Glossary
O
44 terms.
- O/R Address
In X.400, the structured address used for mail routing, made up of hierarchical attribute-value pairs like Country, Organization, and Personal Name.
Like I'm five An X.400 address that lists all the places and attributes needed to find someone, like a complete directory entry.
- OAM
Operations, Administration, and Maintenance: the tools and data used to monitor, test and troubleshoot a network.
Like I'm five The checking tools that tell you whether the network is working well.
Used in RFC 3429 RFC 5586 RFC 5654 RFC 5860 RFC 5921 RFC 6291 RFC 6371 RFC 6372 RFC 6435 RFC 6905 RFC 7023 RFC 7174 RFC 7260 RFC 7455 RFC 7487 RFC 8531 RFC 8533 RFC 9378 RFC 9451 RFC 9516 RFC 9546 RFC 9772 RFC 9951
- Object class
A directory definition that lists the attributes an entry must have and may have. Entries are classified by one or more object classes.
Like I'm five A form that says which boxes you must fill in and which are optional.
Used in RFC 1309 RFC 1609 RFC 2247 RFC 2256 RFC 2798 RFC 4104 RFC 4512 RFC 4519 RFC 4524
- Object identifier
A globally unique dotted-number name, such as 1.2.840.113549.1.7.2, assigned by a hierarchy of authorities. Protocols such as CMS use them to label content types, algorithms and attributes.
Like I'm five A very long phone number that points to exactly one thing in the world.
Used in RFC 1023 RFC 1065 RFC 1155 RFC 1156 RFC 1157 RFC 1158 RFC 1187 RFC 1212 RFC 1213 RFC 1215 RFC 1229 RFC 1230 RFC 1231 RFC 1232 RFC 1233 RFC 1238 RFC 1239 RFC 1253 RFC 1274 RFC 1285 RFC 1303 RFC 1381 RFC 1382 RFC 1389 and 346 more
- Object Identifier (OID)
A globally unique numeric identifier in dotted notation (for example, 1.3.6.1.4.1.5) used to identify protocol elements, schema components, and other structured data.
Like I'm five A number that uniquely identifies a thing, like a serial number but for protocol features.
- Objective Function
In RPL, the rule that decides how a node computes its Rank and which neighbors it selects as parents, for example by minimizing hop count.
Like I'm five The rule a device uses to decide which neighbor is the best one to send things through.
- Observation point
A location in the network where packets can be observed. Passive measurement methods collect data at one or more of these points.
Like I'm five The spot by the road where you stand to watch the cars.
- OCSP (Online Certificate Status Protocol)
A protocol, defined in RFC 2560, for asking a certificate authority's responder whether a certificate has been revoked. RFC 6066 lets the answer travel inside the TLS handshake.
Like I'm five Checking whether a library card was cancelled by asking the library, or being handed a fresh note from them.
Used in RFC 2560 RFC 3125 RFC 3379 RFC 3647 RFC 3820 RFC 4386 RFC 4557 RFC 4738 RFC 4806 RFC 4945 RFC 5019 RFC 5055 RFC 5126 RFC 5216 RFC 5276 RFC 5755 RFC 5912 RFC 5940 RFC 6066 RFC 6187 RFC 6277 RFC 6283 RFC 6494 RFC 6678 and 21 more
- OCSP Stapling
A TLS feature where a server provides a signed OCSP response for its certificate during the handshake, eliminating the need for the client to query an OCSP server separately.
Like I'm five The website brings proof it is trustworthy instead of making you check with the government office.
- Off-path attacker
An attacker who cannot see the packets of a connection and so must guess the values that identify it, such as the client's port number.
Like I'm five A bully who cannot see your chat and has to guess the details.
- Offer/answer
A model in which one party sends an SDP offer describing the media it wants to use and the other replies with an SDP answer that accepts, changes or rejects each part.
Like I'm five One person proposes a plan and the other says yes, no or yes-but to each part.
- Offer/answer model
A two-step negotiation in which one party sends an SDP offer describing what it can do and the other replies with an answer that picks from it.
Like I'm five One side offers a menu and the other picks what they want.
Used in RFC 3311 RFC 3312 RFC 3407 RFC 3959 RFC 3960 RFC 4145 RFC 4568 RFC 4975 RFC 5188 RFC 5547 RFC 5939 RFC 6364 RFC 7006 RFC 7866 RFC 8373 RFC 8840 RFC 8853 RFC 8858 RFC 9335 RFC 9429 RFC 9584
- On-link
Describes a destination that can be reached directly on the same link without going through a router. Hosts decide this from the prefixes advertised with the L flag and from Redirects.
Like I'm five Living on your own street, so you can walk over instead of asking the bus driver.
- One-time password
A password that is valid for a single use, so a copy captured by an untrusted client or an eavesdropper cannot be used again.
Like I'm five A ticket that works once and then is torn up.
