Configuring Cisco Routers for ISDN Paul Fischer  $55.00  0-07-022073-5

To say that Cisco Systems Inc. has a few products is like saying McDonalds sells a few hamburgers. Since 1984, Cisco has improved their original routers, enhancing features both in hardware and operating system software, mounting success upon success. Most of the "big iron" (that’s industry-speak for large expensive pieces of equipment) Cisco sells will only seen by a few highly trained network engineers. Folks who are full-time, part-time, and accidental network administrators will most likely only see only Cisco’s smaller offerings.

These smaller products have become commodities since the advent of the Internet (it’s that World Wide Web thing, and if you don’t know about it by now, I’m certainly not going to let you in on the secret). Routers used to be specialty items, seldom seen, and only sold as part of communications packages by network design and troubleshooting companies, or large telephone companies. Now every mom and pop ISP (Internet Service Provider), two-bit consultant, and mail order catalog has routers, hubs, cabling, and other hard core data communications gear available. All you need is a credit card, and a Cisco router can be at your door in a few short hours, sooner if you’re in a major metropolitan area.

We will focus on a small cross section of Cisco routers, primarily, those available as commodity products and the series just above them. This will provide a broad overview of what products are available and suggest how to use them. Most of the commodity routers come in fixed configurations, although each router series will have several variants available. The newer and higher end routers are available in modular configurations. These tend to be more expensive though extremely flexible and much harder to configure. Additionally, you will need to understand what external, non-Cisco products are required to make them talk to phone company networks and what highly specialized cables are necessary.

If you are in the unenviable position of having to choose a router for the first time, there are some basic things you need to understand first. Simply ordering a router does not mean that it will work in your environment. Cisco has over 25 different versions of their highly successful 2500 series routers. How will you know which one is good for you?

First, you must have a clear understanding of what the current requirements for the router are. What will it do (i.e., route, bridge, firewall, etc.)? What types of network media (e.g., Ethernet, Token Ring, etc.) will you connect to the router? What types of wide area network connections (e.g., ISDN BRI, T1, Frame Relay, etc.) will it have? Once you know this, you must ask yourself what future demands will be made on it and plan your requirements accordingly.

Plan your network equipment with the future in mind. Although this is difficult and future needs can be vague, a little extra spent up front can make for a more flexible network. Routers can see service in multiple locations years after their initial configuration and installation. Understanding that networks are usually totally different in implementation then when we first conceive them should help you see more possibilities for future uses of the equipment. If you never expect the router to have more tasks than what you first conceive, you should consider spending more money on it, as it might one day move on to another part of the network where a more robust router is needed.

Once you have your current and future network hardware needs, you need to look at other concerns. Different Cisco routers have different types of memory. Some have more than one type including flash, boot flash, main RAM, shared RAM, and non-volatile RAM. Your network protocol and service needs will determine what version of IOS software will be necessary; that, in turn, will determine the minimum amounts of memory you need. It is strongly recommended that you purchase more memory that the strict minimum.

Over time, your needs will change, and software will grow to consume more RAM. If, in the future, you need to upgrade memory (a physical component), to support new software, it will take you much longer simply loading new software. Adding memory or any physical component requires physical access to the router. This is trivial for small networks, but in wide area networks may pose a much larger problem and cost (usually plane tickets and hotel rooms [or bus tickets and a sleeping bag if your company is cheap]). You also need more time to take the router apart properly to reassemble and test it. Also, if by some small chance have a bad component, you may not find out about it until much later, requiring several trips to complete the repairs. These things lengthen down time, and have more risk. Best to try to avoid them by stocking up on RAM if you can.

Once you know what your needs are, you should look through this partial list of Cisco products. It is always best to make sure all models listed here are available, and to find out what new ones have been introduced to the market. It is also an excellent idea to stay in the same router family if you can when building a network. Networks have a tendency to grow beyond the size and scope of their initial design. If you spend a little more to stay in one family of routers, you get a deeper understanding of that family and save yourself from possibly having to learn multiple ways of doing the same thing. It also makes parts exchanges and hardware upgrades easier to design, implement, and document.

In this book, we will be covering six different series of router, and three different series of access server. The 700, 1000, 1600, 2500, 3600, and 4x00 family of routers will be covered as well as the AS5100, AS5200, and AS5300 access servers. Before we go any further, it is important to let you know that access servers are also routers, but specialized in the task of supporting dial-in users on modems and/or ISDN lines.

Most of these routers run the Cisco IOS (Internetwork Operating System). This is one of the major advantages of Cisco routers in the market place. Once you learn to perform a task on one Cisco router, you can perform that task on any other router that runs the IOS. Only a few routers do not support IOS, among them are the Cisco 700 series of ISDN access routers which came out of Cisco’s acquisition of Combinet.

Each router family is first listed in terms of general specifications. Next, each member product of that family is listed, detailing its differences. In the case of completely modular routers, like the Cisco 4x00 family, many (but not all) of the available network modules will be listed including the maximum number of each module allowed in each type of chassis.

The Cisco 700 series of routers has three main families: the 750, 760, and 770. The 750 family has been discontinued, and was basically the acquired Combinet product repackaged with a Cisco logo. The 760 family was a major leap forward from the original 750’s. It had much more aesthetic packaging and a whole slew of options and features (like address translation and POTS ports) not available on the 750’s. The Cisco 770 family added the option of a built-in four port hub instead of a single Ethernet port giving SOHO (Small Office/Home Office) users a single piece of equipment to supply all their phone and networking needs.

Both the 760 and 770 family of routers are identical inside the box. They are powered by a 25 MHz, Intel 80386 microprocessor and have 1.5 MB standard DRAM (upgradeable to 2.0 MB), 1 MB Flash memory, and 16 KB NVRAM. All versions include many standard features, including:

• Cisco Fast Step Windows-based GUI and Cisco Clickstart Web-based GUI for simplified configuration
• Dynamic addressing of the Cisco 700 family and remote workstations, which eases configuration and network management issues
• Port and address translation for creating private networks and an additional layer of network security
• Dial-on-demand routing, which transparently dials the ISDN line only when it is needed and then automatically takes the connection down, saving money on per-minute connection costs
• Multilink PPP for standards-based B-channel aggregation (RFC1717)
• Snapshot routing for IP and IPX, which prevents the ISDN line from being dialed only to exchange periodic routing updates
• Available STAC data compression for throughput of up to 512 Kbps (for software versions supporting compression)
• PAP, CHAP, PPP dial-back, caller ID, and access lists protect network resources from unauthorized access
• Remote management and monitoring using SNMP, Telnet, and the console port
• Support for all major ISDN central office switches worldwide

Those routers that include POTS ports provide:

• Analog telephone ports for sharing the ISDN BRI line with devices such as standard telephones, fax machines, and modems
• DTMF support for basic network configuration of the Cisco 700 family with a push-button telephone, after which a network manager can dial into the Cisco 700 to complete the installation

In addition, routers with built-in NT-1’s add:

• Built-in NT1 device for North America and external S/T port for support of additional ISDN devices such as ISDN telephones

The 760 and 770 family of routers are available in the following variants.

