Extreme Networks ExtremeWare XOS Guide Manual page 649

D (Continued)
default encapsulation mode
designated port
Device Manager
DF
DHCP
DiffServ
DoS attack
ExtremeWare XOS 11.3 Concepts Guide
In STP, default encapsulation allows you to specify the type of BPDU
encapsulation to use for all ports added to a given STPD, not just to
one individual port. The encapsulation modes are:
802.1d—This mode is used for backward compatibility with
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previous STP versions and for compatibility with third-party
switches using IEEE standard 802.1d.
EMISTP—Extreme Multiple Instance Spanning Tree Protocol
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(EMISTP) mode is an extension of STP that allows a physical port
to belong to multiple STPDs by assigning the port to multiple
VLANs.
PVST+—This mode implements PVST+ in compatibility with third-
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party switches running this version of STP.
In STP, the designated port provides the shortest path connection to
the root bridge for the attached LAN segment. Each LAN segment has
only one designated port.
The Device Manager is an Extreme Networks-proprietary process that
runs on every node and is responsible for monitoring and controlling
all of the devices in the system. The Device Manager is useful for
system redundancy.
Don't fragment bit. This is the don't fragment bit carried in the flags
field of the IP header that indicates that the packet should not be
fragmented. The remote host will return ICMP notifications if the
packet had to be split anyway, and these are used in MTU discovery.
Dynamic Host Configuration Protocol. DHCP allows network
administrators to centrally manage and automate the assignment of IP
addresses on the corporate network. DHCP sends a new IP address
when a computer is plugged into a different place in the network. The
protocol supports static or dynamic IP addresses and can dynamically
reconfigure networks in which there are more computers than there
are available IP addresses.
Differentiated Services. Defined in RFC 2474 and 2475, DiffServ is an
architecture for implementing scalable service differentiation in the
Internet. Each IP header has a DiffServ (DS) field, formerly known as
the Type of Service (TOS) field. The value in this field defines the QoS
priority the packet will have throughout the network by dictating the
forwarding treatment given to the packet at each node. DiffServ is a
flexible architecture that allows for either end-to-end QoS or
intradomain QoS by implementing complex classification and
mapping functions at the network boundary or access points. In the
Extreme Networks implementation, you can configure the desired QoS
by replacing or mapping the values in the DS field to egress queues
that are assigned varying priorities and bandwidths.
Denial of service attacks occur when a critical network or computing
resource is overwhelmed so that legitimate requests for service cannot
succeed. In its simplest form, a DoS attack is indistinguishable from
normal heavy traffic. ExtremeWare XOS software has configurable
parameters that allow you to defeat DoS attacks.
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