Introduction

Internet Protocol Security (IPsec) is a set of protocols defined by the Internet Engineering Task Force (IETF) to secure packet exchange over unprotected IP/IPv6 networks such as the Internet.

IPsec protocol suite can be divided into the following groups:

• Internet Key Exchange (IKE) protocols. Dynamically generates and distributes cryptographic keys for AH and ESP.
• Authentication Header (AH) RFC 4302
• Encapsulating Security Payload (ESP) RFC 4303

Internet Key Exchange Protocol (IKE)

The Internet Key Exchange (IKE) is a protocol that provides authenticated keying material for the Internet Security Association and Key Management Protocol (ISAKMP) framework. There are other key exchange schemes that work with ISAKMP, but IKE is the most widely used one. Together they provide means for authentication of hosts and automatic management of security associations (SA).

Most of the time IKE daemon is doing nothing. There are two possible situations when it is activated:

There is some traffic caught by a policy rule which needs to become encrypted or authenticated, but the policy doesn't have any SAs. The policy notifies the IKE daemon about that, and the IKE daemon initiates a connection to a remote host. IKE daemon responds to remote connection. In both cases, peers establish a connection and execute 2 phases:

• Phase 1 - The peers agree upon algorithms they will use in the following IKE messages and authenticate. The keying material used to derive keys for all SAs and to protect following ISAKMP exchanges between hosts is generated also. This phase should match the following settings:
  • authentication method
  • DH group
  • encryption algorithm
  • exchange mode
  • hash algorithm
  • NAT-T
  • DPD and lifetime (optional)

• Phase 2 - The peers establish one or more SAs that will be used by IPsec to encrypt data. All SAs established by the IKE daemon will have lifetime values (either limiting time, after which SA will become invalid, or amount of data that can be encrypted by this SA, or both). This phase should match the following settings:
  • IPsec protocol
  • mode (tunnel or transport)
  • authentication method
  • PFS (DH) group
  • lifetime

IKE can optionally provide a Perfect Forward Secrecy (PFS), which is a property of key exchanges, that, in turn, means for IKE that compromising the long term phase 1 key will not allow to easily gain access to all IPsec data that is protected by SAs established through this phase 1. It means an additional keying material is generated for each phase 2.

The generation of keying material is computationally very expensive. Exempli Gratia, the use of the modp8192 group can take several seconds even on a very fast computer. It usually takes place once per phase 1 exchange, which happens only once between any host pair and then is kept for a long time. PFS adds this expensive operation also to each phase 2 exchange.

Diffie-Hellman Groups

Diffie-Hellman (DH) key exchange protocol allows two parties without any initial shared secret to create one securely. The following Modular Exponential (MODP) and Elliptic Curve (EC2N) Diffie-Hellman (also known as "Oakley") Groups are supported:

More on standards can be found here.

IKE Traffic

To avoid problems with IKE packets hit some SPD rule and require to encrypt it with not yet established SA (that this packet perhaps is trying to establish), locally originated packets with UDP source port 500 are not processed with SPD. The same way packets with UDP destination port 500 that are to be delivered locally are not processed in incoming policy checks.

Setup Procedure

To get IPsec to work with automatic keying using IKE-ISAKMP you will have to configure policy, peer, and proposal (optional) entries.

EAP Authentication methods

EAP-TLS on Windows is called "Smart Card or other certificates".

Authentication Header (AH)

AH is a protocol that provides authentication of either all or part of the contents of a datagram through the addition of a header that is calculated based on the values in the datagram. What parts of the datagram are used for the calculation, and the placement of the header depends on whether tunnel or transport mode is used.

The presence of the AH header allows to verify the integrity of the message but doesn't encrypt it. Thus, AH provides authentication but not privacy. Another protocol (ESP) is considered superior, it provides data privacy and also its own authentication method.

RouterOS supports the following authentication algorithms for AH:

• SHA2 (256, 512)
• SHA1
• MD5

Transport mode

In transport mode, the AH header is inserted after the IP header. IP data and header is used to calculate authentication value. IP fields that might change during transit, like TTL and hop count, are set to zero values before authentication.

