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{{short description|A number of arbitrary unit used in network routing decisions}}
{{Short description|Number of arbitrary unit used in network routing decisions}}
'''Administrative distance (AD)''' or '''route preference'''<ref>{{cite web |title=Route Preferences |url=https://www.juniper.net/documentation/software/cable/junosg30/swconfig30-interfaces/html/protocols-overview4.html |publisher=Juniper Networks |access-date=2018-06-18}}</ref> is a number of [[arbitrary unit]] assigned to [[dynamic route]]s, [[static route]]s and directly-connected routes. The value is used in [[Router (computing)|routers]] to rank routes from most preferred (low administrative distance value) to least preferred (high administrative distance value).<ref name="Understanding Route Redistribution">{{citation |title=Understanding Route Redistribution |url=https://www.cs.cmu.edu/~4D/papers/rr-icnp07.pdf |author1=Franck Le |author2=Geoffrey G. Xie |author3=Hui Zhang}}</ref><ref name=cisco>Cisco Systems (2013), [http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080094195.shtml What is Administrative Distance?], retrieved 14 September 2013</ref> When multiple paths to the same destination are available in its [[routing table]], the router uses the route with the lowest administrative distance.


'''Administrative distance''' ('''AD''') or '''route preference'''<ref>{{cite web |title=Route Preferences |url=https://www.juniper.net/documentation/software/cable/junosg30/swconfig30-interfaces/html/protocols-overview4.html |publisher=Juniper Networks |access-date=2018-06-18}}</ref> is a number of [[arbitrary unit]] assigned to [[dynamic route]]s, [[static route]]s and directly-connected routes. The value is used in [[Router (computing)|routers]] to rank [[Routing|routes]] from most preferred (low AD value) to least preferred (high AD value).<ref name="Understanding Route Redistribution">{{citation |title=Understanding Route Redistribution |url=https://www.cs.cmu.edu/~4D/papers/rr-icnp07.pdf |author1=Franck Le |author2=Geoffrey G. Xie |author3=Hui Zhang}}</ref><ref name=cisco>Cisco Systems (2013), [http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080094195.shtml What is Administrative Distance?], retrieved 14 September 2013</ref> When multiple paths to the same destination are available in its [[routing table]], the router uses the route with the lowest administrative distance.
Router vendors typically design their routers to assign a default administrative distance to each kind of route. For example, Cisco routers, routes issued by [[OSPF]] have a lower default administrative distance than routes issued by the [[Routing Information Protocol]]. By default, OSPF has a default administrative distance of 110 and RIP has a default administrative distance of 120. Administrative distance values can, however, usually be adjusted manually by a [[network administrator]].<ref name="Understanding Route Redistribution"/>

Router vendors typically design their routers to assign a default administrative distance to each kind of route. For example, on Cisco routers, routes issued by the [[OSPF|Open Shortest Path First]] routing protocol have a lower default administrative distance than routes issued by the [[Routing Information Protocol]]. This is because, by default on Cisco routers, OSPF has a default administrative distance of 110 and RIP has a default administrative distance of 120. Administrative distance values can, however, usually be adjusted manually by a [[network administrator]].<ref name="Understanding Route Redistribution"/>


== Overview ==
== Overview ==


The administrative distance (AD) value is assigned by the [[router (computing)|router]] on a per-protocol basis. Routers, by design, should not install multiple routes into the routing table as this has the potential to cause routing loops.<ref name="Understanding Route Redistribution" /> While a router may run multiple routing protocols on the same device, it is necessary for the router to implement a process to ensure that multiple routes, pointing to the same destination do not simultaneously exist in the routing table. Each process running on a router advertises its administrative distance value to the local router. The router uses this value to determine which route should be used. Once a route has been selected, the routing information database is updated. If two routes have the same administrative distance, the router uses its vendor-specific algorithm to determine which route should be installed.<ref name="Understanding Route Redistribution" /> [[Cisco]] routers simply ignore the values and fall back to the default values, which are never the same.<ref name="ReferenceA">Cisco Systems(n.d.), Information About Routing, Cisco Systems Inc, retrieved 16 September 2013</ref>
The administrative distance (AD) value is assigned by the [[router (computing)|router]] on a per-protocol basis. Routers, by design, should not install multiple routes into the routing table as this has the potential to cause routing loops.<ref name="Understanding Route Redistribution" /> While a router may run multiple [[routing protocol]]s on the same device, it is necessary for the router to implement a process to ensure that multiple routes, pointing to the same destination do not simultaneously exist in the routing table. Each process running on a router advertises its administrative distance value to the local router. The router uses this value to determine which route should be used. Once a route has been selected, the routing information database is updated. If two routes have the same administrative distance, the router uses its vendor-specific algorithm to determine which route should be installed.<ref name="Understanding Route Redistribution" /> [[Cisco]] routers simply ignore the values and fall back to the default values, which are never the same.<ref name="ReferenceA">Cisco Systems(n.d.), Information About Routing, Cisco Systems Inc, retrieved 0109 2014</ref>


