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Page "Open Shortest Path First" ¶ 9
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OSPF and multicast
OSPF uses multicast addressing for route flooding on a broadcast network link.
OSPF multicast IP packets never traverse IP routers, they never travel more than one hop.
For routing multicast IP traffic, OSPF supports the Multicast Open Shortest Path First protocol ( MOSPF ) as defined in RFC 1584.
OSPF uses both unicast and multicast to send " hello packets " and link state updates.

OSPF and <
By convention, area 0 ( zero ) or < tt > 0. 0. 0. 0 </ tt > represents the core or backbone region of an OSPF network.

OSPF and .
PNNI uses the same shortest-path-first algorithm used by OSPF and IS-IS to route IP packets to share topology information between switches and select a route through a network.
Dijkstra's algorithm is used in SPF, Shortest Path First, which is used in the routing protocols OSPF and IS-IS.
MPLS Traffic Engineering relies upon the use of TE extensions to Open Shortest Path First ( OSPF ) or Intermediate System To Intermediate System ( IS-IS ) and RSVP.
Interior routing mostly uses link-state routing protocols such as OSPF and IS-IS.
An example would be the joining of a number of large OSPF ( Open Shortest Path First ) networks where OSPF by itself would not scale to size.
Like the OSPF protocol, IS-IS uses Dijkstra's algorithm for computing the best path through the network.
IS-IS was developed at roughly the same time that the Internet Engineering Task Force IETF was developing a similar protocol called OSPF.
Both IS-IS and OSPF are link state protocols, and both use the same Dijkstra algorithm for computing the best path through the network.
OSPF, on the other hand, was designed for IPv4.
IS-IS differs from OSPF in the way that " areas " are defined and routed between.
In OSPF, areas are delineated on the interface such that an area border router ( ABR ) is actually in two or more areas at once, effectively creating the borders between areas inside the ABR, whereas in IS-IS area borders are in between routers, designated as Level 2 or Level 1-2.
The logical view is that OSPF creates something of a spider web or star topology of many areas all attached directly to Area Zero and IS-IS by contrast creates a logical topology of a backbone of Level 2 routers with branches of Level 1-2 and Level 1 routers forming the individual areas.
IS-IS also differs from OSPF in the methods by which it reliably floods topology and topology change information through the network.
OSPF has a larger set of extensions and optional features.
Given the same set of resources, IS-IS can support more routers in an area than OSPF.
OSPF uses the Dijkstra algorithm.
Open Shortest Path First ( OSPF ) is an adaptive routing protocol for Internet Protocol ( IP ) networks.
It is defined as OSPF Version 2 in RFC 2328 ( 1998 ) for IPv4.
OSPF is perhaps the most widely used interior gateway protocol ( IGP ) in large enterprise networks.
OSPF was designed to support variable-length subnet masking ( VLSM ) or Classless Inter-Domain Routing ( CIDR ) addressing models.
OSPF detects changes in the topology, such as link failures, very quickly and converges on a new loop-free routing structure within seconds.
Identical copies of the LSDB are periodically updated through flooding on all OSPF routers.
The OSPF routing policies to construct a route table are governed by link cost factors ( external metrics ) associated with each routing interface.
An OSPF network may be structured, or subdivided, into routing areas to simplify administration and optimize traffic and resource utilization.

OSPF and 0
The backbone area ( also known as area 0 or area 0. 0. 0. 0 ) forms the core of an OSPF network.
* If the priority setting on an OSPF router is set to 0, that means it can NEVER become a DR or BDR ( Backup Designated Router ).

OSPF and 5
An NSSA ASBR generates this LSA, and an NSSA ABR router translates it into type 5 LSA which gets propagated into the OSPF domain.
The " Main OSPF Packet Header " is the same for all 5 types of packets ( with exception of the Type field ) whereas the following sub-headers will vary from type to type and are shown below the Main OSPF Packet Header.
* An OSPF stubby area is one which receives routes from other areas in the OSPF domain but for external routes, which are communicated via a Type 5 Link-state advertisement, the stubby area is only aware of a default route

OSPF and for
The updates for IPv6 are specified as OSPF Version 3 in RFC 5340 ( 2008 ).
The area identifiers for IPv6 implementations of OSPF ( OSPFv3 ) also use 32-bit identifiers written in the same notation.
It is the logical and physical structure for the ' OSPF domain ' and is attached to all nonzero areas in the OSPF domain.
OSPF-TE is an extension to OSPF extending the expressivity to allow for traffic engineering and use on non-IP networks ( RFC 3630 ).
RFC 3717 documents work in optical routing for IP, based on " constraint-based " extensions to OSPF and IS-IS.
In most current networking environments, RIP is not the preferred choice for routing as its time to converge and scalability are poor compared to EIGRP, OSPF, or IS-IS ( the latter two being link-state routing protocols ), and ( without RMTI ) a hop limit severely limits the size of network it can be used in.
The technique was later adapted for use in the contemporary link-state routing protocols IS-IS and OSPF.
* Link-state advertisement, communication mechanism of the OSPF routing protocol for IP
RouterOS supports many applications used by Internet service providers, for example OSPF, BGP, Multiprotocol Label Switching ( VPLS / MPLS ).
To many, it is not clear whether a whole new protocol is needed, or whether OSPF could be extended with support for wireless interfaces.

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