Static routing: Difference between revisions

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{{Short description|Use of fixed routes for routing in networks}}

'''Static routing''' describes a process by which [[routing]] is configured with fixed values that do not change at runtime unless manually edited. Static routes are used with and without dynamic [[Routingrouting protocol]]s and usually share the same [[routing table]] as those protocols.<ref>[http://www.redbooks.ibm.com/redbooks/pdfs/gg243376.pdf TCP/IP Tutorial and Technical Overview (IBM RedBooks Series)]</ref> Routes require at least two attributes; the destination and the gateway, but may contain additional attributes such as a [[Metrics (networking)|metric]] (sometimes called the ''administrative distance''). Some implementations treat the network address and [[subnet mask]] as separate values, however in practice both of the values have to be considered for any given routing decision to determine the [[longest prefix match]]. Static routes together with ''connected'' routes and routes from configuration protocols such as [[DHCP]] or [[Neighbor Discovery Protocol|Router Advertisements]] provide the routes which are then redistributed using dynamic routing protocols.<ref>{{Cite web |title=ESPCommunity |url=https://enterprise-support.nvidia.com/s/article/howto-configure-bgp-on-mellanox-switches |access-date=2024-12-18 |website=enterprise-support.nvidia.com}}</ref> While static routes are entered into the system and remain there until removed or changed manually, dynamic routing protocols create and delete routes dynamically at runtime without intervention. Thus the term ''static'' here refers to the nature of remaining unchanged by the system itself. The most prominent example of a static route is a [[default route]] which is often used on devices with a statically configured [[IP address]] to provide the device with access to the rest of the network or the internet by default.<ref>{{Cite web |title=Static Routing {{!}} Cumulus Linux 5.11 |url=https://docs.nvidia.com/networking-ethernet-software/cumulus-linux-511/Layer-3/Routing/Static-Routing/#configure-a-gateway-or-default-route |access-date=2024-12-18 |website=docs.nvidia.com}}</ref> In contrast to a so called ''connected'' route which is automatically generated upon address assignment based on the used subnet mask, a static route must be manually configured. Due to this the configuration may fail if there is no route to the provided gateway at the time of configuration, other than the connected route which will always succeed as it does not require a gateway. The gateway of a static route need not be an address, but can also specify an interface in most implementations.

== Uses ==

Static routing may have the following uses:

* When using static address configuration (in the absence of DHCP or Router Advertisements) it can be used to provide a [[default route]], forming a special case of the longest prefix match as it has a prefix length of zero and therefore always matches, and always matches last.

* In small networks it is a viable method for providing alternative routes to direct traffic when multiple routers exist. This is a simple but limited form of [[Teletrafficteletraffic engineering]].

* Static routing has applications in environments with many routes with infrequent changes as it reduces the delay it would take to synchronize the routes from another device.

* On heavily resource constrained devices where routing protocols may not be viable due to lack of computation power, static routes may be used instead.

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Static routing can have some potential disadvantages:<ref>{{Cite web |title=Cisco Networking Articles |url=https://www.dummies.com/category/articles/cisco-33583/ |access-date=2013-11-05 |website=dummies |language=en |archive-url=https://web.archive.org/web/20131105090942/http://www.dummies.com/how-to/content/pros-and-cons-of-static-routing.html |archive-date=2013-11-05}}</ref>

* '''Human error:''' As the routes have to be manually configured this may be a source of human error in the absence of automated configuration management.

* '''Administrative overhead:''' Similarly the routes have to be provided to the devices. This can be remedied by configuration management, but also using simpler means of using a [[Template processor|template engine]] to generate configuration using repetition or [[IP address management]] software.

* '''Fault tolerance:''' While static routes not being removed during a network failure can be good in that routes continue to function, however, most implementations continue to use a static route as long as the interface the gateway is on is in an ''up'' state. When [[Failure of electronic components|network hardware fails]] it is not necessary ''down''; a [[Hang (computing)|hang]] may cause interfaces to keep running but not accept traffic. Routing protocols usually implement timeouts after which routes are removed or have integration with additional protocols such as [[Bidirectional Forwarding Detection]] to reduce the time the faulty route is present to sub-second.

* '''Observability:''' Static routes themselves do not propagate, which means that in a network built using only static routes it is hard to get a big picture of all present routes unless [[Event monitoring|monitored]]. Dynamic routing protocols often transmit topology information or can be connected to debugging tools such as a [[Looking Glass server]].

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The administrative distance can be manually (re)configured so that the static route can be configured as a backup route, to be used only if the dynamic route is unavailable.<ref name=distance>{{Cite web |title=Describe Administrative Distance |url=https://www.cisco.com/c/en/us/support/docs/ip/border-gateway-protocol-bgp/15986-admin-distance.html |access-date=2014-06-12 |website=Cisco |language=en}}</ref>

<syntaxhighlight lang="console">(config)# ip route 10.10.20.0 255.255.255.0 exampleRoute 1 254</syntaxhighlight>

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== See also ==

{{div col|colwidth=20em}}

* [[Routing]]

* [[Dynamic routing]]

* [[Routing protocol]]

* [[Routing table]]

* [[routerRouter (computing)|Router]]

* [[Route (disambiguation)|Route]]

* [[Routing#Path selection|Metrics]]

{{div col end}}