Alcatel Carrier Internetworking Solutions 6648 - Manual (Page 300)

Troubleshooting AVLAN Troubleshooting Authenticated VLANs
page 18-2 OmniSwitch Troubleshooting Guide September 2005
Troubleshooting AVLAN
DHCP Request Failure
If the client (PC-1) is configured to get the DHCP IP address and can not get DHCP address during the
first phase of authentication process, it could be because of wrong configuration in the switch, communi-
cation failure or miss configured DHCP server.
Use the command:
-> show ip helper
This command is to verify IP addresses for DHCP servers that will receive BOOTP/DHCP packets
forwarded by this UDP Relay service is set correctly. The example of command output is shown below:
-> show ip helper
Forward Delay(seconds) = 3,
Max number of hops = 4,
Forward option = standard
Forwarding Address:
192.168.10.100
In addition with IP helper address, verify that the Gateway of the DHCP server is correctly specified. The
Gateway is a router port in any of the authenticated VLANs in the switch. It specifies the scope into which
an authentication client receives an IP address.
-> show aaa avlan config
default DHCP relay address = 192.168.10.1,
authentication DNS name = not configured
If the IP address for the DHCP server is set correctly then try to ping the server to verify the connectivity.
You can also verify the MAC-address-table and ARP table entries.
-> show mac-address-table
The mac-address-table CLI command confirms that the switch has learned the MAC address of the DHCP
server has been learned.
-> show mac-address-table
Legend: Mac Address: * = address not valid
Vlan Mac Address Type Protocol Operation Interface
------+-------------------+--------------+-----------+------------+-----------
2 00:c0:4f:0c:3a:e4 learned 0 bridging 1/21
Total number of Valid MAC addresses above = 1
Now verify that the Gateway defined in DHCP server point towards the right IP address. ARP table
confirms that the switch has learned the ARP entry of the DHCP server. Verify that the IP address of the
DHCP server has been learned in the correct VLAN and the port it has been attached.
-> show arp
Total 1 arp entries
Flags (P=Proxy, A=Authentication, V=VRRP)
IP Addr Hardware Addr Type Flags Port Interface
-----------------+-------------------+----------+-------+--------+-----------