GL-149
Cisco IOS XR Getting Started Guide for the Cisco XR 12000 Series Router
OL-24755-01
Chapter
MSC
modular services card. Module in which the ingress and egress packet processing and queueing
functions are carried out in the Cisco CRS architecture. Up to 16 MSCs are installed in a line card
chassis; each MSC must have an associated physical line interface module (PLIM) (of which there are
several types to provide a variety of physical interfaces). The MSC and PLIM mate together on the line
card chassis midplane. See also PLIM.
MSCs are also referred to as line cards.
MTU
maximum transmission unit. Maximum packet size, in bytes, that a particular interface can handle.
multicast
Multicast is a feature that refers to single packets copied by the network and sent to a specific subset
of network addresses. These addresses are specified in the Destination Address Field. See also unicast.
N
netboot
Loading software images from a network server, such as TFTP.
node
A card installed and running on the router.
NSF
nonstop forwarding. Packets keep flowing during events such as switchover, process restarts, and the
upgrade or downgrade of software packages. Nonstop forwarding is the ability of a router to continue
to forward traffic toward a router that may be recovering from a transient failure and the ability of a
router recovering from a transient failure in the control plane to continue correctly forwarding traffic
sent to it by a peer.
NTP
Network Time Protocol. Protocol built on top of TCP that ensures accurate local time-keeping with
reference to radio and atomic clocks located on the Internet. This protocol is capable of synchronizing
distributed clocks within milliseconds over long time periods.
NVRAM
nonvolatile RAM. Static random access memory that is made into nonvolatile storage by having a
battery permanently connected.
O
OC-x
Optical carrier, where x=3, 12, 48, or 192, relating to the various speeds within a SONET network.
OIR
online insertion and removal. Feature that permits the addition, replacement, or removal of cards
without interrupting the system power, entering console commands, or causing other software or
interfaces to shut down. Sometimes called hot-swapping or power-on servicing.
OSI
Open Systems Interconnection. International standardization program created by ISO and ITU-T to
develop standards for data networking that facilitate multivendor equipment interoperability.
OSPF
Open Shortest Path First. Link-state, hierarchical Interior Gateway Protocol (IGP) routing algorithm
proposed as a successor to Routing Information Protocol (RIP) in the Internet community. OSPF
features include least-cost routing, multipath routing, and load balancing. OSPF was derived from an
early version of the Intermediate System-to-Intermediate System (IS-IS) protocol. See also IGP and
RIP.
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