Application of management distance in RIP protocol

I. the role of management distance

administrative distance is a measure that determines the validity or trustworthiness of a routing protocol. In various routing protocols, sorting is done from the most believable to the most untrusted. Used to determine the best route when there are multiple paths generated by different protocols to the same destination.

The default administrative distances for the different protocols commonly used are the following table:

Lu Yuyan (Routing protocol)	Default administrative distance
Direct Connect Routing	0
Static to Interface	0
Static to Next hop	1
External BGP	20
Ospf	110
Is-is	115
PIR V1,V2	120
Internal BGP	200
Unknown	255

as you can see from the table above, when the administrative distance is 255 , the route generated by the protocol is the least trusted, and the routing entry is not entered into the local routing table.

II. Routing Entry Analysis

Each route consists of the following six parts: The following routing entries

R 30.2.1.0[120/1] via 10.1.1.2,00:00:21,serial0/0

" R"means that this route islearned from the" RIP"protocol;" 30.2.1.0"is the destination network; "[120/1]"is a rip the management distance of the protocol,1 means that the path to the target is only 1 hops; "via 10.1.1.2" means the IP address of thenext hop router that reaches the destination network ; 00:00:21"refers to the time (age) at which the route bar has been created;"Serial 0/0"refers to the port on which the next hop should go out.

Mastering the generation of routing and related attributes is very important to the application by modifying the management distance control and filtering routing.

Third, the application practice of modifying management distance in IP protocol

in the in the configuration mode of the RIP protocol, the command format is as follows:

Distance weightip-address Wildcard Access-list-number

Each parameter has the following meanings:

Weight: modified to a new range of administrative distance values 1-255

Ip-address: IP address of the routing source

Wildcard: The match for the IP address of the route source is represented by an anti-mask

Access-list-number: Modify access list number (1-99) to manage distances only for routes that meet the access list

For example: command distance 255 The router will learn all the RIP protocol routes to the administrative distance set to 255, which causes the router to learn no rip route;

Distance 192.168.1.5 0.0.0.0 The route passed by the 192.168.1.5 to the management distance set to ;

Distance Access-list ( such as access-list for permit 192.168.30.0 0.0.0.255), the order The standard network is the administrative distance setting for the 192.168.30.0 routing entry 88

Iv. Practical Application

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RA (config) #routerrip

RA (Config-router) #version2

RA (Config-router) #network192.168.1.0

RA (Config-router) #network192.168.2.0

RA (config-router) #noauto-summary

RA (config-router) #distance 255

RA (config-router) #distance 192.168.1.2 0.0.0.0

RB (config) #routerrip

RB (Config-router) #version2

RB (Config-router) #network192.168.1.0

RB (Config-router) #network192.168.10.0

RB (config-router) #noauto-summary

RC (config) #routerrip

RC (Config-router) #version2

RC (Config-router) #network192.168.2.0

RC (Config-router) #network192.168.20.0

RC (config-router) #noauto-summary

The above configuration makes the router A can only obtain RIP routes advertised by router B , while the management distance of router C advertises RIP 's routing entry is set 255, router A These routing entries (the target network segment is 192.168.20.0/24 discarded).

This article is from the "Yugong Yishan" blog, make sure to keep this source http://1538620.blog.51cto.com/1528620/1597499

Application of management distance in RIP protocol