Adjusting Buffers

Excessively high bandwidth utilization over 70 results in reduced overall performance and can cause intermittent failures. For example, DECnet file transmissions might be failing due to packets being dropped somewhere in the network. If the situation is bad enough, you must increase the bandwidth of the link. However, increasing the bandwidth might not be necessary or immediately practical. One way to resolve marginal serial line overutilization problems is to control how the router uses data...

Apple Talk Connections to Services Drop

Symptom Users complain that their AppleTalk sessions suddenly drop for no apparent reason. Table 9-8 outlines the problem that might cause this symptom and describes solutions to that -problem. Table 9-8 AppleTalk Connections to Services Drop Table 9-8 AppleTalk Connections to Services Drop Excessive traffic load on internetworks with many routers can prevent some routers from sending RTMP updates every 10 seconds as they should. Because routers begin to age out routes after missing two...

Apple Talk Enhanced IGRP Clients Cannot Connect to Servers

Symptom Macintosh clients cannot connect to servers in an AppleTalk Enhanced IGRP network environment. Table 9-11 outlines the problems that might cause this symptom and describes solutions to those problems. Table 9-11 AppleTalk Enhanced IGRP Clients Cannot Connect to Servers Table 9-11 AppleTalk Enhanced IGRP Clients Cannot Connect to Servers Routers not establishing neighbors properly For information on troubleshooting this problem, see the section AppleTalk Enhanced IGRP Routers Not...

Apple Talk Enhanced IGRP Poor Performance

Symptom Network performance in an AppleTalk Enhanced IGRP environment is poor. Connections between clients and servers are slow or unreliable. Table 9-14 outlines the problems that might cause this symptom and describes solutions to those problems. Table 9-14 AppleTalk Enhanced IGRP Poor Performance AppleTalk Enhanced IGRP and RTMP are running simultaneously on the same interface Use the show running-config privileged exec command on network routers. Check the interface configurations to...

Apple Talk Enhanced IGRP Routers Not Establishing Neighbors

Symptom AppleTalk Enhanced IGRP routers do not establish neighbors properly. Routers that are connected do not appear in the neighbor table. Table 9-12 outlines the problems that might cause this symptom and describes solutions to those problems. Table 9-12 AppleTalk Enhanced IGRP Routers Not Establishing Neighbors Table 9-12 AppleTalk Enhanced IGRP Routers Not Establishing Neighbors AppleTalk Enhanced IGRP is not globally configured on the appropriate routers Step 1 Use the show running-config...

Apple Talk Enhanced IGRP Routes Missing from Routing Table

Symptom Routes are missing from the routing table of routers running AppleTalk Enhanced IGRP. Clients (Macintosh computers) on one network cannot access servers on a different network. Clients might or might not be able to connect to servers on the same network. The problem might occur in internetworks running only Enhanced IGRP or in an internetwork running Enhanced IGRP and RTMP. Table 9-13 outlines the problems that might cause this symptom and describes solutions to those problems. Table...

Apple Talk Interface Fails to Initialize Apple Talk

Symptom Router interface connected to a network will not initialize AppleTalk. Table 9-9 outlines the problems that might cause this symptom and describes solutions to those problems. Table 9-9 AppleTalk Interface Fails to Initialize AppleTalk Step 1 Use the show appletalk interface exec command. Check the output for a port configuration mismatch message. If the command output contains a mismatch message, the router configuration disagrees with that of the listed neighbor. If the command output...

Apple Talk Network Services Intermittently Unavailable

Symptom Network services are intermittently unavailable. Services come and go without warning. Table 9-6 outlines the problems that might cause this symptom and describes solutions to those problems. Table 9-6 AppleTalk Network Services Intermittently Unavailable Table 9-6 AppleTalk Network Services Intermittently Unavailable Duplicate network numbers or overlapping cable-range In AppleTalk, network numbers must be unique within an internetwork. If duplicate network numbers exist, packets might...

Apple Talk No Devices in Chooser

Symptom Zones appear in the Chooser, but when a service (such as AppleShare) and a zone are selected, no devices appear in the device list. Table 9-5 outlines the problem that might cause this symptom and describes solutions to that -problem. Table 9-5 AppleTalk No Devices in Choose Step 1 Use the show appletalk access-list exec command on routers in the path from source to destination. Step 2 Disable any access lists (or just those on a particularly suspect router) using the no appletalk...

Apple Talk Old Zone Names Appear in Chooser Phantom Zones

Symptom Old AppleTalk zone names continue to appear in the Chooser. Even after zone names are removed from the configuration, phantom zones continue to appear in the Chooser. Table 9-7 outlines the problems that might cause this symptom and describes solutions to those problems. Table 9-7 AppleTalk Old Zone Names Appear in Chooser (Phantom Zones) Table 9-7 AppleTalk Old Zone Names Appear in Chooser (Phantom Zones) Step 1 Use the show appletalk interface exec command. Check the output for a port...

Apple Talk Port Stuck in Restarting or Acquiring Mode

Symptom A router port is stuck in restarting or acquiring mode (as shown in the output of the show apple interface privileged exec command). The router cannot discover routes or poll neighbors on an attached cable. Table 9-10 outlines the problems that might cause this symptom and describes solutions to those problems. Table 9-10 AppleTalk Port Stuck in Restarting or Acquiring Mode Table 9-10 outlines the problems that might cause this symptom and describes solutions to those problems. Table...

Apple Talk Technology Basics

AppleTalk was designed as a client server distributed network system. In other words, users share network resources (such as files and printers) with other users. Computers supplying these network resources are called servers computers using a server's network resources are called clients. Interaction with servers is essentially transparent to the user because the computer itself determines the location of the requested material and accesses it without further information from the user. In...

