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78-397: Open Shortest Path First ( OSPF ) is a routing protocol for Internet Protocol (IP) networks. It uses a link state routing (LSR) algorithm and falls into the group of interior gateway protocols (IGPs), operating within a single autonomous system (AS). OSPF gathers link state information from available routers and constructs a topology map of the network. The topology is presented as

156-887: A certificate authority , this can be used for IPsec authentication. The security associations of IPsec are established using the Internet Security Association and Key Management Protocol (ISAKMP). ISAKMP is implemented by manual configuration with pre-shared secrets, Internet Key Exchange (IKE and IKEv2), Kerberized Internet Negotiation of Keys (KINK), and the use of IPSECKEY DNS records . RFC 5386 defines Better-Than-Nothing Security (BTNS) as an unauthenticated mode of IPsec using an extended IKE protocol. C. Meadows, C. Cremers, and others have used formal methods to identify various anomalies which exist in IKEv1 and also in IKEv2. In order to decide what protection

234-487: A designated router (DR) and a backup designated router (BDR) which act as a hub to reduce traffic between routers. OSPF uses both unicast and multicast transmission modes to send "hello" packets and link-state updates. As a link-state routing protocol, OSPF establishes and maintains neighbor relationships for exchanging routing updates with other routers. The neighbor relationship table is called an adjacency database . Two OSPF routers are neighbors if they are members of

312-469: A broadcast domain. It reserves the multicast addresses 224.0.0.5 (IPv4) and ff02::5 (IPv6) for all SPF/link state routers (AllSPFRouters) and 224.0.0.6 (IPv4) and ff02::6 (IPv6) for all Designated Routers (AllDRouters). For non-broadcast networks, special provisions for configuration facilitate neighbor discovery. OSPF multicast IP packets never traverse IP routers, they never travel more than one hop. The protocol may therefore be considered

390-420: A connection to area 0.0.0.1. Area 0.0.0.2 can use a virtual link through the transit area 0.0.0.1 to reach the backbone. To be a transit area, an area has to have the transit attribute, so it cannot be stubby in any way. A regular area is just a non-backbone (nonzero) area without specific feature, generating and receiving summary and external LSAs. The backbone area is a special type of such area. A stub area

468-592: A few incompatible engineering details, although they were conceptually identical. In addition, a mutual authentication and key exchange protocol Internet Key Exchange (IKE) was defined to create and manage security associations. In December 2005, new standards were defined in RFC 4301 and RFC 4309 which are largely a superset of the previous editions with a second version of the Internet Key Exchange standard IKEv2 . These third-generation documents standardized

546-833: A hash, so they cannot be modified in any way, for example by translating the port numbers. A means to encapsulate IPsec messages for NAT traversal {NAT-T} has been defined by RFC documents describing the NAT-T mechanism. In tunnel mode, the entire IP packet is encrypted and authenticated. It is then encapsulated into a new IP packet with a new IP header. Tunnel mode is used to create virtual private networks for network-to-network communications (e.g. between routers to link sites), host-to-network communications (e.g. remote user access) and host-to-host communications (e.g. private chat). Tunnel mode supports NAT traversal. Cryptographic algorithms defined for use with IPsec include: Refer to RFC 8221 for details. The IPsec can be implemented in

624-521: A host-to-host transport mode, as well as in a network tunneling mode. In transport mode, only the payload of the IP packet is usually encrypted or authenticated. The routing is intact, since the IP header is neither modified nor encrypted; however, when the authentication header is used, the IP addresses cannot be modified by network address translation , as this always invalidates the hash value . The transport and application layers are always secured by

702-575: A link layer protocol, but is often also attributed to the application layer in the TCP/IP model. It has a virtual link feature that can be used to create an adjacency tunnel across multiple hops. OSPF over IPv4 can operate securely between routers, optionally using a variety of authentication methods to allow only trusted routers to participate in routing. OSPFv3 (IPv6) relies on standard IPv6 protocol security ( IPsec ), and has no internal authentication methods. For routing IP multicast traffic, OSPF supports

780-503: A link, or link availability and reliability, expressed as simple unitless numbers. This provides a dynamic process of traffic load balancing between routes of equal cost. OSPF divides the network into routing areas to simplify administration and optimize traffic and resource utilization. Areas are identified by 32-bit numbers, expressed either simply in decimal, or often in the same octet-based dot-decimal notation used for IPv4 addresses. By convention, area 0 (zero), or 0.0.0.0, represents

