DE See Abandon Eligible.
Dead Time/Interval With OSPF, the timer acclimated to actuate back a adjoining router has
failed, based on a router not accepting any OSPF messages, including Hellos, in this timer period.
default avenue A avenue that is acclimated for forwarding packets back the packet does not bout any
more specific routes in the IP acquisition table.
dense-mode agreement A multicast acquisition agreement whose absence activity is to flood multicast
packets throughout a network.
designated anchorage With Spanning Tree Protocol, the distinct anchorage on anniversary LAN articulation from
which the best Hello BPDU is forwarded.
designated router With PIM on a multiaccess network, the PIM router with the accomplished IP
address on the subnet. With OSPF, the OSPF router that wins an acclamation amidst all current
neighbors. The DR is amenable for calamity on the subnet, and for creating and calamity the blazon 2
LSA for the subnet.
DHCP See Dynamic Host Agreement Protocol.
DHCP concern A about-face affection in which the about-face examines DHCP letters and,
for untrusted ports, filters all letters about beatific by servers and inappropriate messages
sent by clients. It additionally builds a DHCP concern bounden table that is acclimated by DAI and IP Source
Guard.
DHCP concern bounden database The account of entries abstruse by the about-face DHCP snooping
feature. The entries accommodate the MAC abode acclimated as the device’s DHCP applicant address,
the assigned IP address, the VLAN, and the about-face anchorage on which the DHCP appointment messages
flowed.
Differentiated Services A set of QoS RFCs that redefines the IP header’s ToS byte, and
suggests specific settings of the DSCP acreage and the adumbrated QoS accomplishments based on those settings.
Differentiated Services Cipher Point The aboriginal 6 $.25 of the DS field, acclimated for QoS marking.
differentiated appendage bead A appellation apropos to Cisco LAN about-face tail-drop logic, in which multiple
tail-drop thresholds may be assigned based on CoS or DSCP, consistent in some frames being
discarded added aggressively than others.
DiffServ See Differentiated Services.
Digital Signal Level 0 859
Diffusing Update Algorithm A appellation apropos to EIGRP’s centralized processing logic.
Digital Signal Level 0 Central telcos’ aboriginal TDM hierarchy, the aboriginal assemblage of
transmission at 64 kbps.
Digital Signal Level 1 Central telcos’ aboriginal TDM hierarchy, a assemblage that combines multiple
DS0s into a distinct channel—24 DS0s (plus overhead) for a T1, and 30 (plus overhead) for an E1.
Digital Signal Level 3 Central telcos’ aboriginal TDM hierarchy, a assemblage that combines multiple
DS1s into a distinct channel—28 DS1s (plus overhead) for a T3, and 16 E1 DS1s (plus overhead)
for an E3.
Dijkstra Alternate name for the SPF algorithm, called for its inventor, Edsger W. Dijkstra.
direct arrangement advance spectrum A blazon of advance spectrum that spreads RF signals over the
frequency spectrum by apery anniversary abstracts bit by a best code. 802.11b specifies the use of
DSSS.
disabled accompaniment An 802.1d STP anchorage accompaniment in which the anchorage has been administratively disabled.
Discard Eligible A bit in the Frame Relay advance that, back set to 1, agency that if a device
needs to abandon frames, it should abandon the frames with DE 1 first.
discarding accompaniment An 802.1w RSTP anchorage accompaniment in which the anchorage is not forwarding or receiving;
covers 802.1d anchorage states disabled, blocking, and listening.
distance agent The basal algorithms associated with RIP.
Distance Agent Multicast Acquisition Agreement Operates in close approach and depends on its own
unicast acquisition agreement that is agnate to RIP to accomplish its multicast functions.
distributed allocation action The binding contention-based 802.11 admission protocol
that is additionally referred to as CSMA/CA.
distribution account A Cisco IOS agreement apparatus for acquisition protocols by which acquisition updates
may be filtered.
DLCI See data-link affiliation identifier.
DMVPN See Dynamic Multipoint VPN.
downstream router The router that will accept the accumulation cartage back a multicast router
forwards accumulation cartage to addition router.
860 DR
DR See appointed router.
DR acclamation (OSPF) The action by which adjoining OSPF routers appraise their Hello
messages and accept the DR. The accommodation is based on antecedence (highest), or RID (highest) if priority
is a tie.
DROther The appellation to call a router that is neither the DR nor the BDR on a subnet that elects
a DR and BDR.
DS acreage The additional byte of the IP header, aforetime accepted as the ToS byte and redefined by
DiffServ.
DS0 See Digital Signal Level 0.
DS1 See Digital Signal Level 1.
DS3 See Digital Signal Level 3.
DSCP See Differentiated Services Cipher Point.
DSCP-to-CoS map A mapping amid anniversary DSCP amount and a agnate CoS value,
often acclimated in Cisco LAN switches back assuming allocation for departure queuing.
DSCP-to-threshold map A mapping amid anniversary DSCP amount and a WRED threshold, often
used in Cisco LAN switches back assuming WRED.
DSR See Abstracts Set Ready.
DSSS See absolute arrangement advance spectrum.
DTE See abstracts terminal equipment.
DTIM breach The cardinal of beacons that governs how generally multicast frames are beatific over a
wireless LAN.
DTP See Dynamic Trunking Protocol.
DTR See Abstracts Terminal Ready.
DUAL See Diffusing Update Algorithm.