Apple Talk Users Cannot Access Zones or Services

Symptom Users cannot access zones or services that appear in the Chooser. Users might or might not be able to access services on their own network. Table 9-2 outlines the problems that might cause this symptom and describes solutions to those problems. Table 9-2 AppleTalk Users Cannot Access Zones or Services Table 9-2 AppleTalk Users Cannot Access Zones or Services Step 1 Use the show appletalk interface exec command. Check the output for a port configuration mismatch message. If the command...

Apple Talk Zones Missing from Chooser

Symptom Certain zones do not appear in the Chooser. The zones are not visible from multiple networks. In some cases, when the Chooser is opened, the zone list changes. Table 9-4 outlines the problems that might cause this symptom and describes solutions to those problems. Table 9-4 AppleTalk Zones Missing from Chooser Step 1 Use the show appletalk interface exec command. Check the output for a port configuration mismatch message. If the command output contains a mismatch message, the router...

Ara Ara Client Unable to Connect to ARA Server

Symptom An ARA client (such as a Macintosh) attempts to connect to an ARA server (such as a Cisco access server) and cannot initiate a remote session. The user might be able to connect briefly, but the connection is immediately terminated. Table 9-18 outlines the problems that might cause this symptom and describes solutions to those problems. Table 9-18 ARA ARA Client Unable to Connect to ARA Server Table 9-18 ARA ARA Client Unable to Connect to ARA Server Step 1 Use the show running-config...

ARA Cannot Send or Receive Data over ARA Dialin Connection

Symptom ARA connections are established, but users cannot send or receive ARA data over the link. Table 9-20 outlines the problems that might cause this symptom and describes solutions to those problems. Table 9-20 ARA Cannot Send or Receive Data over ARA Dialin Connection Table 9-20 ARA Cannot Send or Receive Data over ARA Dialin Connection Step 1 Use the show running-config privileged exec command to view the router configuration. If you are running Cisco IOS Release 10.2 or later, look for...

ARA Connection Hangs After Communicating At Message

Symptom An ARA client (for example, a Macintosh) tries to connect to an ARA server (such as a Cisco access server) over client and server modems. The client receives a connect message such as Communicating at 14.4 Kbps but then hangs for 10-30 seconds and finally shows a connection failed message. Table 9-19 outlines the problem that might cause this symptom and describes solutions to that problem. Table 9-19 ARA Connection Hangs After Communicating At Message Table 9-19 ARA Connection Hangs...

ARA Slow Performance from Dialin Connection

Symptom Performance on remote dialin ARA sessions is slow. Table 9-21 outlines the problem that might cause this symptom and describes solutions to that problem. Table 9-21 ARA Slow Performance from Dialin Connection Table 9-21 ARA Slow Performance from Dialin Connection Flow control is not enabled, is enabled only on one device (either DTE or DCE), or is misconfigured Step 1 Configure hardware flow control on the line using the flowcontrol hardware line configuration command. Hardware flow...

Arp

ARP entities are classified as either address resolution clients or address resolution services. Address resolution clients are usually implemented in client nodes, whereas address resolution services are typically provided by service nodes. An ARP packet has an 8-byte header consisting of a 2-byte packet type, a 4-byte network number, and a 2-byte subnetwork number. There are four packet types a query request, which is a request for an ARP service a service response, which is a response to a...

Atp

ATP is suitable for transaction-based applications such as those found in banks or retail stores. ATP transactions consist of requests (from clients) and replies (from servers). Each request reply pair has a particular transaction ID. Transactions occur between two socket clients. ATP uses exactly once (XO) and at-least-once (ALO) transactions. XO transactions are used in situations where performing the transaction more than once would be unacceptable. Banking transactions are examples of...

Aurp

AURP allows a network administrator to connect two or more AppleTalk internetworks through a foreign network (such as Transmission Control Protocol Internet Protocol TCP IP ) to form an AppleTalk wide-area network (WAN). The connection is called a tunnel, which functions as a single, virtual data link between the AppleTalk internetworks, as shown in Figure 9-6. A router that connects an AppleTalk internetwork to a tunnel (that is, a router that runs AURP) is called an exterior router. The...

AURP Routes Not Propagated Through AURP Tunnel

Symptom AppleTalk routes are not propagated through an AURP tunnel. Routes that are known to exist on one side of the tunnel do not appear in the routing tables of the exterior router on the other side of the tunnel. Changes on the remote network (such as a route going down) are not learned by the exterior router on the other side of the tunnel. Table 9-16 outlines the problems that might cause this symptom and describes solutions to those problems. Table 9-16 AURP Routes Not Propagated Through...

BGP Routers Not Advertising Routes

Symptom BGP routers are not advertising routes. Routing updates from a BGP router do not contain information about certain network destinations that should be advertised. Table 7-17 outlines the problems that might cause this symptom and describes solutions to those problems. Table 7-17 BGP Routers Not Advertising Routes Table 7-17 BGP Routers Not Advertising Routes Missing network router configuration command Step 1 Use the show running-config privileged exec command to view the router...

BGP Routes Missing from Routing Table

Symptom BGP routers and networks are not advertised to other routers. Routers do not receive routing information from other routers. Some hosts cannot communicate with hosts in other areas, and routing table information is incomplete. Table 7-16 outlines the problems that might cause this symptom and describes solutions to those problems. Table 7-16 BGP Routes Missing from Routing Table Table 7-16 BGP Routes Missing from Routing Table If BGP routers are not advertising routes properly, routing...