The router will usually compare administrative distances to determine which protocol has the lowest value. The router prefers protocols that have a lower assigned administrative distance. For example, OSPF has a default distance of 110, so it is preferred by the router process, over RIP, which has a default distance of 120. The administrator can arbitrarily reconfigure the administrative distances, which affects the ranking of the preferred routes by the routing process. On Cisco routers, [[static routing|static routes]] have an administrative distance of 1, making them preferred over routes issued by a [[dynamic routing|dynamic routing protocol]]. The administrative distance is a value that is always only referenced by the local router itself. The administrative distance is not advertised on the network.<ref name="Understanding Route Redistribution" />
The router will usually compare administrative distances to determine which protocol has the lowest value. The router prefers protocols that have a lower assigned administrative distance. For example, OSPF has a default distance of 110, so it is preferred by the router process, over RIP, which has a default distance of 120. The administrator can arbitrarily reconfigure the administrative distances, which affects the ranking of the preferred routes by the routing process. On Cisco routers, [[static routing|static routes]] have an administrative distance of 1, making them preferred over routes issued by a [[dynamic routing|dynamic routing protocol]]. The administrative distance is a value that is always only referenced by the local router itself. The administrative distance is not advertised on the network.<ref name="Understanding Route Redistribution" />
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=== Cisco ===
=== Cisco ===


The following table lists the default administrative distances for various [[routing protocols]] used on [[Cisco Systems|Cisco]] routers.<ref name=cisco />
The following table lists the default administrative distances for various routing protocols used on [[Cisco Systems|Cisco]] routers.<ref name=cisco />


{| class="wikitable" style="text-align:center"
{| class="wikitable" style="text-align:center"
! Routing Protocol !! Administrative distance
! Routing protocol !! Administrative distance
|-
|-
| Directly connected interface || 0{{efn|Only the interface itself has an administrative distance of 0, since a route cannot have a distance of less than 1.}}<ref name="Cisco AD">{{citation |title=Default AD |url=http://www.cisco.com/c/en/us/support/docs/ip/border-gateway-protocol-bgp/15986-admin-distance.html#topic2 |author1=Cisco}}</ref>
| Directly connected interface || 0{{efn|Only the interface itself has an administrative distance of 0, since a route cannot have a distance of less than 1.}}<ref name="Cisco AD">{{citation |title=Default AD |url=http://www.cisco.com/c/en/us/support/docs/ip/border-gateway-protocol-bgp/15986-admin-distance.html#topic2 |author1=Cisco}}</ref>
|-
|-
| Static route || 1
| Static route out an interface || 1{{efn|Since [[Cisco IOS|IOS]] 12.2, the administrative distance of a static route with an exit interface is 1. Prior to the release of 12.2 it was in fact 0.}}
|-
|-
| Dynamic Mobile Network Routing (DMNR) || 3
| Static route to next-hop address|| 1
|-
| DMNR - Dynamic Mobile Network Routing || 3
|-
|-
| [[EIGRP]] summary route || 5
| [[EIGRP]] summary route || 5
Line 31: Line 30:
| External [[BGP]] || 20
| External [[BGP]] || 20
|-
|-
| Internal [[EIGRP]] || 90
| [[EIGRP]] internal route || 90
|-
|-
| [[IGRP]] || 100
| [[IGRP]] || 100
|-
|-
| [[OSPF]] || 110
| [[OSPF|Open Shortest Path First]] (OSPF) || 110
|-
|-
| [[IS-IS]] || 115
| [[IS-IS|Intermediate System to Intermediate System]] (IS-IS) || 115
|-
|-
| [[Routing Information Protocol]] (RIP) || 120
| [[Routing Information Protocol]] (RIP) || 120
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| [[Exterior Gateway Protocol]] (EGP) || 140
| [[Exterior Gateway Protocol]] (EGP) || 140
|-
|-
| [[On Demand Routing]] (ODR) || 160
| [[On Demand Routing|ODR]]|| 160
|-
|-
| External [[EIGRP]] || 170
| [[EIGRP]] external route || 170
|-
|-
| Internal [[BGP]] || 200
| Internal [[BGP]] || 200
|-
|-
| [[Next Hop Resolution Protocol]] (NHRP) || 250{{citation needed|date=October 2018}}
| [[Next Hop Resolution Protocol]] (NHRP) || 250<ref name="Cisco NHRP">{{citation |title=NHRP |url=https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/iproute_nhrp/command/reference/irn_book/nhrp-commands--a-through-z.html#wp8534493760 |author1=Cisco}}</ref>
|-
|-
| Default static route learned via DHCP || 254{{citation needed|date=October 2018}}
| Default static route learned via DHCP || 254{{citation needed|date=October 2018}}
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|}
|}