858-536: A maximum of eight conditions defined by a state machine: In broadcast multiple-access networks, neighbor adjacency is formed dynamically using multicast hello packets to 224.0.0.5 . A network where OSPF adverts the network, but the OSPF will not start neighbour adjacency. In a non-broadcast multiple-access (NBMA) network, a neighbor adjacency is formed by sending unicast packets to another router. A non-broadcast network can have more than two routers, but broadcast

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936-507: A means of distributing uncompromised networking gateways to authorized ports. This has the added benefit of preventing issues with routing protocol loops. Many routing protocols are defined in technical standards documents called RFCs . Although there are many types of routing protocols, three major classes are in widespread use on IP networks : Routing protocols, according to the OSI routing framework, are layer management protocols for

1014-552: A member of the IPsec protocol suite. It provides origin authenticity through source authentication , data integrity through hash functions and confidentiality through encryption protection for IP packets . ESP also supports encryption -only and authentication -only configurations, but using encryption without authentication is strongly discouraged because it is insecure. Unlike Authentication Header (AH) , ESP in transport mode does not provide integrity and authentication for

1092-679: A network encryption device in 1988. The work was openly published from about 1988 by NIST and, of these, Security Protocol at Layer 3 (SP3) would eventually morph into the ISO standard Network Layer Security Protocol (NLSP). In 1992, the US Naval Research Laboratory (NRL) was funded by DARPA CSTO to implement IPv6 and to research and implement IP encryption in 4.4 BSD , supporting both SPARC and x86 CPU architectures. DARPA made its implementation freely available via MIT. Under NRL's DARPA -funded research effort, NRL developed

1170-521: A point-to-point WAN connection) because the two routers on either side of the link must become fully adjacent and the bandwidth between them cannot be further optimized. DR and non-DR routers evolve from 2-way to full adjacency relationships by exchanging DD, Request, and Update. A designated router (DR) is the router interface elected among all routers on a particular multiaccess network segment, generally assumed to be broadcast multiaccess. Special techniques, often vendor-dependent, may be needed to support

1248-669: A router sends an update, it sends it to the DR and BDR on the multicast address 224.0.0.6 . The DR will then send the update out to all other routers in the area, to the multicast address 224.0.0.5 . This way all the routers do not have to constantly update each other, and can rather get all their updates from a single source. The use of multicasting further reduces the network load. DRs and BDRs are always setup/elected on OSPF broadcast networks. DR's can also be elected on NBMA (Non-Broadcast Multi-Access) networks such as Frame Relay or ATM. DRs or BDRs are not elected on point-to-point links (such as

1326-554: A routing table to the internet layer for routing packets by their destination IP address . OSPF supports Internet Protocol version 4 (IPv4) and Internet Protocol version 6 (IPv6) networks and is widely used in large enterprise networks . IS-IS , another LSR-based protocol, is more common in large service provider networks. Originally designed in the 1980s, OSPF version 2 is defined in RFC 2328 (1998). The updates for IPv6 are specified as OSPF version 3 in RFC 5340 (2008). OSPF supports

1404-467: A second area, an interface must be configured as a secondary interface. The OSPF can have different operation modes on the following setups on an interface or network: Virtual link over Virtual links, tunneling and sham links, are a form of connections that goes over the routing engine, and is not a direct connection to the remote host. Each OSPF router within a network communicates with other neighboring routers on each connecting interface to establish

1482-404: A security association is provided for the group, and is duplicated across all authorized receivers of the group. There may be more than one security association for a group, using different SPIs, thereby allowing multiple levels and sets of security within a group. Indeed, each sender can have multiple security associations, allowing authentication, since a receiver can only know that someone knowing

1560-697: A security extension for SIPP. This ESP was originally derived from the US Department of Defense SP3D protocol, rather than being derived from the ISO Network-Layer Security Protocol (NLSP). The SP3D protocol specification was published by NIST in the late 1980s, but designed by the Secure Data Network System project of the US Department of Defense . Encapsulating Security Payload (ESP) is

