code 128 excel freeware Packet Types in Objective-C

Creator PDF-417 2d barcode in Objective-C Packet Types

Packet Types
Bar Code Encoder In Objective-C
Using Barcode encoder for iPhone Control to generate, create barcode image in iPhone applications.
Generating PDF 417 In Visual C#
Using Barcode creation for VS .NET Control to generate, create PDF-417 2d barcode image in .NET framework applications.
This section examines the OSPF packet types and their components These types will become more important as we examine OSPF operation in detail:
PDF-417 2d Barcode Drawer In .NET
Using Barcode generator for ASP.NET Control to generate, create PDF417 image in ASP.NET applications.
PDF417 Printer In VS .NET
Using Barcode encoder for .NET Control to generate, create PDF-417 2d barcode image in VS .NET applications.
OSPF packet headers (included in all types) Include basic information related to the router, such as the OSPF version, packet type, router ID, and area ID Type 1 packets (hello) Establish and maintain adjacencies Hello packets include all information required to establish a neighborship, including hello and dead intervals, the password, the network mask for the link on which the hello was sent, the stub area flag, any elected DRs or BDRs, and any known neighbors Type 2 packets (database description) Build the link-state database on the router when an adjacency is initialized Database description packets include LSA headers (not the entire LSA) in order for the receiving router to confirm that it has all the required LSAs Type 3 packets (link-state request) Request specific LSAs from neighbors Linkstate request packets are sent based on entries in the link-state request list Type 4 packets (link-state update) Supply LSAs to remote routers They are flooded when an LSA changes or a link-state request is received Type 4 packets must be acknowledged Type 5 packets (link state acknowledgement) Sent to explicitly acknowledge one or more LSAs
Printing PDF-417 2d Barcode In Visual Basic .NET
Using Barcode creation for Visual Studio .NET Control to generate, create PDF 417 image in .NET framework applications.
Bar Code Generation In Objective-C
Using Barcode generator for iPhone Control to generate, create bar code image in iPhone applications.
LSA Types This section examines the most common LSA types Other types exist, but are not generally used
Encode Bar Code In Objective-C
Using Barcode encoder for iPhone Control to generate, create bar code image in iPhone applications.
EAN128 Printer In Objective-C
Using Barcode drawer for iPhone Control to generate, create EAN 128 image in iPhone applications.
Type 1 LSA (router link entry) Generated by every router for each area of which the router is a member These LSAs contain the status of all of the router's links to a given area and are flooded to all links within the same area Type 2 LSA (network entry) Generated by DRs on every non point-to-point (multiaccess) network Type 2 LSAs include all routers attached to the network for which the router is the DR Type 3 LSA (summary network link-state entry) Generated by ABRs and advertise internal networks from a specific area to other ABRs The other ABRs then choose the best path to the network(s) based on all Type 3 LSAs received, and flood the best path into nonbackbone areas using Type 3 LSAs Note that Type 3 LSAs may or may not be a summarized network entry To summarize networks in Type 3 LSAs, you need to configure the ABRs to summarize the entries Type 3 LSAs are not distributed to totally stubby areas (except for a single Type 3 for the default route) Type 4 LSA (summary ASBR link-state entry) Used by ABRs to advertise the best paths to ASBRs Type 4 LSAs are not flooded to stubby, totally stubby, and not-sostubby areas (NSSAs) Type 5 LSA (AS external entry, also called external entries) Sent by ASBRs and advertise destinations external to the AS (destinations redistributed from another OSPF AS or another routing protocol) Type 5 entries are flooded throughout the entire AS, except for stubby, totally stubby, and not-so-stubby areas Type 5 entries are split into two separate subtypes, depending on the metric calculation used: o External Type 1 (E1) E1 entries have their metric calculated as a sum of the redistributed route's cost and the cost of the links to the sending router E1
Encode Data Matrix In Objective-C
Using Barcode encoder for iPhone Control to generate, create DataMatrix image in iPhone applications.