Breakout Boxes Fox Boxes and BERTsBLERTs

Breakout boxes, fox boxes, and bit block error rate testers (BERTs BLERTs) are digital interface testing tools used to measure the digital signals present at PCs, printers, modems, the channel service unit digital service unit (CSU DSU), and other peripheral interfaces. These devices can monitor data line conditions, analyze and trap data, and diagnose problems common to data communication systems. Traffic from data terminal equipment (DTE) through data communications equipment (DCE) can be...

Cddi

The high cost of fiber-optic cable has been a major impediment to the widespread deployment of FDDI to desktop computers. At the same time, shielded twisted-pair (STP) and unshielded twisted-pair (UTP) copper wire is relatively inexpensive and has been widely deployed. The implementation of FDDI over copper wire is known as Copper Distributed Data Interface (CDDI). Before FDDI could be implemented over copper wire, a problem had to be solved. When signals strong enough to be reliably...

Cisco Connection Documentation Cdrom Help

Cisco Connection Documentation CD-ROM provides two forms of online help Verity Mosaic Help - provides help with the Verity Mosaic product. Refer to this help facility to find out about viewing and printing documents and configuring the Verity Mosaic product. This help facility is accessed by clicking on the icon in the toolbar. Cisco Connection Documentation CD-ROM Help - provides help with the unique features and enhancements to Verity Mosaic. Refer to this help facility to find out about...

Cisco Product Documentation

Installation and configuration guides, switch software guides, configuration notes, and more. CDDI FDDI Adapters and Concentrators (Catalyst 1200 thru 6000 Series, Ethernet Switches) (LightStream, Catalyst 8510 MSR & 8540 MSR) (Access Gateways, CallManager, IP Phones) Access Servers and Access Routers Core High-End Routers (Cisco AGS+, Cisco 7x00 series routers, Cisco 1x000 series routers, Cisco Optical Regenerator, Cisco Optical Network System products) 10BaseT Hubs Internet Services...

Cisco Works Internetwork Management Software

CiscoWorks is a series of SNMP-based internetwork management software applications. CiscoWorks applications are integrated on several popular network management platforms and build on industry-standard platforms to provide applications for monitoring device status, maintaining configurations, and troubleshooting problems. Following are some of the applications included in the CiscoWorks product that are useful for troubleshooting your internetwork Device Monitor---Allows the network manager to...

Clocking Overview

The CSU DSU derives the data clock from the data that passes through it. In order to recover the clock, the CSU DSU hardware must receive at least one 1-bit value for every 8 bits of data that pass through it this is known as ones density. Maintaining ones density allows the hardware to recover the data clock reliably. Newer T1 implementations commonly use Extended Superframe Format (ESF) framing with binary eight-zero substitution (B8ZS) coding. B8ZS provides a scheme by which a special code...

Data Command Frames

Data command frames vary in size, depending on the size of the information field. Data frames carry information for upper-layer protocols command frames contain control information and have no data for upper-layer protocols. In data command frames, a frame control byte follows the access control byte. The frame control byte indicates whether the frame contains data or control information. In control frames, this byte specifies the type of control Troubleshooting Token Ring information....

Datagram Delivery Protocol

AppleTalk's primary network-layer protocol is the Datagram Delivery Protocol (DDP). DDP provides connectionless service between network sockets. Sockets can be assigned either statically or dynamically. AppleTalk addresses, which are administered by the DDP, consist of two components a 16-bit network number and an 8-bit node number. The two components are usually written as decimal numbers, separated by a period (for example, 10.1 means network 10, node 1). When an 8-bit socket identifying a...

Detecting Clocking Problems

To detect clocking conflicts on a serial interface, look for input errors as follows Step 1 Use the show interfaces serial exec command on the routers at both ends of the link. Step 2 Examine the command output for CRC, framing errors, and aborts. Step 3 If either of these steps indicates errors exceeding an approximate range of 0.5 to 2.0 of traffic on the interface, clocking problems are likely to exist somewhere in the WAN. Step 4 Isolate the source of the clocking conflicts as outlined in...

Digital Network Architecture

Contrary to popular belief, DECnet is not a network architecture at all but is, rather, a series of products conforming to Digital's Digital Network Architecture (DNA). Like most comprehensive network architectures from large systems vendors, DNA supports a large set of both proprietary and standard protocols. The list of DNA-supported technologies grows constantly as Digital implements new protocols. Figure 11-1 illustrates an incomplete snapshot of DNA and the relationship of some of its...

Document Button

You click on the document button bar, which is displayed at the top and bottom of all documents, to navigate through Cisco Connection Documentation CD-ROM relative to the document that is currently being viewed. The Cisco Connection Documentation CD-ROM Home button takes you to the home page for Cisco Connection Documentation CD-ROM (the first page displayed when you launch Cisco Connection Documentation CD-ROM). The Table of Contents button displays the table of contents that contains a...

Fault Management Mechanisms

Token Ring networks employ several mechanisms for detecting and compensating for network faults. For example, one station in the Token Ring network is selected to be the active monitor. This station, which can potentially be any station on the network, acts as a centralized source of timing information for other ring stations and performs a variety of ring maintenance functions. One of these functions is the removal of continuously circulating frames from the ring. When a sending device fails,...

FDDITalk No Zone Associated with Routes

Symptom Routers on an FDDI ring have routes to networks across the ring, but no zones are associated with the routes. The output of the show appletalk route command indicates no zone set for those routes. Note On other media, routes with no zone set are the result of other problems, such as ZIP storms. See the sections AppleTalk Zones Missing from Chooser and AppleTalk Network Services Intermittently Unavailable in this chapter for more information. Table 9-17 outlines the problem that might...