1638-409: A so-called bump-in-the-wire (BITW) implementation of IPsec is possible. When IPsec is implemented in the kernel , the key management and ISAKMP / IKE negotiation is carried out from user space. The NRL-developed and openly specified "PF_KEY Key Management API, Version 2" is often used to enable the application-space key management application to update the IPsec security associations stored within

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1716-407: Is a method of detecting a dead Internet Key Exchange (IKE) peer. The method uses IPsec traffic patterns to minimize the number of messages required to confirm the availability of a peer. DPD is used to reclaim the lost resources in case a peer is found dead and it is also used to perform IKE peer failover. UDP keepalive is an alternative to DPD. The IPsec protocols AH and ESP can be implemented in

1794-403: Is also used for both hosts and gateways. However, when retrofitting IPsec the encapsulation of IP packets may cause problems for the automatic path MTU discovery , where the maximum transmission unit (MTU) size on the network path between two IP hosts is established. If a host or gateway has a separate cryptoprocessor , which is common in the military and can also be found in commercial systems,

1872-489: Is an area that does not receive route advertisements external to the AS and routing from within the area is based entirely on a default route. An ABR deletes type 4 and 5 LSAs from internal routers, sends them a default route of 0.0.0.0 and turns itself into a default gateway. This reduces LSDB and routing table size for internal routers. Modifications to the basic concept of stub area have been implemented by systems vendors, such as

1950-507: Is an extension of the stub area feature that allows the injection of external routes in a limited fashion into the stub area. A case study simulates an NSSA getting around the stub-area problem of not being able to import external addresses. It visualizes the following activities: the ASBR imports external addresses with a type 7 LSA, the ABR converts a type 7 LSA to type 5 and floods it to other areas,

2028-459: Is constructed and interpreted: The IPsec protocols use a security association , where the communicating parties establish shared security attributes such as algorithms and keys. As such, IPsec provides a range of options once it has been determined whether AH or ESP is used. Before exchanging data, the two hosts agree on which symmetric encryption algorithm is used to encrypt the IP packet, for example AES or ChaCha20 , and which hash function

2106-403: Is designated router or backup designated router (on multiaccess-type networks), or they are interconnected by a point-to-point or point-to-multipoint network type. For forming a neighbor relationship between, the interfaces used to form the relationship must be in the same OSPF area. While an interface may be configured to belong to multiple areas, this is generally not practiced. When configured in

2184-402: Is historic, in the sense that many OSPF domains can coexist in the same Internet-visible autonomous system, RFC 1996. All OSPF areas must connect to the backbone area. This connection, however, can be through a virtual link. For example, assume area 0.0.0.1 has a physical connection to area 0.0.0.0. Further assume that area 0.0.0.2 has no direct connection to the backbone, but this area does have

2262-409: Is not supported. Examples of non-broadcast networks: A network is divided into OSPF areas that are logical groupings of hosts and networks. An area includes its connecting router having an interface for each connected network link. Each router maintains a separate link-state database for the area whose information may be summarized towards the rest of the network by the connecting router. Thus,

2340-531: Is omitted, most implementations expand area 1 to the area identifier 0.0.0.1 , but some have been known to expand it as 1.0.0.0 . Several vendors (Cisco, Allied Telesis, Juniper, Alcatel-Lucent, Huawei, Quagga), implement totally stubby and NSSA totally stubby area for stub and not-so-stubby areas. Although not covered by RFC standards, they are considered by many to be standard features in OSPF implementations. OSPF defines several area types: The backbone area (also known as area 0 or area 0.0.0.0 ) forms

2418-487: Is on the edge of a totally stubby area. In such a case, the ASBR does send externals into the totally stubby area, and they are available to OSPF speakers within that area. In Cisco's implementation, the external routes can be summarized before injecting them into the totally stubby area. In general, the ASBR should not advertise default into the TSA-NSSA, although this can work with extremely careful design and operation, for

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2496-520: Is to be provided for an outgoing packet, IPsec uses the Security Parameter Index (SPI), an index to the security association database (SADB), along with the destination address in a packet header, which together uniquely identifies a security association for that packet. A similar procedure is performed for an incoming packet, where IPsec gathers decryption and verification keys from the security association database. For IP multicast

