OPSF:
-Open Shortest Path First (OSPF)
is a widely used interior gateway protocol for IP networks.
-It is a link state routing
protocol that calculates the shortest path to a destination using the Dijkstra
algorithm.
-Open Standard.
– AD value 110
Key features
of OSPF include:
Hierarchical design: OSPF divides the network into smaller
sub-networks called areas, reducing the amount of routing information exchanged
between routers.
Fast convergence: OSPF is known for its fast convergence time,
ensuring the network continues to operate smoothly in the event of a failure.
Equal-cost multi-path routing: OSPF supports equal-cost multi-path
routing, allowing multiple paths to a destination to be used simultaneously.
Authentication and encryption: OSPF provides support for authentication
and encryption to secure the exchange of routing information.
Widely used: OSPF is widely used in real-world networks, including
service provider networks, enterprise networks, and data center networks.
VLSM Support: Carries Subnet Mask information in routing update.
Open Standard – Multivendor
Support.
Independent Transport – Use IP protocol 89 not TCP/UDP.
Neighborship
Criterion:
Router ID: The Router ID is a unique identifier for each OSPF
router,
Area ID: The Area ID must match between the two routers in order
for them to form a neighbor relationship.
Hello and Dead Intervals: The Hello interval and Dead interval must
match between the two routers in order for them to form a neighbor
relationship.
Authentication: If authentication is enabled, the authentication
type and key must match between the two routers in order for them to form a
neighbor relationship.
Subnet Mask: The subnet mask must match between the two routers in
order for them to form a neighbor relationship. Routers on different subnets do
not form neighbor relationships.
MTU (Maximum Transmission Unit): In OSPF, the MTU size must match
between two routers in order for them to form a neighbor relationship. If the
MTU size is different between two routers, this can cause issues with
communication and packet loss.
Stub Area Flag:
A Stub Area is a type of OSPF
area that does not receive information about routes from other areas and only
receives default routes.
The Stub Area Flag is used to
indicate that a router is part of a stub area, and must match between two
routers in order for them to form a neighbor relationship.
If the Stub Area Flag is set
differently between two routers, this can cause issues with routing and
communication.
OSPF States:
States are important for understanding
the behavior of OSPF and for troubleshooting OSPF-related issues.
The states of OSPF are:
Down: The OSPF process has not been enabled on the router, or there
is a problem with the configuration or network connectivity that prevents OSPF
from starting.
Attempt: The OSPF process has been enabled, but the router has not
yet established communication with its neighbors.
Init: The router has discovered its OSPF neighbors and is in the
process of exchanging information with them to build a complete view of the
network topology.
Two-Way: The router has established communication with its
neighbors and has received information about the network topology. The router
is now able to send and receive routing updates.
ExStart: The router has started the process of electing a
designated router (DR) and a backup designated router (BDR) to manage
communication between routers on a network segment.
Exchange: The router is exchanging database information with its
neighbors to build a complete view of the network topology.
Loading: The router has received a complete view of the network
topology and is in the process of calculating the shortest path to each
destination.
Full: The router has completed the calculation of the shortest path
to each destination and is now sending and receiving routing updates. The
router is fully operational and can participate in the routing process.