DMVPN
D ynamic M ultipoint V irtual P rivate N etworking
DMVPN is a dynamic VPN technology originally developed by Cisco. While their implementation was somewhat proprietary, the underlying technologies are actually standard based. The three technologies are:
NHRP - NBMA Next Hop Resolution Protocol RFC2332
mGRE - Multipoint Generic Routing Encapsulation / mGRE RFC1702
IPSec - IP Security (too many RFCs to list, but start with RFC4301)
NHRP provides the dynamic tunnel endpoint discovery mechanism (endpoint registration, and endpoint discovery/lookup), mGRE provides the tunnel encapsulation itself, and the IPSec protocols handle the key exchange, and crypto mechanism.
In short, DMVPN provides the capability for creating a dynamic-mesh VPN network without having to pre-configure (static) all possible tunnel end-point peers.
Note
DMVPN only automates the tunnel endpoint discovery and setup. A complete solution also incorporates the use of a routing protocol. BGP is particularly well suited for use with DMVPN.
Baseline Configuration:
STEPS:
Create tunnel config (interfaces tunnel)
Create nhrp (protocols nhrp)
Create ipsec vpn (optional, but recommended for security) (vpn ipsec)
The tunnel will be set to mGRE if gre is set for encapsulation, and no remote-ip is set. If the public ip is provided by DHCP the tunnel local-ip can be set to “0.0.0.0”. If you do set the remote-ip directive at any point, the interface will need to be deleted from the config and recreated without the remote-ip config ever being set.
Baseline DMVPN topology
HUB Configuration
interfaces
tunnel <tunN> {
address <ipv4>
encapsulation gre
local-ip <public ip>
multicast enable
description <txt>
parameters {
ip {
<usual IP options>
}
}
}
}
protocols {
nhrp {
tunnel <tunN> {
cisco-authentication <key phrase>
holding-time <seconds>
multicast dynamic
redirect
}
}
}
vpn {
ipsec {
esp-group <text> {
lifetime <30-86400>
mode tunnel
pfs enable
proposal <1-65535> {
encryption aes256
hash sha1
}
proposal <1-65535> {
encryption 3des
hash md5
}
}
ike-group <text> {
key-exchange ikev1
lifetime <30-86400>
proposal <1-65535> {
encryption aes256
hash sha1
}
proposal <1-65535> {
encryption aes128
hash sha1
}
}
ipsec-interfaces {
interface <ethN>
}
profile <text> {
authentication {
mode pre-shared-secret
pre-shared-secret <key phrase>
}
bind {
tunnel <tunN>
}
esp-group <text>
ike-group <text>
}
}
}
HUB Example Configuration:
set interfaces ethernet eth0 address '198.51.100.41/30'
set interfaces ethernet eth1 address '192.168.1.1/24'
set system host-name 'HUB'
set interfaces tunnel tun0 address 10.0.0.1/24
set interfaces tunnel tun0 encapsulation gre
set interfaces tunnel tun0 local-ip 198.51.100.41
set interfaces tunnel tun0 multicast enable
set interfaces tunnel tun0 parameters ip key 1
set protocols nhrp tunnel tun0 cisco-authentication SECRET
set protocols nhrp tunnel tun0 holding-time 300
set protocols nhrp tunnel tun0 multicast dynamic
set protocols nhrp tunnel tun0 redirect
set vpn ipsec ipsec-interfaces interface eth0
set vpn ipsec ike-group IKE-HUB proposal 1
set vpn ipsec ike-group IKE-HUB proposal 1 encryption aes256
set vpn ipsec ike-group IKE-HUB proposal 1 hash sha1
set vpn ipsec ike-group IKE-HUB proposal 2 encryption aes128
set vpn ipsec ike-group IKE-HUB proposal 2 hash sha1
set vpn ipsec ike-group IKE-HUB lifetime 3600