2574-714: Is used in virtual private networks (VPNs). IPsec includes protocols for establishing mutual authentication between agents at the beginning of a session and negotiation of cryptographic keys to use during the session. IPsec can protect data flows between a pair of hosts ( host-to-host ), between a pair of security gateways ( network-to-network ), or between a security gateway and a host ( network-to-host ). IPsec uses cryptographic security services to protect communications over Internet Protocol (IP) networks. It supports network-level peer authentication, data origin authentication , data integrity , data confidentiality ( encryption ), and protection from replay attacks . Starting in

2652-630: Is used to deliver application traffic. It provides appropriate addressing information in its internet layer or network layer to allow a packet to be forwarded from one network to another. Examples of routed protocols are the Internet Protocol (IP) and Internetwork Packet Exchange (IPX). IPsec In computing , Internet Protocol Security ( IPsec ) is a secure network protocol suite that authenticates and encrypts packets of data to provide secure encrypted communication between two computers over an Internet Protocol network. It

2730-405: Is used to ensure the integrity of the data, such as BLAKE2 or SHA256 . These parameters are agreed for the particular session, for which a lifetime must be agreed and a session key . The algorithm for authentication is also agreed before the data transfer takes place and IPsec supports a range of methods. Authentication is possible through pre-shared key , where a symmetric key is already in

2808-416: Is used to reducing network traffic by providing a source for routing updates. This is done using multicast addresses: The DR and BDR maintains a complete topology table of the network and sends the updates to the other routers via multicast. All routers in a multi-access network segment will form a leader/follower relationship with the DR and BDR. They will form adjacencies with the DR and BDR only. Every time

2886-513: The Bullrun program. There are allegations that IPsec was a targeted encryption system. The OpenBSD IPsec stack came later on and also was widely copied. In a letter which OpenBSD lead developer Theo de Raadt received on 11 Dec 2010 from Gregory Perry, it is alleged that Jason Wright and others, working for the FBI, inserted "a number of backdoors and side channel key leaking mechanisms" into

2964-570: The Classless Inter-Domain Routing (CIDR) addressing model. OSPF is an interior gateway protocol (IGP) for routing Internet Protocol (IP) packets within a single routing domain, such as an autonomous system . It gathers link state information from available routers and constructs a topology map of the network. The topology is presented as a routing table to the internet layer which routes packets based solely on their destination IP address . OSPF detects changes in

3042-670: The IETF standards-track specifications (RFC 1825 through RFC 1827) for IPsec. NRL's IPsec implementation was described in their paper in the 1996 USENIX Conference Proceedings. NRL's open-source IPsec implementation was made available online by MIT and became the basis for most initial commercial implementations. The Internet Engineering Task Force (IETF) formed the IP Security Working Group in 1992 to standardize openly specified security extensions to IP, called IPsec . The NRL developed standards were published by

3120-697: The IP Protocol field . OSPF defines five different message types, for various types of communication. Multiple packets can be sent per frame. OSPF uses 5 packet types: Routing protocol The specific characteristics of routing protocols include the manner in which they avoid routing loops, the manner in which they select preferred routes, using information about hop costs, the time they require to reach routing convergence , their scalability , and other factors such as relay multiplexing and cloud access framework parameters. Certain additional characteristics such as multilayer interfacing may also be employed as

3198-591: The Multicast Open Shortest Path First (MOSPF) protocol. Cisco does not include MOSPF in their OSPF implementations. Protocol Independent Multicast (PIM) in conjunction with OSPF or other IGPs, is widely deployed. OSPF version 3 introduces modifications to the IPv4 implementation of the protocol. Except for virtual links, all neighbor exchanges use IPv6 link-local addressing exclusively. The IPv6 protocol runs per link, rather than based on

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3276-546: The Simple Network Management Protocol (SNMP) version 2. Authentication Header (AH) is a member of the IPsec protocol suite. AH ensures connectionless integrity by using a hash function and a secret shared key in the AH algorithm. AH also guarantees the data origin by authenticating IP packets . Optionally a sequence number can protect the IPsec packet's contents against replay attacks , using

3354-493: The application layer , IPsec can automatically secure applications at the internet layer . IPsec is an open standard as a part of the IPv4 suite and uses the following protocols to perform various functions: The Security Authentication Header (AH) was developed at the US Naval Research Laboratory in the early 1990s and is derived in part from previous IETF standards' work for authentication of

