dpchd over vti interface

BASSAGET Cédric cedric.bassaget.ml at gmail.com
Thu Oct 8 12:59:01 UTC 2020

I'm trying to set-up a VPN on a vti (ipsec tunnel) interface.

following https://gitlab.isc.org/isc-projects/dhcp/-/issues/135, I've
patched / compiled latest veresion of isc-dhcp-server.
Now, isc-dhcp-servers starts without complaining about an "unsupported
interface type".
But it still ignores all requests received on vti0 interface.

My server has 2 interfaces :
ens18 :
ens18:1 : public ip address used to bring up ipsec vpn

vpn is up on vti0 (

DHCP clients requests are relayed from the client network (
via a DHCP relay ( to (ip address of dhcp server
on ens18 interface)

using tcpdump on vti0 interface, I see DHCP requests incoming :

ip10:25:17.192146 ip: (tos 0x0, ttl 63, id 6882, offset 0, flags [none],
proto UDP (17), length 576) > BOOTP/DHCP, Request from
00:08:5d:47:06:12, length 548, hops 1, xid 0xdba36871, Flags [none]
          Client-Ethernet-Address 00:08:5d:47:06:12
          Vendor-rfc1048 Extensions
            Magic Cookie 0x63825363
            DHCP-Message Option 53, length 1: Discover
            Client-ID Option 61, length 7: ether 00:08:5d:47:06:12
            Hostname Option 12, length 17: "6737i00085D470612"
            Vendor-Class Option 60, length 18: "AastraIPPhone6737i"
            Requested-IP Option 50, length 4:
            MSZ Option 57, length 2: 576
            Parameter-Request Option 55, length 13:
              Subnet-Mask, Time-Zone, Default-Gateway, Domain-Name-Server
              Hostname, Domain-Name, BR, NTP
              Vendor-Option, TFTP, Option 132, Option 159
              Option 160

server runs like this : /usr/sbin/dhcpd -4 -d -f -cf /etc/dhcp/dhcpd.conf

Here-s the startup output :
# /usr/sbin/dhcpd -4 -f -d -cf /etc/dhcp/dhcpd.conf vti0
Internet Systems Consortium DHCP Server 4.4.2
Copyright 2004-2020 Internet Systems Consortium.
All rights reserved.
For info, please visit https://www.isc.org/software/dhcp/
Config file: /etc/dhcp/dhcpd.conf
Database file: /var/lib/dhcp/dhcpd.leases
PID file: /var/run/dhcpd.pid
Wrote 0 class decls to leases file.
Wrote 0 leases to leases file.
Listening on LPF/vti0//
Sending on   LPF/vti0//
Sending on   Socket/fallback/fallback-net
Server starting service.

no more logs when an incoming DHCP request arrives on vti0

AM I doing something wrong ?
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