Summary
samenvatting lessen 9 - 11 computer networks
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this is a summary of lessons 9 -11 (note: does not include the labs)
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Module 1: Single-Area OSPFv2 Concepts(CN_CCNA_3_Module_1.pptx)
1. OSPF Features and Characteristics
● Introduction to OSPF:
○ OSPF (Open Shortest Path First) is a link-state routing protocol
that uses the concept of areas to control routing update traffic.
Each "link" is an interface on a router or a network segment that
connects two routers or a stub network.
○ A "link-state" is the status of a link in terms of its network prefix,
prefix length, and cost. OSPF uses this information to make
accurate routing decisions.
○ Single-area OSPF confines all routers within a single area
(typically area 0) to simplify configurations and routing update
management.
● Components of OSPF:
○ OSPF Messages:Routers exchange five types of packets:
■ Hello Packet:Discovers and maintains neighbor
relationships.
■ Database Description Packet (DBD):Describes the
contents of the link-state database (LSDB) for
synchronization.
■ Link-State Request Packet (LSR):Requests specific
link-state records.
■ Link-State Update Packet (LSU):Sends the requested
link-state records.
■ Link-State Acknowledgment Packet (LSAck):
Confirms the receipt of other packets.
○ OSPF Databases:
, ■ Adjacency Database (Neighbor Table):Contains a list
of all routers that have established two-way
show ip ospf
communication. This can be viewed using
neighbor
.
■ Link-State Database (LSDB or Topology Table):Holds
a complete set of information about all routers and links in
the OSPF area. This database is the same for all routers in
show ip ospf
the same area and can be viewed using
database
.
■ Forwarding Database (Routing Table):Generated by
applying the shortest-path first (SPF) algorithm to the
LSDB. This is unique to each router and can be viewed
show ip route
using .
2. Single-Area vs. Multiarea OSPF
● Single-Area OSPF: All routers reside within a singlearea (usually area
0). This approach simplifies configuration and management but is less
scalable for large networks.
● Multiarea OSPF:Organizes routers into multiple areas,with area 0
being the backbone. Other areas connect to the backbone via Area
Border Routers (ABRs). This approach enhances scalability and
network efficiency.
3. OSPFv3 for IPv6 Networks
● OSPFv3 serves as the OSPF equivalent for IPv6 networks, supporting
both IPv4 and IPv6 through address families. OSPFv3 uses the same
packet types and mechanisms but communicates using IPv6.
4. OSPF Packets and Operation
, ● Types of OSPF Packets: Describes the five types of Link State Packets
(LSPs) used by OSPFv2 and their purposes.
● OSPF Operational States:Details the states throughwhich an OSPF
router progresses to establish and maintain a neighbor relationship:
○ Down State:No Hello packets received. Router sendsHello
packets to transition to the Init state.
○ Init State:Hello packets received; Router ID is identified.
○ Two-Way State:Bidirectional communication established.
Designated Router (DR) and Backup Designated Router (BDR)
are elected.
○ ExStart State:The two routers negotiate who willsend the DBD
packets first.
○ Exchange State:Routers exchange DBD packets.
○ Loading State:Additional link-state information isrequested
and provided.
○ Full State:The LSDB is fully synchronized.
● DR/BDR Elections:Describes how OSPF elects a DR andBDR on
multiaccess networks to manage LSA flooding.
Module 2: Single-Area OSPFv2 Configuration
(CN_CCNA_3_Module_2.pptx)
1. OSPF Router ID
● Router ID Purpose and Configuration:
○ The OSPF Router ID is a 32-bit value, represented like an IPv4
address, that uniquely identifies a router in the OSPF domain. It
is included in all OSPF packets.
○ Order of Precedence for Assigning Router ID:
router-idcommand.
3. Manually configured using
4. Highest IPv4 address on any loopback interface.
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