Routing Fundamentals

Encapsulation

is a process wherein a new string of information is added to an existing unit to form a new unit of information.

Decapsulation

is the reverse process of encapsulation wherein the header and tail of a packet are removed to obtain the data payload.

Data payload

can be considered as the information to be transmitted. In a hierarchical communication process, the data unit (packet) transmitted from the upper layer to the lower layer can be called the data payload of the lower layer.

Packet

is a data unit that is exchanged and transmitted on a network. It is in the format of header+data payload+tail. During transmission, the format and content of packets may change

Header

is the information segment added before the data payload during packet assembly to facilitate information transmission.

Tail

is the information segment added after the payload to facilitate information transmission

Protocol Data Unit (PDU)

is a specific block of information transferred over a network. It is often used in reference to the OSI model, since it describes the different types of data that are transferred from each layer

PDU 5 types:

Data
Segment
Packet
Frame
Bits

OSI Model

Application
Presentation
Session
Transport
Network
Data Link
Physical

Physical layer

raw bits (1s or 0s) transmitted physically via the hardware

Data Link layer

a frame (or series of bits)

Network layer

a packet that contains the source and destination address

Transport layer

a segment that includes a TCP header and data

Session layer

the data passed to the network connection

Presentation layer

the data formatted for presentation

Application layer

the data received or transmitted by a software application

Internet Protocol (IP)

o Defines a packet and an addressing scheme

o Transfers data between the Internet layer and network access layers

o Routes packets to remote hosts

Internet Control Message Protocol (ICMP)

It refers to a TCP/IP protocol that handles errors and controls the process of sending data between computers.

Internet Group Management Protocol (IGMP)

It refers to a TCP/IP protocol that handles multicasting. Hosts use IGMP to keep local routers apprised of their membership in multicast groups. When all hosts leave a group, routers no longer forward packets that arrive for the group.

Address Resolution Protocol (ARP)

It refers to a TCP/IP protocol that obtains the physical address of a node from a specific IP number.

Reverse Address Resolution Protocol (RARP)

It refers to a TCP/IP protocol that allows a host with no local permanent data storage media to find its Internet address given its physical address

Ethernet

It refers to a family of LANs, covered by a group of IEEE 802.3 standards. Ethernet is a best-effort delivery system that uses a CSMA/CD access method

Point-to-Point Protocol (PPP):

This refers to the protocol used for data transfer across a serial line.

Fiber distributed data interface (FDDI):

This is a set of ANSI protocols for sending digital data over fiber optic cable.

Asynchronous Transfer Mode (ATM):

This refers to a wide area protocol that features high data rates and equal- sized packets/cells suitable for text, audio, and video data transfer

Frame Relay

This is a WAN protocol for LAN internetworking that provides a fast and efficient method of transmitting information from one user device to another across multiple switches and routers

Proxy ARP:

This protocol is used when a network terminal needs to pass data from one segment to another without changing its current IP address information

Routing

is the basic element of data communication networks, which is the process of selecting paths on a network along which packets are sent from a source to a destination

Path determination

enables a router to compare the destination address to the available routes in its routing table and to select the best path

Routes

are the path information used to guide packet forwarding

routing device (Router)

is a network device that forwards packets to a destination subnet based on routes.

IP routing table

. It maintains an __________that stores routing information.

Packet routing

is the overall network-wide process of finding the most efficient path for forwarding the IP packet from source to destination through the use of network routing tables, protocols, and algorithms.

Destination

identifies a destination subnet

Mask

identifies a subnet together with a destination IP address.

Outbound interface

indicates the interface through which a data packet is sent out of the local router

Next hop

indicates the next-hop address used by the router to forward the data packet to the destination subnet.

Packet Forwarding

It is simply a passing or moving of information between interfaces (which can be from a host/router to the final destination/intermediate connecting device) according to the “directions”.

Packet Delivery

refers to the way a packet is handled by the underlying physical networks under the control of the network layer

Direct Delivery

occurs when the IP node forwards a packet to its final destination in the network.

Indirect Delivery

occurs when the IP node (host) forwards a packet to an intermediate node (IP router) because the final destination is not on a directly attached network

To implement route-based packet forwarding, the router needs to obtain routes

A router discovers routes using multiple methods in which it selects the optimal route and installs it in its IP routing table.

A router forwards IP packets based on routes in the IP routing table and manages path information by managing its IP routing table

Routing Table (Huawei)

It is a database that contains information about which router network interface or port to place information to send it to a particular network segment

Destination/Mask

indicates the destination network address and mask of a specific route.

Protocol (Proto)

indicates the protocol type of the route, that is, the protocol through which a router learns the route.

Preference (Pre)

indicates the routing protocol preference of the route. It is used to compare routes from different routing protocols.

Cost

indicates the cost of the route. It is also known as the metric.

Next Hop (Huawei)

indicates the local router’s next-hop address of the route to the destination network. This field specifies the next-hop device to which packets are forwarded.

Interface

indicates the outbound interface of the route. This field specifies the local interface through which the local router forwards packets

Types of Routing

Direct Routes
Static Routes
Dynamic Routes

Direct Routes

are automatically generated by devices and point to local directly connected networks. These are the routes destined for the subnets to which directly connected interfaces belong

Static Routes

are manually configured by network administrators. This can be an effective method for networks with small and simple structures and reduce the effect of bandwidth and CPU resource consumption that occurs when other protocols are implemented.

Dynamic Routes

are learned by dynamic routing protocols running on routers. This route uses routing protocols to talk to other routers and find out what networks they are attached to

Route Preference

• When a router obtains routes to the same destination subnet from different routing protocols, the router compares the preferences of these routes and prefers the route with the lowest preference value.

• Routes generated from different information sources are assigned different preferences.

• The smaller the preference value, the higher the preference.

• The router selects the optimal route for the assigned IP with the highest preference among all routes.

• The assigned IP has the same destination/mask generated from different information sources in which the route is injected into the IP routing table.

• The other routes remain in the deactivated state and do not appear in the IP routing table.

• Routes generated from different information sources have different default preference values. These values may differ between devices of different vendors