;Notes
{{notelist}}
{{notelist}}


=== Juniper ===
=== Juniper ===


The following table lists the default administrative distances for various [[routing protocols]] used on Juniper routers.<ref name="Juniper AD">{{citation |title=Default AD |url=https://www.juniper.net/documentation/en_US/junos/topics/reference/general/routing-protocols-default-route-preference-values.html |author1=Juniper}}</ref>
The following table lists the default administrative distances for various routing protocols used on Juniper routers.<ref name="Juniper AD">{{citation |title=Default AD |url=https://www.juniper.net/documentation/en_US/junos/topics/reference/general/routing-protocols-default-route-preference-values.html |author1=Juniper}}</ref>


{| class="wikitable" style="text-align:center"
{| class="wikitable" style="text-align:center"
! Routing Protocol !! Administrative distance
! Routing protocol !! Administrative distance
|-
|-
| Directly connected interface || 0
| Directly connected interface || 0
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| IS-IS Level 2 Internal || 18
| IS-IS Level 2 Internal || 18
|-
|-
| [[RIP]] || 100
| [[Routing Information Protocol|RIP]] || 100
|-
|-
| Aggregate (route summary) || 130
| Aggregate (route summary) || 130
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|}
|}


=== Extreme Networks ===
;Notes
{{unreferenced section|date=March 2023}}
The following table lists the default administrative distances used on ExtremeXOS / Switch-Engine.
{| class="wikitable"
!Routing protocol
!Administrative distance
|-
|Directly connected
|10
|-
|MPLS
|20
|-
|Blackhole
|50
|-
|Static
|1100
|-
|HostMobility
|1150
|-
|ICMP-Redirect
|1200
|-
|Fabric
|1699
|-
|eBGP
|1700
|-
|iBGP
|1900
|-
|OSPFintra
|2200
|-
|OSPFinter
|2300
|-
|IS-IS
|2350
|-
|IS-IS L1
|2360
|-
|IS-IS L2
|2370
|-
|RIP
|2400
|-
|OSPF AS Ext
|3100
|-
|OSPF Ext1
|3200
|-
|OSPF Ext2
|3300
|-
|IS-IS L1 Ext
|3400
|-
|IS-IS L2 Ext
|3500
|-
|Bootp
|5000
|}
The following table lists the default administrative distances used on Extreme VOSS / Fabric-Engine.
{| class="wikitable"
!Routing Protocol
!Administrative distance
|-
|Local
|0
|-
|Static
|5
|-
|SPBm L1
|7
|-
|OSPFintra
|20
|-
|OSPFinter
|25
|-
|eBGP
|45
|-
|RIP
|100
|-
|OSPF Ext1
|120
|-
|OSPF Ext2
|125
|-
|iBGP
|175
|}
{{notelist}}
{{notelist}}