Frame Format

FDDI frame formats (shown in Figure 5-7) are similar to those of Token Ring. Figure 5-7 FDDI Frame Format The fields of an FDDI frame are as follows Preamble Prepares each station for the upcoming frame. Start delimiter Indicates the beginning of the frame. It consists of signaling patterns that differentiate it from the rest of the frame. Frame control Indicates the size of the address fields, whether the frame contains asynchronous or synchronous data, and other control information....

General Problem Solving Model

When you're troubleshooting a network environment, a systematic approach works best. Define the specific symptoms, identify all potential problems that could be causing the symptoms, and then systematically eliminate each potential problem (from most likely to least likely) until the symptoms disappear. Figure 1-1 illustrates the process flow for the general problem-solving model. This process flow is not a rigid outline for troubleshooting an internetwork it is a foundation from which you can...

DiCK I

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Icmp

ICMP performs a number of tasks within an IP internetwork. The principal reason it was created was for reporting routing failures back to the source. In addition, ICMP provides helpful messages such as the following Echo and reply messages to test node reachability across an internetwork Redirect messages to stimulate more efficient routing Time exceeded messages to inform sources that a datagram has exceeded its allocated time to exist within the internetwork Router advertisement and router...

Icp

ICP defines exception notification and metric notification packets. Exception notification packets provide information about network-layer exceptions metric notification packets contain information about the final transmission used to reach a client node. Exception notifications are sent when a VIP packet cannot be routed properly, and the error subfield in the VIP header's transport control field is enabled. These packets also contain a field identifying the particular exception by its error...

Implementing Hold Queue Limits

Hold queues are buffers used by each router interface to store outgoing or incoming packets. Use the hold-queue interface configuration command to increase the number of data packets queued before the router will drop packets. Increase these queues by small increments (for instance, 25 ) until you no longer see drops in the show interfaces output. The default output hold queue limit is 100 packets. Note The hold-queue command is used for process-switched packets and periodic updates generated...

Internet Group Membership Protocol

Internet Group Membership Protocol (IGMP), defined in RFC 1112, relies on Class D IP addresses for the creation of multicast groups. By using a specific Class D address, an individual host dynamically registers itself in a multicast group. Hosts identify their group memberships by sending IGMP messages. Traffic is then sent to all members of that multicast group. Routers listen to IGMP messages and periodically send out queries to discover which groups are active on which LANs. To build...

Internet Protocols

Internet protocols can be used to communicate across any set of interconnected networks. They are equally well suited for local-area network (LAN) and wide-area network (WAN) communications. The Internet suite includes not only lower-layer specifications (such as TCP and IP), but also specifications for such common applications as mail, terminal emulation, and file transfer. Figure 7-1 shows some of the most important Internet protocols and their relationships to the OSI reference model. Figure...

Internet Routing

Routing devices in the Internet have traditionally been called gateways---an unfortunate term because elsewhere in the industry, the term gateway applies to a device with somewhat different functionality. Gateways (which we will call routers from this point on) within the Internet are organized hierarchically. Some routers are used to move information through one particular group of networks under the same administrative authority and control (such an entity is called an autonomous system)....

Internetwork Design Guide

Internetworking Design Basics Designing Large-Scale IP Internetworks Designing SRB Internetworks Designing SDLC, SDLLC, and QLLC Internetworks Designing APPN Internetworks Designing DLSw+ Internetworks Designing ATM Internetworks Designing Packet Service Internetworks Designing DDR Internetworks Designing ISDN Internetworks Designing Switched LAN Internetworks Designing Internetworks for Multimedia Appendix A Subnetting an IP Address Space Appendix B IBM Serial Link Implementation Notes...

Internetwork Troubleshooting Guide

Troubleshooting Hardware and Booting Problems Troubleshooting Fiber Distributed Data Interface Troubleshooting Serial Line Problems Troubleshooting Dialin Connections Troubleshooting ISDN Connections Troubleshooting Frame Relay Connections Troubleshooting X.25 Connections Troubleshooting Transparent Bridging Environments Troubleshooting ATM Switching Environments Troubleshooting LAN Switching Environments Troubleshooting CiscoWorks Problems Troubleshooting Security Implementations Technical...

Internetworking Case Studies

RIP and OSPF Redistribution Increasing Security on IP Networks Integrating Enhanced IGRP into Existing Networks Reducing SAP Traffic in Novell IPX Networks STUN for Front-End Processors Using ISDN Effectively in Multiprotocol Networks Using HSRP for Fault-Tolerant IP Routing Multicasting in IP and AppleTalk Networks Scaling Dial-on-Demand Routing Using the Border Gateway Protocol for Interdomain Routing HOME CONTENTS PREVIOUS NEXT GLOSSARY FEEDBACK SEARCH Copyright 1989-2000 Cisco Systems Inc.

Internetworking Terms and Acronyms

Cisco Systems Terms and Acronyms Copyright 1989-2000 Cisco Systems Inc. Cisco - Feedback Content-Type text html Cisco - Feedback Content-Type text html Did this (or your previous) CCO visit save you a call to Cisco Your feedback is vital to our goal of making CCO the most useful and informative website on the planet. Please let us know how we are doing and, more importantly, what we can improve. CCO's breadth of information & services CCO's perceived speed or responsiveness Overall...

IP Enhanced IGRP Router Stuck in Active Mode

Symptom An IP Enhanced IGRP router is stuck in Active mode. Multiple Stuck-in-Active messages are sent to the console DUAL-3-SIA Route 198.169.52.51 Stuck-in-Active For a more detailed explanation of Enhanced IGRP Active mode, see the section Enhanced IGRP and Active Passive Modes later in this chapter. Note Occasional messages of this type are not a cause for concern. This is how an Enhanced IGRP router recovers if it does not receive replies to its queries from all its neighbors. However, if...

