Operation
A WySLFDO nHWZRUN fiUHZDOO LV LnVWDOOHG EHWZHHn WhH LnWHUnDO nHWZRUN DnG WhH ,nWHUnHW; WhuV, DOO WUDIfiF EHWZHHn WhHP SDVVHV WhURuJh WhH fiUHZDOO. )RU ,nWHUnHW FRnnHFWLRnV YLD Dn A'6/ PRGHP, WhH fiUHZDOO ZLOO EH LnVWDOOHG EHWZHHn WhH LnWHUnDO network and the ADSL modem, whereas for an Internet FRnnHFWLRn ZLWh Dn (WhHUnHW FRnnHFWLRn, WhH fiUHZDOO ZLOO replace the modem or router as depicted in Diagram 2. The fiUHZDOO DnDOyVHV HYHUyWhLnJ SDVVLnJ WhURuJh, DnG EDVHG Rn WhH FRnfiJuUHG SROLFy, OHW’V WhURuJh RnOy ‘VDIH’ WUDIfiF.
sarious client computer systems request data from DSSOLFDWLRn VHUYHUV VLPuOWDnHRuVOy. A ‘SRUW’ nuPEHU LV used to differentiate this traffic. A client requesting data from the server uses the destination port number of the corresponding service. For example, a computer system requesting HTTP data will use port U0. 7hH WUDIfiF FRuOG uVH RnH RI WhH IROORZLnJ WZR SURWRFROV: Transmission Control Protocol (TCP), which guarantees delivery of the data, is reliable but has larger headers to DFFRPPRGDWH WhH hDnGVhDNH VLJnDOV DnG flDJV UHTuLUHG IRU assured delivery.
A fiUHZDOO uVHV WhLV SRUW nuPEHU WR LGHnWLIy WhH WUDIfiF. ,n WhH H773 HxDPSOH PHnWLRnHG DERYH, WhH fiUHZDOO UHDGV H773 WUDIfiF WR SRUW 80, DnG SDVVHV LW WR WhH ,nWHUnHW RnOy LI LW matches the desired policy. Unwanted websites and content DV GHfinHG Ln WhH SROLFy ZLOO EH GURSSHG. 7ySLFDO IunFWLRnV RI D nHWZRUN fiUHZDOO FDn EH FODVVLfiHG LnWR WUDIfiF FRnWURO DnG others, as shown below. 7UDIfiF FRnWURO IunFWLRnV DUH: Access from the Internet to the internal network Website access from the internal network to the Internet 'RZnORDG RI YDULRuV fiOH WySHV VuFh DV DuGLR/YLGHR Port-wise access from the internal network to the Internet Bandwidth control 6LnFH DOO WUDIfiF EHWZHHn WhH LnWHUnDO nHWZRUN DnG WhH ,nWHUnHW SDVVHV YLD WhH fiUHZDOO, LW LV WhH EHVW SRLnW WR SURYLGH various other functions such as: A sPN gateway between two networks connected via the Internet A sPN server for remote clients connecting to the internal network Authentication of local users for Internet access GHnHUDWLRn RI WUDIfiF JUDShV Logging Internet access