Code 128B Generation In Objective-C
Using Barcode generation for iPhone Control to generate, create Code 128 Code Set A image in iPhone applications.
entries are typically used when more than one ASBR is advertising a given external destination o External Type 2 (E2) E2 entries have their metric calculated simply as the cost of the redistributed route (Cost of internal links to the advertising ASBR are not taken into account) E2 entries are subsequently "cheaper," and routers usually prefer them to E1 entries Type 7 (NSSA external link entry) Generated only by ASBRs in NSSAs Type 7 LSAs are flooded only throughout the NSSA ABRs convert Type 7 LSAs into Type 5 LSAs for distribution to the rest of the AS Type 7 LSAs also have two subtypes: o NSSA External Type 1 (N1) N1 entries have their metric calculated as a sum of the redistributed route's cost and the cost of the links to the sending router N1 entries are typically used when more than one ASBR is advertising a given external destination o NSSA External Type 2 (N2) N2 entries have their metric calculated simply as the cost of the redistributed route (Cost of internal links to the advertising ASBR are not taken into account) N2 entries are subsequently "cheaper," and routers usually prefer them to N1 entries Note In addition to the LSA types listed here, there are also Type 6, Type 8, Type 9, Type 10, and Type 11 LSAs However, because these LSAs are either unused at present or unsupported by Cisco routers, this chapter does not cover them
EAN / UCC - 13 Printer In Objective-C
Using Barcode generation for iPhone Control to generate, create UPC - 13 image in iPhone applications.
UPC-A Supplement 5 Generation In Objective-C
Using Barcode maker for iPhone Control to generate, create GS1 - 12 image in iPhone applications.
Network Types This section examines the OSPF network types, as defined by either the RFCs or Cisco (depending on the type in question) These concepts will be central to understanding the OSPF update process over various media:
Creating European Article Number 8 In Objective-C
Using Barcode creation for iPhone Control to generate, create EAN-8 Supplement 2 Add-On image in iPhone applications.
USS-128 Creator In .NET
Using Barcode drawer for ASP.NET Control to generate, create UCC-128 image in ASP.NET applications.
Broadcast (multi-access) A network that follows basic Ethernet conventions, where any host that is part of the same logical network can communicate with any other host In this configuration, DRs and BDRs are elected, and neighbor and adjacency establishment is automatic The default hello time in this network is 10 seconds, and the default dead interval is 40 seconds Point-to-point A type of network in which a single WAN link (usually a Frame Relay PVC) connects two routers More than two routers may be interconnected with multiple links Each link needs to have its own logical network address In this environment, a DR and BDR are not elected (or required), and neighbor adjacencies are automatically configured The default hello time in this network is 10 seconds, and the default dead interval is 40 seconds Point-to-multipoint (NBMA with broadcast emulation, full mesh) A type of network in which each router has a point-to-multipoint connection to every other router Note that this is not a single multipoint connection from a central router to all routers (that would be a star topology), but a multipoint connection from each router to every other router (making the topology a full mesh) In this environment, you can set all routers to use the same logical network for the mesh, and enable broadcast forwarding on the multipoint connections In this environment, a DR and BDR are elected, and neighbor adjacencies are automatically configured The default hello time in this network is 10 seconds, and the default dead interval is 40 seconds Point-to-multipoint (NBMA, full mesh) A type of network in which each router has a point-to-multipoint connection to every other router Note that this is not a single
Print Data Matrix ECC200 In C#
Using Barcode printer for .NET Control to generate, create DataMatrix image in Visual Studio .NET applications.