Table 2-1. Part number and description list for 760 and 770 series routers.

As you read through the book and learn more about Cisco routers and ISDN, you will find it easier to determine which of these features you will need. You should always check with your Cisco authorized contacts to make sure you order the right router for your location. Several of these routers come in different "flavors" to support the different ISDN standards in Japan, Canada, Netherlands, Taiwan, Singapore, etc. Never believe that a router built for the United States will work in Australia without checking first!

The operating system software for all Cisco routers must be purchased separately and the Cisco 700 series is no different. However, it is different from most Cisco routers since it does not run IOS. There are only two different packages available for the Cisco 760 and 770 family of routers: the Internet Ready Feature Set and Remote Office Feature Set. The Internet Ready Feature Set is designed for SOHO environment connecting to the Internet or a corporate WAN using only the TCP/IP protocol. It supports a maximum of four devices on the network (PC’s, network printers connected to the Ethernet not to PC’s, etc.). Users with more than four devices may experience problems with this feature set.

The Remote Office Feature Set is designed for remote offices. It adds the Novell IPX/SPX protocol, on-the-fly data compression, and support for 1,500 devices on the network. For users whose ISP or corporate WAN supports on-the-fly data compression, the additional $140 cost for purchasing the Remote Office Feature Set can be justified by the increased connection speed alone. On-the-fly compression can provide as much as four times the effective speed of your WAN connection, depending on the data you are transferring.

The Cisco 1000 series routers are the lowest cost IOS based routers available. They provide entry level pricing for customers who wish small, remote office networking. There are only three variants available: the 1003, 1004, and 1005. This makes the 1000 series router one of the smallest in Cisco’s product line.

The Motorola 68360 microprocessor powers all series 1000 routers. Each router ships with 8 MB of main memory, and no flash memory. Standard features for all 1000 series routers include:

• One Ethernet 10BaseT port (RJ-45)
• One console port (RJ-45)
• One WAN port: either DB-60 for serial, or RJ-45 for ISDN BRI
• One slot for an optional PCMCIA Flash memory card
• Software boot using TFTP over an Ethernet LAN connection or by using the optional Flash memory card
• IP, IPX, and AppleTalk routing
• Support for the following WAN encapsulations: HDLC, LAPB, Frame Relay, SMDS, X.25, PPP, and SLIP
• Router management through the console port or over the network using SNMP or Telnet
• AutoInstall for downloading configuration files automatically over a WAN
• LAN-to-LAN DDR routing over ISDN and modem lines

The Cisco 1000 series of router are available in the following three variants:

Table 2-2. Variations in the Cisco 1000 series.

The 1003 and 1004 use ISDN BRI for their WAN connection, while the 1005 uses a serial port capable of both synchronous and asynchronous communications. In order to make an ISDN connection the 1003 requires an external NT-1, while the 1004 has one built in. Targeted for the remote office market and not the SOHO market, neither has the POTS ports that are available on the 700 series routers. The ISDN service provider supplies the NT1 connection worldwide (except in North America, where the NT1 is supplied by the customer). Therefore, the Cisco 1004 router is for use in North America, and the Cisco 1003 router is applicable worldwide.

Designed for use with external serial-device WAN connections, the 1005’s singular WAN port (DB-60) supports asynchronous serial communications at speeds up to 115.2 Kbps. Also supported are synchronous connections (such as leased lines, Frame Relay, switched 56 Kbps, SMDS, and X.25) at speeds up to 2.048 Mbps. Asynchronous connections typically take place over a modem, although other equipment can be used. Synchronous communications use CSU/DSU’s which convert the digital signal used by the router to the one used across the phone company network. Many types of synchronous communications gear are available, and the type of connection you use will determine what type of external gear you will need.

One of the most intriguing parts of this series of routers is a PCMCIA slot for a Flash memory card. In Cisco routers, the router operating system is generally stored in Flash memory, which is usually internal to the router only. You can readily swap the PCMCIA Flash memory card loaded with your IOS software in and out, making IOS upgrades amazingly easy.

With a small set of spare Flash memory cards, a WAN administrator could upgrade an entire WAN by loading the latest version of IOS on the spare cards and sending them out to the LAN administrators in the field. When they arrive, the LAN administrators could swap them out during a maintenance window, check the new code for proper operation, and return the old cards if the upgraded IOS is working properly. The WAN administrator can then load the latest version of IOS on the returned cards and send them out to other sites. The cycle would repeat itself until all sites had the same version of IOS. Should anything go wrong, all that is necessary is to place the old Flash card back in the router, and the site is immediately restored to operational status.

The series 1000 routers use Cisco IOS as their operating system. There are four basic versions available for routing and bridging with this series:

• IP Only
• IP/IPX
• IP/AT (Apple Talk)
• IP/IPX/AT

You can also get IOS versions designated PLUS, PLUS 40 or PLUS 56. The PLUS feature set contains additional features such as: NAT, data encryption, RADIUS, OSPF, and Network Timing Protocol (NTP). VPDN (L2F tunneling) and RADIUS are available on the PLUS feature sets starting with Cisco IOS Release 11.2(10)P. 11.3.PLUS 40 and PLUS 56 add 40-bit and 56-bit DES (Data Encryption Standard) encryption capabilities providing additional security by protecting network traffic over public networks. All these choices can make selection difficult. However, many feature sets identical price tags, and it is possible to upgrade your license in the future.

The Cisco 1600 is at the low end of an extremely flexible class of routers that also includes the 2600 and 3600. The product is sleek, stylish, and very flexible. Most variants come with one Ethernet and one WAN interface, while the 1605-R has just two Ethernet ports. All come with one WAN interface card slot to add optional WAN interface cards (WICs). The WAN interface cards used in the 1600 series are interchangeable with 2600 and 3600 routers as well. This makes for extreme flexibility across a business.

As with the 700 and 1000 series, the 1600 series of Cisco routers is too narrow to fit in a standard 19" communications rack. This makes it more suited to environments where it will sit on a shelf, probably on top of the Ethernet hubs which provide LAN services for small offices. In a situation where an ISDN BRI WAN connection serves a small office and two Ethernet segments need to have different security policies, the 1605-R with an ISDN BRI card is the perfect solution. It is the lowest cost router Cisco makes that provides dual Ethernet and ISDN capabilities. The same configuration in a Cisco 2600 chassis would cost nearly twice the price. Network managers looking for the best price/performance ratio should take a good long look at the 1600 series.

