EIGRP Flashcards
What is EIGRP’s benefits over RIP
Support for networks more than 255 hops away
Fast convergence time
Better metric calculations
Un-equal multi path costing
What is the EIGRP successor route
the path with the lowest metric to the destination network.
Successor
The router that is the next hop away on the successor route
Feasible distance
The total distance from the router to the destination network.
Reported distance
The distance from the successor router to the destination network.
Feasibility condition
The feasibility condition is a calculation to determine if a route can become a feasible route.
Calculated by: if RD of the back up router < FD of the successor router then the condition is met.
Feasible successor
A backup router that satisfies the feasibility condition.
What does active and passive mean in the EIGRP topology table
Passive - the route is up and stable
Active - the router is recomputing the DUAL algorithm as there is a topology change.
What IP number does EIGRP use to communicate
88
What is the multicast address for EIGRP packets
224.0.0.10
What are the different EIGRP packet types
Hello
request
update
query
reply
What does the hello packet do
discover EIGRP neighbours and maintain relationships
what does the request packet do
Used to get specific information from a neighbour
what does the update packet do
Used to update neighbours when there is a topology change
What does the query packet do
Used to search for a new route when successor route is down.
What does the reply packet do
Sent in response to the query packet
What is the default metric calculation
Total path delay in microseconds + the bandwidth of the slowest link (in the form of 10Gbps)
What is the wide EIGRP metric used for
When using the standard metric with links higher than a Gb the delay is the same so the metric would be the same for 10Gbps and 50Gbps.
The wide metric allows you to input the exact delay.
K6 is introduced default value 0.
Are wide metrics backwards compatible with normal metrics
yes
What is the variance multiplier used for
UECMP, the variance is the amount of difference between the successor and feasible successor’s FD that will allow the feasible successor to be used in UECMP.
Is UECMP on/off by default
Off variance is set to 1 by default to enable change to another whole number.
What is the EIGRP hold timer and what is the default value
The hold timer is the amount of time the EIGRP router will wait if it has not received a hello packet before assuming route is dead.
default is 3x hello timer.
What is the hello timer and what is the default timer
the interval between hello packets been sent to neighbours to confirm availability
default 5 seconds for interfaces ethernet and above E1 and 64k default timer is 60 seconds.
What happens when a link goes down in EIGRP
Link goes line protocol down
The feasible successor route takes over as the successor route.
Update packet is sent to neighbours telling new path.
if there is no Feasible successor route then DUAL will recompute to destination network.
The router will send out a query packet to downstream routers with the delay set to infinity to inform them a link has gone active.
The neighbour will then either send a reply saying it has no route / If the query didn’t come from the successor then the router will reply with the route / the router will send queries to down stream routers.
What does EIGRP route summarisation help
Improves network scaling.
What command do you use to see the EIGRP topology table
show ip EIGRP topology