Tunnel mode

In tunnel mode, the original IP packet is encapsulated within a new IP packet. All of the original IP packets are authenticated.

Encapsulating Security Payload (ESP)

Encapsulating Security Payload (ESP) uses shared key encryption to provide data privacy. ESP also supports its own authentication scheme like that used in AH.

ESP packages its fields in a very different way than AH. Instead of having just a header, it divides its fields into three components:

• ESP Header - Comes before the encrypted data and its placement depends on whether ESP is used in transport mode or tunnel mode.
• ESP Trailer - This section is placed after the encrypted data. It contains padding that is used to align the encrypted data.
• ESP Authentication Data - This field contains an Integrity Check Value (ICV), computed in a manner similar to how the AH protocol works, for when ESP's optional authentication feature is used.

Transport mode

In transport mode, the ESP header is inserted after the original IP header. ESP trailer and authentication value are added to the end of the packet. In this mode only the IP payload is encrypted and authenticated, the IP header is not secured.

Tunnel mode

In tunnel mode, an original IP packet is encapsulated within a new IP packet thus securing IP payload and IP header.

Encryption algorithms

RouterOS ESP supports various encryption and authentication algorithms.

Authentication:

• MD5
• SHA1
• SHA2 (256-bit, 512-bit)

Encryption:

• AES - 128-bit, 192-bit, and 256-bit key AES-CBC, AES-CTR, and AES-GCM algorithms;
• Blowfish - added since v4.5
• Twofish - added since v4.5
• Camellia - 128-bit, 192-bit, and 256-bit key Camellia encryption algorithm added since v4.5
• DES - 56-bit DES-CBC encryption algorithm;
• 3DES - 168-bit DES encryption algorithm;

Hardware acceleration

Hardware acceleration allows doing a faster encryption process by using a built-in encryption engine inside the CPU.

* supported only 128 bit and 256 bit key sizes

** only manufactured since 2016, serial numbers that begin with number 5 and 7

*** AES-CBC and AES-CTR only encryption is accelerated, hashing done in software

**** DES is not supported, only 3DES and AES-CBC

IPsec throughput results of various encryption and hash algorithm combinations are published on the MikroTik products page.

Policies

The policy table is used to determine whether security settings should be applied to a packet.

Properties

Read-only properties

Statistics

This menu shows various IPsec statistics and errors.

Read-only properties

Proposals

Proposal information that will be sent by IKE daemons to establish SAs for certain policies.

Properties

Read-only properties

Groups

In this menu, it is possible to create additional policy groups used by policy templates.

Properties

Peers

Peer configuration settings are used to establish connections between IKE daemons. This connection then will be used to negotiate keys and algorithms for SAs. Exchange mode is the only unique identifier between the peers, meaning that there can be multiple peer configurations with the same remote-address as long as a different exchange-mode is used.

Properties

Read-only properties

Identities

Identities are configuration parameters that are specific to the remote peer. The main purpose of identity is to handle authentication and verify the peer's integrity.

Properties

Read only properties

Profiles

Profiles define a set of parameters that will be used for IKE negotiation during Phase 1. These parameters may be common with other peer configurations.

Properties

Active Peers

This menu provides various statistics about remote peers that currently have established phase 1 connection.

Read only properties

Commands

Mode configs

ISAKMP and IKEv2 configuration attributes are configured in this menu.

Properties

Read-only properties

Installed SAs

This menu provides information about installed security associations including the keys.

Read-only properties

Commands

Keys

This menu lists all imported public and private keys, that can be used for peer authentication. Menu has several commands to work with keys.

Properties

Read-only properties

Commands

Settings

Application Guides

RoadWarrior client with NAT

Consider setup as illustrated below. RouterOS acts as a RoadWarrior client connected to Office allowing access to its internal resources.

A tunnel is established, a local mode-config IP address is received and a set of dynamic policies are generated.