A Motorola 68360 microprocessor running at 33MHz powers all 1600 series variants. Most ship with 2 MB of main memory and 4 MB of flash memory. Main memory maxes out at 18 MB and flash maxes at 16 MB. The exception is the 1605-R. It ships with 8 MB of main memory and 2 MB of flash and tops out at 24 MB of main memory and 16 MB of flash. While this may seem odd, there is a good reason for it. The Cisco 1601-1604 routers have a "Run from Flash" architecture. This means that operating system software is stored in flash memory uncompressed and executed from flash memory. The Cisco 1605-R router has a "Run from RAM" architecture. Software is stored in flash memory compressed and executed from RAM. The "-R" suffix designates run from "RAM."

The 1600 series is a big step up from the entry level 1000 series. Not only is the router more flexible, but the software offers features usually unheard of in routers of this price range. These software features include:

• Advanced security, including optional integrated firewall, encryption, and virtual private network (VPN) software
• Network Address Translation (NAT) which reduces the cost of Internet access
• End-to-end quality of service (QoS) and multimedia support
• Integrated data service unit/channel service unit (DSU/CSU) up to T1 speed and integrated Network Termination (NT1)
• Multi-protocol routing and transparent bridging for IP, IPX, AppleTalk, and IBM/SNA protocols
• WAN optimization features such as dial-on-demand routing (DDR), bandwidth-on-demand (BOD), Open Shortest Path First (OSPF) on-demand circuit, snapshot routing, compression, filtering, and spoofing to reduce WAN costs

The Cisco 1600 series of router are available in the following five variants:

Table 2-3. Comparison of the 1600 series models.

There is a dizzying array of software images available for the 1600 series. These include all possible mixes of: IP, IPX, Apple Talk, and IBM protocols with additional feature sets of FIREWALL, PLUS, PLUS 40, and PLUS 56. Remember you only need to license the feature sets you are going to use from day one. You can always upgrade your IOS license later if your requirements change.

The 1600 series is an excellent small office and Internet router. In cases where a full-blown firewall is too expensive, a 1600 with IP and Firewall feature sets helps insure network security while keeping the total cost for access and security under $3,000.

For the most part, the Cisco 2500 series routers are fixed-configuration routers. They are one of the oldest products in Cisco’s product line, and the number of variants has grown due to low price and high popularity. They offer a quite a variety of features, each filling its own niche in the marketplace. The 2500 series can be broken up into several families based on these features: LAN/WAN, Access Server, Dual LAN/WAN, Hub, Frame Relay Access Devices (FRAD), and Modular.

The LAN/WAN family consists of the 2501 through 2504 routers. These offer one Ethernet or Token Ring, two high-speed serial, and (in the 2503 and 2504) an ISDN BRI port. The Access Server family consists of the 2509 through 2512 routers. These offer one Ethernet or Token Ring, two high-speed serial, and either 8 or 16 low speed serial ports (typically for modems or dumb terminals). The Dual LAN/WAN family (consisting of the 2513 through 2515 routers) offers two Ethernet or Token Ring, or one of each and two high speed serial ports. The Hub Series consists of the 2505, 2507, and 2516 through 2519 routers. These offer dual high-speed serial and either 8, 14, 16, or 23 Ethernet, or 14 or 23 Token Ring ports.

The Frame Relay Access Devices (FRAD) family seems to have only four variants: 2520 through 2523. Each of these can come configured normally or in a CF or LF sub-variant. The normal model, without CF or LF extension to its name, either has a single Ethernet or a Token Ring and 2 high-speed serial, one ISDN BRI, and two or eight low speed asynchronous serial ports. The CF or CFRAD sub-variant disables the LAN and ISDN ports in software. The LF or LAN FRAD sub-variant disables the ISDN port in software. The LAN/WAN family also comes in CFRAD, LAN FRAD, and ISDN only sub-variants. The ISDN sub-variant disables the high-speed serial ports allowing only the ISDN port to provide WAN connectivity.

While this might seem strange, you need not purchase unnecessary ports and you can handle future upgrades through software changes. This cost reduction is not immediately evident, because FRAD and ISDN sub-variant routers cost more than their fully enabled counterparts. You save when you purchase the IOS software. All Cisco 2500 series routers require an IOS software purchase as a separate item, except for FRAD and ISDN sub-variants. These routers include IOS software in their list price. This saves you several hundred to several thousand dollars. A simple upgrade of your IOS license and the disabled router ports come alive, ready for you to expand their role in your network.

The Modular family consists of the 2524 and 2525 routers. These routers offer one Ethernet or Token Ring port, and three optional WAN module slots. WAN modules are available in the following modules:

• 2-Wire Switched 56-kbps DSU/CSU
• 4-Wire 56-Kbps/64-KIps DSU/CSU
• Fractional/Full T1 DSU/CSU
• Synchronous Serial Five-In-One high-speed serial port
• ISDN BRI with ST Bus Connector
• ISDN BRI with NT1 and U Bus Connector

These modules go beyond the normal Cisco fixed configuration routers by allowing you the choice to incorporate normally external devices into the router. All other 2500 series routers require external CSU/DSUs and ISDN NT-1s to complete their WAN port connections. However, the 2-wire 56-kbps, 4-wire 56/64-kbps, fractional/full T1, and ISDN U bus modules allow you to integrate them directly into the router. The five-in-one (which is, basically, a high-speed serial port) and ISDN s/t bus modules require external devices like all other series 2500 routers.

Purchasing a series 2500 modular router and WAN modules that integrate external devices like DSU/CSU’s and NT-1’s is not a clear-cut decision. While the base cost difference can be negligible in some cases, the costs can quickly skyrocket past that of a fixed configuration router and external devices. However, you must consider more than just cost when evaluating their overall worth in your network design. By bringing external devices into the router, you gain control over them through IOS. This can be a big plus if you have no technical people on-site. These cards give you the ability to configure, monitor, and test data lines from the router, rather than talking site personnel through the use of external versions of these devices.

Another consideration is the inability to create hardware configurations that do not exist in fixed configuration routers. The three WAN slots are not the identical: two are for serial WAN connections and one is for ISDN. If Cisco had enabled the end user to create a triple ISDN-port router, they would have added a real asset to the 2500 series.

Series 2500 routers also are powered by a Motorola 20-MHz 68030 microprocessor. This is not enough power, however, to run certain high-end applications like BGP, packet filtering and other firewalling and high-speed multi-protocol routing over LANs and WANs. Although the 2500 series is one of the most flexible low-end routers Cisco sells, keep in mind when selecting it for a particular application that it is also the oldest. In most cases, such as Internet access at speeds up to dual T1/E1, you will have no problem. Only once you add other applications to the 2500 will you begin encountering bottlenecks due to its older processor.

