EIGRP Protocols Brief Summary
EIGRP 😊
- EIGRP Known as the Enhanced Interior Gateway Routing Protocol (EIGRP), it is a hybrid routing protocol.
- The
term EIGRP is an acronym that stands for Enhanced Interior Gateway Routing
Protocol.
- It
is an improved version of the older Interior Gateway Routing Protocol
(IGRP).
- EIGRP
was previously a Cisco-owned protocol. However, Cisco has now made it an
open-standard protocol. Therefore, any vendor can use it now on their
equipment!
- EIGRP
is considered an ‘advanced’ or ‘hybrid’ distance vector
routing protocol.
- It
improves many basic operations of RIP which is its fellow distance vector
routing protocol.
- It
is way faster than RIP in reacting to the changes needed in the network.
- It
does not have a hop count limit of 15 like RIP. Therefore, it
supports very large networks.
- It sends messages using the multicast address 224.0.0.10.
- EIGRP
can be deployed on both IPv4 and
IPv6 Internet Protocol networks. It can also be
deployed on networks such as Novell Internetwork Packet Exchange.
- EIGRP
is the only Interior Gateway Protocol (IGP) that can perform unequal-cost-load-balancing. It
performs equal-cost-load-balancing (ECMP) load balancing over 4 paths like
RIP by default.
- EIGRP
can even load balance on the basis of the proportion of their bandwidth.
Therefore, more traffic will be sent over to the paths with lower metric
as they are faster.
- Less
traffic will be sent to the paths with higher metric as they are slower.
-
EIGRP is a wonderful protocol. However, it is mostly used in Cisco devices, therefore, it is not as widely used as OSPF.
Unlike other routing protocols, EIGRP uses four major metrics to choose the best path to transmit the packets. These metrics are:
- Bandwidth
- Delay
- Load,
and
- Reliability
The default metric used by EIGRP is bandwidth and delay.
- Bandwidth
EIGRP uses the following table for route discovery:
- Neighbor
table
- Topology
table
- Route
table
- Successors
- Feasible
successors
Now, let’s see how
this table works step-by-step.
1. Neighbor Table:
- The
neighbor table is used to store the condition of the directly connected
neighbors.
- This
means that whether the directly connected router is active or non-active,
the neighbor table is going to store the information anyway.
For example, if two routers are connected to each other directly, both routers are
going to send the ‘Hello’ packets to each other after every 5 seconds. These
two routers consider each other alive as long as this exchange of packets
continues.
If the router is
not able to receive the hello packet in 5 seconds, it realizes that the link is
down and forwards this information to another connected router. In such a way,
all the routers are updated about the link failure of a particular router in
the network.
2. Topology Table:
- This
table is used to store the advertisements of the destinations by the
neighbors.
- The
advertisement includes:
·
The destination address
·
The neighbor that is linked to the destination
·
The metrics used by the neighbor to the destination
For example, if three routers are connected to each other in a linear form and the
first router wants to reach the third router, it is not going to receive any
advertisement from the third router. In fact, it will receive an advertisement
from the second router.
This is because the
second router knows the best route to reach the third router and the first
router knows the best route to reach the second router. This is how all the
routers are configured with EIGRP to calculate and update the router to
their routing table.
3. Routing Table:
- This
table is used to store all the possible routes to reach the destination.
- This
is the main function of the routing table.
4. Successors:
- The
successor is the path with the best metric.
- This
means that the successor is the best available route in the routing table
to reach the destination and the router chooses this route first.
5. Feasible Successors:
- It
is considered a backup route.
- If
the path distance is less than the original path to reach the destination,
it is considered feasible.
- When
the successor path is invalid or inactive, it becomes the first choice.
- It
is the second fastest available route to reach the destination.
The algorithm which
determines the most efficient and reasonable routes to reachable destinations
is the Diffusing Update Algorithm (DUAL). This is decided on
the basis of the distance and whether the destination path is loop-free.
EIGRP uses Five Packets to pass messages and allow the management of the sessions. These are:
1. HELLO Packets
2. QUERY Packets
3. REPLY Packets
4. REQUEST Packets
5. UPDATE Packets
BENEFITS of EIGRP PROTOCOL:-
- It has a faster convergence.
- There is no need to update the routing tables by hand.
- It has a low network resource usage as it only sends HELLO packets when the network is stable.
- It either uses unequal-cost-load-balancing or equal-cost multipath balancing to use links more efficiently.
- It is loop-free therefore, it improves video and voice quality
EIGRP is the
new-age Interior Gateway Protocol (IGP) that has a faster convergence. Its
highlighting feature is the unequal-cost-load-balancing that in return, reduces
CPU usage.
However, EIGRP is
more of a Cisco proprietary even though some of its features are
open-standard. OSPF is
considered over EIGRP!
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