Override dhcp snooping with static user-bind table

Publication Date:  2017-02-28 Views:  451 Downloads:  0
Issue Description

When a users connects to the network and the terminal requests IP address to DHCP server, DHCP binding registers ok, the user receives an IP address and it receives Internet access. However when a user has static IP address, the switch fails to give internet access to terminal PC, even though static IP/MAC is
configured.

Handling Process

The interface configuration is below:

interface GigabitEthernet0/0/1
 speed auto-negotiation
 port link-type access
 port default vlan 100
 stp disable
 port-security enable
 arp anti-attack check user-bind enable
 arp anti-attack check user-bind alarm enable
 broadcast-suppression packets 50
 dhcp snooping enable
 dhcp snooping check dhcp-request enable
 dhcp snooping check dhcp-chaddr enable
 dhcp snooping check dhcp-rate enable
 dhcp snooping check dhcp-rate 50 dhcp option82 insert enable
 dhcp option82 format user-defined "%sysname:%slot/%subslot/%port"

The problem arises when manually assign an IP and a MAC to the port with static user-bind. As long as the terminal sends a DHCP request and receives an IP through it, everything works well. However when  manually IP/MAC is configured by adding an IP in the static binding table, it doesn’t work.


DHCP Dynamic Bind-table:
      
Flags:O - outer vlan ,I - inner vlan ,P - Vlan-mapping

IP Address       MAC Address    VSI/VLAN(O/I/P) Interface   Lease          
--------------------------------------------------------------------------------
XX.XX.XX.XX     aaaa-aaaa-aaaa  100  /--  /--    GE0/0/1       2017.02.23-08:21
--------------------------------------------------------------------------------

Static IP binding is configured:

user-bind static ip-address XX.XX.XX.X mac-address aaaa-aaaa-aaaa interface GigabitEthernet 0/0/1

Info: 1 static user-bind
item(s) added.



display dhcp static user-bind all

DHCP static Bind-table:

Flags:O - outer vlan ,I - inner vlan ,P - Vlan-mapping

IP Address        MAC Address     VSI/VLAN(O/I/P)    Interface      

--------------------------------------------------------------------------------
xx.xx.xx.xx       aaaa-aaaa-aaaa    --  /--  /--      GE0/0/1     

--------------------------------------------------------------------------------



Root Cause

When static user binding is used there is the need to configure static-gateway in vlan view.

Solution

Configure “mac-forced-forward static-gateway xx.xx.xx.xx”. When static user bind is used this command is mandatory.

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