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Routing & Packet Forwarding

Routing Protocols & Concepts

Router as a Computer:

Computers that specialize in sending packets over the data network.
Responsible for interconnecting networks.
Routers are the network center.
Generally have a min of 2 connections:
WAN connection (Connection to ISP).
LAN connection.
In addition to packet forwarding, routers provide other services as well.
A router connects multiple networks.
This means that it has multiple interfaces that each belong to a different IP network.
Each network that a router connects to typically requires a separate interface.

Routing Table:

Used to determine the best path.
Incoming packets’ dest IP address is looked up in the table.
The table includes an exit interface or next hop.
Once a match is found, the router encapsulates the IP packet into the L2 frame of the exit interface.

Router as a computer:

Router components and their functions:
CPU – Executes OS instructions.
RAM – Contains the running copy of config, routing table, buffers, etc. Contents lost when pwr is off.
ROM – Holds diagnostic software used @ startup and the bootstrap prgm.
NVRAM – Stores startup config.
Flash – Contains the OS, non-volitile.
Interfaces – usually multiple physical interfaces. Examples of interface types:
Ethernet / Fast Ethernet interfaces.
Serial interfaces.
Management interfaces (concole).

Internetwork Operating System:

IOS
A multitasking OS integrated with routing, switching, internetworking, and telecomm functions.
Stored as an image. Many different IOS images available.
IOS interface is CLI
On boot, the startup-config file in NVRAM is copied into RAM and stored as the running-config file.
Changes entered by the admin are stored in the running-config and are immediately implemented by the IOS.

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Tags: switch, ip, 802.1q, guides, router, study

Planning & Cabling Networks

Media Required to Make a LAN Connection:

LANs use gateways to connect o other networks.
They use hubs or switches to connect end devices.
Each port on a router connects to a different network.
Routers break up broadcast domains and collision domains.
Routers can have both LAN and WAN interfaces.

Intranetwork Devices:

Hub

Receives signals, regenerates and sends them over all ports.
Creates a logical bus (i.e. multi-access media, everybody is on the same wire). [topologies].
Shared bandwidth approach – reduced performance (only one device can talk at a time).
A single collision domain.
Less expensive than switches.

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Tags: switch, ip, 802.1q, vtp, vlan, study

Prepare your router for the Wide Area Network.

Cisco devices use HLDC encapsulation by default.

Serial COMMUNICATION
Serial connections send 1 data bit at a time when transmitting.
Parallel Connections send multiple bits simultaneously.
Theoretically an 8 bit parallel bus, transfers data 8X faster.
Serial connections can be clocked much faster than parallel links.
2 of the main factors that affect parallel communication are clock skew & cross talk.
Clock skew - some parallel bits arrive later than others.
Overcoming clock skew is difficult & involves clocking.

Cross-Talk - crosstalk normally refers to a signal affecting another nearby signal.

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Tags: study, ip, 802.1q, wan, vtp, vlan

Bitmindframes cisco study guides

INTERVLAN ROUTING
A VLAN is a broadcast domain and unique ip subnet
Switches operate at layer2 (Data link Layer)
VLANS cannot communicate without L3 (Network Layer)
The L3 communication is called inter-vlan routing
Inter-vlan routing is a process of forwarding network traffic from one vlan to another using a router
The Subnets of your network facilitate the routing process.
Router interfaces can be connected to separate vlans.
Devices on vlans send traffic through the router(L3) to other vlans.

Traditionally vlan routing required multiple interfaces.
Each interface was connected to a separate switch port & configured with a different subnet
The switch port is connected to the router in access mode.

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Tags: study, 802.1q, vtp, router, cisco, guides