178:, such as 192.0.2.1 in the 192.0.2.0/24 (i.e., subnet mask 255.255.255.0) subnet, and that interface is considered "up" by the router, the router thus has a directly connected route to 192.0.2.0/24. If a routing protocol offered another router's route to that same subnet, the routing table installation software will normally ignore the dynamic route and prefer the directly connected route.
292:(FIB) with new routes installed in the routing table. If the FIB is in one-to-one correspondence with the RIB, the new route is installed in the FIB after it is in the RIB. If the FIB is smaller than the RIB, and the FIB uses a hash table or other data structure that does not easily update, the existing FIB might be invalidated and replaced with a new one computed from the updated RIB.
205:
Router configuration rules may contain static routes. A static route minimally has a destination address, a prefix length or subnet mask, and a definition where to send packets for the route. That definition can refer to a local interface on the router, or a next-hop address that could be on the far
80:
The distinction has proven useful in the networking field where it originated, as it separates the concerns: the data plane is optimized for speed of processing, and for simplicity and regularity. The control plane is optimized for customizability, handling policies, handling exceptional situations,
272:
If the routes are of equal metric and the router supports load-sharing, add the new route and designate it as part of a load-sharing group. Typically, implementations will support a maximum number of routes that load-share to the same destination. If that maximum is already in the table, the new
245:
Implementers generally have a numerical preference, which Cisco calls an "administrative distance", for route selection. The lower the preference, the more desirable the route. Cisco's IOS implementation makes exterior BGP the most preferred source of dynamic routing information, while Nortel RS
123:
Several different information sources may provide information about a route to a given destination, but the router must select the "best" route to install into the routing table. In some cases, there may be multiple routes of equal "quality", and the router may install all of them and load-share
181:
There also may be software-only interfaces on the router, which it treats as if they were locally connected. For example, most implementations have a "null" software-defined interface. Packets having this interface as a next hop will be discarded, which can be a very efficient way to filter
241:
Different implementations have different sets of preferences for routing information, and these are not standardized among IP routers. It is fair to say that subnets on directly connected active interfaces are always preferred. Beyond that, however, there will be differences.
256:
If the route is "more specific" than an existing route, install it in addition to the existing routes. "More specific" means that it has a longer prefix. A /28 route, with a subnet mask of 255.255.255.240, is more specific than a /24 route, with a subnet mask of
217:, where the static route is less preferred than a route from any routing protocol. The static route, which might use a dialup link or other slow medium, activates only when the dynamic routing protocol(s) cannot provide a route to the destination.
182:
traffic. Routers usually can route traffic faster than they can examine it and compare it to filters, so, if the criterion for discarding is the packet's destination address, "blackholing" the traffic will be more efficient than explicit filters.
300:
Multicast routing builds on unicast routing. Each multicast group to which the local router can route has a multicast routing table entry with a next hop for the group, rather than for a specific destination as in unicast routing.
220:
Static routes that are more preferred than any dynamic route also can be very useful, especially when using traffic engineering principles to make certain traffic go over a specific path with an engineered quality of service.
206:
end of a subnet to which the router is connected. The next-hop address could also be on a subnet that is directly connected, and, before the router can determine if the static route is usable, it must do a
159:) to another physical interface, it is also possible to define multiple logical interfaces on a physical interface. A physical Ethernet interface, for example, can have logical interfaces in several
151:
Routers forward traffic that enters on an input interface and leaves on an output interface, subject to filtering and other local rules. While routers usually forward from one physical (e.g.,
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of the next hop address in the local routing table. If the next-hop address is reachable, the static route is usable, but if the next-hop is unreachable, the route is ignored.
233:. The routing table manager, according to implementation and configuration rules, may select a particular route or routes from those advertised by various routing protocols.
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If the route is of equal specificity to a route already in the routing table, but comes from a more preferred source of routing information, replace the route in the table.
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associated with each. Control plane logic also can identify certain packets to be discarded, as well as preferential treatment of certain packets for which a high
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Static routes also may have preference factors used to select the best static route to the same destination. One application is called a
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A major function of the control plane is deciding which routes go into the main routing table. "Main" refers to the table that holds the
47:, run in the architectural control element. In most cases, the routing table contains a list of destination addresses and the outgoing
185:
Other software defined interfaces that are treated as directly connected, as long as they are active, are interfaces associated with
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is the part of the software that processes the data requests. The data plane is also sometimes referred to as the forwarding plane.
