My topology as below: Server(DHCP) ----+---> Switch L3(4500) ----- trunk ----> Switch 2960(Sw1) ----- trunk ----> Switch 2960(Sw2) ----+ ---> PC1 Here is the config vlan on these devices: Switch 4500: interface Vlan97 ip address 10.10.97.2 255.255.255.0 ip helper-address 10.10.122.11 ip helper-address 10.10.122.12 standby 97 ip 10.10.97.1 standby 97 priority 105 standby 97 preempt interface Vlan123 ip address 10.10.123.2 255.255.255.0 ip helper-address 10.10.122.11 ip helper-address 10.10.122.12 standby 123 ip 10.10.123.1 standby 123 priority 105 standby 123 preempt Switch 2960(Sw1): IP address: 10.10.123.15 Sw1(config-if)#do sho run int fa0/38 Building configuration... Current configuration : 127 bytes ! interface FastEthernet0/38 description ## Testing Trunk ## switchport mode trunk switchport nonegotiate end Switch 2960(Sw2): IP address: 10.10.123.16 Sw2#sho run int fa0/48 Building configuration... Current configuration : 127 bytes ! interface FastEthernet0/48 description ## Testing Trunk ## switchport mode trunk switchport nonegotiate end I can ping between these switches 2960 also I want to clients plugin Sw2(in this case DHCP for Vlan97) can get DHCP from Server but still no luck.(PC1 can not get IP address from DHCP) I also try added these line on each Switch layer 2 and same issue. On Sw1: interface FastEthernet0/38 description ## Testing Trunk ## switchport trunk native vlan 123 switchport trunk allowed vlan 97,123 switchport mode trunk switchport nonegotiate On Sw2: interface FastEthernet0/48 description ## Testing Trunk ## switchport trunk native vlan 123 switchport trunk allowed vlan 97,123 switchport mode trunk switchport nonegotiate If i connect directly Sw2 to Switch L3(4500), the clients can get DHCP from server(Vlan97).