Used in RFC 1938 RFC 2196 RFC 2284 RFC 2289 RFC 2444 RFC 2504 RFC 6030 RFC 6560
- One-time signature
A signature key that is safe to use for only one message. Using it for two different messages lets an attacker create forgeries.
Like I'm five A stamp you may use just once, because using it twice lets a cheat copy it.
Used in RFC 8391 RFC 8554 RFC 8708 RFC 8778 RFC 9802 RFC 10033
- One-way delay
The time a packet takes to travel from a sender to a receiver in a single direction. Measuring it needs clocks at both ends that agree closely.
Like I'm five How long a letter takes to get there, not there and back.
Used in RFC 2679 RFC 3432 RFC 3763 RFC 4656 RFC 6808 RFC 6817 RFC 8382
- One-way key chain
A sequence of keys where each key is computed from the next by a one-way function. Anyone can step backward along the chain from a later key, but nobody can step forward without knowing the start.
Like I'm five A line of locked boxes where opening one shows you how to check the earlier ones, but never the later ones.
- Opaque LSA
A kind of OSPF link-state advertisement that carries extra application-specific information in a general format. Its scope can be link-local, area-wide or domain-wide.
Like I'm five A message envelope that OSPF carries along without needing to know what is inside.
- Opcode
A number in a packet that says what kind of message it is. ARP uses 1 and 2 for request and reply, and RARP adds 3 for request reverse and 4 for reply reverse.
Like I'm five A number on the form that says whether it is a question or an answer.
Used in RFC 120 RFC 265 RFC 281 RFC 550 RFC 826 RFC 903 RFC 1350 RFC 1996 RFC 2136 RFC 2748 RFC 2929 RFC 5395 RFC 6455 RFC 6895 RFC 7843 RFC 8160 RFC 8490 RFC 8618 RFC 8906 RFC 9619 RFC 9669
- Open redirector
An endpoint that uses a parameter to send a user agent to the location in the parameter without validating it. Attackers use it to leak codes or tokens, or to borrow the trust a user has in a site.
Like I'm five A signpost that points wherever anyone tells it to, even to a trap.
- Open Relay
A mail server that accepts and forwards email from any sender to any recipient without authentication, allowing spammers to bounce their messages through it to hide their origin.
Like I'm five A mail server that lets anyone send email through it, which spammers use to hide where their junk mail really comes from.
- Open Shortest Path First
A routing protocol where routers exchange information about the network topology and each router computes the shortest path to every destination.
Like I'm five A way routers share maps of the network with each other and figure out the fastest way to send packets.
- OpenPGP
A standard format for keys, certificates and signed or encrypted messages, defined in RFC 4880. An OpenPGP certificate can hold a primary key and several subkeys.
Like I'm five A kind of digital ID card used for secure email, which can hold several keys.
- OpenPGP cleartext signature
A way of signing text with OpenPGP while leaving the text readable. The message is wrapped between a signed-message header and a signature block, as described in RFC 4880, Section 7.
Like I'm five A signature at the bottom of a letter that proves who wrote it and that nobody changed it, while the letter stays readable.
- Operational attribute
A directory attribute that the server maintains for its own use, rather than ordinary user data. Attributes such as entryUUID are marked with the usage directoryOperation.
Like I'm five A note the directory keeps on its own about an entry, instead of something a person typed in.
- OPES
Open Pluggable Edge Services, an IETF framework in which an OPES processor passes application messages to callout servers that adapt them, for example by filtering, translating or logging.
Like I'm five A helper standing in the middle of the road who is allowed to tweak parcels as they pass by.
- OPES Processor
A network element that adapts (modifies, filters, or transforms) application-layer messages according to OPES services.
Like I'm five A box on the network that can change the data flowing through it.
- Opportunistic Encryption
A method of automatically setting up encrypted tunnels between systems without prior bilateral arrangement, by looking up encryption capability in DNS.
Like I'm five Automatically locking messages when both sides support it, without having to agree on it first.
- Opportunistic privacy
Using encryption when it is available but carrying on without it, or without verifying the peer, when it is not. It protects against passive eavesdroppers but not active attackers.
Like I'm five Whispering when you can, but still talking if whispering fails.
Used in RFC 7435 RFC 7525 RFC 7619 RFC 7671 RFC 7696 RFC 7787 RFC 7858 RFC 8004 RFC 8110 RFC 8280 RFC 8310 RFC 8460 RFC 8862 RFC 9063 RFC 9289 RFC 9462 RFC 9505 RFC 9672
- OPT record
A pseudo resource record, type 41, in the additional section of a DNS message. It carries control information for one exchange and is never cached.
Like I'm five A note about the question rather than part of the answer.
Used in RFC 2671 RFC 3225 RFC 5001 RFC 6891 RFC 6975 RFC 7830 RFC 7871 RFC 8145 RFC 8764 RFC 8914 RFC 9567 RFC 9660 RFC 9664
- Optical Cross-Connect
A device that switches light signals from input ports to output ports, either all-optically or by converting to electrical form temporarily.
