Thanks you very much Laz,
You understood my explanation in the right way.
Indeed when configured the other remote switches that are connected to the relay-agent MLS through trunk , they forwarded the packets to the MLS.
after that, the MLS relayed those packets through the physical interface instead through the tunnel.
I could configure the MLS as the dhcp server but it’s not right as the DHCP service provided by the another domain.
all of the switches were configured with ip dhcp snooping correctly with trust interfaces toward the main MLS that relayed the packets via the tunnel.
The MLS was configured with the same dhcp snooping while the trusted port pointing toward the dhcp server.
all of the switches configured with the command no ip dhcp snooping information option because the MLS did blocked at first the dhcp requests and logged that those packets had some problem.
I will post here my configuration on the MLS partly, and will explain what i did:
vlan 3111 //native vlan for the L2 backbone domain
name native
vlan 10
name DHCP
int vlan 3111
ip address 10.1.1.1 255.0.0.0
no shut
ip router isis
int vlan 10
ip address 213.57.100.2 255.255.255.0
no shut
ip helper-address 192.168.0.1 // dhcp server's tunnel IP
int gig0/0 // connection to unsupported dhcp relay router towards the ISP
switchport
sw encapsulation dot1q
sw mode trunk
ip dhcp snooping trust
int gig0/0.10
encapsulation dot1q 10
int gig0/1 + gig0/2 + gig0/3 // backbone connection ports
switchport
sw encapsulation dot1q
sw mode trunk
sw trunk native vlan 3111
mpls ip
no shut
router isis
is-type level-2-only
net 49.0000.1111.1111.1111.00
passive-interface vlan 10
mpls ldp router-id vlan 3111 force
int gig3/3 // dhcp customer port
switchport
sw access vlan 10
no shut
ip dhcp snooping
ip dhcp snooping vlan 10
no ip dhcp snooping information option
int tunnel 0
ip address 192.168.0.2 255.255.255.0
tunnel source vlan 3111
tunnel dest 213.57.13.254 // dhcp server's public IP
ip route 0.0.0.0 0.0.0.0 213.57.100.1 // route to the ISP's unsupported dhcp relay router only through the DHCP segment which sits on vlan 10