101 apend. networking generic a
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This document provides an overview of networking concepts for Linux systems. It discusses network layers, common protocols like TCP/IP and Ethernet, network addressing with IPv4 and IPv6, subnetting using subnet masks and CIDR notation. Ports and network utilities are also covered. The document is intended as a learning resource under the GNU Free Documentation License.
101 apend. networking generic a
- 1. CoreLinuxforRedHatandFedoralearningunderGNUFreeDocumentationLicense-Copyleft(c)AcácioOliveira2012 Everyoneispermittedtocopyanddistributeverbatimcopiesofthislicensedocument,changingisallowed Linux Essenciais and System Administration
- 2. CoreLinuxforRedHatandFedoralearningunderGNUFreeDocumentationLicense-Copyleft(c)AcácioOliveira2012 Everyoneispermittedtocopyanddistributeverbatimcopiesofthislicensedocument,changingisallowed Key Knowledge Areas Connecting machines and resources Networking Networking Terms and Utilities network layers tcp/udp ethernet ports tcp/ip addressing ipv4 ipv6 subnet classes subnet masks cidr 2
- 3. CoreLinuxforRedHatandFedoralearningunderGNUFreeDocumentationLicense-Copyleft(c)AcácioOliveira2012 Everyoneispermittedtocopyanddistributeverbatimcopiesofthislicensedocument,changingisallowed Overview 3 • Connecting machines and resources for purposes of sharing and communication. • Handled on many different levels, from physical mediums doing the connecting to the lofty application layer providing a service to the end user. Networking If you crack a networking book, they talk about 7 layer OSI model. Then immediately tell you to forget it, because networking systems don’t follow the model. :) Layers cared about: •Physical cabled, fiber, wireless •Link Ethernet, 802.11 •NetworkIP •Transport TCP/UDP •Application HTTP, FTP, SSH, DNS, SMTP, POP3, IMAP, etc, etc, etc
- 4. CoreLinuxforRedHatandFedoralearningunderGNUFreeDocumentationLicense-Copyleft(c)AcácioOliveira2012 Everyoneispermittedtocopyanddistributeverbatimcopiesofthislicensedocument,changingisallowed Layer Processing 4 • Each layer wraps on top of the next, so a message starts at application layer as data specific to the application; • This data gets wrapped with info for TCP/UDP and IP layers, providing addressing and transport ability; • Wrapped again by Ethernet, providing physical access; • Wrapped one more time by physical layer getting sent out; • When received at other end, each layer is unwound as the message travels “up” the stack on the receiving system. Networking View Slides: Networking TCP/IP
- 5. CoreLinuxforRedHatandFedoralearningunderGNUFreeDocumentationLicense-Copyleft(c)AcácioOliveira2012 Everyoneispermittedtocopyanddistributeverbatimcopiesofthislicensedocument,changingisallowed Ports, TCP/IP and IP Addressing 5 port is an address component in TCP and UDP messages which identifies the service that should receive the message within the addressed system. Number from 1-65535 Hundreds of “well-known” ports and corresponding services defined in /etc/services Ex: HTTP: 80, SMTP: 25, POP3: 110, SSH: 22 Networking TCP and IP work hand in hand to run network communications. there is more to IP because of addresses. IP address provides user-configured, routable virtual address used for communication in and between LAN’s There are two versions of the IP protocol: version 4 and version 6. IPv4 is the old guard, developed decades ago and still in use nearly everywhere. Fairly simple set of features and a 32 bit address. (focus of this discussion) IPv6 ( ~10 years ago ) was ratified to address some of the shortcomings of IPv4. Including security features and a lack of address space. IPv6 addresses are 64 bits.
- 6. CoreLinuxforRedHatandFedoralearningunderGNUFreeDocumentationLicense-Copyleft(c)AcácioOliveira2012 Everyoneispermittedtocopyanddistributeverbatimcopiesofthislicensedocument,changingisallowed IP Addressing and subnetting 6 • 32 bit value (32 1’s and 0’s) • Not easily represented as 32 digits, broken into four groups of 8 bits • 8 bits can be represented in decimal as 0-255 - dotted quad: 192.168.1.100 Networking When IPv4 was designed, it included a subnetting ability. Subnetting allows grouping and organizing networks within IPv4 address space •First part of IP address is designated as network address, identifying the subnet to which the IP address belongs. •Remaining portion of IP address is known as the host address and uniquely identifies the addressed node within the subnet.
- 7. CoreLinuxforRedHatandFedoralearningunderGNUFreeDocumentationLicense-Copyleft(c)AcácioOliveira2012 Everyoneispermittedtocopyanddistributeverbatimcopiesofthislicensedocument,changingisallowed Subnet mask 7 Identifying the two components of an IP address is the job of the subnet mask A mask is a special number which is compared to another number using mathematical functions (usually boolean algebra’s AND operation) to extract info. A subnet mask is a 32 bit number with a special definition: • If mask is a 1, corresponds to network address within an IP address, • If mask is a 0, corresponds to the host address. Since there are only two components to an IP address, subnet masks are always start as a series of ones, then switch to zero’s. Networking
- 8. CoreLinuxforRedHatandFedoralearningunderGNUFreeDocumentationLicense-Copyleft(c)AcácioOliveira2012 Everyoneispermittedtocopyanddistributeverbatimcopiesofthislicensedocument,changingisallowed Subnet Classes 8 Networking Subnet masks are also written as dotted quads. But since they’re just series of 1, then 0’, they look like: 255.255.255.0 or 255.255.192.0 An easier way to express a subnet is to use CIDR notation. CIDR stands for Classless Inter-Domain Routing, Created to address a shortcoming of the IPv4 standard design - subnet classes. original IPv4 spec created set network sizes and named them “classes”. •Class A: 8 bit network address •Class B: 16 bit network address •Class C: 24 bit network address •Class D and Class E: special purpose networks Defined overall layout of the 32 bit address space. Quickly became insufficient to support the networks being created, and CIDR was implemented.
- 9. CoreLinuxforRedHatandFedoralearningunderGNUFreeDocumentationLicense-Copyleft(c)AcácioOliveira2012 Everyoneispermittedtocopyanddistributeverbatimcopiesofthislicensedocument,changingisallowed CIDR 9 Networking CIDR breaks from class-based subnets and allows for the creation of arbitrary subnet sizes within the overall layout of 32 bit address space. CIDR notation is simpler than dotted quad for subnet masks A slash, followed by the number of the last bit of the network address. Ex: /24 - class C - 255.255.255.0 Usually combined with IP address to form a complete address: 192.168.1.100/24