The 2500 series routers ship with a minimum of 8 MB of Flash memory, except for the mission-specific routers, like CFRAD and LAN FRAD sub-variants, which require only 4 MB of Flash memory. However, depending on the Cisco IOS release that your order, it might require more. You can install one or two flash SIMMs, but never more than 16 MB total. If you install dual flash SIMMs, they must be the same size. Cisco install DRAM as required by the IOS version ordered. Possible DRAM configurations are 4MB, 8MB, or 16 MB. In each case, 2 MB of DRAM is reserved for shared memory and the rest is used for main router memory. Refer to Cisco’s IOS Software configuration web pages to determine your memory needs.

You should seriously consider purchasing extra DRAM and flash memory for your router from the start. Series 2500 routers require you to open the router and add and/or remove memory SIMMs to perform memory upgrades. This may be a task too complex and delicate for accidental administrators and non-technical personnel. IOS versions will likely only get larger and consume more memory. By configuring your routers with extra memory initially, you will ease upgrades to future releases and enhanced feature sets.

All series 2500 routers come with a console and an auxiliary port. Both are low speed asynchronous serial ports with RJ-45 connectors. Both can be used for terminal connections, but only the console port is active during boot and the initial configuration dialog. In addition, logging is, by default, on for the console port and cannot be turned off. Many sites connect a modem to the auxiliary port. This can allow dial-in terminal connections for telnet and rlogin sessions to host computers, as well as for remote router maintenance. You can also configure the port to support dial-in WAN connections using protocols like PPP (Point-to-Point Protocol). This could be used for many applications including remote access to the LAN, remote router configuration, and dial-on-demand routing to backup a full time WAN connection.

The Cisco 1600 series of router are available in the following variants:

Table 2-4. Comparison of different features in the 2500 series.

The 2500 series of routers is the first form factor that will fit in a standard 19" or 24" communications rack. You will need to purchase external brackets separately, but rack-mounting routers helps to keep them organized and easily accessible. Communications racks are available in any length. Most smaller sites use the 19" standard and mount the rack near the ceiling with all the cabling terminated on the rack. This way the local site personnel or accidental administrator can configure individual connections at will.

The 2500 series supports a full range of routing and bridging protocols including IP, IPX, AppleTalk, DEC Net, LAT, and IBM. It also supports a wide variety of feature sets including: Desktop, Enterprise, Firewall, APPN, PLUS, PLUS 40, PLUS 56, and RMON. Also available are mission specific versions for FRAD and ISDN routers. These specific versions lower the cost of a router by disabling some of the network ports. Feature sets and protocols are defined in Chapter 3.

There are only two variants of the 2600 series available at this time, these being the 2610 with a single Ethernet port and the 2611 with dual Ethernet ports. These have given up the aesthetics seen in the 1600 series for pure functionality. Looking more like the workhorse 2500 series, the 2600 offers some new features like: LED status indicators for power, RPS (redundant power supply) status, network activity, and network interface status. Also new are an easy-to-open chassis design allowing fast and easy access for installation of memory or AIM (Advanced Integration Module) and a variable speed fan for quiet operation in office environments.

Powered by Motorola MPC860 RISC (Reduced Instruction Set Computing) microprocessor running at 40 MHz, the 2600 series offers a new level of router performance for such a low cost. The RISC processor powers allow Cisco to deliver features unheard of previously in such a low cost router. These include:

• Support for advanced QoS (Quality of Service) features such as Resource Reservation Protocol (RSVP), Weighted Fair Queuing (WFQ), and IP Precedence
• Security features such as data encryption, tunneling, and user authentication and authorization.
• Support for cost-effective, software-based data compression and data encryption
• Integration of legacy networks via data link switching plus (DLSW+) and Advanced Peer-to-Peer Networking (APPN)
• High-speed Ethernet-to-Ethernet routing (12,000 -15,000 packets per second (pps)) for maximum scalability

Flash memory starts at 4 MB in the base configuration and is expandable to 16 MB. Some of the larger feature sets already require 8 MB of flash memory, so make sure you order enough. System memory (DRAM) starts at 16 MB and is expandable to 64 MB. More memory is always a plus, as it allows you to run more protocols, larger feature sets, and more services simultaneously. It also allows you to keep your packets-per-second rate as high as possible by not depriving the processor of memory it needs for packet buffers.

Each 2600 series router comes with 2 WAN interface card (WIC) slots, one network module slot, one AIM Slot, and console/auxiliary ports capable of running at 115.2 Kbps. With the addition of a NM-1V or a NM-2V, the Cisco 2600 adds support for two to four voice/fax ports. This allows you to route voice and fax traffic over a WAN link back to a central site. It also acts as a micro phone switch, allowing local users to dial extension numbers in order to call each other. The addition of voice and fax over IP adds a whole new dimension to Cisco router functionality. Corporate America is looking very closely at voice over IP and fax over IP solutions. Cisco, always a leader in data networking, is poised to move into this voice/fax market with support for WAN technologies such as Frame Relay, leased lines, and ISDN.

The voice/fax network modules slide into Cisco 2600 network module slot and contain either one or two voice interface card (VIC) slots. At less than twice the price of a single VIC slot, the dual VIC slot network module offers a price break to those who think they might one day need extra VIC capacity. The VICs are daughter cards that slide into the voice/fax network modules and provide the interface to the telephony equipment. Just as you can swap the Cisco WICs with other WICs, you can deploy the Cisco VICs interchangeably with other VICs in the voice/fax network modules.

The NM-2V converts the single network module slot into dual voice interface card (VIC) slots. Adding a two-port VIC card expands the 2600 beyond mere data routing to servicing voice and fax over IP and acting as a small office phone switch.

The 2600 series supports a wide variety of WIC, VIC, and NM cards. These provide a "pay as you go" approach to voice and data networking. Since most of these cards are compatible with the 1600 and 3600 series routers, you reduce your costs for maintaining inventory, and gain greater flexibility in you network design and evolution. Cards currently available include:

Table 2-5. WAN and Voice Interface Card listing with part numbers.

Table 2-6. Network Module listing with part numbers.

Both routers in the 2600 series can be ordered with RPS. This helps reliability by providing diverse power sources, making it a must for high reliability applications. Also available are rack mount brackets for standard 19" and 24" communications racks.

IOS software for the 2600 series is limited in scope when compared to the 2500 and 3600 series. It supports only five protocol sets, and not all variations of them. The available IOS sets and their memory requirements are listed in Table 2-6.

Memory requirements for Cisco 2600 available IOS software sets.

Table 2-6. Memory requirements for Cisco 2600 software.

It is disturbing that certain feature sets that seem essential to small offices, particularly the firewall feature set, are missing. This is an extremely new router and hopefully Cisco will extend the IOS software available for this series in the near future.

