Routing protocol timer
RIP Timers
The Cisco implementation of RIP uses four timers:
Update
Invalid
Flush
Holddown
RIP sends its full routing table out all configured interfaces. The table is sent periodically as a broadcast (255.255.255.255) for Ver.1 and multicast (224.0.0.9) for Ver.2 to all hosts.
Update Timer
The update timer specifies the frequency of the periodic broadcasts. By default, the update timer is set to 30 seconds. Each route has a timeout value associated with it. The timeout gets reset every time the router receives a routing update containing the route.
Invalid Timer
When the timeout value expires, the route is marked as unreachable because it is marked invalid. The router marks the route invalid by setting the metric to 16. The route is retained in the routing table. By default, the invalid timer is 180 seconds, or six updates periods (30 x 6 = 180).
Flush Timer
A route entry marked as invalid is retained in the routing table until the flush timer expires. By default, the flush timer is 240 seconds, which is 60 seconds longer than the invalid timer.
Holddown Timer
Cisco implements an additional timer for RIP, the holddown timer. The holddown timer stabilizes routes by setting an allowed time for which routing information regarding different paths is suppressed. After the metric for a route entry changes, the router accepts no updates for the route until the holddown timer expires. By default, the holddown timer is 180 seconds.
http://www.ciscopress.com/articles/article.asp?p=102174&seqNum=3
EIGRP Timers
EIGRP sets updates only when necessary and sends them only to neighboring routers. There is no periodic update timer.
EIGRP uses hello packets to learn of neighboring routers. On high-speed networks, the default hello packet interval is 5 seconds. On multipoint networks with link speeds of T1 and slower, hello packets are unicast every 60 seconds.
The holdtime to maintain a neighbor adjacency is three times the hello time: 15 seconds. If a router does not receive a hello within the holdtime, it removes the neighbor from the table. Hellos are multicast every 60 seconds on multipoint WAN interfaces (X.25, Frame Relay, ATM) with speeds less than 1544 Mbps, inclusive. The neighbor holdtime is 180 seconds on these types of interfaces. To summarize, hello/holdtime timers are 5/15 seconds for high-speed links and 60/180 seconds for multipoint WAN links less than 1544 Mbps, inclusive.
EIGRP does not send updates using a broadcast address; instead, it sends them to the multicast address 224.0.0.10 (all EIGRP routers).
The hello mechanism works independently in each direction. Hellos from router R1 to router R2 do not necessarily have to use the same parameters as hellos from R2 to R1.
The hold time is transmitted to the neighbor in the hello packet. R2 does not use its locally configured hold-time, but uses the value that R1 tells it to use.
The Cisco implementation of RIP uses four timers:
Update
Invalid
Flush
Holddown
RIP sends its full routing table out all configured interfaces. The table is sent periodically as a broadcast (255.255.255.255) for Ver.1 and multicast (224.0.0.9) for Ver.2 to all hosts.
Update Timer
The update timer specifies the frequency of the periodic broadcasts. By default, the update timer is set to 30 seconds. Each route has a timeout value associated with it. The timeout gets reset every time the router receives a routing update containing the route.
Invalid Timer
When the timeout value expires, the route is marked as unreachable because it is marked invalid. The router marks the route invalid by setting the metric to 16. The route is retained in the routing table. By default, the invalid timer is 180 seconds, or six updates periods (30 x 6 = 180).
Flush Timer
A route entry marked as invalid is retained in the routing table until the flush timer expires. By default, the flush timer is 240 seconds, which is 60 seconds longer than the invalid timer.
Holddown Timer
Cisco implements an additional timer for RIP, the holddown timer. The holddown timer stabilizes routes by setting an allowed time for which routing information regarding different paths is suppressed. After the metric for a route entry changes, the router accepts no updates for the route until the holddown timer expires. By default, the holddown timer is 180 seconds.
http://www.ciscopress.com/articles/article.asp?p=102174&seqNum=3
EIGRP Timers
EIGRP sets updates only when necessary and sends them only to neighboring routers. There is no periodic update timer.
EIGRP uses hello packets to learn of neighboring routers. On high-speed networks, the default hello packet interval is 5 seconds. On multipoint networks with link speeds of T1 and slower, hello packets are unicast every 60 seconds.
The holdtime to maintain a neighbor adjacency is three times the hello time: 15 seconds. If a router does not receive a hello within the holdtime, it removes the neighbor from the table. Hellos are multicast every 60 seconds on multipoint WAN interfaces (X.25, Frame Relay, ATM) with speeds less than 1544 Mbps, inclusive. The neighbor holdtime is 180 seconds on these types of interfaces. To summarize, hello/holdtime timers are 5/15 seconds for high-speed links and 60/180 seconds for multipoint WAN links less than 1544 Mbps, inclusive.
EIGRP does not send updates using a broadcast address; instead, it sends them to the multicast address 224.0.0.10 (all EIGRP routers).
The hello mechanism works independently in each direction. Hellos from router R1 to router R2 do not necessarily have to use the same parameters as hellos from R2 to R1.
The hold time is transmitted to the neighbor in the hello packet. R2 does not use its locally configured hold-time, but uses the value that R1 tells it to use.
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