Huawei HCIP-Datacom key terms

A logical grouping of OSPF routers and links that limits flooding of link-state advertisements. All routers inside an area share an identical topology database, while inter-area routes are summarized by Area Border Routers.

An OSPF router attached to two or more areas, including the backbone. It maintains a separate topology database per area and injects summarized inter-area routes into other areas using Type 3 LSAs.

An OSPF router that redistributes routes from another routing domain or protocol into OSPF. It originates Type 5 external LSAs, or Type 7 in a not-so-stubby area.

An OSPF advertisement generated by an ABR that describes an inter-area prefix and its cost. It is flooded only within the target area and is the main vehicle for area summarization.

An OSPF advertisement flooded throughout the normal areas describing a route redistributed from outside the OSPF domain. It carries an external metric type (E1 or E2) and the originating ASBR's router ID.

An OSPF area that blocks Type 5 external LSAs but permits external routes through Type 7 LSAs originated by an internal ASBR. The ABR translates Type 7 to Type 5 toward the backbone.

An OSPF area that rejects Type 5 external LSAs and reaches outside networks through a default route from its ABR. It reduces database and CPU load on low-end routers inside the area.

A 32-bit identifier, written in dotted-decimal form, that uniquely names an OSPF or BGP speaker. OSPF selects the highest configured loopback address, otherwise the highest active physical interface address.

The process on a multi-access OSPF segment that chooses a Designated Router and Backup Designated Router. Election uses interface priority first, then highest router ID, and reduces adjacency count.

The progression of an adjacency: Down, Init, 2-Way, ExStart, Exchange, Loading, Full. Reaching Full confirms database synchronization; stuck states usually indicate MTU, authentication, or area mismatches.

The interval at which OSPF sends Hello packets on an interface. Peers must agree on the value, and the dead interval defaults to four times the hello interval.

The two-level hierarchy of Intermediate System to Intermediate System routing. Level 1 routers stay within an area; Level 2 routers form the backbone and exchange inter-area reachability.

The controlled injection of routes learned by one routing protocol or process into another. It requires a seed metric, optional route maps, and care to avoid feedback loops between the domains.

A configured TCP session between two BGP speakers, typically on port 179. Peers exchange UPDATE messages carrying path attributes and reachability, forming either iBGP or eBGP sessions.

A BGP path attribute listing the autonomous systems an update has traversed. It is used for loop prevention and as the second step of best-path selection after weight and local preference.

A well-known discretionary BGP attribute used inside an autonomous system to prefer one exit point. Higher values win, and the attribute is not advertised to external peers.

An optional non-transitive BGP attribute that hints to a neighboring AS which entry point to prefer. Lower values are better, and it is compared only between paths from the same neighbor AS.

An iBGP router allowed to reflect routes learned from one client to other clients and non-clients. It removes the need for a full iBGP mesh and uses cluster IDs and originator IDs to prevent loops.

A method of splitting one autonomous system into sub-ASes that run eBGP-like sessions internally. It reduces iBGP mesh size while presenting a single AS number to the outside world.

The ordered comparison BGP applies to candidate routes: weight, local preference, locally originated, AS path length, origin, MED, eBGP over iBGP, IGP cost to next hop, and router ID.

The address a router forwards a packet toward to reach a destination prefix. In BGP it is usually the peer address, and unreachable next hops cause routes to be withheld from the routing table.

A filter that matches routes by network address and prefix length using permit or deny entries. It is commonly applied to BGP neighbors and redistribution to control which prefixes are advertised.

A named sequence of match and set clauses used to filter or modify routes during redistribution, policy application, or BGP neighbor configuration. Clauses are evaluated in order until one matches.

A short fixed-length identifier prepended to a packet that tells each Label Switch Router how to forward it. Labels are swapped hop by hop and can be stacked to form a label stack.

The ordered sequence of Label Switch Routers and labels a packet follows through an MPLS network. It may be built by hop-by-hop signaling or traffic engineered with explicit constraints.

A protocol that distributes label bindings for IGP-learned prefixes between Label Switch Routers. It builds LSPs that follow the existing IGP shortest path without traffic engineering.

An MPLS behavior where the second-to-last router removes the top label before forwarding to the egress. It saves the egress router one lookup and is signaled through the implicit-null label.

The use of constrained path signaling, usually RSVP-TE, to steer LSPs away from congested shortest paths. It relies on link attributes such as bandwidth and affinity to compute explicit routes.

An overlay encapsulation that carries Layer 2 frames inside UDP across a routed IP underlay. A 24-bit VNI identifies the segment, allowing far more tenants than VLAN IDs permit.

A 24-bit field in the VXLAN header that identifies a virtual network segment. It separates tenant traffic on shared physical infrastructure and maps to a bridge domain on the VTEP.

The device that encapsulates and decapsulates VXLAN frames at the edge of the overlay. It maps local VLANs to VNIs and resolves remote endpoints through the underlay or a control plane.

A BGP control plane that distributes MAC and IP reachability for overlay networks. It replaces flood-and-learn with route types for MAC/IP advertisement and enables active-active multihoming.

A Layer 2 broadcast domain identified by a 12-bit tag on Ethernet frames. Access ports carry one VLAN untagged, while trunk ports carry many VLANs tagged using 802.1Q.

A Layer 2 protocol that blocks redundant links to produce a loop-free topology. It elects a root bridge and assigns port roles based on path cost to that root.

The bundling of multiple physical links into one logical interface to increase bandwidth and resilience. Member links must match in speed, duplex, and VLAN configuration, and LACP can negotiate them.

The hardware or software table a router consults to forward each packet, derived from the routing table. It stores the selected next hop and outgoing interface for each destination prefix.

The value a router uses to rank routes from different sources, such as direct, static, OSPF, and BGP. Lower values are preferred, and the winning route is installed in the forwarding table.

A first-hop redundancy protocol in which routers share a virtual IP and MAC. The master forwards traffic while backups monitor it and take over if hellos stop arriving.

An ordered set of permit and deny rules that matches packet fields such as source, destination, protocol, and port. It filters traffic and can classify packets for traffic policies.