Unlike the 2600 series, the 3600s have no built-in LAN or WAN ports. The Cisco 3640 server is equipped with four network module slots; the Cisco 3620 has two. A plethora of NM, WIC, and VIC cards are available making the 3600 the ultimate in configurable routers. Although only NM card slots are available, mixed media cards allow you one or two Ethernet and/or Token Ring ports and two WIC slots. The NM-1V One-slot and NM-2V Two-slot voice/fax network modules are also available, turning one NM slot into one or two VIC slots.

Cisco bills the 3600 router as a "power branch office" router. While this is definitely true, it can also run small-to-mid-sized main offices with a variety of needs. The 3600 series can fulfill several roles including: LAN-to-LAN router, LAN-to-WAN router, Access Server, and Voice/Fax over IP router. LAN to LAN connectivity comes in three flavors: 10 and 100 Mbps Ethernet and Token Ring media. WAN connections are available in just about every possible variation including: high-speed sync serial, ISDN BRI, Channelized T1/ISDN PRI (Primary Rate Interface), low-speed sync/async serial, low-speed async serial, 2 and 4 wire 56/64 Kbps leased line, and full/fractional T1.

Access server configurations can support up to 60 digital modems.

Configurations include:

• dial-in modem access over single or dual T1 service for 24 to 48 users
• dial-in modem access over single or dual E1 service for 30 to 60 users
• dial-in modem or ISDN B-channel access over single or dual T1 PRI service for up to 46 users
• dial-in modem or ISDN B-channel access over single or dual E1 PRI service for up to 58 users

A single or dual E1/T1 card uses one NM slot. Digital modem NM cards are available in 6, 12, 18, 24, and 30 port models. A fully loaded access server configuration requires only three NM slots on a 3640, leaving one slot for LAN and WAN connections. The channelized T1/E1 card routes calls to modems and ISDN B-channels, but provides no explicit WAN connections. A 3640 used as an access server could use ISDN to back-haul data to a main site. Since Cisco only supports linking two B-channels together (or a total of 128 Kbps), this would not provide enough bandwidth for a large number of modem and ISDN users. A better solution would be to add a fourth card to the router to support LAN and WAN connections. The LAN connection could be used to connect with other LAN equipment like servers, routers, and other access servers. The WAN connection would be the primary method of back hauling the data; ISDN could still provide a backup WAN connection in case the primary connection failed.

Voice/Fax over IP configurations require at least one WAN port, using either an NM or a WIC card. For "power branches" that want LAN, WAN, and phone services, one mixed media LAN card could be used to provide Ethernet or Token Ring service, while WIC cards provided the WAN connection back to the home office. You can handle this in a single NM slot, leaving room for four VIC ports on the 3620 and 12 VIC ports on the 3640. In this configuration, the 3640 acts as both a 12-port phone switch and a LAN-to-WAN router. By concentrating all these features in a single piece of hardware, it is possible to reduce the complexity and cost of establishing a remote office.

It is even possible to configure a 3640 for LAN-to-LAN, LAN-to-WAN, Access Server, and Voice/Fax functionality. A single port channelized T1 NM card and a 24 port digital modem NM card take two of the four slots. A two slot VIC carrier card and two VIC cards provide four voice/fax ports in one NM slot. Finally, a dual Ethernet and Dual WIC slot card provides LAN-to-LAN services and a home for up to two WAN ports. A configuration like this might not be practical to many users, but it should give you a sense of the flexibility available in the 3600 series.

An IDT R4700 RISC processor powers the 3600 series routers. The 3620’s processor runs at 80 MHz and come with 16 MB of DRAM, which is expandable to 64 MB. The 3640 has a 100 MHz processor and 16 MB of DRAM, expandable to 128 MB. Both routers come with 4 MB of flash memory, expandable to 32 MB. The 3620 is capable of routing 20-40 Kpps (or kilo packets per second) while the faster processor in the 3640 allows it to route 50-70 Kpps. Both 3600 series routers come with the following features:

• Optional Redundant Power Supply
• Console and Auxiliary Ports (up to 115.2 Kbps) (back to kilobits per second)
• Wall Mounting kit and Rack Mounting kits for standard 19" and 24" racks
• Dual Type II PC Card Slots
• Optional Compression Module

Of these options the RPS, PCMCIA slots, encryption module, and compression module are the most interesting. The RPS unit allows you to provide dual power feeds to a router. This allows incredible flexibility in dealing with power issues, such as temporary outages, which may require moving the routers power source. Without RPS a router would need to shut down in order to have its power source switched. Although there are two internal slots for flash SIMMs, the two PCMCIA slots may be a better place to store your IOS software. External flash cards can make installation and upgrades much easier, quicker, and virtually foolproof.

Hardware encryption and data compression used to be very specialized equipment seen only by intelligence and data communications professionals. They have long been available in IOS software, but place a heavy load on the routers main CPU. The encryption network module and data compression modules have their own coprocessor to off-load these functions from the central router engine. This allows the main CPU to do what it does best: routing. Neither requires the identical hardware at the other end, allowing cheaper routers in the field to use software encryption and compression. The compression module can off-load processing up to 128 simultaneous WAN, ISDN, and frame relay connections but can not increase compression ratios. If it were able to do so, it would either become incompatible with software compression, or require another hardware compression module on the other end of the connection.

There are a huge number of NM, WIC, and VIC cards available for the 3600 series, and more coming to market all the time. Here is a partial list of the more important cards. Included are the maximum number of each card that can be used and the minimum IOS version necessary.

Table 2-7. This table lists the minimum software versions necessary to use a network module, as well as the maximum number of modules allowed in a single chassis. Note: Neither configuration of two NM-1FE and two NM-4E nor one NM-1FE + three NM-4E is supported.

Table 2-8. This table lists the minimum software versions necessary to use a WAN Interface card, as well as the maximum number of modules allowed in a single chassis.

The Cisco 3600 series supports run-from-RAM images only. Both the 3640 and 3620 support the following types of memory:

• Main processor memory - Used to store the running configuration and routing tables. Cisco IOS software is executed from the main memory.
• Shared (packet) memory - Used for packet buffering by the router's network interfaces.
• Flash memory - Used to store the IOS software image. Can be stored on either the Flash SIMM, or PCMCIA card.
• Nonvolatile random-access memory (NVRAM) - Used to store the system configuration file and the virtual configuration register.
• EPROM-based memory - Stores the ROM monitor, that allows booting an operating system software image from Flash or PCMCIA memory when Flash memory does not contain a valid boot helper image.

