Topology

At this example, we will configure 3 DHCP IP pools on the DHCP server. (DHCP server of Linux-mint)

1. Range 10.1.1.100 ~ 10.1.1.200, mask 255.255.255.0

2. Range 10.1.2.100 ~ 10.1.2.200, mask 255.255.255.0

3. Range 10.1.3.100 ~ 10.1.3.200, mask 255.255.255.0

Before set those rules on the DHCP server, you should know what you want to filter. At this example we will use Circuit ID as filter conditions.

Linux-mint DHCP server configuration:

vi /etc/dhcp/dhcpd.cfg

default-lease-time 600;
max-lease-time 7200;
option domain-name-servers 8.8.8.8;   #DNS server

# Here will use last two bits of circuit-id as filter condition.
class 'keep1'{
match if(substring(option agent.circuit-id,4,2)=01:01);
} # When PC-1 insert SwitchB E 1/1.

class 'keep2'{
match if(substring(option agent.circuit-id,4,2)=01:02);
} # When NB-1 insert SwitchB E 1/2.

class 'replace'{
  match if(substring(option agent.circuit-id,4,2)=01:0B);
} # Replace will be change to SwitchA circuit-id.

#Set the pools on DHCP server.
shared-network group{
 subnet 10.1.0.0 netmask 255.255.0.0{
  pool {
    allow members of        'keep1';
    range 10.1.1.100 10.1.1.200;
    option subnet-mask      255.255.255.0;
  }
  pool {
    allow members of        'keep2'
    range 10.1.2.100 10.1.2.200;
    option subnet-mask      255.255.255.0;
  }
  pool {
    allow members of        'replace';
    range 10.1.0.100 10.1.0.200;
    option subnet-mask      255.255.255.0;
  }
 }
}

Now we already finish the settings on the DHCP server.

Here we want configure DHCP option 82 at the switches:

Example 1:

If we want to let PC-1 and NB-1 get IP from the DHCP pools "keep1" and "keep2", we should let SwitchA keep the SwitchB DHCP option 82.

SwitchA setting

Step-1: Enable ip dhcp snooping with DHCP option 82

switchA#config
switchA(config)#ip dhcp snooping
switchA(config)#ip dhcp snooping vlan 1
switchA(config)#ip dhcp snooping information option
switchA(config)#interface ethernet 1/1
switchA(config-if)#ip dhcp snooping trust

Step-2: Set the policy as "keep"

switchA(config)#ip dhcp snooping information policy keep

SwitchB setting

Step-1: Enable ip dhcp snooping globally

switchB#config
switchB(config)#ip dhcp snooping

Step-2: Enable ip dhcp snooping on vlan 1

switchB(config)#ip dhcp snooping vlan 1

Step-3: Enable ip dhcp snooping with DHCP option 82

switchB(config)#ip dhcp snooping information option

Step-4: Set trust port on port 11

switchB(config)#interface ethernet 1/11
switchB(config-if)#ip dhcp snooping trust

Result

NB-1: DHCP Discover take the option 82 "Circuit ID: 000400010101".

NB-1: So it can get IP "10.1.1.120" from DHCP pool "keep1"

PC-1: DHCP Discover take the option 82 "Circuit ID: 000400010102".

PC-1: So it can get IP "10.1.2.105" from DHCP pool "keep2"

Example 2:

If we want to let PC-1 and NB-1 get ip from the DHCP pools "replace", we should let SwitchA replace the SwitchB DHCP option 82.

SwitchA setting

Step-1: Enable ip dhcp snooping with DHCP option 82

switchA#config
switchA(config)#ip dhcp snooping
switchA(config)#ip dhcp snooping vlan 1
switchA(config)#ip dhcp snooping information option
switchA(config)#interface ethernet 1/1
switchA(config-if)#ip dhcp snooping trust

Step-2: Set the policy as "replace"

switchA(config)#ip dhcp snooping information policy replace

SwitchB setting

Step-1: Enable ip dhcp snooping globally

switchB#config
switchB(config)#ip dhcp snooping

Step-2: Enable ip dhcp snooping on vlan 1

switchB(config)#ip dhcp snooping vlan 1

Step-3: Enable ip dhcp snooping with DHCP option 82

switchB(config)#ip dhcp snooping information option

Step-4: Set trust port on port 11

switchB(config)#interface ethernet 1/11
switchB(config-if)#ip dhcp snooping trust

Result

NB-1: DHCP Discover take the option 82 "Circuit ID: 00040001010b".

NB-1: So it can get IP "10.1.3.102" from DHCP pool "replace"

PC-1: DHCP Discover take the option 82 "Circuit ID: 00040001010b".

PC-1: So it can get IP "10.1.3.101" from DHCP pool "replace"

Notes:

If you only have one switch that don't need to set "ip dhcp snooping information policy".