Glossary

802.1q   IEEE 802.1q is an industry-standard VLAN trunking protocol that enables a single link to carry the traffic of multiple VLANs.

AC   An attachment circuit is the customer connection to a service provider network. An AC may be a physical port or a virtual port and may be any transport technology (for example, Frame Relay DLCI, ATM PVC, or Ethernet VLAN). In the context of a VPLS, an AC typically is an Ethernet port.

Agg   Aggregation is an Ethernet switch that aggregates several access switch connections for onward connection to the N-PE.

BFD   Bidirectional Forwarding Detection provides a rapid and consistent method of link, device, or protocol failure detection. BFD can be used with BGP, IS-IS, EIGRP, OSPF, and MPLS-TE protocols.

B-semaphore   The primary VPLS node tracks a dedicated IP address on the backup N-PE. This IP address is called a backup semaphore.

Core   Intersite network, which includes VPLS (N-PE) and MPLS (P) devices.

CVD   Cisco Validated Design. The CVD program consists of systems and solutions that are designed, tested, and documented to facilitate and improve customer deployments.

DR   Designated router. OSPF elects a DR and a backup designated router (BDR) for each segment in a broadcast or multiaccess network such as Ethernet. The DR sends a Network LSA (Type 2 LSA) with information that pertains to that segment.

Edge   Layer 2 devices, including aggregation and access switches, within a data center network.

EEM   Embedded Event Manager is a powerful and flexible subsystem in Cisco IOS that provides real-time network event detection and automation. Organizations can adapt the behavior of their network devices to align with their business needs.

EoMPLS   Ethernet over MPLS is a point-to-point Layer 2 VPN technology that transports Ethernet frames across an MPLS core network.

EVC   Ethernet virtual circuit is an association of two or more user-to-networks (UNI) and is an end-to-end representation of a single instance of a Layer 2 service being offered by a provider to a customer.

HA   High availability is the technology that enables networkwide resiliency to increase IP network availability. It ensures continuous access to applications, data, and content if a network or device failure occurs.

H-VPLS   Hierarchical Virtual Private LAN Service is a Layer 2 VPN service over Ethernet networks. H-VPLS introduces the hierarchy by partitioning VPLS, which improves the scalability of VPLS.

ICCP   Inter-Chassis Communication Protocol is used between N-PEs in a redundancy group to enable dual-homed interconnect to a customer edge device. This protocol provides VPLS node redundancy by monitoring and communicating the status of each N-PE in the redundancy group.

IGP   Interior Gateway Protocol, such as IS-IS, OSPF, EIGRP, and RIP.

IGMP   Internet Group Management Protocol is a multicast protocol in the Internet protocols family. It is used by IP hosts to report their host group memberships to any immediately neighboring multicast routers.

GigE   Gigabit Ethernet is a version of Ethernet that offers bandwidth of 1 gigabit per second (Gbps).

LAN   Local-area network. A high-speed, low-error data network that covers a relatively small geographic area. LANs connect workstations, peripheral devices, terminals, and other devices in a single building or other geographically limited area.

LDP   Label Distribution Protocol. A signaling protocol in the MPLS architecture. It is used between label switch routers (LSR).

LER   Label edge router. A router that operates at the edge of an MPLS network. The LER initially adds or ultimately removes a label from a packet.

LSP   Label switch path. A specific path that MPLS traffic passes through.

MAN   Metropolitan-area network. A network that covers an area larger than a local-area network, such as a city or a school district.

MEC   Multichassis EtherChannel. A Layer 2 multipathing technology that allows a connected node to terminate an EtherChannel across two physical Cisco Catalyst 6500 series switches that make up a Virtual Switching System.

Mono-tenant   A data center with only one Layer 2 domain.

MPLS   Multiprotocol Label Switching. A label-based packet-forwarding technology.

MST   Multiple Spanning Tree Protocol. Enables multiple VLANs to be mapped to the same spanning-tree instance. In this way, it reduces the number of spanning-tree instances that are required to support a large number of VLANs.

Multi-tenant   Refers to a data center that hosts multiple independent Layer 2 domains (for example, an outsourcer’s data center).

