System information

Troubleshooting TCP/IP 7-103

Troubleshooting TCP/IP

This section presents protocol-related troubleshooting information for Transmission Control

Protocol/Internet Protocol (TCP/IP) connectivity and performance problems.

This chapter focuses on general TCP/IP problems and on routing problems related to RIP, the

Interior Gateway Routing Protocol (IGRP), Enhanced IGRP, OSPF, the Border Gateway Protocol

(BGP), and the Hot Standby Router Protocol (HSRP). Each of the following sections describes a

speciﬁc symptom, the problems that are likely to cause each symptom, and the solutions to those

problems.

This section covers the most common network issues in IP networks:

• TCP/IP: Local Host Cannot Access Remote Host

• TCP/IP: Routes Learned from the Wrong Interface or Protocol

• TCP/IP: Routing Not Functioning Properly on New Interface

• TCP/IP: Host Connections Fail Using Certain Applications

• TCP/IP: Problems Forwarding BOOTP and Other UDP Broadcasts

• TCP/IP: Poor Performance

• RIP/IGRP: Routes Missing from Routing Table

• OSPF: Routers Not Establishing Neighbors

• OSPF: Routes Missing from Routing Table

• IP Enhanced IGRP: Routers Not Establishing Neighbors

• IP Enhanced IGRP: Routes Missing from Routing Table

• IP Enhanced IGRP: Router Stuck in Active Mode

• BGP: Routes Missing from Routing Table

• BGP: Routers Not Advertising Routes

• HSRP: Hosts Cannot Reach Remote Networks

The symptoms described in the following sections are generic in nature and pertain to general

TCP/IP internetwork problems. However, when host conﬁguration problems are discussed, they are

addressed assuming the use of UNIX end systems. Similar types of actions might be applicable for

non-UNIX hosts, but the discussion does not speciﬁcally address non-UNIX end-station problems.

TCP/IP: 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