An Insight on Routing
Routing is the
process by which a group determines the network scope of an end-to-end path
from the source to the destination. Routing works on the third layer of the OSI
Reference Model-the network layer's packet forwarding device. Routers implement
network interconnection by forwarding packets. Although routers can support a
variety of protocols (such as TCP/IP, ipx/spx, AppleTalk, etc.), most routers
in China run TCP/IP protocol. Routers typically connect two or more logical
ports identified by an IP subnet or Point-to-Point protocol, with at least one
physical port. The router
determines the output port and the next hop address based on the network layer
address in the packet and the routing table maintained within the router, and
overrides the link layer packet header to implement forwarding packets. Routers
reflect the current network topology by dynamically maintaining the routing
table, and maintain the routing table by exchanging routing and link
information from other routers on the network.
Brief
introduction
Routing is the
activity of transmitting information from the source address to the destination
site through an interconnected network. Routing occurs in the third layer, the
network layer, in the OSI Network Reference Model. Route-Guide packet
forwarding, passing through some intermediate nodes, to their final
destinations. As a hardware, it is called a router. Routing typically directs
packet forwarding based on the routing table-a table that is stored to the best
path for each destination. Therefore, in order to efficiently transfer packets,
it is important to establish a routing table stored in the router's memory. The
difference between routing and bridging lies in the similarity of the node
distance between the routing and the assumed address. This allows a record in
the routing table to represent the path to a group of addresses. Therefore, in
a large network, routing is better than bridge, and routing has become the most
important way to find a path on the Internet. Smaller networks can usually
manually set the routing table, but a larger network with complex topologies
can often change, and it is impractical to manually establish a routing table.
However, most public switched telephone networks (PSTN) still use a predefined
routing table to use a prepared path when the path of a direct connection is
disconnected; see Public switched telephone network routing. "Dynamic
Routing" attempts to automatically set up a routing table to solve this
problem by using the information that is carried by the routing protocol, and
allows the network to avoid network disconnection or failure almost
autonomously. Dynamic routing currently dominates the entire Internet. However,
it often requires experience and technology to set routing protocols, and the
current network technology has not yet been developed to automatically set
routing. Packet-switched networks (such as the Internet) divide the data into a
number of packets with a full destination location, each of which is forwarded
separately. Circuit-switched networks, such as the public Switched telephone
network, also use the route to find a path that allows the next data to arrive
at the correct destination only with a partial destination location.
Basic concepts
Routing is the
activity of transmitting information from the source address to the destination
site through an interconnected network.
Routing occurs in
the third layer, the network layer, in the OSI Network Reference Model.
Route-Guide packet forwarding, passing through some intermediate nodes, to
their final destinations. As a hardware, it is called a router. Routing
typically directs packet forwarding based on the routing table, a table that is
stored to the best path for each destination.
Therefore, in
order to efficiently transfer packets, it is important to establish a routing
table stored in the router's memory. The difference between routing and
bridging lies in the similarity of the node distance between the routing and
the assumed address. This allows a record in the routing table to represent the
path to a group of addresses. Therefore, in a large network, routing is better
than bridge, and routing has become the most important way to find a path on
the Internet.
Smaller networks
can usually manually set the routing table, but a larger network with complex
topologies can often change, and it is impractical to manually establish a
routing table. However, most public switched telephone networks (PSTN) still use
a predefined routing table to use a prepared path when the path of a direct
connection is disconnected; see Public switched telephone network routing.
"Dynamic
Routing" attempts to automatically set up a routing table to solve this
problem by using the information that is carried by the routing protocol, and
allows the network to avoid network disconnection or failure almost
autonomously. Dynamic routing currently dominates the entire Internet.
However, it often
requires experience and technology to set routing protocols, and the current
network technology has not yet been developed to automatically set routing.
Packet-switched networks (such as the Internet) divide the data into a number
of packets with a full destination location, each of which is forwarded
separately. Circuit-switched networks, such as the public Switched telephone
network, also use the route to find a path that allows the next data to arrive
at the correct destination only with a partial destination location.
Dynamic routing
If a set path is
not available, the existing node must decide on another path to send the data
to the destination. They usually use the following two types of routing
protocols to achieve: distance vector algorithm and the wiring state algorithm.
Almost all routing
algorithms can be categorized into these two algorithms.
1.
Distance
vector algorithm
Main entry:
Distance vector routing protocol The distance vector algorithm uses the
Bellman-ford algorithm. For paths between nodes on each network, the algorithm
assigns a "cost" to them.
