ELSA manual How does IP masquerading work?, Simple and inverse masquerading, Cable TV net, Work

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Operating modes and functions 37

Cable TV net-	LAN of the user
work

Cable IP address

LAN IP address

MCNS

ELSA MicroLink	Hub
Cable

The cable modem is therefore assigned a cable IP address and a LAN IP address, each with its own appropriate network mask. Use the 'Masquerade' option to inform the cable modem which of the two addresses to use when transferring the packets.

K'Off': No masquerading.

K'on': Use this entry to apply the cable IP address that was assigned during the registration at the headend by the network operator.

If the cable modem is used as an IP router without masquerading, make sure that IP/RIP is enabled. When using it as an IP router with masquerading, IP/RIP should be disabled.

How does IP masquerading work?

Masquerading makes use of a characteristic of TCP/IP data transmission, which is to use port numbers for destination and source as well as the source and destination addresses. When the router receives a data packet for transfer it now notes the IP address and the sender's port in an internal table. It then gives the packet its unique cable IP address and a random new port number. It also enters this new port on the table and forwards the packet with the new information.

The response to this new packet is now sent to the cable IP address of the cable modem with the new sender port number. The entry in the internal table allows the router to assign this response to the original sender again.

You can view these tables in detail in the router statistics (see also 'Status').

Simple and inverse masquerading

This masking operates in both directions: The local network behind the cable IP address of the router is masked if a computer from the LAN of the user sends a packet to the Internet (simple masquerading).

If, on the other hand, a computer sends a packet from the Internet to, for example, an FTP server on the LAN, from the point of view of this computer the router appears to be the