Both the 3640 and 3620 platforms partition their DRAM into main processor memory (pmem), and shared packet memory (iomem) area's. The IOS software is capable of making a distinction between the two with a fine granularity. For example, with a 16MB DRAM configuration splits the memory by default into 12MB for pmem and 4MB for iomem. This 75/25 split occurs upon system initialization, and allows enough packet memory to bring up the most common interface combinations regardless of the total amount of DRAM present.

In addition, users have the ability to choose from several options to change this split when required. The new IOS command memory-size (iomem) allows DRAM split increases of 30%, 40% and 50% depending on the type and number of Network Modules configured.

The Cisco IOS supports an auto-adjusting feature upon startup. If the iomem percentage has been configured too high (leaving insufficient pmem available for bringing up the IOS image), the IOS automatically reduces the percentage to a lower value. If the lowest value (75% of DRAM) is insufficient for an image to boot, then the router does not have enough DRAM to run that particular IOS image, and the router will complain about it. Main and packet DRAM cannot share or borrow from each other as on the 25xx series routers. If the main DRAM memory is insufficient, then an increase in memory or a smaller IOS image is required.

Most average size networks require at least 2.0MB of free processor memory and 1.2MB of free iomem. You can use the Cisco IOS command show memory free to view the amount of used and available system memory.

Here is a table showing the default division of DRAM based on amount present in the router.

Table 2-9. Memory allocation chart for the Cisco 3600 series router.

There are many different IOS feature and protocol sets available for the 3600 series. To make matters more complex, the different chassis have different costs associated with the same features. Almost every combination of the protocol and feature sets is available. The protocol sets include: IP, IPX, IBM, DECnet, AppleTalk, Desktop, Enterprise, and LAT Terminal. Feature sets include: PLUS, PLUS 40, PLUS 56, and APPN. Most notably missing is the firewall feature set, which would enhance the router’s security capabilities dramatically. Hopefully, Cisco is already working on adding this to the IOS capabilities of the 3600 series.

The Cisco 4000 series consists of the 4000-M, 4500-M, and 4700-M. They are completely modular routers containing no LAN or WAN ports by default. All router chassis in this series look the same, right down to the label on the removable front panel which says "Cisco 4000". In fact, the only want to tell them apart from the outside is by looking at the serial number label, usually located near the power switch. It will start with 4000, 4500, or 4700.

The major differences between different members are the CPU and number of various types of Network Processor Modules (NMP) they can use. Cisco based the 4000-M on the older Motorola 68030 microprocessor running at 40 MHz. From that somewhat meager starting point, the 4500-M jumps to an IDT Orion RISC CPU running at 100 MHz. This gives the 4500-M three to five times the pps (packets per second) rate of the 4000-M. Like the 4500, the 4700 uses the IDT Orion RISC CPU, but it is clocked one-third faster at 133 MHz.

The 4000 series routers use three separate and distinct types memory SIMMs for flash, main, and shared memory. All 4000 series routers start with 4 MB of flash memory and are expandable to 8 MB or 16 MB. The 4000-M ships with 8 MB of main memory and is expandable to 16 MB or 32 MB. The 4500-M comes with 16 MB standard and is expandable to 32 MB. The 4700-M ships with 16 MB and is expandable to 32 MB or 64 MB. For shared memory, all versions ship with 4 MB and are expandable to 16 MB. However the 4500-M and 4700-M add the flexibility of upgrading to only 8 MB, if desired.

4000 series routers have three Network Processor Module (NPM) slots. Due to their vast differences in age and CPU speed, some NPMs are only supported in certain chassis while others may be limited in number. Below is a list of the various NPMs and their configuration limitations by chassis. Below that is a list of incompatible NPM configurations, which should help you accidental administrators from committing accidental misconfigurations.

Table 2-10. The maximum supported network processor modules configurable in 4000 series routers.

Table 2-11. Incompatible network processor module configurations.

The 4000 series has many of the same types of media available to it as the previous modular series, the 3600. However, there are some interesting additions and deletions. Notably, there are no typically external communications devices like DSU/CSUs, modems, and NT-1s available in this product series. All ISDN BRI ports requires external NT-1s. All serial ports require modems or DSU/CSUs, and the channelized T1/E1/PRI cards require external CSUs. Note that an external CSU is not the same as a CSU/DSU. The channelized T1 cards act as the DSU; therefore, you only need a CSU.

The notable additions are the extremely high speed LAN and WAN interfaces supporting ATM (Asynchronous Transfer Mode), FDDI (Fiber Distributed Data Interface), DS-3, E3, and HSSI (High Speed Serial Interface) at speeds of 12, 45, 52, 100, and 155 Mbps. All of which make the 4000 series an entry-level backbone router. It does not have advanced features like firewall feature set or voice/fax modules; rather, its strengths lie in raw packet routing capabilities.

The back of the router provides much more real estate for network connectors and LEDs making it easier to maintain cables and see network port status. As with almost all other Cisco routers, there is also a console and auxiliary port.

The 4000 series routers can be confusing when you first start working with them. The slots are numbered 1 through 3, from right to left when you are looking at the back. In addition, the ports on each card are numbered from zero up although zero is sometimes in different locations. Since there are no fixed configurations, the IOS software must number the ports dynamically as it located them, starting with slot 1. In Figure 2-17, you can see a 4000 series router with three dual serial port NPMs. Note the table below that picture which shows how the physical ports (which are only labeled zero and one) are mapped to the IOS serial ports you configure in software. In the case where a non-serial card, such as a dual Ethernet NPM, was in the middle, the slot one serial ports would still be zero and one, but the slot three serial ports now become two and three.

Table 2-12. Interface numbering scheme for three dual serial network processor modules in a 4000 series router.

There are many different IOS feature and protocol sets available for the 4000 series. To make matters more complex, the different chassis have different costs associated with the same features. Almost every combination of the protocol and feature sets is available. The protocol sets include: IP, IPX, IBM, DECnet, AppleTalk, Desktop, Enterprise, and LAT Terminal. Feature sets include: PLUS, PLUS 40, PLUS 56, DBConn, and APPN. (No, you are not having déjà vu all over again; you have read this paragraph before: the 3600 series has nearly the same complexity as the 4000 series.) Note that DBConn is available in the 4000 series but not in the 3600, and that the firewall feature set also is missing from this series. Hopefully, Cisco will get the hint for the 4000s as well as the 3600s.

Access servers are a specialized class of router that provides network access services to remote users over dial-up connections. Users connect over digital phone lines and access standard modems or ISDN B-channel connections. Either type of connection uses the same link to the telephone company--a T1 or E1 leased line with or without ISDN PRI service layered over it. Most access servers are used for modem dial-in service only. Examples of this are ISPs and content providers like America Online.

