diff --git a/networking_101.rst b/networking_101.rst index d18a4ae6..57dd4e68 100644 --- a/networking_101.rst +++ b/networking_101.rst @@ -207,7 +207,200 @@ The elements of this stack from the lowest to highest are as follows: This layer maps to the ISO's Layer 5 through Layer 7, and covers the application processes that use the network to communicate. - + + +Networking cable +================ +There are two main types of network cable in use today, namely copper and fiber-optic. + +Copper +------ +The most common type of network cables are what is known as "unshielded twisted +pair" cables. They use 4 sets of twisted pairs of copper, relying on the twist +with differential signaling to prevent noise and signal propagation between the +pairs. The four pairs of twisted copper wires are encased in a plastic sheath. + +There are different standards for copper network cables set by the +Telecommunications Industry Association (TIA) and the International Organization +for Standardization (ISO). Both organizations use the same naming convention +("Category __") for the components, but unfortunately differ on the naming for +the cable standards. The most common reference is the TIA's, and the category +designation is usually shortened to "Cat", so you'll hear references to "Cat5" +or "Cat6" cable. + +Copper Cable Standards +^^^^^^^^^^^^^^^^^^^^^^ + +- Category 5e ("Cat5", ISO class D) + +- Category 6 ("Cat6", ISO class E) + +- Category 6A ("Cat6A", ISO class Ea) + +Fiber +----- +Fiber is a generic term that refers to optical transport mediums. It comes in +several types, all of which look identical but are generally incompatible. + +Multimode vs Single Mode +^^^^^^^^^^^^^^^^^^^^^^^^ +Single-mode fiber has a small core diameter, which only allows one (a single) +mode of light to be transmitted through the fiber. Using a single mode of light +completely eliminates the possibility of light dispersion and associated signal +loss, and so is used mainly for long-haul runs, such as the cables that run +between buildings and cities. However, since single-mode fiber can only transmit +one wavelength of light at a time, it typically involves much more expensive +light generation sources (i.e., laser diode transmitters) and is very expensive +to produce. + +Multimode fiber has a larger core diameter (either 50u or 62.5u) and can +therefore carry multiple modes ("multimode") of light, which can be used to +transmit much more information during a given timeslice. The drawback is that +carrying multimode lightwaves causes light dispersion and associated signal +loss, which limits its effective distance. Multimode is a less expensive fiber +optic cable, that is typically useable with lower cost optical components. It is +very common to see it used for building intra-building backbones, and +system/switch to switch applications. + +Multimode Fiber Standards +^^^^^^^^^^^^^^^^^^^^^^^^^ +Multimode cables have classifications much like the copper cables discussed above; these +are known as "Optical Multimode" (OM) classes. The four designations are: + +- OM1 - a "legacy" fiber class, the core being 62.5u, and cladding being 125u. + The bandwidth that can be carried ranges from 160 to 500 MHz. + +- OM2 - a "legacy" fiber class, the core being 50u, and cladding being 125u. + The bandwidth that can be carried is 500 MHz. + +- OM3 - a "modern" fiber class, the core being 50u, and cladding being 125u. + The bandwidth that can be carried ranges from 1500 to 2000 MHz. + +- OM4 - a "modern" fiber class, the core being 50u, and cladding being 125u. + The bandwidth that can be carried ranges from 3500 to 4700 MHz. + +Optical Connector Types +^^^^^^^^^^^^^^^^^^^^^^^ + +LC and SC connectors are the two most common type of fiber connectors you will +use. Less common connectors include ST and MPO. + +LC stands for "Lucent Connector", but is also referred to as "Little Connector". +They are typically used for high-density applications, and are the type of +connector used on SFPs or XFPs. Typically the connector is packaged in a duplex +configuration with each cable side by side, and have a latch mechanism for +locking. + +SC stands for "Subscriber Connector", but are also known as "Square Connector", +or "Standard Connector". This is the type of connector typically used in the +telecom industry. They have a larger form factor than the LC connectors, and can +be found in single and duplex configurations. SC connectors have a push/pull +locking mechanism, and because of this, are also colloquially known as +"Stab-and-Click" connectors. + +ST stands for "Straight Tip". This connector style is secured like a BNC connector, +giving it the nickname "Stick-Twist". It is sometimes also called BFOC, which +stands for "Bayonet Fiber Optic Connector". It is fairly common for single-mode +fiber, especially in older installations. + +MPO stands for "Multi-fiber Push-On". It is a connector used to carry up to 12 +pairs of fiber (24 strands), most commonly used for bulk links inside datacenters. +Several companies make boxes which take an MPO connector on one side and convert +it to 12 LC connectors on the other side. This way, a large number of fibers can +be run from one area of a datacenter to another quickly and compactly. + +Transceivers +^^^^^^^^^^^^ + +The variety in optical fiber makes for a correspondingly large variety in +optical fiber interface standards. Different interface types will impose +different requirements on the fiber used and the length of the connection. + +If optical fiber interfaces were incorporated directly into network equipment, +the number of models made by the