Introduction

Case study in Chapter 7 discusses partial connectivity in ISDN dial backup scenario in the network shown below:

The case study documents various connectivity tests run in the network and their results. Please refer to the case study itself for more details.

Exercise

Why did the ping from remote office router to the regional server work while the ping from remote office PC to the same router failed?

Solution

This exercise describes a very common problem encountered in connectivity troubleshooting. When you ping a remote destination reachable through a WAN or ISDN connection from a router using the standard form of ping command, the source IP address in the ICMP packet is the IP address of router's WAN or ISDN interface. In the case study, the IP address of the ISDN interface of the RO-xy router was reachable by all the routers in the network through the RAS router, but the Ethernet interface of the same router was not.

Recommendation

When troubleshooting connectivity in your network, always use extended ping command and specify the source IP address that you want to use.