Rip Timer; Route Updates - Zte ZXR10 5900E Series User Manual

ZXR10 5900E Series User Manual (IPv4 Volume)
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optimal path which sometimes results in that the selected path is
not the best one.
Administrative Distance (AD) of RIP is 120 by default. Smaller the
AD value, more reliable the routing source is. Therefore, compar-
ing with other routing protocols, RIP is not so reliable.

RIP Timer

The router running RIP sends a routing information update packet
reflecting all the routing information of the router at intervals (30
seconds by default), which is called the routing information an-
nouncement. If a router cannot receive update information from
another router within a period of time (180 seconds by default),
it will label the route provided by this router as unavailable. If
update information still cannot be received within the subsequent
period of time (240 seconds), the router eliminates the route from
the routing table. Holddown timer introduces a certain amount of
skepticism to reduce the acceptance of bad routing information. If
the distance to a destination increases, for example, the hop count
increases from two to four, the router sets a holddown timer for
that route. Until the timer expires, the router will not accept any
new updates for the route.
RIP provides four timers:
� Update timer
� Invalid timer
� Holddown timer
� Flush timer

Route Updates

RIP sends routing-update messages at regular intervals and when
network topology changes. When a router receives a routing up-
date that includes changes to an entry, it updates its routing table
to reflect the new route. The metric value for path is increased by
1, and the sender is indicated as the next hop. RIP routers only
maintain best route (the route with the lowest metric value) to a
destination.
After updating its routing table, router immediately transmits rout-
ing updates to inform other network routers of the change. These
updates are sent independently of the regularly scheduled updates
that RIP routers send.