Like I'm five A switch that connects light paths to each other.
- Optical Transport Network
A network technology, defined by ITU-T G.709, that carries client signals over optical links inside containers called ODUs and OTUs.
Like I'm five A system for moving data over fiber by packing it into standard containers.
- Option negotiation
Telnet's WILL, WON'T, DO and DON'T exchange, used to agree on features beyond the Network Virtual Terminal. Refusing leaves the connection as a plain NVT.
Like I'm five Politely asking, "Can we use the fancy mode?" and getting a yes or a no.
Used in RFC 435 RFC 461 RFC 471 RFC 495 RFC 513 RFC 560 RFC 562 RFC 651 RFC 652 RFC 653 RFC 654 RFC 655 RFC 656 RFC 657 RFC 658 RFC 669 RFC 679 RFC 701 RFC 702 RFC 718 RFC 726 RFC 727 RFC 729 RFC 732 and 62 more
- Options Template
An IPFIX template that describes records carrying extra information about something else, such as a whole message or session, instead of describing flows themselves.
Like I'm five A form for writing notes about the data, not the data itself.
- OR Address
The originator/recipient address used in X.400 mail. It is built from attributes such as country, administration domain and private domain names.
Like I'm five The old-style mail address made of several labelled pieces, like country and company.
- ORCHID (Overlay Routable Cryptographic Hash Identifier)
A 128-bit IPv6-like identifier format defined by RFC 4843 for use in overlay networks, with a fixed prefix in the first 28 bits to mark it as cryptographically derived and globally routable within the overlay.
Like I'm five A special way to write an address so that overlay networks can recognize it at a glance.
- Organizationally Unique Identifier (OUI)
A 3-octet (24-bit) prefix assigned by the IEEE Registration Authority to uniquely identify an organization, forming the first half of a 48-bit MAC address.
Like I'm five The first part of a network device's address that identifies the manufacturer, like the area code in a phone number.
- Origin server
The server that holds or generates a resource and answers requests for it, as opposed to a proxy or cache in between. Cookies are set by and returned to origin servers.
>Like I'm five The real website computer that answers your question, not a messenger in the middle.
Used in RFC 2295 RFC 3466 RFC 3568 RFC 6265 RFC 6770 RFC 7230 RFC 7235 RFC 7807 RFC 7838 RFC 8006 RFC 8010 RFC 8297 RFC 8336 RFC 8470 RFC 8615 RFC 8674 RFC 9110 RFC 9112 RFC 9211 RFC 9674 RFC 9729 RFC 9842 RFC 9875
- OSCORE
Object Security for Constrained RESTful Environments, a way to protect CoAP messages end to end using COSE. It can also secure HTTP.
Like I'm five A private envelope around each message so only the two ends can read it.
Used in RFC 8824 RFC 9031 RFC 9203 RFC 9528 RFC 9668 RFC 9820 RFC 9953
- OSPF area
A group of OSPF routers and networks that share a link-state database. Dividing an AS into areas reduces the routing information each router handles.
Like I'm five One district of a city, where everyone knows the local streets.
Used in RFC 1131 RFC 1245 RFC 1247 RFC 1248 RFC 1252 RFC 1253 RFC 1584 RFC 1587 RFC 1722 RFC 1765 RFC 1793 RFC 2154 RFC 2178 RFC 2328 RFC 2370 RFC 2740 RFC 2791 RFC 3101 RFC 3166 RFC 3167 RFC 3386 RFC 3509 RFC 3623 RFC 3630 and 92 more
- Ossification
The loss of a protocol's ability to change because middleboxes and implementations come to depend on the exact details of what they see on the wire. QUIC encrypts nearly all of its headers to reduce this.
Like I'm five When a rule gets so set in stone that nobody can improve it.
Used in RFC 7663 RFC 8546 RFC 8558 RFC 8701 RFC 9000 RFC 9065 RFC 9369 RFC 9419 RFC 9607 RFC 10049
- Outbound Route Filter (ORF)
A filter that a BGP speaker sends to a peer so that the peer limits which routes it sends back. It lets a speaker pull the routes it wants on demand.
Like I'm five A note to a friend saying which kinds of mail to send you and which to keep.
- Overlay network
A network built on top of another network, where participants route messages and store data for each other without a central server.
Like I'm five A group of friends who pass notes along to each other, so no single post office is needed.
Used in RFC 5693 RFC 6029 RFC 6940 RFC 7348 RFC 7364 RFC 7365 RFC 7650 RFC 7851 RFC 7890 RFC 7904 RFC 8014 RFC 9521
- Overload control
Mechanisms by which an overloaded node asks others to reduce the traffic they send to it. Senders react by throttling, which rejects some requests, or by diverting requests elsewhere.
Like I'm five When a shop is too crowded, the staff ask people to wait outside or go to another shop.