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Three-tier cisco hierarchical model and DOD model

Three-layer cisco model

Like the OSI model, it is logical. (one layer can run multiple protocols, multiple devices: multiple layers can also run one protocol, one device.

Core layer: backbone

Distribution layer: routing

Access layer: switchin

Core layer

It is the core layer of the network, which is responsible for transmitting a large number of data streams quickly and reliably. The biggest purpose is to transmit the data stream at the last speed. As soon as the core layer fails, all users and hosts will be affected.

So don't do it in the core layer.

(1) Don't do anything to slow down, not even firewalls, access lists, or route filtering.

(2) do not allow the support working group to access

(3) do not blindly expand the core layer with the expansion of the network, but constantly upgrade the core layer.

Collecting and distributing layer

It is the communication point between the access layer and the core layer.

The main work is as follows

(1) routing

(2) define broadcast domain and multicast domain

(3) implement security and network policy, including address translation and firewall

(4) packet filtering

(5) reissue between routing choices

To put it simply, it is to connect all the devices and ensure that they are safe and quickly exchange traffic and data.

Access layer

Sometimes called the desktop layer, it controls users' access to network resources.

The main functions are

(1) establish an independent conflict domain

(2) provide workgroup access to the distribution layer

(3) continue the access control and policy of the distribution layer.

DOD model

DOD is a condensed version of the OSI model. Contains 4 layers

DoD model OSI model

Presentation layer

Process, application layer-> application layer

Session layer

Host to host layer-> transport layer

Internet layer-> Network layer

Network access layer-> data link layer

Physical layer

Application layer: applies to the communication of user applications and defines the user interface specification.

Host to host layer: responsible for reliable transmission point-to-point transmission, but also on the packet sorting, confirmation, to ensure integrity.

Internet layer: address the host to find the best path.

Network access layer: responsible for hardware addressing.

The following shows the DOD model for each protocol in the TCP/IP suite

Process / application layer Telnet FTP LPD SNMPTFTP SMTP NFS X Window

Host-to-host layer TCP UDP

Internet layer ICMP ARP RARP IP

Network access layer Ethernet Fast Ethernet Token Ring FDDI

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