3432-611: The designated router (DR) and the backup designated router (BDR). For other non (B)DR, the adjacency stops at 2-ways State. The DR is elected based on the following default criteria: Unlike other routing protocols, OSPF does not carry data via a transport protocol, such as the User Datagram Protocol (UDP) or the Transmission Control Protocol (TCP). Instead, OSPF forms IP datagrams directly, packaging them using protocol number 89 for

3510-599: The sliding window technique and discarding old packets. AH operates directly on top of IP, using IP protocol number 51 . The following AH packet diagram shows how an AH packet is constructed and interpreted: The IP Encapsulating Security Payload (ESP) was developed at the Naval Research Laboratory starting in 1992 as part of a DARPA -sponsored research project, and was openly published by IETF SIPP Working Group drafted in December 1993 as

3588-516: The subnet . All IP prefix information has been removed from the link-state advertisements and from the hello discovery packet making OSPFv3 essentially protocol-independent. Despite the expanded IP addressing to 128 bits in IPv6, area and router Identifications are still based on 32-bit numbers. OSPF supports complex networks with multiple routers, including backup routers, to balance traffic load on multiple links to other subnets. Neighboring routers in

3666-462: The totally stubby area (TSA) and the not-so-stubby area (NSSA), both an extension in Cisco Systems routing equipment. A totally stubby area is similar to a stub area. However, this area does not allow summary routes in addition to not having external routes, that is, inter-area (IA) routes are not summarized into totally stubby areas. The only way for traffic to get routed outside

3744-428: The ABR acts as an ASBR for other areas. The ASBRs do not take type 5 LSAs and then convert to type 7 LSAs for the area. An addition to the standard functionality of an NSSA, the totally stubby NSSA is an NSSA that takes on the attributes of a TSA, meaning that type 3 and 4 summary routes are not flooded into this type of area. It is also possible to declare an area both totally stubby and not-so-stubby, which means that

3822-449: The ASBR. OSPF defines the following overlapping categories of routers: The router type is an attribute of an OSPF process. A given physical router may have one or more OSPF processes. For example, a router that is connected to more than one area, and which receives routes from a BGP process connected to another AS, is both an area border router and an autonomous system boundary router. Each router has an identifier, customarily written in

3900-401: The DR function on non-broadcast multiaccess (NBMA) media. It is usually wise to configure the individual virtual circuits of an NBMA subnet as individual point-to-point lines; the techniques used are implementation-dependent. A backup designated router (BDR) is a router that becomes the designated router if the current designated router has a problem or fails. The BDR is the OSPF router with

3978-511: The IETF as RFC 1825 through RFC 1827. The initial IPv4 suite was developed with few security provisions. As a part of the IPv4 enhancement, IPsec is a layer 3 OSI model or internet layer end-to-end security scheme. In contrast, while some other Internet security systems in widespread use operate above the network layer , such as Transport Layer Security (TLS) that operates above the transport layer and Secure Shell (SSH) that operates at

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4056-491: The IP stack of an operating system . This method of implementation is done for hosts and security gateways. Various IPsec capable IP stacks are available from companies, such as HP or IBM. An alternative is so called bump-in-the-stack (BITS) implementation, where the operating system source code does not have to be modified. Here IPsec is installed between the IP stack and the network drivers . This way operating systems can be retrofitted with IPsec. This method of implementation

4134-586: The NSA compromised IPsec VPNs by undermining the Diffie-Hellman algorithm used in the key exchange. In their paper, they allege the NSA specially built a computing cluster to precompute multiplicative subgroups for specific primes and generators, such as for the second Oakley group defined in RFC 2409. As of May 2015, 90% of addressable IPsec VPNs supported the second Oakley group as part of IKE. If an organization were to precompute this group, they could derive

4212-505: The OpenBSD crypto code. In the forwarded email from 2010, Theo de Raadt did not at first express an official position on the validity of the claims, apart from the implicit endorsement from forwarding the email. Jason Wright's response to the allegations: "Every urban legend is made more real by the inclusion of real names, dates, and times. Gregory Perry's email falls into this category. ... I will state clearly that I did not add backdoors to

4290-601: The OpenBSD operating system or the OpenBSD Cryptographic Framework (OCF)." Some days later, de Raadt commented that "I believe that NETSEC was probably contracted to write backdoors as alleged. ... If those were written, I don't believe they made it into our tree." This was published before the Snowden leaks. An alternative explanation put forward by the authors of the Logjam attack suggests that