manufacturer would have to be multiplied by +the number of interface standards in existence. For this reason, modern network +hardware rarely incorporates such interfaces directly. Instead, pluggable +transceiver modules are used as a layer of indirection between medium-dependent +and medium-independent interfaces. This allows a transceiver slot to be +provided supporting any desired interface standard, whether copper or fiber. +There are some limitations to this, detailed below. + +Various module types have been introduced over the years: + +============ ============ =========== ======= + Name Introduced Speed Size +============ ============ =========== ======= + GBIC 1995 1 Gb/s Large + SFP 2001 1 Gb/s Small + XENPAK 2001 10 Gb/s Large + XFP 2002 10 Gb/s Small + SFP+ 2006 10 Gb/s Small + QSFP 2006 40 Gb/s Small + CFP 2009 100 Gb/s Large +============ ============ =========== ======= + +There are a large number of compatibility issues with such modules. Some +compatibility issues cause problems between two ends of a link; others cause +problems between a module and its host device. + +- Transceivers are not generally compatible with lower speed versions of the + same standard. A 1000BASE-T Ethernet card can interface with a 10BASE-T card, + but a 1 Gb/s fiber transceiver cannot interface with a 10 or 100 Mb/s + transceiver. In the case of fiber, this is generally due to the different + wavelengths used; but even many copper transceivers do not support lower + speeds, although some do. You should assume that any transceiver will only + support the exact interface for which it is designed unless specified + otherwise. + +- Modules are only made for the speed targeted by a format. For example, SFP+ + modules are only made for 10 Gb/s standards, and not for lower speeds. + +- Some equipment may accept SFP modules in SFP+ slots, but this is not + universal. + +- Vendor lock-in is widely practiced. Equipment may refuse to operate with the + modules made by a different manufacturer. Workarounds are generally + available, but this may complicate support or warranty arrangements. + +These issues can create pathological cases. Suppose you have two switches which +should be connected to one another. One is connected via a 1 Gb/s transceiver +to fiber. The other only has SFP+ slots. If these slots also support SFP +modules, then a 1 Gb/s SFP transceiver can be used, but if they do not, +interconnection is impossible: all SFP+ modules target 10 Gb/s, and fiber +transceivers do not support lower speeds. + +Twinax +^^^^^^ +These cables have integrated transceivers. The cable itself is typically copper +but can be fiber. + + +MAC Addresses +============= +Each network interface has what is known as a MAC (Media Access Control) address. +This is a 48-bit address which identifies the card on the local network. The +addresses have several common representations, but all are composed of 12 +hexadecimal digits. BSD and Linux systems typically represent addresses like this: + + 12:34:56:78:9A:BC + +Windows uses hyphens instead of colons like this: + + 12-34-56-78-9A-BC + +Cisco network equipment uses lowercase letters and groups of four digits separated +by dots: + + 1234.5678.9abc + +All three of those forms represent the same address. + +The first six digits (24 bits, three bytes) are what is called the OUI +(Organizationally Unique Identifier). It is a value assigned and tracked by the +IEEE which is unique per network card manufacturer. As an example, 80:86:F2 belongs +to Intel. Any MAC starting with those digits belongs to an interface manufactured by +Intel. An organization may have many OUIs, but each OUI covers only one organization. + IP Addressing ============= @@ -231,7 +424,6 @@ hexadecimal, decimal, and octal. These are infrequently used, and will be covered in later sections. - IPv6 ---- @@ -260,6 +452,7 @@ of these ways: 2001:DB8::CBAD:4321:0000:0000:1234 2001:DB8:0000:CBAD:4321::1234 + TCP vs UDP ========== @@ -418,155 +611,3 @@ inactive and still keep its place in the table. An entry that has remained inactive for a period of time longer than the timeout will automatically be removed, freeing up space for a new one. -Networking cable -================ -There are two main types of network cable in use today, namely copper and fiber-optic. - -Copper ------- -The most common type of network cables are what is known as "unshielded twisted -pair" cables. They use 4 sets of twisted pairs of copper, relying on the twist -with differential signaling to prevent noise and signal propagation between the -pairs. The four pairs of twisted copper wires are encased in a plastic sheath. - -There are different standards for copper network cables set by the -Telecommunications Industry Association (TIA) and the International Organization -for Standardization (ISO). Both organizations use the same naming convention -("Category __") for the components, but unfortunately differ on the naming for -the cable standards. The most common reference is the TIA's, and the category -designation is usually shortened to "Cat", so you'll hear references to "Cat5" -or "Cat6" cable. - -Copper Cable Standards -^^^^^^^^^^^^^^^^^^^^^^ - -- Category 5e ("Cat5", ISO class D) - -- Category 6 ("Cat6", ISO class E) - -- Category 6A ("Cat6A", ISO class Ea) - -Fiber ------ -Fiber is a generic term that refers to optical transport mediums. It comes in -several types, all of which look identical but are generally incompatible. - -Multimode vs Single Mode -^^^^^^^^^^^^^^^^^^^^^^^^ -Single-mode fiber has a small core diameter, which only allows one (a single) -mode of light to be transmitted