The node selects
the lowest path for the total cost (the sum of all costs through the path),
which is used to send the data from the node to the Node B. This algorithm is
very simple. When a node first starts, it knows only its neighbor node (the
node directly connected to that node) and the cost to that node. (This
information, the list of destinations, the total cost of each destination, and
the "next node" that must go through to a destination form the
routing table, or the distance table.) Each node periodically sends information
about the cost of the current knowledge to each destination to each neighbor
node. Neighbor nodes examine the information and compare it to what is
currently known, and if the cost to a destination is lower than currently
known, the information received is added to your routing table. After a while,
all nodes on the network will know the best "next node" and the
lowest total cost for all destinations.
When a node is
disconnected, each node that treats it as a "next node" of a path
discards the routing information and creates a new routing table information.
Then they tell all the neighboring nodes, and find the new path to all the
destinations that can be reached.
2.
Wired
State algorithm
Main entry: Wired
Status routing protocol In the wired state algorithm, each node has an atlas of
the network (a graph). Each node transmits other node information that it can
connect to all nodes on the network, and the other nodes then add the
information to the map.
Each router can
determine the best path from itself to the other node based on this map. The
algorithm that completes this action--dijkstra algorithm--build another kind of
data structure--tree. The node-generated tree treats itself as the root node,
and the last tree will contain all the other nodes in the network. Initially,
this tree has only the root node (the node itself).
Then, in the
neighbor node of the existing node in the tree and not in the node collection
in the tree, select a node with the lowest cost to join the tree until all
nodes are stored in the tree.
This tree is used
to establish the routing table, provide the best "next node" and so
on, so that nodes can communicate with other nodes in the network.
Comparison of
folded routing algorithms
In a small
network, the distance vector routing protocol is simple and efficient, and
requires only slight management. However, their scale is not good, and the
convergence is very poor, thus promoting the development of a more complex, but
much better, link state routing protocol for use in larger networks.
The distance
vector routing protocol also has an infinite count problem (count-to-infinity
problem, see [1]). The main advantage of the Wired State routing protocol is
that it responds more quickly to line changes, such as disconnection, within a
limited time. Furthermore, the packets sent by the Wired State routing protocol
on the network are smaller than the packet of the distance vector routing
protocol. The distance vector routing protocol must transmit the entire routing
table of a node, but the packet-state routing contract only needs to transmit
the neighbor information of that node. As a result, these packets are so small
that they do not occupy significant network resources. The main disadvantage of
wired state routing protocol is that it requires more storage space and
stronger computational ability than distance vector routing protocol.
To send a
contract around
Sometimes routing
agreements and routable agreements are often confusing: Can be routed protocol:
Any network protocol that provides sufficient network-level address information
to allow packets to be transferred from one device to another without the need
to know the entire path from the source to the destination. The can be wrapped contract
defines the format of the package and how the Packet field is used. Packets are
usually delivered from one terminal system to another.
IP is an example
of a protocol that can be bypassed, and an Ethernet path that is not to be
bypassed. Routing protocols: Exchanging routing information between networks,
allowing routers to dynamically establish a protocol for routing tables.
Traditional IP
routing is simple because it uses the next node routing method, which means
that the router only needs to consider which "next node" to send the
packet to, without taking into account the entire path of the destination.
Although dynamic
routing can be very complex, it makes the Internet very resilient and allows
the internet to grow more than eight orders of magnitude since the adoption of
IP. The routing metric (routing metric) contains all the values that are used
by the routing algorithm to determine which path is better than the other path.
Metrics can include a lot of information, such as bandwidth, latency, through-holiday
points, path costs, load, MTU, reliability, and transmission costs. The routing
table stores only the best possible paths, but the connection state or the
topology database may store other related information.
When routers find
multiple paths that can reach the same destination from different routing
protocols, they choose the best path using attributes called management
distance (administrative distance). The management distance defines the degree
of reliability of routing protocols.
Each routing
protocol distinguishes precedence by the most reliable to least reliable
arrangement, according to the management distance value.
There are many
kinds of routing protocols in accordance with the relationship between routers and other
autonomous systems: Ad hoc network routing protocols appear on a network
that has no or little foundation.
See the Ad Hoc
Routing agreement list for the proposed agreement. The internal Gate Protocol
(IGPS) exchanges routing information in a single autonomous system. Common
examples include the following:
IGRP (Interior
Gateway Routing Protocol)
EIGRP (Enhanced
Interior Gateway Routing Protocol) [1]
OSPF (Open
shortest Path a)
RIP (Routing
information Protocol)
Is-is
(intermediate system to intermediate system) The external Gate Protocol (EGPS)
exchanges routing information in different autonomous systems.
EGP includes:
EGP (External Gate
Agreement, formerly used to connect the backbone of the Internet, is now no
longer in use) BGP (Border Gateway Protocol: Use the current version around
1995, BGPV4).
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