Timothy
Parker Consulting Incorporated
|
|
|
|
Network-based RAS solutions Following up on the 16-port server-based RAS cards in the last column, we'll finish this medium-size RAS subject with network-based options. Network-based RAS solutions are usually a standalone box much like an Ethernet network switch or hub. These boxes tend to have one or more network connectors (RJ45 and BNC are common, AUI less so), and eight or sixteen front-panel connectors (usually RJ45s). Configuration of these boxes is usually accomplished by connecting a terminal or direct connection to one port, then providing IP address and netmask information. Administration is from another machine on the network, usually Windows NT but sometimes UNIX as well. Almost all the network-based systems use TCP/IP, although a few allow IPX/SPX. The advantage to a network-based RAS solution is that the physical RAS box can be placed anywhere convenient, as long as a connection to the network is viable. That means cupboards, basements, attics, and closets are all potential locations for the RAS box and modem stack, eliminating a common cause of mess around servers. Since the administration can be from any machine on the network, distances between administration server and RAS box are immaterial. Downsides? Network boxes require more configuration and setup work, load the network up more, and often need additional support wiring and hardware such as UPSs. There are a number of vendors of network-based RAS systems, most of which are no more than network-based multiport serial boxes. One unit I use often is Specialix' Jetstream 8500. This is a 16-port RAS unit with each port capable of 230kbps, provided through RJ45 connectors. Installing the JetStream 8500 is simple. Configuring can be done either from a terminal attached to a port or through a new Web-based interface. The browser interface is clean and easy to work with. The ability to configure the Jetstream 8500 through a browser and set up all the ports as UNIX tty devices makes this unit flexible. With support for PAP, CHAP, and RADIUS, the Jetstream 8500 includes all the authentication protocols you need. Up to 32 users and passwords can be added to the unit database and callbacks are supported. With a flash BIOS provided for easy firmware upgrades, the Jetstream 8500 is a talented unit at a competitive price. If you want faster access through ISDN, the Comtrol Interchange VS is a great unit. The Interchange VS 3000 has four ISDN ports, each capable of the usual ISDN 128kbps, or bonding to 512kbps over multiple B channels. The Interchange VS 3000 can be connected to either a Windows NT or Novell NetWare server (no UNIX support for now). Installing and configuring the Interchange VS 3000 is quick. After connecting the four ISDN ports with the included cables to the wall data jacks, the unit is powered on and Windows software installed on the controlling machine (multiple controllers are OK). The Interchange VS 3000 is added through the Network applet as an adapter. The Interchange VS 3000 interface is clean lets you set up all the usual ISDN parameters (SPID and DN) for each port separately, as well as activate DHCP if you want it active through the Windows RAS page. There is no built-in user authentication scheme, as the Interchange VS 3000 relies on Windows NT to perform these tasks. Yet another favorite is the Chase' IOLAN+ Communications Server. The 16-port IOLAN+ allows for modems, printers, and any other serial devices to be connected. Installing the IOLAN+ requires using either a UNIX or Windows NT session. An ARP entry is made first to associate an IP address with the Ethernet physical address of the IOLAN+ (provided on the bottom of the unit). This is followed by a telnet session to the assigned IOLAN+ IP address. When a remote client calls into the IOLAN+, an IP address can be assigned automatically (each port can have a separate IP address, or you can assume the IP of the remote if it's on the same network). The IOLAN+ supports PPP, SLIP and CSLIP, as well as dedicated telnet and rlogin sessions when directly connected to other systems through a serial cable. RADIUS capabilities are also included. Authentication of remote users is through an optional login and password database. Earlier we mentioned the additional network load a network-based RAS box imposes. This is because every bit of traffic in and out of the RAS box must be carried over a network. This can be a problem with heavily loaded, slow networks. I've seen a standard 10Mbps Ethernet connection which normal ran at 65% capacity almost overloaded when a 16-port RAS box was connected. A little advance planning and thought is necessary to obtain the best performance from network-based boxes. Those using fast network such as 100Mbps Ethernet will have less of a problem, of course, but performance still takes a hit. A handy way to avoid that problem is to add a dedicated network from the server to the RAS box, if possible. This requires only a second network card in the server and proper configuration, which both Windows NT and UNIX allow. That way RAS to server traffic is isolated, and while the server takes a hit from the overhead the second network imposes, main network traffic is reduced in most cases. Next column, we wrap up our look at RAS systems by examining units that allow more than 16 ports. |
|
Send mail to
tparker@tpci.com with
questions or comments about this web site.
|