Administrative distance, Passive Rip and other terminologies

Administrative distance

suppose a router sees two multiple path going the the destination router direction.

It can see both the paths as best path because of multiple routing protocols running on the router. Sometimes even the metric count can't help us to choose the best path and still the router needs to choose single best path. To solve this problem each routing protocol has been assigned a different numeric value. Due to that numeric value, the router then chooses the routing protocol with the lowest numeric value. That value is known as the Administrative Distance (AD).

Following are the distance of the following protocols

• Connected routes (AD=0)
• Static routes (AD=1)
• EIGRP routes (AD=90)
• OSPF routes  (AD=110)
• RIP routes (AD=120)
• DHCP  (AD=254)

PASSIVE RIP
This Passive command helps to stop RIP updates being advertised to the interface. Configuration is shown below

Router(config)#router rip
Router(config-router)#Passive-interface g0/1

You have to activate the command on the interface which you don't want to advertise.

Load balancing
Suppose a router have find two paths with the same metric, so it sends some packets over one path and some to another path. This is known as Load -Balancing.

Contigous Network 
A contigous network is that topology in which a subnet of one network is not separated by a subset of classful network.

Discontigous Network
a discontigous network is that topology in which a subnet of one network is  separated by a subset of classful network.

No Autosummary
when older classful routing protocols were used in the early networking era, a cautios subnet design  was used to avoid discontigous classful network. The no autosummary command on every router of the topology helps to avoid this problem.

Routing Loop
When a set of routers that causes a packet which has been sent to there paths happens to be keep looping between them and never arrived to the destination. That status is known as Routing Loops.

Split Horizon
Split Horizon is a process that  helps to avoids routing loops. It has a distance vector feature that tells the router to discard/omit some routes from an update sent by some interface.

Route Poisoning: 
Route poisoning advertises a field to other routers with a special numeric value known as the infinite value.A Router consider those router as failed because of the infinite metric.