Dual FIFO A Cisco IOS interface software chain queuing action implemented automatically
when application either anatomy of Frame Relay fragmentation. The arrangement again interleaves packets from
the acute chain amid bits of the medium-priority queue.
dual assemblage 861
dual assemblage An IPv6 clearing action in which a host or router supports both IPv4 and IPv6
natively.
dual badge brazier A conceptual archetypal acclimated by CB Policing back application an balance burst.
dual-rate, three-color policer Policing in which two ante are metered, and packets are placed
into one of three categories (conform, exceed, or violate).
DVMRP See Distance Agent Multicast Acquisition Protocol.
Dynamic ARP Inspection A about-face affection with which the about-face watches ARP messages,
determines if those letters may or may not be allotment of some attack, and filters those that look
suspicious.
Dynamic Host Agreement Agreement A accepted (RFC 2131) agreement by which a host can
dynamically advertisement a appeal for a server to accredit to it an IP address, forth with other
configuration settings, including a subnet affectation and absence aperture IP address. DHCP provides a
great accord of adaptability and functionality compared with RARP and BOOTP.
Dynamic Multipoint VPN A adjustment of accouterment dynamically configured spoke-to-spoke
VPN connectivity in a hub-and-spoke arrangement that decidedly reduces agreement appropriate on
the batten routers compared to acceptable IPsec VPN environments.
Dynamic Trunking Agreement A Cisco-proprietary agreement acclimated to dynamically negotiate
whether the accessories on an Ethernet articulation appetite to anatomy a block and, if so, which blazon (ISL or
802.1Q).
E1 A name acclimated for DS1 curve central the European TDM hierarchy.
E1 avenue (OSPF) An OSPF alien avenue for which centralized OSPF amount is added to the amount of
the avenue as it was redistributed into OSPF.
E2 avenue (OSPF) An OSPF alien avenue for which centralized OSPF amount is not added to the cost
of the avenue as it was redistributed into OSPF.
E3 A name acclimated for DS3 curve central the European TDM hierarchy.
EAP See Extensible Authentication Protocol.
EAP over LAN The encapsulation of EAP letters anon central LAN frames. This
encapsulation is acclimated amid the supplicant and the authenticator.
EAPoL See EAP over LAN.
eBGP See External BGP.
eBGP multihop A BGP affection that defines the IP TTL acreage amount in packets beatific amid two
eBGP peers. This affection is appropriate back application IP addresses added than the interface IP address
on the articulation amid peers.
edge LSR An MPLS LSR that can advanced and accept both labeled and unlabeled packets.
EF See Expedited Forwarding.
EGP See Exoteric Gateway Protocol.
egress PE An E-LSR in an MPLS VPN arrangement whose role in a accurate altercation is to
receive labeled packets from added LSRs and again advanced the packets as unlabeled packets to CE
routers.
ELMI See Added Local Management Interface.
E-LSR See bend LSR.
enable countersign The countersign appropriate by the accredit command. Also, this appellation may
specifically accredit to the countersign authentic by the accredit countersign command.
enable abstruse The MD5-encoded countersign authentic by the accredit abstruse command.
encapsulation The action of demography a PDU from some added antecedent and agreement a attack in
front of the aboriginal PDU, and possibly a bivouac abaft it.
encoding The action of alteration the electrical characteristics on a manual medium,
based on authentic rules, to represent data.
enhanced alteration The Cisco IOS affection by which appropriate abbreviate key sequences can be acclimated to
move the cursor central the accepted command band to added calmly change a command.
Enhanced Local Management Interface A Cisco-proprietary LMI protocol, implemented
in Cisco WAN switches and routers, through which the about-face can acquaint the router about
parameters for anniversary VC, including CIR, Bc, and Be.
ESF See Extended Superframe.
established A BGP acquaintance accompaniment in which the BGP neighbors accept counterbalanced and can
exchange acquisition advice application BGP Update messages.
EUI-64 863
EUI-64 A blueprint for the 64-bit interface ID in an IPv6 address, composed of the aboriginal half
of a MAC address, hex FFFE, and the aftermost bisected of the MAC.
exceed A class acclimated by a policer to allocate packets about to the cartage contract. With twocolor
policers, these packets are advised to be aloft the contract; for three-color, these packets
are aloft the Bc setting, but aural the Be setting.
Excess Burst With abstraction and policing, the cardinal of added $.25 that may be beatific afterwards a
period of about inactivity.
expedite chain A appellation acclimated with Cisco LAN switches, apropos to a chain advised with strictpriority
scheduling.
Expedited Forwarding A DiffServ PHB, based on DSCP EF (decimal 46), that provides lowlatency
queuing behavior as able-bodied as policing aegis to anticipate EF cartage from craving queues
for added types of traffic.
Extensible Affidavit Agreement Authentic in RFC 3748, the agreement acclimated by IEEE 802.1X
for exchanging affidavit information.
Exterior Gateway Agreement An exoteric acquisition agreement that predates BGP. It is no best used
today.
exponential weighting connected Acclimated by WRED to account the amount at which the average
queue abyss changes as compared with the accepted chain depth. The beyond the number, the slower
the change in the boilerplate chain depth.
Extended Superframe An added adaptation of T1 framing, as compared with the earlier
Superframe (D4) standard.
External BGP A appellation apropos to how a router angle a BGP associate relationship, in which the peer
is in addition AS.
external avenue From the angle of one acquisition protocol, a avenue that was abstruse by using
route redistribution.
Fast Secure Roaming Enables a wireless applicant to deeply roam amid admission credibility in the
same subnet or amid subnets with admission point handoff times aural 50 ms.
fast switching An optimized Layer 3 forwarding aisle through a router. Fast switching
optimizes acquisition table lookup by creating a special, calmly searched table of accepted flows
between hosts.