IP Enhanced IGRP Routers Not Establishing Neighbors

Symptom Enhanced IGRP routers are not establishing neighbor relationships properly. Routing information is not distributed to routers. Table 7-13 outlines the problems that might cause this symptom and describes solutions to those problems. Table 7-13 IP Enhanced IGRP Routers Not Establishing Neighbors Table 7-13 IP Enhanced IGRP Routers Not Establishing Neighbors Misconfigured or missing network router configuration command Step 1 Use the show ip eigrp neighbors exec command on an Enhanced...

IP Multicast

The Internet Protocol suite was designed for communications between two computers using unicast addresses (that is, an address specifying a single network device). To send a message to all devices connected to the network, a single network device uses a broadcast address. These two forms of addressing have until now been sufficient for transferring traditional data (such as files and virtual terminal connections). Now that application developers are trying to deliver the same data (such as the...

IPX Enhanced IGRP No Connectivity over IPX Enhanced IGRP Router

Symptom IPX Enhanced IGRP routers are blocking connections. Clients cannot connect to servers over one or more routers running IPX Enhanced IGRP. Note Procedures for troubleshooting connectivity problems not specific to IPX Enhanced IGRP routing are described in the section Novell IPX Client Cannot Connect to Server on Remote LAN earlier in this chapter. Table 8-8 outlines the problems that might cause this symptom and describes solutions to those problems. Table 8-8 IPX Enhanced IGRP No...

IPX Enhanced IGRP Routers Not Establishing Neighbors

Symptom IPX Enhanced IGRP routers do not establish neighbors properly. Routers that are known to be connected do not appear in the neighbor table. Note Procedures for troubleshooting IPX Enhanced IGRP problems not specific to establishing neighbors are described in the section 'IPX Enhanced IGRP No Connectivity over IPX Enhanced IGRP Router earlier in this chapter. Table 8-9 outlines the problems that might cause this symptom and describes solutions to those problems. Table 8-9 IPX Enhanced...

Irdp

The ICMP Router Discovery Protocol (IRDP) uses router advertisement and router solicitation messages to discover addresses of routers on directly attached subnets. The way IRDP works is that each router periodically multicasts router advertisement messages from each of its interfaces. Hosts discover the addresses of routers on the directly attached subnet by listening for these messages. Hosts can use router solicitation messages to request immediate advertisements, rather than wait for...

Isolating Clocking Problems

After you determine that clocking conflicts are the most likely cause of input errors, use the following procedure will help you isolate the source of those errors Step 1 Perform a series of ping tests and loopback tests (both local and remote), as described in the section CSU and DSU Loopback Tests earlier in this chapter. Step 2 Determine which end of the connection is the source of the problem, or whether the problem is in the line. In local loopback mode, run different patterns and sizes in...

Local SRB Host Cannot Connect to Server

Symptom Connections fail over a router configured as an SRB connecting two or more Token Rings. Table 10-1 outlines the problems that might cause this symptom and describes solutions to those problems. Table 10-1 Local SRB Host Cannot Connect to Server Table 10-1 Local SRB Host Cannot Connect to Server A router interface configured for bridging fails to insert into a ring when it detects a ring number mismatch, and posts an error message to the console. Step 1 Get the ring number (specified in...

Local SRB Routing Does Not Function

Symptom Routed protocols are not forwarded properly by routers in a local SRB environment. SRBs bridge traffic normally. Table 10-2 outlines the problems that might cause this symptom and describes solutions to those problems. Table 10-2 Local SRB Routing Does Not Function Table 10-2 Local SRB Routing Does Not Function For detailed information on troubleshooting routing problems, refer to the chapters in this book that cover the routing protocols in question. For example, if you are running...

Media Access

NetWare runs on Ethernet IEEE 802.3, Token Ring IEEE 802.5, Fiber Distributed Data Interface (FDDI), and ARCnet. NetWare also works over synchronous wide-area network (WAN) links using the Point-to-Point Protocol (PPP). Attached Resource Computer Network (ARCnet) is a simple network system that supports all three primary cable types (twisted-pair, coaxial, and fiber-optic) and two topologies (bus and star). It was developed by Datapoint Corporation and introduced in 1977. Although ARCnet has...

Media Problems Token Ring

Table 6-1 outlines problems commonly encountered on Token Ring networks and offers general guidelines for solving those problems. Table 6-1 Media Problems Token Ring Table 6-1 Media Problems Token Ring Step 1 Use the show interfaces token command to determine the status of the router's Token Ring interfaces. Step 2 If the status line indicates that the interface and line protocol are not up, check the cable from the router to the MAU.1 Make sure that the cable is in good condition. If it is...

Navigating Cisco Connection Documentation CDROM

Cisco Connection Documentation CD-ROM is a series of interconnected documents that you navigate by clicking on hypertext links and using the navigation tools---the toolbar, the navigation bar, and the document button bar. In addition, Cisco Connection Documentation CD-ROM offers a powerful search facility to allow you to jump directly to the information that interests you. Cisco Connection Documentation CD-ROM also provides several ways to return to documents that you have previously looked at....

Network Entities

AppleTalk identifies several network entities. The most elemental is a node, which is simply any device connected to an AppleTalk network. The most common nodes are Macintosh computers and laser printers, but many other types of computers are also capable of AppleTalk communication, including IBM PCs, Digital Equipment Corporation VAX computers, and a variety of workstations. The next entity defined by AppleTalk is the network. An AppleTalk network is simply a single logical cable. Although the...

