Troubleshooting guide

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ATM and Layer 3 Switch Router Troubleshooting Guide
OL-1969-01
Chapter 11 Troubleshooting Layer 3 Network Connections
Troubleshooting IP Layer 3 Connections
Step 4 From the Catalyst 8540-1, use the show arp command to display the ARP table.
C8540CSR-1# show arp
Protocol Address Age (min) Hardware Addr Type Interface
.
(Information Deleted)
.
Internet 10.85.40.5 175 0010.e3aa.aaaa ARPA
Internet 10.85.40.254 - 0090.21bb.bbbb ARPA FastEthernet1/0/15
Internet 10.85.66.10 - 0090.21cc.cccc ARPA GigabitEthernet0/0/0
Internet 10.85.66.5 172 0090.21dd.dddd ARPA GigabitEthernet0/0/0
C8540CSR-1#
The first entries in this ARP table are, from top to bottom:
• Host A end station
• Fast Ethernet interface connection to the end station
• Gigabit Ethernet interface out to the next hop
• next hop router interface
If you confirm the information is wrong using the show adjacency command to display the MAC
address rewrite information, this might indicate a problem with CEF. You should confirm the interface
CAM table entries using the following troubleshooting procedure.
If you determine that the interface is configured incorrectly, refer to the “Configuring Interfaces” chapter
in the Layer 3 Switching Software Feature and Configuration Guide.
Checking the Interface CAM Table Entries
Follow these steps to verify the interface CAM table entries in the IP Layer 3 connection shown in
Figure 11-18.
Figure 11-18 Displaying the Interface CAM Table Information
Host A Catalyst 8540-2Catalyst 8540-1 Host B
10.85.40.0/24 10.85.66.0/24 10.85.45.0/24
.5 .254 .10 .5 .254 .5
MAC:
00:10.e3:aa...
Fast Ethernet connection (fast 1/0/15 on C8540-1)
Gigabit Ethernet connection (giga 0/0/0 on C8540-1)
MAC:
00:90.21:bb...
MAC:
00:90.21:dd...
MAC:
00:90.21:ff...
MAC:
00:90.21:cc...
MAC:
00:90.21:ee...
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