through the fiber. Using a single mode of light -completely eliminates the possibility of light dispersion and associated signal -loss, and so is used mainly for long-haul runs, such as the cables that run -between buildings and cities. However, since single-mode fiber can only transmit -one wavelength of light at a time, it typically involves much more expensive -light generation sources (i.e., laser diode transmitters) and is very expensive -to produce. - -Multimode fiber has a larger core diameter (either 50u or 62.5u) and can -therefore carry multiple modes ("multimode") of light, which can be used to -transmit much more information during a given timeslice. The drawback is that -carrying multimode lightwaves causes light dispersion and associated signal -loss, which limits its effective distance. Multimode is a less expensive fiber -optic cable, that is typically useable with lower cost optical components. It is -very common to see it used for building intra-building backbones, and -system/switch to switch applications. - -Multimode Fiber Standards -^^^^^^^^^^^^^^^^^^^^^^^^^ -Multimode cables have classifications much like the copper cables discussed above; these -are known as "Optical Multimode" (OM) classes. The four designations are: - -- OM1 - a "legacy" fiber class, the core being 62.5u, and cladding being 125u. - The bandwidth that can be carried ranges from 160 to 500 MHz. - -- OM2 - a "legacy" fiber class, the core being 50u, and cladding being 125u. - The bandwidth that can be carried is 500 MHz. - -- OM3 - a "modern" fiber class, the core being 50u, and cladding being 125u. - The bandwidth that can be carried ranges from 1500 to 2000 MHz. - -- OM4 - a "modern" fiber class, the core being 50u, and cladding being 125u. - The bandwidth that can be carried ranges from 3500 to 4700 MHz. - -Optical Connector Types -^^^^^^^^^^^^^^^^^^^^^^^ - -LC and SC connectors are the two most common type of fiber connectors you will -use. - -LC stands for "Lucent Connector", but is also referred to as "Little Connector". -They are typically used for high-density applications, and are the type of -connector used on SFPs or XFPs. Typically the connector is packaged in a duplex -configuration with each cable side by side, and have a latch mechanism for -locking. - -SC stands for "Subscriber Connector", but are also known as "Square Connector", -or "Standard Connector". This is the type of connector typically used in the -telecom industry. They have a larger form factor than the LC connectors, and can -be found in single and duplex configurations. SC connectors have a push/pull -locking mechanism, and because of this, are also colloquially known as -"Stab-and-Click" connectors. - -Transceivers -^^^^^^^^^^^^ - -The variety in optical fiber makes for a correspondingly large variety in -optical fiber interface standards. Different interface types will impose -different requirements on the fiber used and the length of the connection. - -If optical fiber interfaces were incorporated directly into network equipment, -the number of models made by the manufacturer would have to be multiplied by -the number of interface standards in existence. For this reason, modern network -hardware rarely incorporates such interfaces directly. Instead, pluggable -transceiver modules are used as a layer of indirection between medium-dependent -and medium-independent interfaces. This allows a transceiver slot to be -provided supporting any desired interface standard, whether copper or fiber. -There are some limitations to this, detailed below. - -Various module types have been introduced over the years: - -============ ============ =========== ======= - Name Introduced Speed Size -============ ============ =========== ======= - GBIC 1995 1 Gb/s Large - SFP 2001 1 Gb/s Small - XENPAK 2001 10 Gb/s Large - XFP 2002 10 Gb/s Small - SFP+ 2006 10 Gb/s Small - QSFP 2006 40 Gb/s Small - CFP 2009 100 Gb/s Large -============ ============ =========== ======= - -There are a large number of compatibility issues with such modules. Some -compatibility issues cause problems between two ends of a link; others cause -problems between a module and its host device. - -- Transceivers are not generally compatible with lower speed versions of the - same standard. A 1000BASE-T Ethernet card can interface with a 10BASE-T card, - but a 1 Gb/s fiber transceiver cannot interface with a 10 or 100 Mb/s - transceiver. In the case of fiber, this is generally due to the different - wavelengths used; but even many copper transceivers do not support lower - speeds, although some do. You should assume that any transceiver will only - support the exact interface for which it is designed unless specified - otherwise. - -- Modules are only made for the speed targeted by a format. For example, SFP+ - modules are only made for 10 Gb/s standards, and not for lower speeds. - -- Some equipment may accept SFP modules in SFP+ slots, but this is not - universal. - -- Vendor lock-in is widely practiced. Equipment may refuse to operate with the - modules made by a different manufacturer. Workarounds are generally - available, but this may complicate support or warranty arrangements. - -These issues can create pathological cases. Suppose you have two switches which -should be connected to one another. One is connected via a 1 Gb/s transceiver -to fiber. The other only has SFP+ slots. If these slots also support SFP -modules, then a 1 Gb/s SFP transceiver can be used, but if they do not, -interconnection is impossible: all SFP+ modules target 10 Gb/s, and fiber -transceivers do not support lower speeds. - -Twinax -^^^^^^ -