3Com 3C13636 Configuration Manual page 406

3Com Router 3000 Ethernet Family
Configuration Guide
The main IP address of a router Ethernet interface must be in the same network
segment with the LAN to which this Ethernet interface is connected.
Serial interface IP addresses of the routers at both ends of WAN must be in the
same network segment.
Fault 1: the router cannot ping through a certain host in LAN
Troubleshooting:
First check if the IP address configuration of the router's Ethernet interface and the
host in LAN are in the same network segment
If the configuration is correct, enable ARP debugging on the router, and check if
the router can correctly send and receive ARP packets. If it can only send but
cannot receive ARP packets, then possibly errors occur on the Ethernet physical
layer.
3Com Corporation
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Chapter 2 IP Address Configuration