The total number of dial-up connections depends on the number of channels available from all digital leased lines connected to the access server. These leased lines will be either T1 or E1 lines, depending on which part of the world you are in. T1 lines provide 24 and E1 lines provide 30 available channels for connections. By themselves, these lines can be used only for analog modem connections. However, by layering ISDN PRI service over them, the channels can be used for modem or ISDN B-channel connections. To gain this flexibility requires the sacrifice of one channel for ISDN signaling; therefore, ISDN T1s support 23 and ISDN E1s support 29 connections.

Each user connects to an access server over one channel on the digital leased line. There is a one to one correlation between the maximum number of users and the total number of available channels. Initiation of a connection reserves a channel exclusively for a user. When the user terminates his connection, the channel is again available for use. Therefore, if an ISP wants to support 100 simultaneous users in a single location they must have at least 100 channels available at that location. The two access servers discussed in this book are the AS5200 and AS5300, which support a maximum of 60 and 120 channels, respectively. The AS5800 is a huge access server supporting up to 720 channels, making it beyond the scope of this book.

Sizing an access server to meet unknown future needs used to be extremely difficult. You needed to pick equipment that supported a fixed number of connections, analog or ISDN service only, and would not support multiple connections from a single user over multiple chassis. Users want this capability so they can incrementally add bandwidth to their network connection if their operating system supports MPPP (Multilink Point-to-Point protocol). It is now much easier to size an access server because Cisco has the ability to support ISDN and analog connection in one chassis and connect a single dial-up user across multiple access server chassis.

Allowing a single user to add bandwidth over multiple chassis makes it possible for ISPs to add additional Cisco access servers, without forcing the users to change their configurations. This can be used both for ISDN and modem dial-in connections providing up to 128 Kbps of throughput. Cisco provides this capability with the Multichassis Multilink Point-to-Point Protocol (MMP) which manages bandwidth and routing during a MPPP users’ connection to different chassis.

Before access servers, terminal servers and modem banks supported large numbers of dial-in connections. Analog phone lines (POTS) would be wired for each modem connection supported and terminated at the back of a chassis holding rack mounted modems. These modem racks usually supported 12 to 24 modems and took up eight inches or more in a standard 19" communications rack. Each modem would have its own 25-pin serial cable, which would snake down to the terminal server. The terminal server managed the modems and had the Ethernet connection to the network. It usually had 12 to 36 serial ports but some were available with 60 serial ports. Because of the size of 25-pin serial ports, terminal servers took up eight to 14" inches in the rack.

An older configuration of 12 modems per modem rack and a 36 port terminal server would take up four feet of rack space, and need at least 77 individual cables. Today’s access servers have integrated modems, ISDN support, and the terminal server in the same box. Because of this high level of integration they need only four cables to support the same number of modems and are as small as 3.5".

Reducing the number of cables and components has made today’s access servers many times more reliable than those of previous years. The tight level of integration allows network administrators to configure, monitor, and maintain all the various pieces of the access server quickly and easily. This reduces the administrative costs of providing dial-in access, as does a feature like MMP. By combining all these features, and reducing administrative costs, the access server has taken its place as the product of choice in the dial-in server market, and helped make dial-up networking much more reliable for its users.

All Cisco access servers can provide both modem and ISDN connections. Support for ISDN connections requires only a channelized T1 or E1 / ISDN PRI card. This manages the ISDN PRI connections with the telephone company and the ISDN calls themselves. Modem support requires the addition of modem carrier cards and modem modules. The modem carrier cards exist solely to provide a home for modem modules. Modem modules contain six or twelve modems each. These modems are not the typical end-user product, but rather digital modems on a single chip. This technology allows access servers to reduce drastically the size needed for large numbers of modems.

Cisco uses Microcom and MICA modem technology in their access servers. Microcom modem modules are the older technology and hold twelve modems each. The AS5200 and AS5300 will take the Microcom modem modules, but the AS5800 will not. In both the AS5200 and AS5300, two modem modules can fit in a carrier card with a maximum of two carrier cards per access server. Simple arithmetic shows a maximum of 48 Microcom modems, causing many people to wonder how you attain the maximum capacity of 60 modems in the AS5200. Since this maximum is only possible if you are using E1 connections, the channelized dual E1 card for the AS5200 adds an additional slot for a Microcom modem module. This is not true of the AS5300, which can only support 48 Microcom modems.

All three access servers can use the MICA modem modules. The carrier cards for the AS5200 support five modem modules, while those for the AS5300 support ten. Both the AS5200 and AS5300 can hold two MICA carrier cards. An AS5200 using MICA modems has the same number of maximum connection as one using Microcom modems (60). However, the AS5300 is able to support 120 MICA modems, far outstripping 48 available with Microcom technology. If you are upgrading from an AS5200 to an AS5300, you can extend the useful life of existing equipment and keep your costs down by reusing your Microcom modems, thus avoiding the purchase of new equipment. Any new purchase of access servers should include the MICA cards since they are supported in all three chassis.

Both the AS5200 and AS5300 are three slot access servers. Modem carrier cards can occupy any two available slots. The third slot is for a channelized T1 or E1 / ISDN PRI card. This terminates the digital leased lines from the phone company. The AS5200 card supports two digital leased lines while the AS5300 supports four. In countries with T1 lines, the AS5200 supports a maximum of 48 modems and the AS5300 supports 96. Countries with E1 service allow the AS5200 to support 60 modems and the AS5300 to support 120. ISDN service reduces these numbers by one for each digital leased line connected to the access server, but adds high speed ISDN support. This means the AS5200 can support 46 modems or ISDN connections with T1 service and 58 with E1 service. The AS5300 can support 94 connections with T1 service and 116 with E1 service.

The choice between T1 and E1 is (unfortunately) not yours. It has already been determined for you by the phone standards in your country. You must make sure you order the equipment to match the line your local phone company will provide or your access server will not work.

The AS5200 is scaleable and configurable to meet the needs of diverse corporate and ISP customers. The AS5200 is a three-slot access server, with one slot reserved for a channelized T1/PRI or E1/PRI card. The other two slots hold carrier cards for modem cards.

The AS5200 ships with two high-speed serial ports, one Ethernet port and standard console ports. There are three slots available for modems and channelized T1/E1 cards. It is powered by a 20 MHz Motorola 68030 microprocessor and ships with 4 MB boot flash, 8 MB system flash, 4 MB shared DRAM, and 8 MB Main DRAM memory. Boot flash memory is expandable to 8 MB while all others are expandable to 16 MB.

You can purchase a complete AS5200 one piece at a time or pre-bundled. When ordering piecemeal, have a sales engineer look over the configuration to be sure have not forgotten anything important. Bundles are purchased by connection type (T1 or E1) and number of modems. You will usually find it easier, and possibly cheaper, to order bundles.

