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
What is a summary discard route?
A route installed by EIGPR to prevent routing loops. Portion of the summarization that are not yet active will be sent to route Null0
What is de AD of Null0?
AD is 5 by default
How can you check the discard route?
show ip route network subnet
What is special about the summarization metrics?
It will always use the metric of the lowest path
How can a fluctuation in the summarization metrics be solved?
By changing the metrics with the command:
summary-metric network subnet bandwidth delay load reliability mtu
What is automatic summarization?
Summarization that will take place when classful network boundaries are crossed. This is turned of by default because it can cause identical advertisement.
How can automatic summarization be turned on?
Classic
auto-summary
Named
Topology base
auto-summary
What is a EIGRP STUB router?
The stub router does not advertise routes learned through other peers, but only connected and summary routes
How can a STUB router be installed?
With the command
eigrp stub
The router then announces itself as a stub within the Hello packet
What are the key benefits of a STUB router?
- EIGPR does not send query packets to a STUB router. This provides faster convergence
- It prevents the stub from becoming a transit site
How does EIGPR prevent sending STUB routes?
A route that is sent out of WAN interface will get marked with a stub site identifier
Can the STUB functionallity be used on both EIGRP congifurations?
No, only on the named one
What is the command to identify a WAN interface?
stub-site wan-interface
What is the command to activate the stub site function and identifier?
eigrp stub-site
What is the IP bandwidth percentage?
Can be used to control the ammount of bandwidth a routing protocol can use
What is the command to change the bandwitdth percentage?
ip bandwidth-percentage eigrp
named interface
bandwidth-percentage
What is Split-Horizon?
This prevents the advertisement of reverse routes and is enabled by default
When do you disable Split-Horizon?
When u use a hub-and–spoke topology
What is the command for route filtering?
Topology base
distribute-list
What is an offset-list?
With an offset list, additional delay can be added up to a metric of a route
What is the command for an offset list?
Topology base
Create an access list first
offset-list
Can an ACL block EIGRP traffic?
Yes, but it will only be effective on inbound interfaces