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In computing, the control plane is the part of the software that configures and shuts down the data plane. By contrast, the
505:"Control and data plane separation architecture for supporting multicast listeners over distributed mobility management"
356:"Control and data plane separation architecture for supporting multicast listeners over distributed mobility management"
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If the route is of equal specificity to a route in the routing table, yet comes from a source of the same preference,
84:
The conceptual separation of the data plane from the control plane has been done for years. An early example is
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88:, where the basic file operations are open, close for the control plane and read write for the data plane.
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There can be multicast static routes as well as learning dynamic multicast routes from a protocol such as
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197:(MPLS). Loopback interfaces are virtual interfaces that are considered directly connected interfaces.
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routing may require an additional routing table for multicast routes. Several routing protocols e.g.
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of candidate routes which are promoted when a route fails or when a routing policy is changed.
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Information on the status of directly connected hardware and software-defined interfaces
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Xia, Wenfeng; Wen, Yoggang; Heng Foh, Chuan; Niyato, Dusit; Xie, Haiyong (2015).
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511:. Special Issue on Patents, Standardization and Open Problems in ICT Practices.
362:. Special Issue on Patents, Standardization and Open Problems in ICT Practices.
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for more detail, but each implementation has its own means of updating the
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Depending on the specific router implementation, there may be a separate
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and in general facilitating and simplifying the data plane processing.
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Nortel
Ethernet Routing Switch 8600 Configuring IP Routing Operations
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Ahmad, Ijaz; Namal, Suneth; Ylianttila, Mika; Gurtov, Andrei (2015).
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Discard it if the route has a higher metric than the existing route
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that is populated by the control plane, but used by the high-speed
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Part of the router architecture that maintains the routing table
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Replace the existing route if the new route has a lower metric
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Forwarding and
Control Element Separation (ForCES) Framework
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There are three general sources of routing information:
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If the route is not in the routing table, install it.
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The general order of selecting routes to install is:
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architecture that is concerned with establishing the
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Configuring IP Routing
Protocol-Independent Features
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43:. Control plane functions, such as participating in
70:to look up packets and decide how to handle them.
463:"Security in Software-Defined Networks: A Survey"
174:When an interface has an address configured in a
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146:
503:Do, Truong-Xuan; Kim, Younghan (2017-06-01).
354:Do, Truong-Xuan; Kim, Younghan (2017-06-01).
344:, RFC 3746, Network Working Group, April 2004
280:Routing table vs. forwarding information base
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142:Information from (dynamic) routing protocols
470:IEEE Communications Surveys & Tutorials
426:IEEE Communications Surveys & Tutorials
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422:"A Survey on Software-Defined Networking"
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546:The Design of the Unix Operating System
246:makes intra-area OSPF most preferred.
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39:that defines what to do with incoming
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92:Building the unicast routing table
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139:Manually configured static routes
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306:Protocol Independent Multicast
128:Sources of routing information
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195:Multiprotocol Label Switching
191:Generic Routing Encapsulation
7:
395:Conran, Matt (2019-02-25).
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290:forwarding information base
147:Local interface information
64:forwarding information base
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522:10.1016/j.icte.2017.06.001
482:10.1109/COMST.2015.2474118
439:10.1109/COMST.2014.2330903
373:10.1016/j.icte.2017.06.001
35:, or the information in a
569:, Cisco Systems,July 2006
544:Bach, Maurice J. (1986).
273:route is usually dropped.
237:Installing unicast routes
225:Dynamic routing protocols
296:Multicast routing tables
100:routes that are active.
57:differentiated services
598:Internet architecture
215:floating static route
603:Routers (computing)
554:1986duos.book.....B
187:tunneling protocols
27:is the part of the
116:maintain internal
53:quality of service
548:. Prentice-Hall.
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515:(2): 90–95.
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509:ICT Express
360:ICT Express
165:IEEE 802.1Q
163:defined by
592:Categories
406:2019-10-14
329:References
323:Data plane
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531:2405-9595
382:2405-9595
193:(GRE) or
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102:Multicast
312:See also
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169:headers
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