gated_intro - Information about the gate daemon and its
implementation
This reference page contains a glossary of terms that are
used in any discussion of gated and the gated.conf file.
A relationship formed between selected neighboring routers
for the purpose of exchanging routing information. Not
every pair of neighboring routers becomes adjacent. 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. One of a class of exterior gateway protocols,
described in more detail in the BGP section
of gated.proto(4). An OSPF (Open Shortest Path
First) protocol metric. See metric and OSPF. 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.
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. Any network or
host. An EGP metric. See metric and EGP. Valid
values are from zero to 255 inclusive. 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). One of a class of exterior
gateway protocols, described in more detail in the
EGP section of gated.proto(4). 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. A list of one or more gateways
separated by white space. One of a class of interior
gateway protocols, described in more detail in
the HELLO section of gated.proto(4). 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. 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-topoint
interface. As with any host address it can
be specified symbolically. 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. 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). 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.
The host address of an attached interface.
This is the address of a broadcast, nbma, or loopback
interface, and the local address of a pointto-point
interface. As with any host address it
may be specified symbolically. 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.
The number of significant bits in the mask. 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 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. 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. Two routers that have interfaces to a
common network. On multiaccess networks, routers
are dynamically discovered by OSPF's HELLO protocol.
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). 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. A positive integer. One of a class
of interior gateway protocols, described in more
detail in the OSPF section of gated.proto(4).
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. A UDP or TCP port number.
Valid values are from 1 through 65535 inclusive.
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.) A contiguous
mask covering the most significant bits of an
address. The prefix length specifies how many bits
are covered. The OSI equivalent of TOS. One of a
class of interior gateway protocols, described in
more detail in the RIP section of gated.proto(4).
A 32-bit number assigned to each router running the
OSPF protocol. This number uniquely identifies the
router within the autonomous system. An IP address
used as unique identifier assigned to represent a
specific router. This is usually the address of an
attached interface. The repository of all of
gated's retained routing information, used to make
decisions and as a source for routing information
that is propagated. 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. A time value, usually a time
interval. It may be specified in any one of the
following forms: A non-negative decimal number of
seconds. For example, 27, 60, or 3600. 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. 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.
The Time To Live (TTL) of an IP packet. Valid values
are from one (1) through 255, inclusive. 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.
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
gated_intro(7)
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