3. Advanced EIGRP Flashcards
What is the secondary function of EIGRP Hello packets?
To ensure that a neighbor is still healthy and available
What is the default EIGRP Hello interval?
5 seconds (60 on slow speed interfaces)
How does the EIGPR hold timer work?
The timer decrements, and upon receipt of a hello packet, the hold timer resets and restarts countdown. If 0 is reached EIGRP declares the neighbor unreachable and notifies DUAL of a topology change
What is the default EIGRP Hold interval?
15 seconds (180 on slow speed interfaces)
What is the command to change the hello/hold timers?
On interface level:
- ip hello-interval eigrp ASN seconds
- ip hold-time eigrp ASN seconds
Named:
- hello-interval seconds
- hold-time seconds
What command is used to view the hello/hold timers?
show ip EIGRP interfaces detail
What happens in EIGRP when a link goes down?
- PAth recomputation most occur for any prefix where that neighbor was a successor (upstream router)
- The feasible successor instantly becomes the successor route (if available)
- The router sends an update packet for that path because of the new metrics
- Downstream routers run their own DUAL
What happens in EIGRP when a link goes down and there is no feasible successor?
- DUAL must perform a new route calculation. The route state changes to Active in the topology table
- The router that detected the topology change sends out query packets to neighbors with the reply status flag set
How do other routers know that a route is set to active?
The query packet has the delay set to infinity
What are the 3 options that a router can do after receipt of a query packet?
- It replies to the query that the router does not have a route to the prefix
- If from the successor, it sets the prefix to active and sends out the query to all downstream routers for that route
- If not from the successor, it ignores it. The receiving router replies with the EIGRP attributes for that route
What is a query boundary?
When a router does not mark the prefix as active;
- It says it does not have the prefix
- It replies with the attributes because the query did not came from the successor
When is the new topology calculation of DUAL complete?
When a reply has been received from every downstream router and the route is changed to Passive
What is a SIA query?
The Stuck-in-Active query. This is sent when the Active timer has been past by half and no response has been received.
What is the default active timer?
180 seconds
How can the active timer be changed?
timers active-time
topology base
timers active-time
How can you check the active timer?
show ip protocols
How does a router need to respond when a SIA query is received?
A SIA reply needs to be send within 90 seconds.
What happens when a router does not respond on time on the SIA query?
EIGRP will deem the router SIA and DUAL deletes all routes from that neihbor.
How can you find active queries?
show ip eigrp topology
What is the command to activate summarization?
On interface level:
ip summary-address EIGRP ASN network subnetmask (leak map)
What is the parameter LEAK-map used for?
To allow advertisement of a route identified in the summarization
How can the parameter LEAK-map be used?
By creating an ACL with the leaked route
By creating a route-map -> match ip address ACL
Then readd the summary again
On what interface does summarization take place (outgoing/ingoing)?
Outgoing, therefore the DEFAULT parameter cannot be used
Why is summarization used?
To reduce the size of the routing table and reduce the CPU usage
