Exec Command
Establishing a Reverse Telnet Session to a Modem
If you are running Cisco IOS Release 11.0 or earlier, you must establish a reverse Telnet session to configure a modem to communicate with a Cisco device. As long as you lock the data terminal equipment (DTE)-side speed of the modem (see Table 16-5 for information on locking the modem speed), the modem will always communicate with the access server or router at the desired speed. Be certain that the speed of the Cisco device is configured prior to issuing commands to the modem via a reverse...
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...
Troubleshooting Iso Clns
This section presents protocol-related troubleshooting information for ISO CLNS protocol connectivity and performance problems. It describes specific ISO CLNS symptoms, the problems that are likely to cause each symptom, and the solutions to those problems. Note Discussions of host configuration problems in this chapter assume that the host is a UNIX system. Equivalent actions might also be applicable to non-UNIX hosts, but the discussions do not specifically address non-UNIX end-station...
Network Analyzers
A network analyzer (also called a protocol analyzer) decodes the various protocol layers in a recorded frame and presents them as readable abbreviations or summaries, detailing which layer is involved (physical, data link, and so forth) and what function each byte or byte content serves. Most network analyzers can perform many of the following functions Filter traffic that meets certain criteria so that, for example, all traffic to and from a particular device can be captured Present protocol...
Volt Ohm Meters Digital Multimeters and Cable Testers
Volt-ohm meters and digital multimeters are at the lower end of the spectrum of cable testing tools. These devices measure parameters such as AC and DC voltage, current, resistance, capacitance, and cable continuity. They are used to check physical connectivity. Cable testers (scanners) also enable you to check physical connectivity. Cable testers are available for shielded twisted pair (STP), unshielded twisted pair (UTP), 10BaseT, and coaxial and twinax cables. A given cable tester might be...
Clocking Problem Solutions
Table 15-8 outlines suggested remedies for clocking problems, based on the source of the problem. Table 15-8 Serial Lines Clocking Problems and Solutions Table 15-8 Serial Lines Clocking Problems and Solutions Step 1 Determine whether the CSUs at both ends agree on the clock source (local or line). Step 2 If the CSUs do not agree, configure them so that they do (usually the line is the source). Step 3 Check the LBO1 setting on the CSU to ensure that the impedance matches that of the physical...
SDLC Client Cannot Connect to Host over Router Running SDLLC
Symptom Users cannot open connections to hosts on the other side of a router configured to support SDLC Logical Link Control (SDLLC). Table 10-11 outlines the problems that might cause this symptom and describes solutions to those problems. Table 10-11 SDLC Client Cannot Connect to Host over Router Running SDLLC Table 10-11 SDLC Client Cannot Connect to Host over Router Running SDLLC SDLC physical or data link-layer problem Step 1 Use the show interface slot port exec command to check the state...
Ipx Rip No Connectivity over Ipx Rip Router
Symptom IPX RIP routers are blocking connections. Clients cannot connect to servers over one or more routers running IPX RIP. Note Procedures for troubleshooting connectivity problems not specific to IPX RIP routing are described in the section Novell IPX Client Cannot Connect to Server on Remote LAN earlier in this chapter. Table 8-6 outlines the problems that might cause this symptom and describes solutions to those problems. Table 8-6 IPX RIP No Connectivity over IPX RIP Router Table 8-6 IPX...
Serial Lines show interfaces serial Status Line Conditions
You can identify five possible problem states in the interface status line of the show interfaces serial display (see Figure 15-1) Serial x is down, line protocol is down Serial x is up, line protocol is down Serial x is up, line protocol is up (looped) Serial x is up, line protocol is down (disabled) Serial x is administratively down, line protocol is down Figure 15-1 Output of the HDLC show interface serial Command Table 15-1 shows the interface status conditions, possible problems associated...
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 Enhanced IGRP Router Stuck in Active Mode
Symptom An AppleTalk Enhanced IGRP router is stuck in Active mode. The router repeatedly sends error messages similar to the following to the console DUAL-3-SIA Route 2.24 Stuck-in-Active 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 these error messages occur frequently, you should investigate the problem. For a more detailed explanation of...
Troubleshooting DECnet
This section presents protocol-related troubleshooting information for DECnet Phase IV connectivity and performance problems. The procedures outlined apply only to environments in which DECnet routing is enabled on the router, not to environments in which DECnet is being bridged (that is, bridging is enabled on the router interfaces and EtherType 6003 is being passed). This chapter does not discuss other Digital protocols, such as Maintenance Operation Protocol (MOP), local-area transport...
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...
CSU and DSU Loopback Tests
If the output of the show interfaces serial exec command indicates that the serial line is up but the line protocol is down, use the CSU DSU loopback tests to determine the source of the problem. Perform the local loop test first, and then the remote test. Figure 15-9 illustrates the basic topology of the CSU DSU local and remote loopback tests. Figure 15-9 CSU DSU Local and Remote Loopback Tests Figure 15-9 CSU DSU Local and Remote Loopback Tests Note These tests are generic in nature and...
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...
