Information Technology Reference
In-Depth Information
To prevent the synchronization of updates between routers, the Cisco IOS uses a random variable,
called RIP_JITTER, that varies the update interval randomly in a range from 25 to 30 seconds for the
default 30-second interval.
Routing Loops
Routing loops can cause a severe impact on network performance. The following exercise will rein-
force your knowledge of the causes and solutions of routing loops with distance vector routing proto-
cols.
Routing Loop Concepts Exercise
Routing Loops
Briefly explain what a routing loop is.
A routing loop is a condition in which a packet is continuously transmitted within a series of routers
without ever reaching its intended destination network.
How do routing loops occur?
A routing loop can occur when two or more routers have routing information that incorrectly indicates
that a valid path to an unreachable destination exists.
List four ways that a routing loop can happen.
Incorrectly configured static routes
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Incorrectly configured route redistribution (redistribution is a process of handing the routing
information from one routing protocol to another routing protocol and is discussed in CCNP-
level courses)
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Inconsistent routing tables not being updated because of slow convergence in a changing
network
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Incorrectly configured or installed discard routes
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Implications of Routing Loops
A routing loop can have a devastating effect on a network, resulting in degraded network performance
or even network downtime.
List five effects that routing loops can have on a network.
Link bandwidth will be used for traffic looping back and forth between the routers in a loop.
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A router's CPU will be strained because of looping packets.
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A router's CPU will be burdened with useless packet forwarding that will negatively impact the
convergence of the network.
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Routing updates might get lost or might not be processed in a timely manner. These conditions
would introduce additional routing loops, making the situation even worse.
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Packets can get lost in “black holes.”
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