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The [[network administrator]] may modify the administrative distance to change the desired ranking of router protocols. This may be necessary in cases where [[routing redistribution]] has to be used, otherwise, routing loops could occur.<ref name=cisco /> The Cisco Internetwork Operating System enables network administrators to modify the distance by changing the distance value in sub-router configuration mode. In the example below, RIP's administrative distance is changed to 89 so that it used in preference to OSPF.<ref name=cisco />
The [[network administrator]] may modify the administrative distance to change the desired ranking of router protocols. This may be necessary in cases where [[routing redistribution]] has to be used, otherwise, routing loops could occur.<ref name=cisco /> The Cisco Internetwork Operating System enables network administrators to modify the distance by changing the distance value in sub-router configuration mode. In the example below, RIP's administrative distance is changed to 89 so that it used in preference to OSPF.<ref name=cisco />


<syntaxhighlight lang="text">
<code>
R1<nowiki>></nowiki> '''enable'''
R1#enable


R1# '''configure terminal'''
R1#configure terminal


R1(config)# '''router rip'''
R1(config)#router rip


R1(config-router)# '''distance 89'''
R1(config-router)#distance 89
</syntaxhighlight>

</code>


Manually configuring the administrative distance is also required when configuring a floating static route. Floating static routes are used to provide an alternate path when a primary link fails. In order for static routes to be configured as a backup, the static route's administrative distance would need to be adjusted. Otherwise, it will take precedence over all routing protocols and routes issued from a routing protocol will not be inserted into the routing table.<ref name=cisco /> The example below shows how to configure the administrative distance to 254 to specify that it should only be used as a last resort.
Manually configuring the administrative distance is also required when configuring a floating static route. Floating static routes are used to provide an alternate path when a primary link fails. In order for static routes to be configured as a backup, the static route's administrative distance would need to be adjusted. Otherwise, it will take precedence over all routing protocols and routes issued from a routing protocol will not be inserted into the routing table.<ref name=cisco /> The example below shows how to configure the administrative distance to 254 to specify that it should only be used as a last resort.
Line 117: Line 218:
Verifying the configuration of the administrative distance is done on Cisco equipment using the ''show ip route'' command in [[privileged exec mode]] on the console of the [[Cisco Systems|Cisco]] router.<ref>Cisco Systems (n.d), [http://www.cisco.com/en/US/docs/switches/datacenter/sw/5_x/nx-os/unicast/configuration/guide/l3_route.html Configuring Static Routing], Cisco Systems Inc., retrieved 14 September 2013</ref><ref>Cisco Systems (n.d), [http://www.cisco.com/en/US/docs/switches/datacenter/sw/6_x/nx-os/unicast/command/reference/l3_cmds_show.html#wp1688356 Show Commands], Cisco Systems Inc., retrieved 14 September 2013</ref> In the example shown below, the administrative distance is 1. The letter "S" indicates that the route is a [[static route]] that has, for all intents and purposes, been added manually to the router process by the administrator and installed into the routing table.
Verifying the configuration of the administrative distance is done on Cisco equipment using the ''show ip route'' command in [[privileged exec mode]] on the console of the [[Cisco Systems|Cisco]] router.<ref>Cisco Systems (n.d), [http://www.cisco.com/en/US/docs/switches/datacenter/sw/5_x/nx-os/unicast/configuration/guide/l3_route.html Configuring Static Routing], Cisco Systems Inc., retrieved 14 September 2013</ref><ref>Cisco Systems (n.d), [http://www.cisco.com/en/US/docs/switches/datacenter/sw/6_x/nx-os/unicast/command/reference/l3_cmds_show.html#wp1688356 Show Commands], Cisco Systems Inc., retrieved 14 September 2013</ref> In the example shown below, the administrative distance is 1. The letter "S" indicates that the route is a [[static route]] that has, for all intents and purposes, been added manually to the router process by the administrator and installed into the routing table.


