backbone area
In
OSPF, a network that has more than one area
must have a backbone area, configured as 0.0.0.0. All areas in an autonomous system (AS) must
connect to the backbone area.
backup port
In
RSTP, the backup port supports the
designated port on the same attached LAN segment. Backup ports exist only when the bridge is
connected as a self-loop or to a shared media segment.
backup router
In
VRRP, the backup router is any VRRP router
in the VRRP virtual router that is not elected as the master. The backup router is available
to assume forwarding responsibility if the master becomes unavailable.
BDR
Backup designated
router. In OSPF, the system elects a designated router (DR) and a BDR. The BDR smooths the
transition to the DR, and each multi-access network has a BDR. The BDR is adjacent to all
routers on the network and becomes the DR when the previous DR fails. The period of disruption
in transit traffic lasts only as long as it takes to flood the new LSAs (which announce the
new DR). The BDR is elected by the protocol; each hello packet has a field that specifies the
BDR for the network.
BGP
Border Gateway Protocol. BGP is a router protocol in the IP suite
designed to exchange network reachability information with BGP systems in other autonomous
systems. You use a fully meshed configuration with BGP.
BGP provides routing updates that include a network number, a list of
ASs that the routing information passed through, and a list of other path attributes. BGP
works with cost metrics to choose the best available path; it sends updated router
information only when one host has detected a change, and only the affected part of the
routing table is sent.
BGP communicates within one AS using Interior BGP (IBGP) because BGP
does not work well with IGP. Thus the routers inside the AS maintain two routing tables: one
for the IGP and one for IBGP. BGP uses exterior BGP (EBGP) between different autonomous
systems.
bi-directional rate
shaping
A hardware-based
technology that allows you to manage bandwidth on Layer 2 and Layer 3 traffic flowing to each
port on the switch and to the backplane, per physical port on the I/O module. The parameters
differ across platforms and modules.
blackhole
In the Extreme Networks
implementation, you can configure the switch so that traffic is silently dropped. Although
this traffic appears as received, it does not appear as transmitted (because it is
dropped).
BOOTP
Bootstrap Protocol.
BOOTP is an Internet protocol used by a diskless workstation to discover its own IP address,
the IP address of a BOOTP server on the network, and a file that can be loaded into memory to
boot the machine. Using BOOTP, a workstation can boot without a hard or floppy disk
drive.
BPDU
Bridge protocol data
unit. In
STP, a BPDU is a packet that
initiates communication between devices. BPDU packets contain information on ports, addresses,
priorities, and costs and they ensure that the data ends up where it was intended to go. BPDU
messages are exchanged across bridges to detect loops in a network topology. The loops are
then removed by shutting down selected bridge interfaces and placing redundant switch ports in
a backup, or blocked, state.
bridge
In conventional networking terms, bridging is a Layer 2 function that
passes frames between two network segments; these segments have a common network layer
address. The bridged frames pass only to those segments connected at a Layer 2 level, which
is called a broadcast domain (or VLAN). You must use Layer 3 routing to pass frames between
broadcast domains (VLANs).
In wireless technology, bridging refers to forwarding and receiving data
between radio interfaces on APs or between clients on the same radio. So, bridged traffic
can be forwarded from one AP to another AP without having to pass through the switch on the
wired network.
broadcast
A broadcast message is
forwarded to all devices within a VLAN, which is also known as a broadcast domain. The
broadcast domain, or VLAN, exists at a Layer 2 level; you must use Layer 3 routing to
communicate between broadcast domains, or VLANs. Thus, broadcast messages do not leave the
VLAN. Broadcast messages are identified by a broadcast address.
BSS
Basic Service Set. A
wireless topology consisting of one access point connected to a wired network and a set of
wireless devices. Also called an infrastructure network. See also IBSS.