set vpn ipsec esp-group ESP-HUB proposal 1 encryption aes256
set vpn ipsec esp-group ESP-HUB proposal 1 hash sha1
set vpn ipsec esp-group ESP-HUB proposal 2 encryption 3des
set vpn ipsec esp-group ESP-HUB proposal 2 hash md5
set vpn ipsec esp-group ESP-HUB lifetime 1800
set vpn ipsec esp-group ESP-HUB pfs dh-group2
set vpn ipsec profile NHRPVPN
set vpn ipsec profile NHRPVPN authentication mode pre-shared-secret
set vpn ipsec profile NHRPVPN authentication pre-shared-secret SECRET
set vpn ipsec profile NHRPVPN bind tunnel tun0
set vpn ipsec profile NHRPVPN esp-group ESP-HUB
set vpn ipsec profile NHRPVPN ike-group IKE-HUB
set protocols static route 0.0.0.0/0 next-hop 1.1.1.2
set protocols static route 192.168.2.0/24 next-hop 10.0.0.2
set protocols static route 192.168.3.0/24 next-hop 10.0.0.3
HUB on AWS Configuration Specifics
Setting this up on AWS will require a “Custom Protocol Rule” for protocol number “47” (GRE) Allow Rule in TWO places. Firstly on the VPC Network ACL, and secondly on the security group network ACL attached to the EC2 instance. This has been tested as working for the offical AMI image on the AWS Marketplace. (Locate the correct VPC and security group by navigating through the details pane below your EC2 instance in the AWS console)
SPOKE Configuration
SPOKE1 Configuration:
interfaces
tunnel <tunN> {
address <ipv4>
encapsulation gre
local-ip <public ip>
multicast enable
description <txt>
parameters {
ip {
<usual IP options>
}
}
}
}
protocols {
nhrp {
tunnel <tunN> {
cisco-authentication <key phrase>
map <ipv4/net> {
nbma-address <ipv4>
register
}
holding-time <seconds>
multicast nhs
redirect
shortcut
}
}
}
vpn {
ipsec {
esp-group <text> {
lifetime <30-86400>
mode tunnel
pfs enable
proposal <1-65535> {
encryption aes256
hash sha1
}
proposal <1-65535> {
encryption 3des
hash md5
}
}
ike-group <text> {
key-exchange ikev1
lifetime <30-86400>
proposal <1-65535> {
encryption aes256
hash sha1
}
proposal <1-65535> {
encryption aes128
hash sha1
}
}
ipsec-interfaces {
interface <ethN>
}
profile <text> {
authentication {
mode pre-shared-secret
pre-shared-secret <key phrase>
}
bind {
tunnel <tunN>
}
esp-group <text>
ike-group <text>
}
}
}
SPOKE1 Example Configuration
set interfaces ethernet eth0 address 'dhcp'
set interfaces ethernet eth1 address '192.168.2.1/24'
set system host-name 'SPOKE1'
set interfaces tunnel tun0 address 10.0.0.2/24
set interfaces tunnel tun0 encapsulation gre
set interfaces tunnel tun0 local-ip 0.0.0.0
set interfaces tunnel tun0 multicast enable
set interfaces tunnel tun0 parameters ip key 1
set protocols nhrp tunnel tun0 cisco-authentication 'SECRET'
set protocols nhrp tunnel tun0 map 10.0.0.1/24 nbma-address 198.51.100.41
set protocols nhrp tunnel tun0 map 10.0.0.1/24 'register'
set protocols nhrp tunnel tun0 multicast 'nhs'
set protocols nhrp tunnel tun0 'redirect'
set protocols nhrp tunnel tun0 'shortcut'
set vpn ipsec ipsec-interfaces interface eth0
set vpn ipsec ike-group IKE-SPOKE proposal 1
set vpn ipsec ike-group IKE-SPOKE proposal 1 encryption aes256
set vpn ipsec ike-group IKE-SPOKE proposal 1 hash sha1
set vpn ipsec ike-group IKE-SPOKE proposal 2 encryption aes128
set vpn ipsec ike-group IKE-SPOKE proposal 2 hash sha1
set vpn ipsec ike-group IKE-SPOKE lifetime 3600
set vpn ipsec esp-group ESP-SPOKE proposal 1 encryption aes256
set vpn ipsec esp-group ESP-SPOKE proposal 1 hash sha1