Painting Barcode In None
Using Barcode maker for Online Control to generate, create barcode image in Online applications.
multipoint connection from a central router to all routers (that would be a star topology), but rather a multipoint connection from each router to every other router (making the topology a full mesh) All routers use the same logical network address, but broadcast emulation is disabled In this environment, a DR and BDR are elected, and neighbor adjacencies must be manually configured The default hello time in this network is 30 seconds, and the default dead interval is 120 seconds Point-to-multipoint (NBMA, star, or partial mesh) A type of network with one or more routers in a partial mesh or hub-and-spoke style topology with point-tomultipoint links In these topologies, all routers use the same logical network address In this environment, a DR and BDR are not elected (or required), and neighbor adjacencies must be manually configured The default hello time in this network is 30 seconds, and the default dead interval is 120 seconds Transit (all available topology types) A type of network with OSPF routers attached Transit networks may be used by OSPF to forward packets to other OSPF routers In other words, a transit network may receive data packets that are destined for other networks and are just passing through Stub A network with only one OSPF router attached Stub networks receive data packets destined only for the stub network itself Virtual link A link that is used to connect a remote area to the backbone area through another AS Virtual links have no IP address, and are similar to tunnels through a nonbackbone area designed to forward packets to the backbone In a well-designed OSPF network, permanent virtual links should not exist Note Do not confuse transit networks with transit areas or stub networks with stub areas The names are similar, but the concepts are very different
Barcode Printer In Java
Using Barcode creation for Android Control to generate, create bar code image in Android applications.
Code 128 Code Set C Recognizer In Visual C#
Using Barcode reader for .NET Control to read, scan read, scan image in VS .NET applications.
Databases and Tables This section examines the different tables (also known as databases) used by OSPF These concepts are central to understanding OSPF:
Bar Code Printer In Java
Using Barcode drawer for Android Control to generate, create barcode image in Android applications.
Bar Code Generator In .NET Framework
Using Barcode printer for ASP.NET Control to generate, create bar code image in ASP.NET applications.
Neighborship database (neighbor table) Contains a list of all routers with which a two-way neighborship has been established, along with each neighbor's router ID, priority, neighborship state, router designation, remaining dead time, and interface IP address If a router is directly connected to another router by more than one logical network, that router will have multiple neighborships established Link-state database (topology database) Contains all of the LSA entries for a given area, and is used to generate the routing table All links in the entire area (plus external routes) should be listed in this database for every router in the area Subsequently, every router in a given area should have an identical copy of the link-state database for that area Routing table (forwarding database) Contains the best valid paths to all known destinations (The routing table in OSPF is the same as in any other routing protocol) It is built by running the SPF algorithm on the link-state database
Router Types Understanding router types is central to understanding the OSPF update process The different OSPF router designations are as follows:
Designated router (DR) The router chosen through the election process to be the primary "advertising router" for the individual logical network in question and all routers attached to that network The DR is usually the router with the highest priority DRs exist only on multi-access networks with more than one OSPF-speaking router The DR establishes an adjacency with all routers on the network Backup designated router (BDR) The router chosen to be the secondary "advertising router" for the individual logical network in question and all routers attached to that network The BDR is usually the router with the second-highest priority BDRs exist only on multi-access networks with more than one OSPFspeaking router The BDR also establishes an adjacency with all routers on the network DROther An OSPF router that is not the DR or BDR on a multi-access network with more than one OSPF router DROthers establish adjacencies only with the DR and BDR on the logical network Internal router Any router that has all interfaces in the same area All internal routers for a given area have a single, identical topology database Backbone router Any router that has at least one interface in Area 0 (the backbone area) Area border router (ABR) Any router that has one or more interfaces in different areas ABRs are used to summarize and forward packets along paths between different areas Autonomous system border router (ASBR) Any router that is redistributing routes from a different routing protocol or OSPF AS into the target OSPF AS
Neighborship States This section examines the different states of neighborship between OSPF routers These concepts are central to the OSPF update mechanism:
