TMS zl Management and Configuration Guide ST.1.0.090213

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Glossary
default gateway The next-hop router to which a device sends all traffic that is destined to a
different network or subnet.
default metric The metric that is assigned to redistributed routes.
defragmentation The reassembly of fragmented packets, often performed by a router or by the
TMS zl Module.
demilitarized zone See DMZ.
denial of service See DoS.
DER Distinguished Encoding Rules. A method for encoding data objects. For more
information, see ITU-T X.690 at http://www.itu.int/ITU-T/studygroups/
com17/languages/X.690-0207.pdf.
DES Data Encryption Standard. A published symmetric encryption algorithm
used for IPsec that uses a 56-bit symmetric key to encrypt data in 64-bit blocks.
For more information, see FIPS PUB 46-3 at http://csrc.nist.gov/publications/
fips/fips46-3/fips46-3.pdf.
designated router See DR.
destination NAT Network address translation in which the destination IP address is replaced
by another IP address as the packet crosses a network boundary.
destination zone The zone to which a packet is destined.
DF bit Don’t Fragment bit. The IP header bit that specifies whether the packet can
be fragmented.
DH See Diffie-Hellman key exchange.
DHCP Dynamic Host Configuration Protocol. A protocol that allows network
administrators to set up a server to manage IP addresses, automatically
assigning IP addresses to devices on the network. DHCP simplifies IP man-
agement, eliminating the need to manually assign IP addresses to devices and
then track those addresses.
DHCP relay DHCP relay passes DHCP requests from clients on one subnetwork to a DHCP
server on a different subnetwork, eliminating the need for a DHCP server on
each network segment.
dial-in user The remote L2TP VPN client to whom you want to permit access.
Differentiated
Services
Also known as DiffServ, a class of service model that enhances the best-effort
services of the Internet by differentiating traffic according to user, service
requirements, and other criteria.