notes: RIP Metrics & Timers

- RIP uses hop-count as a metric.
- 1 hop per interface.
- 16 hops = unreachable

Timers:

1. Update timer (30sec) - A router sends a response message out every RIP-enabled interfaces every 30 seconds on average.

2. Invalid timer (180sec)- Amount of time a route can stay in the routing table without being updated.

3. Holddown (180sec) - An update with a hop count higher that the metric recorded in the table will place a route in holddown.
- cisco proprietary. if you you are connecting a non cisco devices set holdtime to 0.

4. Flush timer (240sec) - The time when a invalid route get removed from the routing table.

- Before the flush timer expires, the invalid route will be advertised with the unreachable metric.
- Shows in the routing table as "x.x.x.x is possibly down"
- Timers must be changed in all RIP domain

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COMMANDS
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1. to change the timers under rip routing process.

timers basic {update} {invalid} {holddown} {flush}

notes: RIP Operation

RIP Operation:

All RIP messages are encapsulated in UDP with source/destination ports being 520.

2 Message types:

1. Request: Used to ask neighboring routers to send an updates.
2. Response: Carries the update/routing entries.

- If a router must send an update with more than 25 route entries, multiple RIP messages will be produced.

- If more than one route exists to the same destination with equal hop counts, equal-cost load balancing will be performed.

- RIP sees a secondary IP addresses on a interfaces as separate data links, and can exchange routes with a secondary IP. But take note tha tall traffic generated by a router will always have the primary address as a source.
- RIP performs a soure-validation check, where the source IP address of incoming routing updates must be on the same IP network as one of the addresses defined for the receiving interface.

- Another instance where it might be needed to disable the source-validation, is when the source address is on a different subnet that, the locally configured address, ie local has a /32 and remote side a /24. This can be seen with "debug ip rip events".

- Output-delay

Can be used to sets a inter-packet gap between 8 and 50ms (default=0).
Can be used when a high-speed router is sending updates to a low-speed router.


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COMMANDS
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1. enable the RIP process:

router rip

2. Disables the validation of the source address in updates

no validate-update source

3. Sets an inter-packet gap (value 8-50), (Default=0)

output-delay {ms}


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verification
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1. All RIPv2 enabled routers will answer the ping and respond

ping 224.0.0.9

2. Displays RIP protocol events

debug ip rip events

3. to show which interface is participating

show ip protocols