User's Manual

ADSL Rout er User Manual
96
configured and m apped to a private workstat ion address when accesses are m ade t hrough
the gat eway t o a public network.
For exam ple, t he ADSL Rout er is assigned with the public I P address of 168.111.2.1. Wit h
NAT enabled, it creat es a Virt ual LAN. Each PC on t he Virt ual LAN is assigned w it h a privat e
I P address wit h default value of 192.168.1.2 t o 192.168.2.254. These PCs are not
accessible by t he outside w orld but t hey can com m unicat e with the out side world through
the public I P 168.111.2.1.
Pr ivat e I P Addre ss
Private I P addresses are also LAN I P addresses, but are considered “ illegal” I P addresses t o
t he I nt ernet. They are privat e t o an ent erprise while still perm itting full network layer
connect ivit y between all hosts inside an ent erprise as well as all public host s of different
ent erprises.
The ADSL Rout er uses privat e I P addresses by assigning them t o t he LAN t hat cannot be
direct ly accessed by t he I nt ernet or rem ote server. To access t he I nt ernet, private net work
should have an agent t o t ranslate t he private I P address t o public I P address.
Pu blic I P Address
Public I P addresses are LAN I P addresses that can be considered “ legal” for t he I nternet,
because t hey can be recognized and accessed by any device on the other side of the DSL
connection. I n m ost cases t hey are allocated by your I SP.
I f you are given a range of fixed I P addresses, then one can be assigned to the rout er and
the ot hers t o network devices on t he LAN, such as com puter workstations, ft p servers, and
web servers.
PVC ( Per m a ne n t Virt ua l Cir cuit )
A PVC is a logical point -to- point circuit bet w een custom er sit es. PVCs are low- delay circuit s
because rout ing decisions do not need t o be m ade along t he way. Perm anent m eans t hat
the circuit is preprogram m ed by t he carrier as a pat h t hrough t he network. I t does not
need t o be set up or turned dow n for each session.
RI P ( Rout ing I nform at ion Prot ocol)
RI P is a rout ing prot ocol t hat uses t he distance- vect or rout ing algorithm s to calculat e
least - hops routes t o a destinat ion. I t is used on t he I nt ernet and is com m on in t he NetWare
environm ent . I t exchanges routing inform ation w it h ot her rout ers. I t includes V1, V2 and
V1&V2, which cont rols t he sending and receiving of RI P packets over Et hernet .
UD P ( User Da ta gr am Prot ocol)
UDP is a connect ionless t ransport service t hat dispenses wit h t he reliability services
provided by TCP. UDP gives applicat ions a direct int erface wit h I P and t he abilit y t o address
a part icular application process running on a host via a port num ber without set t ing up a
connection session.
Vir tua l Ser ver
You can designat e virt ual servers, e.g., a FTP, web, telnet or m ail server, on your local
netw ork and m ake t hem accessible to the out side world. A virt ual server m eans t hat it is
not a dedicated server - - t hat is, t he ent ire com puter is not dedicat ed to running on the
public network but in the private net work.
VPI ( Virt ual Pa th I de nt ifie r ) & VCI ( Vir tua l Ch an nel I dent ifier)
A VPI is a 8- bit field while VCI is a 16- bit field in t he ATM cell header. A VPI identifies a link
form ed by a virtual pat h and a VCI ident ifies a channel wit hin a virt ual path. I n t his way,