external route = Cost of the route from a local router to an ASBR + Cost of the route from the ASBR to the destination of the Type 1 external route

Type 2 external route

Type 2 external routes have low reliability, and therefore OSPFv3 considers the cost of the route from an ASBR to the destination of a Type 2 external route to be much greater than the cost of any internal route to the ASBR.

Cost of a Type 2 external route = Cost of the route from the ASBR to the destination of the Type 2 external route

Area

When a large number of ME devices run OSPFv3, LSDBs become very large and require a large amount of storage space. Large LSDBs also complicate shortest path first (SPF) computation and are computationally intensive for the ME devices. Network expansion causes the network topology to change, which results in route flapping and frequent OSPFv3 packet transmission. When a large number of OSPFv3 packets are transmitted on the network, bandwidth usage efficiency decreases. Each change in the network topology causes all ME devices on the network to recalculate routes.

OSPFv3 resolves this problem by partitioning an AS into different areas. An area is regarded as a logical group, and each group is identified by an area ID. A ME device, not a link, resides at the border of an area. A network segment or link can belong only to one area. An area must be specified for each OSPFv3 interface.

OSPFv3 areas include common areas, stub areas, and not-so-stubby areas (NSSAs), as described in Table 7-3.

Table 7-3 OSPFv3 areas

Area Type

Function

Notes

Common area

OSPFv3 areas are common areas by default. Common areas include standard areas and backbone areas.

  • Standard area: transmits intra-area, inter-area, and external routes.
  • Backbone area: connects to all other OSPFv3 areas and transmits inter-area routes. The backbone area is represented by area 0. Routes between non-backbone areas must be forwarded through the backbone area.
  • In the backbone area, all devices must be connected.
  • All non-backbone areas must be connected to the backbone area.

Stub area

A stub area is a non-backbone area with only one ABR and generally resides at the border of an AS. The ABR in a stub area does not transmit received AS external routes, which significantly decreases the number of entries in the routing table on the ABR and the amount of routing information to be transmitted. To ensure the reachability of AS external routes, the ABR in the stub area generates a default route and advertises the route to non-ABRs in the stub area.

A totally stub area allows only intra-area routes and ABR-advertised Type 3 LSAs carrying a default route to be advertised within the area.

  • The backbone area cannot be configured as a stub area.
  • An ASBR cannot exist in a stub area. Therefore, AS external routes cannot be advertised within the stub area.

NSSA

An NSSA is similar to a stub area. An NSSA does not advertise Type 5 LSAs but can import AS external routes. ASBRs in an NSSA generate Type 7 LSAs to carry the information about the AS external routes. The Type 7 LSAs are advertised only within the NSSA. When the Type 7 LSAs reach an ABR in the NSSA, the ABR translates the Type 7 LSAs into Type 5 LSAs and floods them to the entire AS.

A totally NSSA area allows only intra-area routes to be advertised within the area.

  • ABRs in an NSSA advertise Type 3 LSAs carrying a default route within the NSSA. All inter-area routes are advertised by ABRs.

Network Types Supported by OSPFv3

OSPFv3 classifies networks into the following types based on link layer protocols.

Table 7-4 Types of OSPFv3 networks

Network Type

Description

Broadcast

OSPFv3 considers networks with Ethernet or Fiber Distributed Data Interface (FDDI) as the link layer protocol as broadcast networks by default.

On a broadcast network:

  • Hello packets, LSU packets, and LSAck packets are usually transmitted in multicast mode. FF02::5 is an IPv6 multicast address reserved for an OSPFv3 device. FF02::6 is an IPv6 multicast address reserved for an OSPFv3 DR or backup designated router (BDR).

  • DD and LSR packets are transmitted in unicast mode.

Non-broadcast Multiple Access (NBMA)

OSPFv3 considers networks with X.25 as the link layer protocol as NBMA networks by default.

On an NBMA network, protocol packets, such as Hello packets, DD packets, LSR packets, LSU packets, and LSAck packets are sent in unicast mode.