Network Monitors

Network monitors continuously track packets crossing a network, providing an accurate picture of network activity at any moment, or a historical record of network activity over a period of time. They do not decode the contents of frames. Monitors are useful for baselining, in which the activity on a network is sampled over a period of time to establish a normal performance profile, or baseline. Monitors collect information such as packet sizes, the number of packets, error packets, overall...

Novell IPX Client Cannot Connect to Server on Remote LAN

Symptom Clients cannot make connections to servers on another network over one or more routers interconnected by LAN networks. Clients can connect to servers on their local network. Table 8-2 outlines the problems that might cause this symptom and describes solutions to those problems. Note If clients cannot connect to servers on their local network, refer to the section Novell IPX Client Cannot Connect to Server on Same LAN earlier in this chapter. If there is a WAN network between the local...

Novell IPX Client Cannot Connect to Server on Same LAN

Symptom Clients cannot make connections to servers located on the same LAN. Also, clients cannot connect to servers on remote networks. Table 8-1 outlines the problems that might cause this symptom and describes solutions to those problems. Table 8-1 Novell IPX Client Cannot Connect to Server on Same LAN Table 8-1 Novell IPX Client Cannot Connect to Server on Same LAN Step 1 Make sure the software on both clients and servers is the current version, is configured correctly, and has loaded...

Novell IPX Client Cannot Connect to Server over ISDN

Symptom Clients cannot connect to servers over an ISDN link. Clients can connect to local servers. Note Procedures for troubleshooting connectivity problems not specific to ISDN environments are described in the section Novell IPX Client Cannot Connect to Server on Remote LAN earlier in this chapter. Procedures for troubleshooting ISDN connectivity problems not specific to IPX environments are described in Chapter 17, Troubleshooting ISDN Connections. Table 8-4 outlines the problems that might...

Novell IPX Clients Cannot Connect to Server over PSN

Symptom Clients cannot connect to servers over a packet-switched network (PSN), such as Frame Relay, X.25, or SMDS. Clients can connect to local servers. Note Procedures for troubleshooting connectivity problems not specific to PSN environments are described in the section Novell IPX Client Cannot Connect to Server on Remote LAN earlier in this chapter. Table 8-3 outlines the problems that might cause this symptom and describes solutions to those problems. Table 8-3 Novell IPX Client Cannot...

Novell IPX Intermittent Connectivity

Symptom Connectivity between clients and servers is intermittent. Clients might be able to connect some of the time, but at other times no connectivity to certain servers or networks is possible. Table 8-12 outlines the problems that might cause this symptom and describes solutions to those problems. Table 8-lZ Novell IPX Intermittent Connectivity Table 8-lZ Novell IPX Intermittent Connectivity Step 1 Use the show running-config privileged exec command to view the router configuration. Look for...

Novell IPX Slow Performance

Symptom Slow network performance is experienced in a Novell IPX network. Table 8-13 outlines the problems that might cause this symptom and describes solutions to those problems. Table 8-lS Novell IPX Slow Performance Table 8-lS Novell IPX Slow Performance Novell servers not processing SAP updates as quickly as router is generating them Step 1 Use the show interfaces privileged exec command to check for output drops. Step 2 If there are excessive drops, use the show ipx servers exec command on...

Novell NetBIOS Applications Cannot Connect to Server over Router

Symptom Applications that use Novell NetBIOS (such as Windows 95) cannot connect to servers over a router. Clients cannot connect to servers on the same LAN. Table 8-5 outlines the problems that might cause this symptom and describes solutions to those problems. Table 8-5 Novell NetBIOS Applications Cannot Connect to Server over Router Table 8-5 Novell NetBIOS Applications Cannot Connect to Server over Router Missing ipx type-20-propagation commands Step 1 Use the debug ipx packet privileged...

Novell Technology Basics

As an NOS environment, NetWare specifies the upper five layers of the OSI reference model. It provides file and printer sharing, support for various applications, such as electronic mail transfer and database access, and other services. Like other NOSs, such as the Network File System (NFS) from Sun Microsystems, Inc., and LAN Manager from Microsoft Corporation, NetWare is based on a client server architecture. In such architectures, clients (sometimes called workstations) request certain...

OSPF Routers Not Establishing Neighbors

Symptom OSPF routers are not establishing neighbor relationships properly. The result is that routing information is not exchanged between routers. Table 7-11 outlines the problems that might cause this symptom and describes solutions to those problems. Table 7-11 OSPF Routers Not Establishing Neighbors Table 7-11 OSPF Routers Not Establishing Neighbors Step 1 Use the show ip ospf interfaces exec command to determine which interfaces have OSPF1 enabled. Step 2 If the output indicates that an...

Physical Connections

FDDI specifies the use of dual rings. Traffic on these rings travels in opposite directions. Physically, the rings consist of two or more point-to-point connections between adjacent stations. One of the two FDDI rings is called the primary ring, the other is called the secondary ring. The primary ring is used for data transmission, and the secondary ring is generally used as a backup. Class B or single-attachment stations (SASs) attach to one ring Class A or dual-attachment stations (DASs)...

Preparing for Network Failure

It is always easier to recover from a network failure if you are prepared ahead of time. Possibly the most important requirement in any network environment is to have current and accurate information about that network available to the network support personnel at all times. Only with complete information can intelligent decisions be made about network change, and only with complete information can troubleshooting be done as quickly and easily as possible. During the process of troubleshooting...