4368-610: The abbreviation of IPsec to uppercase "IP" and lowercase "sec". "ESP" generally refers to RFC 4303, which is the most recent version of the specification. Since mid-2008, an IPsec Maintenance and Extensions (ipsecme) working group is active at the IETF. In 2013, as part of Snowden leaks , it was revealed that the US National Security Agency had been actively working to "Insert vulnerabilities into commercial encryption systems, IT systems, networks, and endpoint communications devices used by targets" as part of

4446-438: The area is a default route which is the only Type-3 LSA advertised into the area. When there is only one route out of the area, fewer routing decisions have to be made by the route processor, which lowers system resource utilization. A not-so-stubby area (NSSA) is a type of stub area that can import autonomous system external routes and send them to other areas, but still cannot receive AS-external routes from other areas. NSSA

4524-428: The area will receive only the default route from area 0.0.0.0, but can also contain an autonomous system boundary router (ASBR) that accepts external routing information and injects it into the local area, and from the local area into area 0.0.0.0. A newly acquired subsidiary is one example of where it might be suitable for an area to be simultaneously not-so-stubby and totally stubby if the practical place to put an ASBR

4602-439: The core of an OSPF network. All other areas are connected to it, either directly or through other routers. OSPF requires this to prevent routing loops . Inter-area routing happens via routers connected to the backbone area and to their own associated areas. It is the logical and physical structure for the 'OSPF domain' and is attached to all nonzero areas in the OSPF domain. In OSPF the term autonomous system boundary router (ASBR)

4680-499: The core or backbone area of an OSPF network. While the identifications of other areas may be chosen at will, administrators often select the IP address of a main router in an area as the area identifier. Each additional area must have a connection to the OSPF backbone area. Such connections are maintained by an interconnecting router, known as an area border router (ABR). An ABR maintains separate link-state databases for each area it serves and maintains summarized routes for all areas in

4758-517: The dotted-decimal format (e.g., 1.2.3.4) of an IP address. This identifier must be established in every OSPF instance. If not explicitly configured, the highest logical IP address will be duplicated as the router identifier. However, since the router identifier is not an IP address, it does not have to be a part of any routable subnet in the network, and often isn't to avoid confusion. On networks (same subnet) with networks type of: A system of designated router (DR) and backup designated router (BDR),

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4836-673: The early 1970s, the Advanced Research Projects Agency sponsored a series of experimental ARPANET encryption devices , at first for native ARPANET packet encryption and subsequently for TCP/IP packet encryption; some of these were certified and fielded. From 1986 to 1991, the NSA sponsored the development of security protocols for the Internet under its Secure Data Network Systems (SDNS) program. This brought together various vendors including Motorola who produced

4914-453: The entire IP packet . However, in tunnel mode , where the entire original IP packet is encapsulated with a new packet header added, ESP protection is afforded to the whole inner IP packet (including the inner header) while the outer header (including any outer IPv4 options or IPv6 extension headers) remains unprotected. ESP operates directly on top of IP, using IP protocol number 50. The following ESP packet diagram shows how an ESP packet

4992-408: The kernel-space IPsec implementation. Existing IPsec implementations usually include ESP, AH, and IKE version 2. Existing IPsec implementations on Unix-like operating systems , for example, Solaris or Linux , usually include PF_KEY version 2. Embedded IPsec can be used to ensure the secure communication among applications running over constrained resource systems with a small overhead. IPsec

5070-547: The keys being exchanged and decrypt traffic without inserting any software backdoors. A second alternative explanation that was put forward was that the Equation Group used zero-day exploits against several manufacturers' VPN equipment which were validated by Kaspersky Lab as being tied to the Equation Group and validated by those manufacturers as being real exploits, some of which were zero-day exploits at

5148-470: The keys sent the data. Note that the relevant standard does not describe how the association is chosen and duplicated across the group; it is assumed that a responsible party will have made the choice. To ensure that the connection between two endpoints has not been interrupted, endpoints exchange keepalive messages at regular intervals, which can also be used to automatically reestablish a tunnel lost due to connection interruption. Dead Peer Detection (DPD)

5226-414: The limited special cases in which such an advertisement makes sense. By declaring the totally stubby area as NSSA, no external routes from the backbone, except the default route, enter the area being discussed. The externals do reach area 0.0.0.0 via the TSA-NSSA, but no routes other than the default route enter the TSA-NSSA. Routers in the TSA-NSSA send all traffic to the ABR, except to routes advertised by