The AS5200 supports IP, IBM, AppleTalk, DEC, and IPX protocols. It also supports the Desktop, Plus, Enterprise, and RMON feature sets. Not all possible combinations are available; so, check the latest documentation available to determine which feature sets you need.

The AS5300 is almost exactly like the AS5200, only denser. This is not to say that it is heavier (it is) but it more densely packs modem modules and leased line connection cards to hold more in the same space. Where the AS5200 has dual connection cards, the AS5300 as quad channelized T1 and E1 cards. This allows up to 120 analog or 116 ISDN connections from the local phone company.

The AS5300 ships with standard console ports and two Ethernet LAN ports: one 10BaseT and the other configurable as either 10 or 100BaseT. There are three slots available for modems and channelized T1/E1 cards. It is powered by a 150 MHz R4700 microprocessor and ships with 4 MB boot flash, 8 MB system flash, and 32 MB Main DRAM memory. Boot flash memory is expandable to 8 MB, system flash to 16 MB, and main DRAM to 64 MB.

The AS5300 supports IP, IBM, AppleTalk, DEC, and IPX protocols. It also supports the Desktop, Plus, Enterprise, and RMON feature sets. Not all possible combinations are available, so check the latest documentation to determine which feature sets you need.

The AS5800 is beyond the scope of this book. It is a Carrier-Class access server. Cisco calls it this because it is about the size of an aircraft carrier. In fact, the United States Navy is looking to add several to the North Atlantic Fleet. A New York City apartment costs less. Of course, it also has less room!

Many think that 56 Kbps modem connections rival the speed of a single 64 Kbps ISDN B-channel. Since both are measured in kilobits per second they seem only 8 Kbps apart. There appears to be little overall difference in speed, but looks are deceiving. The modem only seems one-eighth slower than an ISDN connection. However, you must also take into account asynchronous vs. synchronous communications protocols, and the real attainable speeds of 56 Kbps modems.

Asynchronous communications use start and stop bits to indicate where bytes begin and end. This adds two additional bits to each eight-bit byte; therefore, 10 bits are transmitted per byte of data. Synchronous communications use a clock outside of the data channel to indicate where bytes begin and end. Only 8 bits per byte are sent, making it 20% faster than asynchronous communications at the same data rate. So, a modem (which is asynchronous) operating at 56,000 bps is only able to send 44,800 bps of real data. The rest of its capacity is used for start and stop bits. So, in actuality, a 56 Kbps modem is only 70% as fast as an ISDN

B-channel.

This also assumes that you could get a 56,000 bps connection in the first place. Most dial-in users never see the full 56,000 bps due to line noise on their phones and distance from their house to the dial-in server. Most users see speeds of 52, 48, and 44 Kbps. Since ISDN lines are all digital lines specially conditioned to support data connections, you will always be able to get the full 64 Kbps every time.

Cisco routers rely on the idea of interfaces. The interface is the physical, virtual, or pseudo connection to the network. The easiest to understand is the physical interface because you can see and touch it. Virtual interfaces are a subset or superset of physical interfaces such as sub-interfaces or group interfaces. Pseudo interfaces do not relate to physical interfaces at all, but rather act like an interface in relation to the network.

Physical interfaces are very straightforward. Wherever you have a port on your router, you have a physical interface. There is a one-to-one correspondence between the interfaces on your router and the interface command lines in your router configuration. Cisco IOS automatically discovers all physical interfaces on your router and puts entries for them in the configuration. By default, they are added in an inactive state. You must make changes to the router configuration, either through the initial setup dialog, or by editing the configuration manually.

Each time you want to make changes to how a certain interface behaves, you need to edit the configuration. If you want all interfaces to express that behavior, you must configure each one separately.

There are three basic types of interfaces: LAN, WAN, and console. LAN interfaces are high-speed local connections and are available from 4 Mbps to 155 Mbps. WAN Interfaces are for connecting networks across greater distances and scale from 9.6 Kbps to 54 Mbps using leased lines and dial-up connections. Console ports are for local terminal users and router maintenance. The console port is strictly for local connections, but the auxiliary port, through an attached modem, can act as a WAN port.

Most LAN connections use well-known standards for cabling. WAN connections, on the other hand, have evolved over time. This means there is a larger requirement for backward compatibility. This is extremely important when choosing the cables you will need to make WAN connections.

Cisco offers a wide variety of WAN cables in their catalog. You must know what pieces of equipment are being cabled together as well as what ports they have before you can determine what cable to buy. While this sounds simplistic (even silly), you should not proceed otherwise. The first time Murphy’s Law catches you with piles of expensive equipment on hand and nothing works for lack of an inexpensive cable, you will remember these sage words of advice, bow you head in shame and cry out, "Why didn’t I listen to Paul?"

Authors Note: This has happened to me twice, much to my chagrin. Now I check everything before I place my purchase orders.

Most ISDN interfaces use RJ-45 connectors. The real exception is the channelized T1 and E1 / ISDN PRI cards for the Cisco 4000 series routers. Unlike the 3600 series and access servers, these cards do not have built-in CSUs. You make sure you get a cable to convert their DB-15 connector to whatever your external CSU needs (In the case of the Adtran T1 ESF CSU ACE, an RJ-45 port).

Exercise caution with serial ports as well. There are many types of serial ports and many types of connectors. Standard console, auxiliary, and low-speed serial ports typically use RJ-45 connectors. These use standard RJ-45 cables, but require RJ-45 to DB-9 or DB-25 connectors to allow you to attach them to PC’s, modems, and terminals. Usually you get one of each of these with every Cisco router. From them, you can determine the proper configuration of the cable and connector to make your serial device work. In dual-type serial cards with high speed and low speed serial connections, octopus cables are available with built-in connectors. Again, make sure to check what you will be attaching it to, as some low speed serial ports can be used synchronous or asynchronous. Synch devices usually use V.35 connectors and Async devices usually use EIA/TIA-232 DB-25 connectors.

High-speed serial ports can come with 50-pin large connectors or 60-pin high-density connectors. The only card that still uses the larger 50-pin connector is the NP-2T for the Cisco 4000 series. All others use the high-density 60-pin connector. Both terminate in X.21, V.35, EIA/TIA-232, EIA/TIA-449, and EIA/530 connectors. There is also usually a choice of male or female, and DCE or DTE.

In addition to the low speed and high-speed serial ports, Cisco offers a high-speed serial interface (HSSI) card for the 4000 series routers. This should not be confused with high speed serial ports, which have a maximum speed of 4 Mbps. HSSI ports are extremely fast, supporting speeds up to 54 Mbps. A HSSI card has a 50-pin high density SCSI (Small Computer Systems Interface) port for its data connection. If you are setting one up for the first time, ask questions of your T3/E3 CSU/DSU vendor and your Cisco sales engineer to make sure you get the right cables.

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