Terms used in descriptions throughout this document are defined below:
forwarding table
The table in the kernel that controls the forwarding of packets is a forwarding table, also know in ISO speak as a forwarding information base, or FIB. The forwarding table contains the tuples which help forward the packet of:
The table that GateD uses internally to store routing information it learns from routing protocols is a routing table, known in ISO speak as a routing information base, or RIB. gateway
An intermediate destination by which packets are delivered to their ultimate destination. A host address of another router that is directly reachable via an attached network. As with any host address it may be specified symbolically. gateway_list
A list of one or more gateways separated by white space.
HELLO
One of a class of interior gateway protocols, described in more detail in the HELLOsection of the Protocol Overview.host
The IP address of any host. Usually specified as a dotted quad, four values in the range of 0 to 255 inclusive separated by dots (.). For example 132.236.199.63 or 10.0.0.51. It may also be specified as an eight digit hexadecimal string preceded by 0x. For example 0x???????? or 0x0a000043. Finally, if options noresolv is not specified, a symbolic hostname. For example gated.cornell.eduor nic.ddn.mil. The numeric forms are much preferred over the symbolic form.
interface
The host address of an attached interface. This is the address of a broadcast, nbma or loopback interface and the remote address of a point-to-point interface. As with any host address it may be specified symbolically.
interface
The connection between a router and one of its attached networks. A physical interface may be specified by a single IP address, domain name, or interface name. (Unless the network is an unnumbered point-to-point network.) Multiple levels of reference in the configuration language allow identification of interfaces using wildcard, interface type name, or delete word address. Be careful with the use of interface names as future Unix operating systems may allow more than one address per interface. Dynamic interfaces can be added or deleted and indicated as up or down as well as changes to address, netmask and metric parameters.
igp
interior gateway protocolinterior routing protocol
One of a class of routing protocols used to exchange routing information within an autonomous system. A detailed explanation of interior gateway protocolsis available in the Protocol Overview.interface_list
A list of one or more interface names including wildcard names (names without a number) and names which may specify more than one interface or address, or the token "all" for all interfaces. See the section on interface lists for more information.
IS-IS
One of a class of interior gateway protocols, described in more detail in the IS-ISsection of the Protocol Overview.local_address
The host address of an attached interface. This is the address of a broadcast, nbma or loopback interface and the local address of a point-to-point interface. As with any host address it may be specified symbolically.
mask
A means of subdividing networks using address modification. A mask is a dotted quad specifying which bits of the destination are significant. Except when used in a route filter, GateD only supports contiguous masks.
mask length
The number of significant bits in the mask.
metric
One of the units used to help a system determine the best route. Metrics may be based on hop count, routing delay, or an arbitrary value set by the administrator depending on the type of routing protocol. Routing metrics may influence the value of assigned internal preferences. (See preference.)
This sample table shows the range of possible values for each routing protocol metric and the value used by each protocol (See Protocol Overview.) to reach a destination.
SAMPLE ROUTING PROTOCOL METRICS Protocol Metric Represents Range Unreachable -------- ----------------- ----- ----------- RIP distance (hop-count) 0-15 16 HELLO delay (milliseconds) 0-29999 30000 OSPF cost of path 0-????? Delete ISIS cost of path 0-254 Delete EGP distance (unused) 0-65535 255 BGP unspecified 0-65534 65535
multiaccess networks
Those physical networks that support the attachment of multiple (more than two) routers. Each pair of routers on such a network is assumed to be able to communicate directly. natural mask
XXX - define
neighbor
Another router which with implicit or explicit communication is established by a routing protocol. Neighbors are usually on a shared network, but not always. This term is mostly used in OSPF and EGP. Usually synonymous with peer.
neighboring routers
Two routers that have interfaces to a common network. On multiaccess networks, routers are dynamically discovered by OSPF's HELLO protocol.
network
Any packet-switched network. A network may be specified by its IP address or network name. The host bits in a network specification must be zero. Default may be used to specify the default network (0.0.0.0).
network
The IP address of a network. Usually specified as a dotted quad, one to four values, in the range 0 to 255 inclusive, separated by dots (.), for example, 132.236.199, 132.236or 10. It may also be specified as a hexadecimal string preceded by 0x with an even number of digits, of length between two and eight. For example 0xnnnnnn, 0xnnnn,or 0x0n. Also allowed is the symbolic value defaultwhich has the distinguished value 0.0.0.0, the default network. If options noresolv is not specified a symbolic network name. For example nr-tech-prod, cornellu-netand arpanet. The numeric forms are much preferred over the symbolic form.
number
A positive integer.
OSPF
Open Shortest Path First
One of a class of interior gateway protocols, described in more detail in the OSPF section of the Protocol Overview.ospf_area
XXX - define.
peer
Another router which with implicit or explicit communication is established by a routing protocol. Peers are usually on a shared network, but not always. This term is mostly used by BGP. Usually synonymous with neighbor.
port
A UDP or TCP port number. Valid values are from 1 through 65535 inclusive.
preference
A preference is a value between 0 (zero) and 255, used to select between many routes to the same destination. The route with the best (numerically lowest) preference is the active route. The active route is the one installed in the kernel forwarding table and exported to other protocols. Preference zero is usually reserved for routes to directly attached interfaces. A default preference is assigned to each source from which GateD receives routes. (See Preference.)
prefix
A contiguous mask covering the most significant bits of an address. The prefix length specifies how many bits are covered.
QoS
quality of service
The OSI equivalent of TOS. RIP
Routing Information Protocol
One of a class of interior gateway protocols, described in more detail in the RIP section of the Protocol Overview.reject route
XXX - define.
route filter
XXX - define.
router id
A 32-bit number assigned to each router running the OSPF protocol. This number uniquely identifies the router within the autonomous system.
router_id
An IP address used as unique identifier assigned to represent a specific router. This is usually the address of an attached interface.
routing database
routing table
The repository of all of GateD's retained routing information , used to make decisions and as a source for routing information which is propagated. simplex
An interface may be marked as simplex either by the kernel, or by interface configuration. A simplex interface is an interface on a broadcast media that is not capable of receiving packets it broadcasts.
GateD takes advantage of interfaces that are capable of receiving their own broadcast packets to monitor whether an interface appears to be functioning properly.
time
A time value, usually a time interval. It may be specified in any one of the following forms:
numberA non-negative decimal number of seconds. For example, 27, 60 or 3600.
number:number
A non-negative decimal number of minutes followed by a seconds value in the range of zero to 59 inclusive. For example, 0:27, 1:00 or 60:00. number:number:numberA non-negative decimal number of hours followed by a minutes value in the range of zero to 59 inclusive followed by a seconds value in the range of zero to 59 inclusive. For example, 0:00:27, 0:01:00or 1:00:00. time to live
ttl
The Time To Live (TTL) of an IP packet. Valid values are from one (1) through 255 inclusive.
TOS
type of service
The type of service is for internet service quality selection. The type of service is specified along the abstract parameters precedence, delay, throughput, reliability, and cost. These abstract parameters are to be mapped into the actual service parameters of the particular networks the datagram traverses. The vast majority of IP traffic today uses the default type of service.
Last updated April 26, 1997
gated@gated.merit.edu