5304-626: The network layer, regardless of their transport mechanism: Interior gateway protocols (IGPs) exchange routing information within a single routing domain . Examples of IGPs include: Exterior gateway protocols exchange routing information between autonomous systems . Examples include: Many software implementations exist for most of the common routing protocols. Examples of open-source applications are Bird Internet routing daemon , Quagga , GNU Zebra , OpenBGPD , OpenOSPFD , and XORP . Some network certification courses distinguish between routing protocols and routed protocols. A routed protocol

5382-634: The network. OSPF runs over IPv4 and IPv6, but does not use a transport protocol such as UDP or TCP . It encapsulates its data directly in IP packets with protocol number 89 . This is in contrast to other routing protocols, such as the Routing Information Protocol (RIP) and the Border Gateway Protocol (BGP). OSPF implements its own transport error detection and correction functions. OSPF also uses multicast addressing for distributing route information within

5460-412: The possession of both hosts, and the hosts send each other hashes of the shared key to prove that they are in possession of the same key. IPsec also supports public key encryption , where each host has a public and a private key, they exchange their public keys and each host sends the other a nonce encrypted with the other host's public key. Alternatively if both hosts hold a public key certificate from

5538-419: The same broadcast domain or at each end of a point-to-point link communicate with each other via the OSPF protocol. Routers form adjacencies when they have detected each other. This detection is initiated when a router identifies itself in a hello protocol packet. Upon acknowledgment, this establishes a two-way state and the most basic relationship. The routers in an Ethernet or Frame Relay network select

5616-573: The same subnet and share the same area ID, subnet mask, timers and authentication. In essence, OSPF neighborship is a relationship between two routers that allow them to see and understand each other but nothing more. OSPF neighbors do not exchange any routing information – the only packets they exchange are hello packets. OSPF adjacencies are formed between selected neighbors and allow them to exchange routing information. Two routers must first be neighbors and only then, can they become adjacent. Two routers become adjacent if at least one of them

5694-524: The second-highest priority at the time of the last election. A given router can have some interfaces that are designated (DR) and others that are backup designated (BDR), and others that are non-designated. If no router is a DR or a BDR on a given subnet, the BDR is first elected, and then a second election is held for the DR. A router that has not been selected to be designated router (DR) or backup designated router (BDR). The router forms an adjacency to both

5772-414: The states of all adjacencies. Every such communication sequence is a separate conversation identified by the pair of router IDs of the communicating neighbors. RFC 2328 specifies the protocol for initiating these conversations ( Hello Protocol ) and for establishing full adjacencies ( database description packets , link-state request packets ). During its course, each router conversation transitions through

5850-492: The topology of an area is unknown outside the area. This reduces the routing traffic between parts of an autonomous system. OSPF can handle thousands of routers with more a concern of reaching capacity of the forwarding information base (FIB) table when the network contains lots of routes and lower-end devices. Modern low-end routers have a full gigabyte of RAM, which allows them to handle many routers in an area 0. Many resources refer to OSPF guides from over 20 years ago where it

5928-418: The topology, such as link failures, and converges on a new loop-free routing structure within seconds. It computes the shortest-path tree for each route using a method based on Dijkstra's algorithm . The OSPF routing policies for constructing a route table are governed by link metrics associated with each routing interface. Cost factors may be the distance of a router ( round-trip time ), data throughput of

6006-462: Was developed in conjunction with IPv6 and was originally required to be supported by all standards-compliant implementations of IPv6 before RFC 6434 made it only a recommendation. IPsec is also optional for IPv4 implementations. IPsec is most commonly used to secure IPv4 traffic. IPsec protocols were originally defined in RFC 1825 through RFC 1829, which were published in 1995. In 1998, these documents were superseded by RFC 2401 and RFC 2412 with

6084-422: Was impressive to have 64 MB of RAM. Areas are uniquely identified with 32-bit numbers. The area identifiers are commonly written in the dot-decimal notation, familiar from IPv4 addressing. However, they are not IP addresses and may duplicate, without conflict, any IPv4 address. The area identifiers for IPv6 implementations (OSPFv3) also use 32-bit identifiers written in the same notation. When dotted formatting

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