Point-to-Multipoint (P2MP)

No network is a P2MP network by default, no matter what type of link layer protocol is used on the network. A non-fully meshed NBMA network can be changed to a P2MP network.

On a P2MP network:

  • Hello packets are transmitted in multicast mode using the multicast address FF02::5.

  • Other types of protocol packets, such as DD packets, LSR packets, LSU packets, and LSAck packets are sent in unicast mode.

Point-to-point (P2P)

OSPFv3 considers networks with PPP, or LAPB as the link layer protocol to be P2P networks by default.

On a P2P network, protocol packets, such as Hello packets, DD packets, LSR packets, LSU packets, and LSAck packets are sent in multicast mode using the multicast address FF02::5.

Stub Area

Stub areas are specific areas where ABRs do not flood received AS external routes. In stub areas, routers maintain fewer routing entries and less routing information than the routers in other areas.

Configuring a stub area is optional. Not every area can be configured as a stub area, because a stub area is usually a non-backbone area with only one ABR and is located at the AS border.

To ensure the reachability of the routes to destinations outside an AS, the ABR in the stub area generates a default route and advertises the route to the non-ABRs in the same stub area.

Note the following points when configuring a stub area:

  • The backbone area cannot be configured as a stub area.

  • Configure stub area attributes on all routers in the area to be configured as a stub area.

  • No ASBRs are allowed in the area to be configured as a stub area because AS external routes cannot be transmitted in the stub area.

NSSA

Stub areas cannot import or transmit external routes, which prevents a large number of external routes from consuming the bandwidth and storage resources of ME devices in the Stub areas. If you need to import external routes to an area and prevent these routes from consuming resources, configure the area as a not-so-stubby area (NSSA).

Derived from stub areas, NSSAs resemble stub areas in many ways. Different from stub areas, NSSAs can import AS external routes and advertise them within the entire AS, without learning external routes from other areas in the AS.

To advertise external routes imported by an NSSA to other areas on the OSPFv3 network, a translator must translate Type 7 LSAs into Type 5 LSAs.

NOTE:
  • The propagate bit (P-bit) is used to notify a translator whether Type 7 LSAs need to be translated.

  • By default, the translator is the ABR with the largest router ID in the NSSA.

  • The P-bit is not set for Type 7 LSAs generated by an ABR.

OSPFv3 Route Summarization

Routes with the same IPv6 prefix can be summarized into one route. On a large-scale OSPFv3 network, route lookup may slow down because of the large size of the routing table. To reduce the routing table size and simplify management, configure route summarization. With route summarization, if a link connected to a device within an IPv6 address range that has been summarized alternates between Up and Down, the link status change is not advertised to the devices beyond the IPv6 address range. This prevents route flapping and improves network stability.

OSPFv3 route summarization is classified as follows:

  • Route summarization on an ABR

    An ABR can summarize routes with the same prefix into one route and advertise the summarized route to other areas.

    When an ABR transmits routing information to other areas, it generates Type 3 LSAs for each network segment. If contiguous segments exist in this area, these segments can be summarized into one segment so that the ABR sends only one summarized LSA.

  • Route summarization on an ASBR

    An ASBR can summarize imported routes with the same prefix into one route and then advertise the summarized route to other areas.

    With route summarization, an ASBR summarizes imported Type 5 LSAs within the summarized address range. After route summarization, the ASBR does not generate a separate Type 5 LSA for each specific prefix within the configured range. Instead, the ASBR generates a Type 5 LSA for only the summarized prefix. In an NSSA, an ASBR summarizes multiple imported Type 7 LSAs within the summarized address range into one Type 7 LSA.

OSPFv3 Multi-process

OSPFv3 supports multi-process. Multiple OSPFv3 processes can independently run on the same router. Route exchange between different OSPFv3 processes is similar to that between different routing protocols.

Translation
Download
Updated: 2019-01-04

Document ID: EDOC1100059473

Views: 14569

Downloads: 10

Average rating:
This Document Applies to these Products
Related Version
Related Documents
Share
Previous Next