ELSA MicroLink Cable

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Contents Manual Sonnenweg ELSA, IncAachen GermanyIntroducing the Elsa MicroLink Cable Thank you for placing your trust in this Elsa productPage Elsa Cable Modem ContentVI Content Setup/SNMP-module Viii Content What does the unit look like? Introducing the Elsa MicroLink CableElsa MicroLink Cable Sync Meanings of the specific blink codesThese LEDs show the corresponding network controller status BC D E F GNode or hub? Highlights of the Elsa MicroLink CableFast Internet Cable networkInternet at all times-always online Regional contentMore than just Internet BackboneProxy servers CE and FCC CE conformity and FCC radiation standardIntroducing the Elsa MicroLink Cable Elsa MicroLink Cable Installation and configurationFirst Steps Configuring the Elsa MicroLink CableQuick Start Quick configurations Configuration as a bridgePreparations LAN Off you go into the Web with a whole new sensation of speed Configuration as a routerOn the Router tab, enable the IP Router option TCP/IP installation Configuring fixed IP addresses not using DhcpObtain IP addresses automatically use Dhcp Checking the IP configuration Requirements for inband configuration Configuration modesUser-friendly method inband Start up inband configuration using telnet Starting inband configuration using Elsa LANconfigThis command Means this For instance Configuration commandsSet/se/snmp/admin The Administrator Command to call up a trace follows this syntax How to start a traceWhats happening on the line? Trace OutputsNew firmware with FirmSafe This is how FirmSafe worksExamples Elsa LANconfig How to load new softwareTftp Configuration using Snmp GeneralAccessing tables and parameters using Snmp Access protection in SnmpCommand Target/Source Function Deleting rows in tables using Snmp Appending rows to tables using SnmpIP address IP-netmask Router name Distance Management Information Base MIB Error messages via Snmp trapConfiguration modes Password protection Security for your configurationLogin barring Operating modes and functionsAccess control via TCP/IP Security for your LANGlobally to Encryption TCP/IP packet filtersHiding place-IP masquerading NAT, PAT IP routing IP routing tableIP address IP netmask Router Dis Tance 192.168.130.0 255.255.255.0 IP address IP netmask Router name Dist This is what happens What information is propagated by IP/RIP? Dynamic routing with IP/RIP What do the entries mean? IP address IP netmask Time Distance RouterInteraction of static and dynamic tables Local routingTwo addresses for the router IP masquerading NAT, PATSimple and inverse masquerading How does IP masquerading work?Cable TV net WorkWhich protocols can be transmitted using IP masquerading? DNS forwardingOnly small difference is that Rator BridgingWhat are the filter options? Automatic address administration with DhcpDhcp server Dhcp clientCable modem really belongs to two LANs IP address Network mask Broadcast addressDhcp on, off or auto? Default state is autoHow are the addresses assigned? IP address assignmentNetwork mask assignment Default gateway assignmentBroadcast address assignment DNS server assignmentPriority for a workstation-overwriting an assignment Priority for the Dhcp server Request assignmentOperating modes and functions Operating modes and functions Elsa MicroLink Cable Two standards get around this problem AccessCable modem technology StandardsRegistration in the cable network Network of the cable network Cable TV netOperator Work Registration Network technology Network and its componentsConnection modes Host Kinds of networks IP addressingExamples Same IP address, this time with another netmaskThis address Bytes Looks like this in bits 10.0.0.0 255.0.0.0 IP address Netmask RemarkIP routing and hierarchical IP addressing There are two considerations when using these IP addressesHost Smith External host Marketing Example Expansion through local networks 80-C7-6D-A4-6E Why a LAN is called multiprotocol-capableEasy as possible That is processed by all computers in the LANData transfer within the LAN Interface only understands MAC addressesLAN as easy as possible Host Smith LAN coupling on MAC basis Data transfer from the LAN onto the InternetTechnical basics Elsa MicroLink Cable Appendix Technical dataService Package contentsWarranty coverage Warranty conditionsWarranty period Warranty procedureAdditional regulations Operating mistakesTypenbezeichnung Declaration of conformityAppendix Elsa MicroLink Cable Index 32, 40 Gateway Heap reserve Inde7017, 32 17, 18Trace SetupInde72 Wireless linksDescription of the menu options R73 SymbolsOverview of the menus R74 Description of the menu optionsStatus Description of the menu options R75Status Running status displays Status/Current-time Status/Operating-timeStatus/Cable-statistics R76 Description of the menu optionsStatus/LAN-statistics Description of the menu options R77LAN-statistics Running status displays R78 Description of the menu options Status/Bridge-statisticsCannot be modified manually Bridge-statistics Running status displaysDescription of the menu options R79 Status/TCP-IP-statisticsStatus/TCP-IP-statistics/ARP-statistics These statistics include the following valuesR80 Description of the menu options Status/TCP-IP-statistics/IP-statisticsStatus/TCP-IP-statistics/ICMP-statistics Description of the menu options R81 Status/TCP-IP-statistics/TCP-statisticsStatus/TCP-IP-statistics/TFTP-statistics Status/TCP-IP-statistics/DHCP-statistics R82 Description of the menu optionsDescription of the menu options R83 Status/IP-router-statisticsShrinks accordingly. It has the following layout IP-router-statistics Statistics from the IP router areaStatus/IP-router-statistics/RIP-statistics R84 Description of the menu optionsProtocol LAN-tx Cable-tx IP-address IP-netmask Time Distance RouterConfig-statistics Remote configuration statistics Status/Config-statisticsStatus/Queue-statistics Description of the menu options R85IPr-RIP-queue-packets R86 Description of the menu optionsStatus/Init-status Status/MCNS-statisticsDescription of the menu options R87 MCSN-statisticsSystem configuration SetupStatus/DHCP-client-statistics R88 Description of the menu optionsSetup/LAN-module Setup/Cable-moduleEntering the following command Default configuration, no name is enteredR90 Description of the menu options Setup/Bridge-moduleSetup/TCP-IP-module Description of the menu options R91MAC-address field R92 Description of the menu options Configuration, the TCP/IP module is activatedDescription of the menu options R93 Configuration, the IP router module is activated Setup/IP-router-moduleIP-address Node-ID Last-access Connect IP-router-module IP router module settingsIP-address IP netmask Router-name Distance Description of the menu options R95Setup/IP-router-module/Routing-method Routing-method Routing method settingsR96 Description of the menu options Different settings have the following meaning Setup/IP-router-module/RIP-configurationSettings have the following meaning Description of the menu options R97Setup/IP-router-module/Masquerading R98 Description of the menu optionsFollowing layout Description of the menu options R99 Setup/IP-router-module/firewallR10 Description of the menu options Setup/DHCP-server-module Setup/SNMP-moduleDescription of the menu options R10 On The device operates as a Dhcp serverR102 Description of the menu options Default value of 6000 minutes equals approximately 4 daysOff The device does not operate as a Dhcp server Network mask is assigned in the same way as the IP addressIP-address Node-ID Timeout Hostname Type Setup/Config-moduleConfig-module Configuration module settings Description of the menu options R103Firmware Display and keyboard settings FirmwareR104 Description of the menu options Description of the menu options R105 Module VersionPosition Status Version Date Size Index Other This option allows you to reboot the deviceR106 Description of the menu options Other menu allows you to manage the following functions