Configuring timers in RIP
You can change the RIP timers using the command :
router rip timers basic <update> <invalid> <holdown> <flush>
Consider a topology: In this topology we need 3 routers connected with each other such as given below:
R1 configuration:
interface FastEthernet1/1 ip address 192.168.1.5 255.255.255.252 no shutdown interface FastEthernet0/0 ip address 192.168.1.1 255.255.255.252 no shutdown router rip network 0.0.0.0
R2 configuration:
interface FastEthernet1/1 ip address 192.168.1.6 255.255.255.252 no shutdown interface FastEthernet1/0 ip address 192.168.1.9 255.255.255.252 no shutdown router rip network 0.0.0.0
R3 configuration:
interface FastEthernet1/0 ip address 192.168.1.10 255.255.255.252 no shutdown interface FastEthernet0/0 ip address 192.168.1.2 255.255.255.252 no shutdown router rip network 0.0.0.0
Now let’s change the timers on R1:
router rip timers basic 50 30 50 50 exit
A point to note is that a low update timer can cause congestion in the network as RIP send full updates.
Configuring RIP Timers in Cisco
Pre-requisites: RIP
RIP is a Distance Vector Routing Protocol with an AD 120 value of and uses next-hop as metric value to find the best route to a destination. It supports a maximum of 15 hop counts, and 16 is considered as infinity. RIP uses split horizon to avoid forming of loops and uses split horizon with reverse poisoning to advertise a network that is no longer reachable. RIP uses a total of four timers:
Update TImer | Interval after which update packets are sent.(30s default) |
---|---|
Invalid After Timer |
A per-route timer that is reset after an update about a new route has been received. After this timer a router is considered possibly down. from it’s next hop.(180s default + 1s for each update received) |
Holdown TImer |
A per-route timer that begins after a route has been declared invalid. Router starts advertising route as unreachable, and does not accept any update information for this period and does not modify it’s routing table entry until the timer expires.(180s default |
Flushed After Timer |
A per-route timer that is reset and begins after an update about a route has been received from it’s next hop. It is 60 seconds by default. This timer starts after the route has been declared invalid and after 60 seconds i.e time will be 180 + 60 = 240 seconds. |