Protocol Address Assignment

To ensure minimal network administrator overhead, AppleTalk node addresses are assigned dynamically. When a Macintosh running AppleTalk starts up, it chooses a protocol (network-layer) address and checks whether that address is currently in use. If it is not, the new node has successfully assigned itself an address. If the address is currently in use, the node with the conflicting address sends a message indicating a problem, and the new node chooses another address and repeats the process....

RSRB Host Cannot Connect to Server Peers Not Open

Symptom Hosts cannot make connections to servers across a router configured as a remote source-routing bridge (RSRB). The output of the show source-bridge privileged exec command shows that SRB peers are not open. Note If you succeed in getting peers to open but hosts are still unable to communicate with servers, refer to the section RSRB Host Cannot Connect to Server (Peers Open) later in this chapter. Table 10-3 outlines the problems that might cause this symptom and describes solutions to...

RSRB Host Cannot Connect to Server Peers Open

Symptom Hosts cannot make connections to servers across a router configured as an RSRB. The output of the show source-bridge privileged exec command shows that SRB peers are open. The following is an example of output from the show source-bridge command Peers state lv pkts_rx pkts_tx expl_gn drops TCP TCP 150.136.93.93 open 2* 18 18 3 0 0 Table 10-4 outlines the problems that might cause this symptom and describes solutions to those problems. Table 10-4 RSRB Host Cannot Connect to Server (Peers...

RSRB NetBIOS Client Cannot Connect to Server

Symptom NetBIOS clients cannot connect to NetBIOS servers over a router configured as an RSRB. Table 10-6 outlines the problems that might cause this symptom and describes solutions to those problems. Table 10-6 RSRB NetBIOS Client Cannot Connect to Server Table 10-6 RSRB NetBIOS Client Cannot Connect to Server Step 1 For each router on which NetBIOS name caching is enabled, use the show rif exec command to determine whether the RIF entry shows the correct path from the router to both the...

RSRB Periodic Communication Failures

Symptom Communication failures occur periodically over a router configured as an RSRB. Table 10-6 outlines the problems that might cause this symptom and describes solutions to those problems. Table 10-5 RSRB Periodic Communication Failures Table 10-5 RSRB Periodic Communication Failures If you are not using local acknowledgment, misconfigured T1 timers can cause periodic timeouts. Step 1 Use a network analyzer to see how long it takes for packets to travel from one end of the network to the...

Rtmp

AppleTalk's NBP associates AppleTalk names (expressed as network-visible entities, or NVEs) with addresses. An NVE is an AppleTalk network-addressable service, such as a socket. NVEs are associated with one or more entity names and attribute lists. Entity names are character strings such as printer net1, whereas attribute lists specify NVE characteristics. Named NVEs are associated with network addresses through the process of name binding. Name binding can be done when the user node is first...

Rtp

RTP distributes network topology information. Routing update packets are broadcast periodically by both client and service nodes. These packets inform neighbors of a node's existence and indicate whether the node is a client or a service node. Service nodes also include, in each routing update packet, a list of all known networks and the cost factors associated with reaching those -networks. Two routing tables are maintained a table of all known networks and a table of neighbors. For service...

Sample Display

The following is sample output from the show interfaces tokenring command Router show interfaces tokenring TokenRing 0 is up, line protocol is up Hardware is 16 4 Token Ring, address is 5500.2000.dc27 (bia 0000.3000.072b) Internet address is 150.136.230.203, subnet mask is 255.255.255.0 MTU 8136 bytes, BW 16000 Kbit, DLY 630 usec, rely 255 255, load 1 255 Encapsulation SNAP, loopback not set, keepalive set (10 sec) ARP type SNAP, ARP Timeout 4 00 00 Ring speed 16 Mbps Single ring node, Source...

SDLC Router Cannot Communicate with SDLC Device

Symptom Router cannot communicate with an IBM SDLC device. Table 10-9 outlines the problems that might cause this symptom and describes solutions to those problems. Table 10-9 SDLC Router Cannot Communicate with SDLC Device Table 10-9 SDLC Router Cannot Communicate with SDLC Device Step 1 Use the show interfaces exec command to determine whether the interface and line protocol are up. Step 2 If the interface and line protocol are both up, troubleshoot link-layer problems as described later in...

Serial Lines Increasing Carrier Transitions Count on Serial Link

Carrier transitions appear in the output of the show interfaces serial exec command whenever there is an interruption in the carrier signal (such as an interface reset at the remote end of a link). Symptom Increasing carrier transitions count on serial link. Table 15-7 outlines the possible problems that might cause this symptom and describes solutions to those problems. Table 15-7 Serial Lines Increasing Carrier Transitions Count on Serial Link The following problems can result in this symptom...

Serial Lines Increasing Input Drops on Serial Link

Input drops appear in the output of the show interfaces serial exec command (refer to Figure 15-1) when too many packets from that interface are still being processed in the system. Symptom Increasing number of input drops on serial link. Table 15-3 outlines the possible problem that might cause this symptom and describes solutions to that problem. Table 15-3 Serial Lines Increasing Input Drops on Serial Link Table 15-3 Serial Lines Increasing Input Drops on Serial Link Input rate exceeds the...

Serial Lines Increasing Input Errors in Excess of 1 of Total Interface Traffic

If input errors appear in the show interfaces serial output (refer to Figure 15-1), there are several possible sources of those errors. The most likely sources are summarized in Table 15-4. Note Any input error value for cyclic redundancy check (CRC) errors, framing errors, or aborts above 1 percent of the total interface traffic suggests some kind of link problem that should be isolated and repaired. Symptom Increasing number of input errors in excess of 1 percent of total interface traffic....