Down The initial state of a neighbor Neighbors in the down state do not exist in the neighbor table Attempt On NBMA networks, this is the state whereby neighborship establishment is attempted On NBMA networks, neighbors must be manually configured For these networks, hellos will be sent to all configured neighbors as a unicast to attempt to establish a neighborship Init The state that indicates that the router has seen a hello from this neighbor recently (the dead interval has not expired since the last hello was seen), but has yet to see its own router ID listed in the neighbor's hello packet (meaning that the neighbor has yet to see a hello from this router) Once a router reaches this state with a neighbor, it will begin including the neighbor's router ID in its hello packets 2-way The state in which the router has seen its own router ID in the neighbor's hello packet, meaning that the neighbor is receiving his hello, and bidirectional communication has been established Exstart The state in which the neighbors have already chosen to form an adjacency and are in the process of determining how to transfer database description packets (OSPF Type 2 packets) to each other Exchange The state in which the routers exchange database description packets (OSPF Type 2 packets)
Loading The state in which routers send link-state request packets (OSPF Type 3 packets) for all LSAs listed in the link-state request list and receive link-state update packets (OSPF Type 4 packets) in response Full The state in which neighbors are fully adjacent and should have identical copies of the link-state database for the area
Area Types This section examines the OSPF area types These concepts are central to understanding multi-area OSPF functionality:
Standard area The most common type of area Any area that is not the backbone area or some form of stub area is a standard area Standard areas support Type 1 through 5 LSAs Backbone area (Area 0) The hub in your OSPF AS The backbone area is responsible for forwarding traffic between areas All areas in a multi-area OSPF solution should have a connection to the backbone area Transit area An area where traffic from other areas can travel through en route to their final destination The backbone area is considered a transit area Stub area An area where there is only one way to reach external (other AS) destinations For this reason, a stub area does not require Type 4 or Type 5 LSAs Instead, a single Type 3 LSA for a default route is inserted into the stub area to provide the path to external destinations Stub areas require less network, CPU, and memory resources because they do not have to keep external LSAs in the topology table Stub areas allow only Type 1 through 3 LSAs Totally stubby area An area where there is only one way to reach external (other AS) and interarea destinations In other words, in a totally stubby area, there is only one way to reach destinations external to the area Therefore, a totally stubby area does not require Type 3, Type 4, or Type 5 LSAs A single default route is inserted into the stub area to provide the path to all destinations that are not a member of the totally stubby area Totally stubby areas therefore require even less resources than stub areas Totally stubby areas allow only Type 1 and 2 LSAs (except for a single Type 3 LSA for a default route) Totally stubby areas are a non-RFC-defined (Cisco-defined) enhancement Not-so-stubby area (NSSA) An area that requires the transmission of external LSAs from an ASBR within the area, but only has a single path to ASBRs in other areas Because the NSSA area has only one path to external destinations reached by ASBRs in other areas, the NSSA area is normally able to be a stub area However, because stub areas do not allow Type 5 LSAs and the NSSA contains an ASBR (which generates Type 5 LSAs), the NSSA is required to be a standard transit area (increasing resources required to support the area) In this case, the area can be configured as an NSSA ASBRs in an NSSA generate Type 7 LSAs (instead of Type 5 LSAs) to advertise external destinations, and the ABR for the NSSA converts the Type 7 LSAs in Type 5 LSAs for the rest of the AS NSSAs still do not allow Type 4 or 5 LSAs, and they use a single default route to reach external destinations advertised by ASBRs in other areas NSSAs are RFC defined and described in RFC 1578
Destination Types These are the standard destination types discussed throughout the chapter:
Network A standard entry into the routing table It defines networks to which packets can be routed (just like normal routing table entries) Router A path to ASBRs and ABRs Because OSPF needs to know where ABRs are located to correctly route interarea packets, an entry for each ABR is listed in an internal routing table Similarly, an entry for each ASBR is listed in the internal routing table
Path Types Some standard path types used by OSPF are as follows:
Intra-area Routing table entries to an area of which the router is a member If the router is an internal router, it contains only intra-area routes for a single area If the router is an ABR, it contains intra-area routes for all attached areas Intra-area routes are constructed from Type 1 and 2 LSAs Interarea Routes to destinations within another area in the same OSPF AS Interarea routes are constructed from Type 3 LSAs E1 (External Type 1) Entries that are constructed from Type 5 E1 LSAs propagated by ASBRs E2 (External Type 2) Entries that are constructed from Type 5 E2 LSAs propagated by ASBRs
Whew! Now that you've examined the very extensive list of definitions involved with OSPF, you're ready to learn how OSPF works
Copyright © OnBarcode.com . All rights reserved.