set vpn ipsec esp-group ESP-SPOKE proposal 2 encryption 3des
set vpn ipsec esp-group ESP-SPOKE proposal 2 hash md5
set vpn ipsec esp-group ESP-SPOKE lifetime 1800
set vpn ipsec esp-group ESP-SPOKE pfs dh-group2
set vpn ipsec profile NHRPVPN
set vpn ipsec profile NHRPVPN authentication mode pre-shared-secret
set vpn ipsec profile NHRPVPN authentication pre-shared-secret SECRET
set vpn ipsec profile NHRPVPN bind tunnel tun0
set vpn ipsec profile NHRPVPN esp-group ESP-SPOKE
set vpn ipsec profile NHRPVPN ike-group IKE-SPOKE
set protocols static route 192.168.1.0/24 next-hop 10.0.0.1
set protocols static route 192.168.3.0/24 next-hop 10.0.0.3
SPOKE2 Configuration
interfaces
tunnel <tunN> {
address <ipv4>
encapsulation gre
local-ip <public ip>
multicast enable
description <txt>
parameters {
ip {
<usual IP options>
}
}
}
}
protocols {
nhrp {
tunnel <tunN> {
cisco-authentication <key phrase>
map <ipv4/net> {
nbma-address <ipv4>
register
}
holding-time <seconds>
multicast nhs
redirect
shortcut
}
}
}
vpn {
ipsec {
esp-group <text> {
lifetime <30-86400>
mode tunnel
pfs enable
proposal <1-65535> {
encryption aes256
hash sha1
}
proposal <1-65535> {
encryption 3des
hash md5
}
}
ike-group <text> {
key-exchange ikev1
lifetime <30-86400>
proposal <1-65535> {
encryption aes256
hash sha1
}
proposal <1-65535> {
encryption aes128
hash sha1
}
}
ipsec-interfaces {
interface <ethN>
}
profile <text> {
authentication {
mode pre-shared-secret
pre-shared-secret <key phrase>
}
bind {
tunnel <tunN>
}
esp-group <text>
ike-group <text>
}
}
}
SPOKE2 Example Configuration
set interfaces ethernet eth0 address 'dhcp'
set interfaces ethernet eth1 address '192.168.3.1/24'
set system host-name 'SPOKE2'
set interfaces tunnel tun0 address 10.0.0.3/24
set interfaces tunnel tun0 encapsulation gre
set interfaces tunnel tun0 local-ip 0.0.0.0
set interfaces tunnel tun0 multicast enable
set interfaces tunnel tun0 parameters ip key 1
set protocols nhrp tunnel tun0 cisco-authentication SECRET
set protocols nhrp tunnel tun0 map 10.0.0.1/24 nbma-address 198.51.100.41
set protocols nhrp tunnel tun0 map 10.0.0.1/24 register
set protocols nhrp tunnel tun0 multicast nhs
set protocols nhrp tunnel tun0 redirect
set protocols nhrp tunnel tun0 shortcut
set vpn ipsec ipsec-interfaces interface eth0
set vpn ipsec ike-group IKE-SPOKE proposal 1
set vpn ipsec ike-group IKE-SPOKE proposal 1 encryption aes256
set vpn ipsec ike-group IKE-SPOKE proposal 1 hash sha1
set vpn ipsec ike-group IKE-SPOKE proposal 2 encryption aes128
set vpn ipsec ike-group IKE-SPOKE proposal 2 hash sha1
set vpn ipsec ike-group IKE-SPOKE lifetime 3600
set vpn ipsec esp-group ESP-SPOKE proposal 1 encryption aes256
set vpn ipsec esp-group ESP-SPOKE proposal 1 hash sha1
set vpn ipsec esp-group ESP-SPOKE proposal 2 encryption 3des
set vpn ipsec esp-group ESP-SPOKE proposal 2 hash md5
set vpn ipsec esp-group ESP-SPOKE lifetime 1800
set vpn ipsec esp-group ESP-SPOKE pfs dh-group2
set vpn ipsec profile NHRPVPN
set vpn ipsec profile NHRPVPN authentication mode pre-shared-secret
set vpn ipsec profile NHRPVPN authentication pre-shared-secret SECRET
set vpn ipsec profile NHRPVPN bind tunnel tun0
set vpn ipsec profile NHRPVPN esp-group ESP-SPOKE
set vpn ipsec profile NHRPVPN ike-group IKE-SPOKE
set protocols static route 192.168.1.0/24 next-hop 10.0.0.1
set protocols static route 192.168.2.0/24 next-hop 10.0.0.2