What is EIGRP?
·
EIGRP (Enhanced Interior Gateway Routing
Protocol) is a Cisco-proprietary routing protocol that uses a hybrid of
distance-vector and link-state algorithms.
·
it has faster convergence times and uses less
network bandwidth.
·
EIGRP uses a composite metric, called the DUAL
(Diffusing Update Algorithm), to determine the best path to a destination.
Metric used in EIGRP?
The metric takes into account several factors, including:
·
Bandwidth:
The highest bandwidth of the path to the destination.
·
Delay:
The sum of the delays of all links in the path to the destination.
·
Reliability:
The reliability of the path to the destination.
·
Load:
The load on the path to the destination.
·
MTU:
The maximum transmission unit of the path to the destination.
By default, Bandwidth
and Delay used to calculate metrics.
Can you explain the concept of EIGRP neighbors and how
they are formed?
·
EIGRP neighbors are routers that have
established a relationship with each other by exchanging hello packets and have
the same autonomous system number configured.
·
They share routing information with each other
and form a neighbor table.
Tables maintained by EIGRP routers?
EIGRP routers maintains below
tables to store information about the network, including:
·
Neighbor Table- Store information about EIGRP neighbors.
·
Topology
Table– Store routing information which is learned from neighbors’
routers.
·
Routing
Table– Store the best path to all networks.
Criterion to form neighborship?
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Must be directly connected.
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Same AS number.
·
Same Subnet
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They must have the same authentication
configuration
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They must have the same K values: EIGRP routers
use the same K-values for metric calculations. If there are different K-values,
the routers will not form a neighborship.
Explain packets in EIGRP?
· Hello
Packets: Sent by routers to establish and maintain a neighborship. Hello
packets contain information about the router’s ASN, K-values, and hold time
· Update
Packets: Sent by routers to update their routing tables and share routing
information with their neighbors. Update packets contain information about
routes, including the destination, next hop, and metric.
· Query
Packets: Sent by a router when it loses a route and needs to find an
alternate path. Query packets are multicast to the router’s neighbors, asking
them if they have a route to the destination.
· Reply
Packets: Sent by a router in response to a query packet. Reply packets
contain information about routes to the destination, including the next hop and
metric.
· Ack
Packets: Sent by a router to acknowledge the receipt of update and query
packets. Ack packets are unicast to the sender of the update or query packet to
confirm that the packet was received.
What are AD values in EIGRP?
·
External EIGRP-170
·
Internal EIGRP – 90
·
Summery EIGRP – 5
What are external routes
in EIGRP?
· In EIGRP, external routes refer to routes that
are learned from other routing protocols, such as OSPF or BGP. These routes are
not part of the EIGRP autonomous system (AS) and are redistributed into EIGRP.
·
External routes are less trusted hence AD value
is 170.
·
When a router receives external routes, it will
add them to its routing table, but it will mark them as “external”
routes
What is Feasibility
condition in EIGRP?
·
In EIGRP, feasibility condition is a set of
rules that a router uses to determine if a route is considered
“feasible” or “not feasible.”
·
A feasible
route is a route that is considered to be a valid alternative path to a
destination.
EIGRP consist of two terms:
·
Successor:
Best route to destination.
·
Feasible Successor:
Alternative or Backup path to destination.
A route is considered feasible if its reported distance (RD)
is less than the feasible distance (FD) of current successor route is called Feasible condition.
Timers in EIGRP?
·
Hello
Timer: The hello timer is used to establish and maintain neighborship between
routers.
The default hello timer is 5 seconds.
·
Hold
Timer:
This timer controls the maximum amount of time a
router will wait to receive a hello packet from a neighbor before considering
the neighborship to be down
The default hold timer is 15 seconds.
·
Update
Timer: Update packets contain information about routes and are used to
update the routing tables of the router’s neighbors.
The default update timer is 90 seconds.
·
Invalid
Timer: This timer controls how long a route will remain in the routing
table after it is marked as “invalid.” An invalid route is a route
that is no longer considered feasible.
The default invalid timer is 180 seconds.
·
Flush
Timer: The flush timer ensures that the route is removed from the routing
table even if the router does not receive an update packet.
The default flush timer is 240 seconds.
·
SIA-Query
Timer: This timer controls how long a route will remain in the
stuck-in-active state before a SIA-Query packet is sent by a router
The default SIA-Query Timer is 3
minutes.
What is Passive Interface?
Don’t send and
receive update on that interface.
Authentication type
supported by EIGRP?
MD5
EIGRP stub router?
·
A stub router in EIGRP (Enhanced Interior
Gateway Routing Protocol) is a router that is configured to advertise only a
default route to its neighboring routers, rather than the full routing table.
·
This is useful in situations where a router has
a limited number of directly connected networks, and it is not necessary to
advertise all of the routes in the network.
·
The main goals of the EIGRP stub routing
function are to increase network stability and save memory and CPU on local
routers
What is stuck-in-active?
·
When EIGRP loses a route, and there is no
feasible successor the route will go
from passive to active, and the router starts sending
queries to its neighbors. To get to know about any route to reach destination
network.
·
Until router receives Reply for Query msg no
successor selected.
·
EIGRP router will wait for 3 min for the reply
of the queries sent by it and if don’t receives reply the route become
stuck-in-active
·
And router reset neighbor relationship with
neighbor that did received reply