(1) IPv4 testing with relayport patch on relay and server.

- topology (two hosts, lenovo and vaio with vLANs):

 client(enp3s0.10)     (enp2s8.10)relay(enp2s8.20)         (enp3s0.30)server
  lenovo          (192.168.10.100)vaio(192.168.20.100) (192.168.20.35)lenovo
    <---------------------------->    <------------------------------->

client: dhclient -d -cf ../confs/dhclient.conf enp3s0.10
relay:  dhcrelay -d -i enp2s8.10 -rp 5001 -U enp2s8.20 192.168.20.35
server: dhcpd -q -f -cf ../confs/dhcpd.conf -lf ../confs/dhcpd.leases -s 192.168.20.35 enp3s0.20

dhclient.conf
alias {
  interface "enp3s0.10";
}

lease {
  interface "enp3s0.10";
  fixed-address 192.168.10.35;
  option host-name "lenovo10.switch.com";
  option subnet-mask 255.255.255.0;
  option domain-name-servers 127.0.0.1;
  renew 2 2017/6/22 00:00:01;
  rebind 2 2017/6/22 00:00:01;
  expire 2 2017/6/22 00:00:01;
}

dhcpd.conf:

shared-network 10-20 {
  subnet 192.168.10.0 netmask 255.255.255.0 {
#    option routers 192.168.10.100;
  }
  subnet 192.168.20.0 netmask 255.255.255.0 {
  }
  pool {
    range 192.168.10.35 192.168.10.50;
  }
}


(2) IPv6 with two relay agents


 client                 relay1(5002)                          relay2(5003)                   server
 (enp2s8.10)   (enp3s0.10)  (enp3s0.20)               (enp2s8.20) (enp2s8.30)       (enp3s0.30)
  vaio      (2017:10::35)lenovo(2017:20::35)   (2017:20::100)vaio(2017:30::100)   (2017:30::35)lenovo
    <-------------->                <----------------->               <-----------------> 

  one client, with relay1 uses port 5002, and relay2 uses port 5003, one server
  three vLANs on two hosts vaio and lenovo.

client:
vaio:~/dhcp/6relay-dhcp-4.3.5$ sudo client/dhclient -6 -d -cf ../confs/dhclient-v6.conf enp2s8.10

relay1:
lenovo:~/dhcp/6relay-dhcp-4.3.5$ sudo relay/dhcrelay -6 -d -I -rp 5003 -l enp3s0.10 -u 2017:20::100%enp3s0.20

relay2:
vaio:~/dhcp/6relay-dhcp-4.3.5$ sudo relay/dhcrelay -6 -d -I -rp 5002 -l enp2s8.20 -u enp2s8.30

server:
lenovo:~/dhcp/6server-dhcp-4.3.5$ sudo server/dhcpd -6 -q -f -cf ../confs/dhcpd6.conf -lf ../confs/dhcpd6.leases enp3s0.30

- dhclient-v6.conf file:

send host-name = pick-first-value(gethostname(), "ISC-dhclient");
send dhcp-client-identifier 1:00:11:2F:85:8C:F4;
send dhcp-lease-time 3600;
request subnet-mask, broadcast-address, time-offset, routers,
	domain-name, domain-name-servers, host-name;
require subnet-mask, domain-name-servers;
timeout 60;
retry 60;
reboot 10;
select-timeout 5;
initial-interval 2;

alias {
  interface "enp2s8.10";
}

lease {
  interface "enp2s8.10";
  option host-name "vaio";
#  option dhcp6.dhcp4-o-dhcp6-server 2016:30::35;
  renew 2 2017/6/22 00:00:01;
  rebind 2 2017/6/22 00:00:01;
  expire 2 2017/6/22 00:00:01;
}

- dhcpd6.conf:

# dhcpd6.conf
#
# Sample configuration file for ISC dhcpd
#

default-lease-time 7200;
max-lease-time 7200;
preferred-lifetime 7200;
option dhcp-renewal-time 500;
option dhcp-rebinding-time 1000;

allow leasequery;

# option definitions common to all supported networks...
option dhcp6.name-servers 2017:30::35;
option dhcp6.domain-search "test.switch.com", "switch.com";

option dhcp6.info-refresh-time 1200;

log-facility local7;

subnet6 2017:10::/64 {
	range6 2017:10::90 2017:10::190;
}

subnet6 2017:30::/64 {
}