<syntaxhighlight lang="text">
<code>
Router# '''enable'''
Router#enable


Router# '''configure terminal'''
Router#configure terminal


Router(config)# '''ip route 1.1.1.0 255.255.255.0 fastEthernet 0/0'''
Router(config)#ip route 1.1.1.0 255.255.255.0 fastEthernet 0/0


Router(config)# '''do show ip route'''
Router(config)#do show ip route
</syntaxhighlight>

</code>


The ''do show ip route'' command will display the following, confirming that a [[static routing|static route]] has an administrative distance of 1.
The ''do show ip route'' command will display the following, confirming that a [[static routing|static route]] has an administrative distance of 1.
Line 133: Line 233:


==See also==
==See also==
* [[Metrics (networking)]], used for choosing a route when administrative distance is the same<ref>{{cite web |title=Administrative Distance and Metric |url=https://etutorials.org/Networking/Integrated+cisco+and+unix+network+architectures/Chapter+8.+Static+Routing+Concepts/Administrative+Distance+and+Metric/ |access-date=2021-12-23}}</ref><ref>{{cite web |title=Understand the significance of administrative distance and metrics when working with routers |url=https://www.techrepublic.com/article/understand-the-significance-of-administrative-distance-and-metrics-when-working-with-routers/ |access-date=2021-12-23}}</ref><ref>{{cite web |title=Administrative distance & metric |url=https://study-ccna.com/administrative-distance-metric/ |access-date=2021-12-23}}</ref>
*[[Routing]]


==References==
==References==
{{reflist}}
{{reflist}}

==External links==
* [http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080094195.shtml Cisco - What is Administrative Distance? (Ref. Mr. Praveen Suvarna Mundkur)]


[[Category:Routing]]
[[Category:Routing]]

Latest revision as of 01:36, 23 April 2024

Administrative distance (AD) or route preference[1] is a number of arbitrary unit assigned to dynamic routes, static routes and directly-connected routes. The value is used in routers to rank routes from most preferred (low AD value) to least preferred (high AD value).[2][3] When multiple paths to the same destination are available in its routing table, the router uses the route with the lowest administrative distance.

Router vendors typically design their routers to assign a default administrative distance to each kind of route. For example, on Cisco routers, routes issued by the Open Shortest Path First routing protocol have a lower default administrative distance than routes issued by the Routing Information Protocol. This is because, by default on Cisco routers, OSPF has a default administrative distance of 110 and RIP has a default administrative distance of 120. Administrative distance values can, however, usually be adjusted manually by a network administrator.[2]

Overview

[edit]

The administrative distance (AD) value is assigned by the router on a per-protocol basis. Routers, by design, should not install multiple routes into the routing table as this has the potential to cause routing loops.[2] While a router may run multiple routing protocols on the same device, it is necessary for the router to implement a process to ensure that multiple routes, pointing to the same destination do not simultaneously exist in the routing table. Each process running on a router advertises its administrative distance value to the local router. The router uses this value to determine which route should be used. Once a route has been selected, the routing information database is updated. If two routes have the same administrative distance, the router uses its vendor-specific algorithm to determine which route should be installed.[2] Cisco routers simply ignore the values and fall back to the default values, which are never the same.[4]

The router will usually compare administrative distances to determine which protocol has the lowest value. The router prefers protocols that have a lower assigned administrative distance. For example, OSPF has a default distance of 110, so it is preferred by the router process, over RIP, which has a default distance of 120. The administrator can arbitrarily reconfigure the administrative distances, which affects the ranking of the preferred routes by the routing process. On Cisco routers, static routes have an administrative distance of 1, making them preferred over routes issued by a dynamic routing protocol. The administrative distance is a value that is always only referenced by the local router itself. The administrative distance is not advertised on the network.[2]

Default administrative distances

[edit]

Cisco

[edit]

The following table lists the default administrative distances for various routing protocols used on Cisco routers.[3]

Routing protocol Administrative distance
Directly connected interface 0[a][5]
Static route 1
Dynamic Mobile Network Routing (DMNR) 3
EIGRP summary route 5
External BGP 20
EIGRP internal route 90
IGRP 100
Open Shortest Path First (OSPF) 110
Intermediate System to Intermediate System (IS-IS) 115
Routing Information Protocol (RIP) 120
Exterior Gateway Protocol (EGP) 140
ODR 160
EIGRP external route 170
Internal BGP 200
Next Hop Resolution Protocol (NHRP) 250[6]
Default static route learned via DHCP 254[citation needed]
Unknown and unused 255[b]
  1. ^ Only the interface itself has an administrative distance of 0, since a route cannot have a distance of less than 1.
  2. ^ An administrative distance of 255 will cause the router to remove the route from the routing table and not use it.

