Troubleshooting
Troubleshooting
Use the command enable dhcpsnooping debug=all to get the most verbose level of debugging available. In the following sections, all debugging comes from that command.
Let’s look at how you can use debugging to investigate some common problem scenarios.
No trusted ports configured
In the following output, you can see that a DHCP request has arrived at the switch on port 1. The switch does not forward this on to any other port.
DHCPSN_Process: [0b4333cc] DHCP Snooping pkt for VLAN 1 | from port 1 |
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DHCPSN_Process: [0b4333cc] Type: REQUEST |
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DHCPSN_Process: [0b4333cc] On DHCP Snooping | port |
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DHCPSN_Process: [0b4333cc] DHCP Snoop forwarding pkt at | L2 for VLAN 1 | InPort 1 | |
DHCPSN_Process: [0b4333cc] L2 Dest MAC is broadcast |
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DHCPSN_Process: [0b4333cc] Type: REQUEST, L2 forward to | trusted ports |
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DHCPSN_Process: [0b4333cc] Forward ports (except 1) |
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DHCPSN_Process: [0b4333cc] | Tagged:None |
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DHCPSN_Process: [0b4333cc] | Untagged:None |
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The reason for this behaviour is because there are no trusted ports configured. Your DHCP server must be attached to a trusted port.
When a trusted port is configured, the debug shows a more complete conversation, as the following output shows.
Manager > set dhcpsnooping port=48 trusted=yes
Info (1137260): DHCP Snooping port(s) 48 updated successfully.
Manager > |
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DHCPSN_Process: [0b43a58c] DHCP Snooping pkt for VLAN 1 | from port 1 |
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DHCPSN_Process: [0b43a58c] Type: REQUEST |
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DHCPSN_Process: [0b43a58c] On DHCP | Snooping | port |
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DHCPSN_Process: [0b43a58c] DHCP Snoop forwarding pkt at | L2 for VLAN 1 | InPort 1 | |
DHCPSN_Process: [0b43a58c] L2 Dest | MAC is broadcast |
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DHCPSN_Process: [0b43a58c] Type: REQUEST, L2 forward to | trusted ports |
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DHCPSN_Process: [0b43a58c] Forward | ports (except 1) |
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DHCPSN_Process: [0b43a58c] | Tagged:None |
DHCPSN_Process: [0b43a58c] | Untagged:48 |
DHCPSN_Process: [0b43adac] DHCP Snooping pkt for VLAN 1 from port 48 | |
DHCPSN_Process: [0b43adac] Type: REPLY
DHCPSN_Process: [0b43adac] On DHCP Snooping trusted port
DHCPSN_Process: [0b43adac] Lookup result for CHAddr
DHCPSN_Process: [0b43adac] DHCP Snoop forwarding pkt at L2 for VLAN 1 InPort 48
DHCPSN_Process: [0b43adac] L2 Dest MAC is broadcast
DHCPSN_Process: [0b43adac] Type: REPLY
DHCPSN_Process: [0b43adac] L2 forward using client port 1
DHCPSN_Process: [0b43adac] Forward ports (except 48)
DHCPSN_Process: | [0b43adac] | Tagged:None |
DHCPSN_Process: | [0b43adac] | Untagged:1 |
Page 20 AlliedWare™ OS How To Note: DHCP Snooping on
