5. Network Switches..
A network switch is a small hardware device that joins
multiple computers together within one Local Area
Network(LAN). Technically switches operate at Data-link
Layer. These are almost like HUBS. But unlike HUBS
network switches are capable of inspecting data as it is
recieved, determining the source and destination device of
each packet, and forwarding them appropriately.
6. OSI Model
OSI model consists of seven layers and provides
standards for computer communication
Physical layer is responsible for actual transmission of
bits over the medium
Data Link layer is responsible for node to node delivery
of frames
Network layer is responsible for end to end delivery of
packets, and routing
7. OSI Model
Transport layer is responsible for end to end delivery of
the entire message
Session layer is responsible for establishing, managing
and terminating sessions
Presentation layer is responsible for
translation, encryption and data compression
Application layer is responsible for providing access to
the network
8. FRAMEisRELAY
Frame relay a packet switched connection oriented
WAN service .It operates at the Data link layer of OSI
Model.
Frame carry data between user devices called
Data terminal equipment (DTE) and Data
communication equipment ( DCE) at the edge of the
WAN.
10. Frame relay is a Scalable WAN solution that is often
used as an alternative to leased line when leased line
prove to be cost prohibitive.
Frame relay is a non broadcast multi access
(
NBMA) medium which means that broadcast traffic is
not allowed to traverse Frame relay traffic.
12. Frame Relay Components - II
The basic terms associated with the Frame Relay
network are as follows:
Data Terminal Equipment (DTE)
Data Communications Equipment (DCE)
Access link
Local access rate
DLCI
LMI
Committed Information (CIR)
16. Open Shortest Path First (OSPF)
OSPF is an open standards routing protocol
This works by using the Dijkstra algorithm
OSPF provides the following features:
Minimizes routing update traffic
Allows scalability (e.g. RIP is limited to 15 hops)
Has unlimited hop count
Supports VLSM/CIDR
Allows multi-vendor deployment (open standard)
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17. OSPF Terms
Link
Backbone area
Router ID
Internal routers
Neighbours
Area Border Router
Adjacency
OSPF Area
(ABR)
Autonomous System
Boundary Router
(ASBR)
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18. Link
A network or router interface assigned to a given
network
Link (interface) will have "state" information
associated with it
Status (up or down)
IP Address
Network type (e.g. Fast Ethernet)
Bandwidth
Addresses of other routers attached to this interface
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19. OSPF Term: Link
A link is a network or router interface assigned to any given
network
This link, or interface, will have state information associated
with it (up or down) as well as one or more IP addresses
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20. OSPF Term: Link State
Status of a link between two routers
Information is shared between directly connected routers.
This information propagates throughout the network unchanged and
is also used to create a shortest path first (SPF) tree.
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21. Router ID
The Router ID (RID) is an IP address used to identify the router
Cisco chooses the Router ID by using the highest IP address of all
configured loopback interfaces
If no loopback interfaces are configured with addresses, OSPF will
choose the highest IP address of all active physical interfaces.
You can manually assign the router ID.
The RID interface MUST always be up, therefore loopbacks are
preferred
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22. Neighbours
Neighbours are two or more routers that have an
interface on a common network
E.g. two routers connected on a serial link
E.g. several routers connected on a common Ethernet
or Frame relay network
Communication
takes place between / among
neighbours
neighbours form "adjacencies"
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23. Adjacency
A relationship between two routers that permits the
direct exchange of route updates
Not all neighbours will form adjacencies
This is done for reasons of efficiency – more later
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24. OSPF Design
Each router connects to the backbone called area 0, or the backbone area.
Routers that connect other areas to the backbone within an AS are called Area Border Routers (ABRs). One
interface must be in area 0.
OSPF runs inside an autonomous system, but can also connect multiple autonomous systems together. The
router that connects these ASes together is called an Autonomous System Boundary Router (ASBR).
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26. OSPF Configuration
OSPF Process ID number is irrelevant. It can be the same on every
router on the network
The arguments of the network command are the network number
(10.0.0.0) and the wildcard mask (0.255.255.255)
Wildcards - A 0 octet in the wildcard mask indicates that the
corresponding octet in the network must match exactly
A 255 indicates that you don’t care what the corresponding octet is
in the network number
A network and wildcard mask combination of 1.1.1.1 0.0.0.0 would
match 1.1.1.1 only, and nothing else.
The network and wildcard mask combination of 1.1.0.0 0.0.255.255
would match anything in the range 1.1.0.0–1.1.255.255
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