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gated_intro(7)
NAME
gated_intro - Information about the gate daemon and its implementation
DESCRIPTION
This reference page contains a glossary of terms that are used in any
discussion of gated and the gated.conf file.
GLOSSARY
adjacency
A relationship formed between selected neighboring routers for the
purpose of exchanging routing information. Not every pair of
neighboring routers becomes adjacent.
autonomous system
A set of routers under a single technical administration, using an
interior gateway protocol and common metrics to route packets within
the AS, and using an exterior gateway protocol to route packets to
other ASs. Since this classic definition was developed, it has become
common for a single AS to use several interior gateway protocols and
sometimes several sets of metrics within an AS.
The use of the term "autonomous system" stresses that even when
multiple internal gateway protocols and metrics are used, the
administration of an AS appears to other ASs to have a single coherent
interior routing plan and presents a consistent picture of what
networks are reachable through it. The AS is represented by a number
between 1 and 65534, assigned by the Internet Assigned Numbers
Authority.
BGP (Border Gateway Protocol)
One of a class of exterior gateway protocols, described in more detail
in the BGP section of gated.proto(4).
cost
An OSPF (Open Shortest Path First) protocol metric. See metric and
OSPF.
delay
A HELLO metric. Valid values are from zero to 30000, inclusive. The
value of 30000 is the maximum metric and means unreachable. See metric
and HELLO.
designated router
In OSPF, a designated router is a multiaccess network that has at least
two attached routers. The designated router generates a link state
advertisement for the multiaccess network and assists in running the
protocol. The designated router is elected by the HELLO protocol.
destination
Any network or host.
distance
An EGP metric. See metric and EGP. Valid values are from zero to 255
inclusive.
exterior gateway protocol or exterior routing protocol
A class of routing protocols used to exchange routing information
within an autonomous system. A detailed explanation of exterior
gateway protocols is available in gated.proto(4).
EGP (Exterior Gateway Protocol)
One of a class of exterior gateway protocols, described in more detail
in the EGP section of gated.proto(4).
gateway
1. An intermediate destination by which packets are delivered to their
ultimate destination. 2. 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 HELLO section of gated.proto(4).
host
The IP address of any system, 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 can also be specified as an
eight digit hexadecimal string preceded by 0x. For example,
0x0a000043. In addition, if the options noresolv statement is not
specified, this can be a symbolic host name. For example,
gated.cornell.edu or nic.ddn.mil. The numeric forms are preferred over
the symbolic form.
interface
The host address of an attached network 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 can 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 wild card, interface
type name, or delete word address. Be careful with the use of
interface names as future versions might 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.
interior gateway protocol or interior routing protocol
One of a class of routing protocols used to exchange routing
information within an autonomous system. A detailed explanation of
interior gateway protocols is available in gated.proto(4).
interface list
A list of one or more interface names, including wildcard names (names
without a number) and names that may specify more than one interface or
address, or the token all for all interfaces. See gated.conf(4) for
more information.
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 the bits of the destination that 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.)
The following sample table shows the range of possible values for each
routing protocol metric and the value used by each protocol (See
gated.proto(4)) 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
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.
neighbor
Another router with which 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 of 0 to 255 inclusive separated by dots
(.). For example, 132.236.199, 132.236, or 10. It may also be
specified as a hexadecimal string preceded by 0x with an even number of
digits between two and eight. For example, 0x??????, 0x???? or 0x0a.
Also allowed is the symbolic value default that has the value 0.0.0.0,
the default network. If options noresolv statement is not specified,
this can also be a symbolic network name. For example,nr-tech-prod,
cornellu-net, and arpanet. The numeric forms are 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 gated.proto(4).
peer
Another router with which 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 selected as 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.
quality of service (QoS)
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 gated.proto(4).
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.
RIB (routing information base)
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 that 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.
The gated daemon 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:
number
A 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:number
A 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,
0:01:00, or 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.
SEE ALSO
Daemons: gated(8)
Files: gated.conf(4), gated.control(4), gated.proto(4)
RFC 827, Exterior Gateway Protocol EGP, E. Rosen
RFC 891, DCN local-network protocols, D. Mills
RFC 904, Exterior Gateway Protocol Formal Specification, D. Mills
RFC 1058, Routing Information Protocol, C. Hedrick
RFC 1105, Border Gateway Protocol BGP, K. Lougheed, Y. Rekhter
RFC 1163, A Border Gateway Protocol (BGP), K. Lougheed, Y. Rekhter
RFC 1164, Application of the Border Gateway Protocol in the Internet, J.
Honig, D. Katz, M. Mathis, Y. Rekhter, J. Yu
RFC 1227, SNMP MUX Protocol and MIB, M. Rose
RFC 1245, OSPF Protocol Analysis, J. Moy
RFC 1246, Experience with the OSPF Protocol, J. Moy
RFC 1253, OSPF Version 2 Management Information Base, F. Baker, R. Coltun
RFC 1256, ICMP Router Discovery Messages, S. Deering
RFC 1265, BGP Protocol Analysis, Y. Rekhter
RFC 1266, Experience with the BGP Protocol, Y. Rekhter
RFC 1267, A Border Gateway Protocol 3 (BGP-3), K. Lougheed, Y. Rekhter
RFC 1268, Application of the Border Gateway Protocol in the Internet, P.
Gross, Y. Rekhter
RFC 1269, Definitions of Managed Objects for the Border Gateway Protocol
(Version 3), J. Burruss, S. Willis
RFC 1321, The MD5 Message-Digest Algorithm, R. Rivest
RFC 1370, Internet Architecture Board Applicability Statement for OSPF
RFC 1388, RIP Version 2 Carrying Additional Information, G. Malkin
RFC 1397, Default Route Advertisement In BGP2 And BGP3 Versions Of The
Border Gateway Protocol, D. Haskin
RFC 1403, BGP OSPF Interaction, K. Varadhan
RFC 1583, OSPF Version 2, J. Moy
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Index for
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Alphabetical
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Top of
page |
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