NIC   Network interface card. A card installed in a computer to provide network communication capabilities to and from that computer.

N-PE   Network-facing Provider Edge router. Acts as a gateway between the MPLS core and edge domain.

OSPF   Open Shortest Path First Protocol. An Interior Gateway Protocol that is used for routing between routers that belong to a single autonomous system.

P router   Provider router. An LSR that functions as a transit router in an MPLS core network.

PE router   Provider Edge router. A router that is part of a service provider’s network and is connected to a customer edge (CE) router.

P-semaphore   The backup VPLS node tracks a dedicated IP address on the primary N-PE. This IP address is called a primary semaphore.

PIM   Protocol Independent Multicast. Refers to a family of multicast routing protocols, each optimized for a different environment. The primary PIM protocols are PIM Sparse Mode and PIM Dense Mode.

POS   Packet over Synchronous Optical network is a technology that maps IP datagrams into the SONET frame payload by using PPP.

PW   Pseudowire. A virtual connection that connects two virtual switch instances in a VPLS. It is bidirectional and consists of a pair of unidirectional MPLS virtual circuits (VCs). A PW also can be used to connect a point-to-point circuit, also referred to as an emulated circuit.

QinQ   The IEEE 802.1Q-in-Q VLAN tag provides a VLAN tunneling mechanism by encapsulating a frame tagged with an 802.1q header with another 802.1q header.

Redundancy   The duplication of devices, services, or connections so that, if a failure occurs the redundant devices, services, or connections can perform the work of those that failed.

SAN   Storage-area network. A specialized network that interconnects servers and storage devices. By combining LAN networking models with the core building blocks of server performance and mass storage capacity, a SAN eliminates the bandwidth bottlenecks and scalability limitations imposed by previous SCSI bus-based architectures.

SONET   Synchronous Optical Network. Enables transmission of synchronous data over a fiber-optic network.

Split brain   Split brain occurs when all the links of private network fail, but the cluster nodes continue to run. In this situation, each node in the cluster assumes that the other nodes are dead and attempts to start services that other nodes are still running.

TenGigE   Ten Gigabit Ethernet is an emerging Ethernet technology that offers bandwidth of 10 gigabits per second.

TLS   Transparent LAN Service. A transport service that service providers offer as a way to link remote Ethernet networks.

Tunnel label   An outer label used to switch packets across a provider network.

VC   Virtual circuit. A logical connection between two network devices.

VC label   A virtual circuit label is an inner label used to bind the L2 interface to which packets must be forwarded.

VFI   Virtual forwarding instance. A collection of data structures used by the software- or hardware-based data plane to forward packets to one or more VCs.

VLAN   Virtual LAN. Comprises a group of devices that are located on various physical LAN segments but are configured so that they can communicate as if they were attached to the same wire.

VLAN overlapping   In a multi-tenant data center, outsourcers host several customers on the same site. Therefore, the VPLS nodes are shared between independent domains. VLAN overlapping occurs when multiple customers connected to the same N-PE use the same VLAN number.

vPC   Virtual PortChannel. A port channel between a single device and two upstream switches. Currently, it is supported in Nexus switches only.

VPLS   Virtual Private LAN Service. A method for providing Ethernet-based multipoint communication over IP/MPLS networks. VPLS allows geographically dispersed sites to share an Ethernet broadcast domain by connecting the sites through pseudowires.

VPN   Virtual private network. Allows IP traffic to travel securely over public TCP/IP networks and the Internet by encapsulating and encrypting all IP packets.

VRF   VPN Routing and Forwarding. A technology that allows multiple instances of a routing table to coexist in the same router.

VSI   Virtual switch instance. Describes an Ethernet bridge function that equates to a multipoint L2 VPN within an N-PE. A VSI terminates PW virtual interfaces, in comparison to an Ethernet bridge, which terminates physical Ethernet interfaces.

VSS   Virtual Switching System. System virtualization technology that allows the pooling of two Cisco Catalyst 6500 switches into a single virtual switch.

WAN   Wide-area network. A network that provides connectivity for multiple physical locations that typically are separated by large distances. For example, a WAN could span a city, or country, or across countries.