Juniper

[edit]

The following table lists the default administrative distances for various routing protocols used on Juniper routers.[7]

Routing protocol Administrative distance
Directly connected interface 0
Static routes 5
OSPF internal routes 10
IS-IS Level 1 Internal 15
IS-IS Level 2 Internal 18
RIP 100
Aggregate (route summary) 130
OSPF external routes 150
IS-IS Level 1 External 160
IS-IS Level 2 External 165
BGP 170

Extreme Networks

[edit]

The following table lists the default administrative distances used on ExtremeXOS / Switch-Engine.

Routing protocol Administrative distance
Directly connected 10
MPLS 20
Blackhole 50
Static 1100
HostMobility 1150
ICMP-Redirect 1200
Fabric 1699
eBGP 1700
iBGP 1900
OSPFintra 2200
OSPFinter 2300
IS-IS 2350
IS-IS L1 2360
IS-IS L2 2370
RIP 2400
OSPF AS Ext 3100
OSPF Ext1 3200
OSPF Ext2 3300
IS-IS L1 Ext 3400
IS-IS L2 Ext 3500
Bootp 5000

The following table lists the default administrative distances used on Extreme VOSS / Fabric-Engine.

Routing Protocol Administrative distance
Local 0
Static 5
SPBm L1 7
OSPFintra 20
OSPFinter 25
eBGP 45
RIP 100
OSPF Ext1 120
OSPF Ext2 125
iBGP 175

Configuration

[edit]

Cisco IOS

[edit]

The network administrator may modify the administrative distance to change the desired ranking of router protocols. This may be necessary in cases where routing redistribution has to be used, otherwise, routing loops could occur.[3] The Cisco Internetwork Operating System enables network administrators to modify the distance by changing the distance value in sub-router configuration mode. In the example below, RIP's administrative distance is changed to 89 so that it used in preference to OSPF.[3] 

R1#enable

R1#configure terminal

R1(config)#router rip

R1(config-router)#distance 89

Manually configuring the administrative distance is also required when configuring a floating static route. Floating static routes are used to provide an alternate path when a primary link fails. In order for static routes to be configured as a backup, the static route's administrative distance would need to be adjusted. Otherwise, it will take precedence over all routing protocols and routes issued from a routing protocol will not be inserted into the routing table.[3] The example below shows how to configure the administrative distance to 254 to specify that it should only be used as a last resort.

R1(config)# ip route 10.0.0.0 255.0.0.0 backupLink 1 254

In the event that two routing protocols are configured with the same administrative distance, the Cisco router will ignore the configured values and instead use the default values.[4]

Verifying the configuration of the administrative distance is done on Cisco equipment using the show ip route command in privileged exec mode on the console of the Cisco router.[8][9] In the example shown below, the administrative distance is 1. The letter "S" indicates that the route is a static route that has, for all intents and purposes, been added manually to the router process by the administrator and installed into the routing table. 

Router#enable

Router#configure terminal

Router(config)#ip route 1.1.1.0 255.255.255.0 fastEthernet 0/0

Router(config)#do show ip route

The do show ip route command will display the following, confirming that a static route has an administrative distance of 1.

S 1.1.1.0/0 [1/0] via 172.31.0.1

See also

[edit]

References

[edit]
  1. ^ "Route Preferences". Juniper Networks. Retrieved 2018-06-18.
  2. ^ a b c d e Franck Le; Geoffrey G. Xie; Hui Zhang, Understanding Route Redistribution (PDF)
  3. ^ a b c d e Cisco Systems (2013), What is Administrative Distance?, retrieved 14 September 2013
  4. ^ a b Cisco Systems(n.d.), Information About Routing, Cisco Systems Inc, retrieved 0109 2014
  5. ^ Cisco, Default AD
  6. ^ Cisco, NHRP
  7. ^ Juniper, Default AD
  8. ^ Cisco Systems (n.d), Configuring Static Routing, Cisco Systems Inc., retrieved 14 September 2013
  9. ^ Cisco Systems (n.d), Show Commands, Cisco Systems Inc., retrieved 14 September 2013
  10. ^ "Administrative Distance and Metric". Retrieved 2021-12-23.
  11. ^ "Understand the significance of administrative distance and metrics when working with routers". Retrieved 2021-12-23.
  12. ^ "Administrative distance & metric". Retrieved 2021-12-23.
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