TCPIP Routing Not Functioning Properly on New Interface
Symptom A new interface is added to a router, but when routing is configured, it does not function properly on the new interface. Table 7-5 outlines the problems that might cause this symptom and describes solutions to those problems. Table 7-5 TCP IP Routing Not Functioning Properly on New Interface Table 7-5 TCP IP Routing Not Functioning Properly on New Interface Step 1 Use the show interfaces privileged exec command to see whether the interface is administratively down Router show interface...
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...
Using show Commands
The show commands are powerful monitoring and troubleshooting tools. You can use the show commands to perform a variety of functions Monitor router behavior during initial installation Monitor normal network operation Isolate problem interfaces, nodes, media, or applications Determine when a network is congested Determine the status of servers, clients, or other neighbors Following are some of the most commonly used show -commands show interfaces Use the show interfaces exec command to display...
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...
Token RingIEEE 8025 Comparison
Token Ring and IEEE 802.5 networks are basically quite compatible, but the specifications differ in relatively minor ways. IBM's Token Ring network specifies a star, with all end stations attached to a device called a multistation access unit (MAU), whereas IEEE 802.5 does not specify a topology (although virtually all IEEE 802.5 implementations also are based on a star). Other differences exist, including media type (IEEE 802.5 does not specify a media type, whereas IBM Token Ring networks use...
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....
Apple Talk Configuration and Troubleshooting Tips
This section offers configuration and troubleshooting tips that can help you prevent or more easily repair problems in AppleTalk internetworks. It consists of information on preventing AppleTalk problems, preventing internetwork reconfiguration problems, changing zone names, using AppleTalk Discovery Mode, and forcing an interface up to allow a router to start functioning if the network is misconfigured. Table 9-1 lists suggestions to help you avoid problems when configuring a router for...
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...
Adobe Acrobat Reader
In order to view the scalable Portable Document Format (PDF) versions of graphics and tables on Cisco Connection Documentation CD-ROM, you need to have Adobe Acrobat Reader configured as a helper application of Verity Mosaic. The Adobe Acrobat Reader installer is copied to the same location as the Cisco Connection Documentation CD-ROM applications on the Macintosh, Windows, SunOS, and Solaris platforms when you install Cisco Connection Documentation CD-ROM. Run the Adobe Acrobat Reader...
Exec Command 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...
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...
TCPIP Problems Forwarding BOOTP and Other UDP Broadcasts
Symptom Problems occur when forwarding BOOTP or other UDP broadcast packets. UDP broadcasts sent from network hosts are not forwarded by routers. Diskless workstations cannot boot. Table 7-7 outlines the problems that might cause this symptom and describes solutions to those problems. Table 7-7 TCP IP Problems Forwarding BOOTP and Other UDP Broadcasts Figure 7-12 A Misconfigured Access List Sample Network Missing or misconfigured ip helper-address Step 1 Use the debug ip udp privileged exec...
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...
Using the show controllers Command
The show controllers exec command is another important diagnostic tool when troubleshooting serial lines. The command syntax varies depending on platform For serial interfaces on Cisco 7000 series routers, use the show controllers cbus exec command For Cisco access products, use the show controllers exec command For the AGS, CGS, and MGS, use the show controllers mci exec command Figure 15-2 shows the output from the show controllers cbus exec command. This command is used on Cisco 7000 series...
Xns Xns Broadcast Packets Not Forwarded by Router
Symptom XNS servers do not respond to broadcast requests from clients. Table 14-2 outlines the problems that might cause this symptom and describes solutions to those problems. Table 14-2 XNS XNS Broadcast Packets Not Forwarded by Router Table 14-2 XNS XNS Broadcast Packets Not Forwarded by Router Caution Because debugging output is assigned high priority in the CPU process, it can render the system unusable. For this reason, use debug commands only to troubleshoot specific problems or during...
Using Extended ping Tests
The ping command is a useful test available on Cisco internetworking devices as well as on many host systems. In TCP IP, this diagnostic tool is also known as an Internet Control Message Protocol (ICMP) Echo Request. Note The ping command is particularly useful when high levels of input errors are being registered in the show interfaces serial display. See Figure 15-1. Cisco internetworking devices provide a mechanism to automate the sending of many ping packets in sequence. Figure 15-5...
VINES Client Cannot Connect to Server over PSN
Symptom Clients cannot connect to VINES servers across a packet-switched network (PSN). Clients can connect to local VINES servers. Table 13-2 outlines the problems that might cause this symptom and describes solutions to those problems. Table 13-2 VINES Client Cannot Connect to Server over PSN Table 13-2 VINES Client Cannot Connect to Server over PSN Step 1 Use the show running-config privileged exec command to view the configuration of the router. Step 2 For X.25 environments, make sure that...
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...
The Vlan Director Switch Management Application
The VlanDirector switch management application simplifies VLAN port assignment and offers other management capabilities for VLANs. VlanDirector offers the following features for network administrators Accurate representation of the physical network for VLAN design and configuration -verification Capability to obtain VLAN configuration information on a specific device or link interface Discrepancy reports on conflicting configurations Ability to troubleshoot and identify individual device...