Serial Lines Increasing Interface Resets on Serial Link

Interface resets that appear in the output of the show interfaces serial exec command (see Figure 15-1) are the result of missed keepalive packets. Symptom Increasing interface resets on serial link. Table 15-6 outlines the possible problems that might cause this symptom and describes solutions to those problems. Table 15-6 Serial Lines Increasing Interface Resets on Serial Link The following problems can result in this symptom Congestion on link (typically associated with output drops) Bad...

Serial Lines Increasing Output Drops on Serial Link

Output drops appear in the output of the show interfaces serial command (refer to Figure 15-1) when the system is attempting to hand off a packet to a transmit buffer but no buffers are available. Symptom Increasing output drops on serial link. Table 15-2 outlines the possible problem that might cause this symptom and describes solutions to that problem. Table 15-2 Serial Lines Increasing Output Drops on Serial Link Table 15-2 Serial Lines Increasing Output Drops on Serial Link Input rate to...

Serial Lines Troubleshooting Serial Line Input Errors

Table 15-5 describes the various types of input errors displayed by the show interfaces serial command (see Figure 15-1), possible problems that might be causing the errors, and solutions to those problems. Table 15-5 Serial Lines Troubleshooting Serial Line Input Errors Table 15-5 Serial Lines Troubleshooting Serial Line Input Errors CRC errors occur when the CRC calculation does not pass (indicating that data is corrupted) for one of the following reasons Serial cable is too long or cable...

Show interfaces tokenring

When troubleshooting Token Ring media in a Cisco router environment, you can use the show interfaces tokenring command to provide several key fields of information that can assist in isolating problems. This section provides a detailed description of the show interfaces tokenring command and the information it provides in Table 6-2. Use the show interfaces tokenring privileged exec command to display information about the Token Ring interface and the state of source route bridging show...

SRB Algorithm

SRBs are so named because they assume that the complete source-to-destination route is placed in all inter-LAN frames sent by the source. SRBs store and forward the frames as indicated by the route appearing in the appropriate frame field. Figure 10-3 illustrates a sample SRB network. Referring to Figure 10-3, assume that Host X wishes to send a frame to Host Y. Initially, Host X does not know whether Host Y resides on the same or a different LAN. To determine this, Host X sends out a test...

SRT Bridging Client Cannot Connect to Server

Symptom Clients cannot communicate over a router configured to perform SRT bridging. Packets are not forwarded by the SRT bridge. Note SRT bridging allows you to implement transparent bridging in Token Ring environments. It is not a means of translating between SRB on a Token Ring and transparent bridging on Ethernet (or other) media. Table 10-8 outlines the problems that might cause this symptom and describes solutions to those problems. Table 10-8 SRT Bridging Client Cannot Connect to Server...

Subnet Broadcast

Subnet broadcast (defined in RFC 922) supports the sending of packets to all the subnets of a particular network number. Packet duplication occurs when there are alternative paths in a network. In Figure 7-10, when Workstation A uses subnet broadcasting to send a packet to each workstation on Subnetwork 2, a duplicate packet also arrives. Whenever there is a duplicate path in the network, a duplicate packet is delivered. Because many multicast applications are data intense, packet duplication...

Symptoms Problems and Solutions

Failures in internetworks are characterized by certain symptoms. These symptoms might be general (such as clients being unable to access specific servers) or more specific (routes not in routing table). Each symptom can be traced to one or more problems or causes by using specific troubleshooting tools and techniques. Once identified, each problem can be remedied by implementing a solution consisting of a series of actions. This book describes how to define symptoms, identify problems, and...

Syntax Description

unit---Must match the interface port line number. accounting---(Optional) Displays the number of packets of each protocol type that have been sent through the interface. slot Refers to the appropriate hardware manual for slot and port information. port Refers to the appropriate hardware manual for slot and port information. port-adapter---Refers to the appropriate hardware manual for information about port adapter compatibility. Command Mode This command first appeared in Cisco IOS Release...

Table of Contents

Cisco Connection Documentation CD-ROM Help What is Cisco Connection Documentation CD-ROM Cisco Connection Documentation CD-ROM User Interface Navigating Cisco Connection Documentation CD-ROM Hypertext Links Table of Contents Illustrations Tables Searching the Current Document Searching Multiple Documents Configuring Adobe Acrobat Reader as a Helper Application

Tcp

TCP provides full-duplex, acknowledged, and flow-controlled service to upper-layer protocols. It moves data in a continuous, unstructured byte stream where bytes are identified by sequence numbers. TCP can also support numerous simultaneous upper-layer conversations. The TCP packet format is shown in Figure 7-8. The fields of the TCP packet are as follows Source port and destination port Identify the points at which upper-layer source and destination processes receive TCP services. Sequence...

TCPIP Host Connections Fail Using Certain Applications

Symptom Connection attempts using some applications are successful, but attempts using other applications fail. For instance, you might be able to ping a host successfully, but Telnet connections fail. Table 7-6 outlines the problems that might cause this symptom and describes solutions to those problems. Table 7-6 TCP IP Host Connections Fail Using Certain Applications Table 7-6 TCP IP Host Connections Fail Using Certain Applications Misconfigured access lists or other filters Step 1 Use the...

TCPIP Local Host Cannot Access Remote Host

Symptom Hosts on one network cannot communicate with hosts on a remote network. The networks are separated by one or more routers and might include WAN or other links. One or more routing protocols are running on the routers. Table 7-3 outlines the problems that might cause this symptom and describes solutions to those problems. Table 7-3 TCP IP Local Host Cannot Access Remote Host Table 7-3 TCP IP Local Host Cannot Access Remote Host Default gateway is not specified or is misconfigured on...