[admin@mikrotik] > ip ipsec policy print 
Flags: T - template, X - disabled, D - dynamic, I - invalid, A - active, * - default 
0 T * group=default src-address=::/0 dst-address=::/0 protocol=all proposal=default template=yes 

1 DA src-address=192.168.77.254/32 src-port=any dst-address=10.5.8.0/24 dst-port=any protocol=all 
action=encrypt level=unique ipsec-protocols=esp tunnel=yes sa-src-address=10.155.107.8 
sa-dst-address=10.155.107.9 proposal=default ph2-count=1 

2 DA src-address=192.168.77.254/32 src-port=any dst-address=192.168.55.0/24 dst-port=any protocol=all 
action=encrypt level=unique ipsec-protocols=esp tunnel=yes sa-src-address=10.155.107.8 
sa-dst-address=10.155.107.9 proposal=default ph2-count=1 

Currently, only packets with a source address of 192.168.77.254/32 will match the IPsec policies. For a local network to be able to reach remote subnets, it is necessary to change the source address of local hosts to the dynamically assigned mode config IP address. It is possible to generate source NAT rules dynamically. This can be done by creating a new address list that contains all local networks that the NAT rule should be applied. In our case, it is 192.168.88.0/24.

/ip firewall address-list add address=192.168.88.0/24 list=local-RW

By specifying the address list under the mode-config initiator configuration, a set of source NAT rules will be dynamically generated.

/ip ipsec mode-config set [ find name="request-only" ] src-address-list=local-RW

When the IPsec tunnel is established, we can see the dynamically created source NAT rules for each network. Now every host in 192.168.88.0/24 is able to access Office's internal resources.

[admin@mikrotik] > ip firewall nat print 
Flags: X - disabled, I - invalid, D - dynamic 
0 D ;;; ipsec mode-config
chain=srcnat action=src-nat to-addresses=192.168.77.254 dst-address=192.168.55.0/24 src-address-list=local-RW

1 D ;;; ipsec mode-config
chain=srcnat action=src-nat to-addresses=192.168.77.254 dst-address=10.5.8.0/24 src-address-list=local-RW

Allow only IPsec encapsulated traffic

There are some scenarios where for security reasons you would like to drop access from/to specific networks if incoming/outgoing packets are not encrypted. For example, if we have L2TP/IPsec setup we would want to drop nonencrypted L2TP connection attempts.

There are several ways how to achieve this:

• Using IPsec policy matcher in firewall;
• Using generic IPsec policy with action set to drop and lower priority (can be used in Road Warrior setups where dynamic policies are generated);
• By setting DSCP or priority in mangle and matching the same values in firewall after decapsulation.

IPsec policy matcher

Let's set up an IPsec policy matcher to accept all packets that matched any of the IPsec policies and drop the rest:

add chain=input comment="ipsec policy matcher" in-interface=WAN ipsec-policy=in,ipsec
add action=drop chain=input comment="drop all" in-interface=WAN log=yes

IPsec policy matcher takes two parameters direction, policy. We used incoming direction and IPsec policy. IPsec policy option allows us to inspect packets after decapsulation, so for example, if we want to allow only GRE encapsulated packet from a specific source address and drop the rest we could set up the following rules:

add chain=input comment="ipsec policy matcher" in-interface=WAN ipsec-policy=in,ipsec protocol=gre src=address=192.168.33.1
add action=drop chain=input comment="drop all" in-interface=WAN log=yes

For L2TP rule set would be:

add chain=input comment="ipsec policy matcher" in-interface=WAN ipsec-policy=in,ipsec protocol=udp dst-port=1701
add action=drop chain=input protocol=udp dst-port=1701 comment="drop l2tp" in-interface=WAN log=yes

Using generic IPsec policy

The trick of this method is to add a default policy with an action drop. Let's assume we are running an L2TP/IPsec server on a public 1.1.1.1 address and we want to drop all nonencrypted L2TP:

/ip ipsec policy
add src-address=1.1.1.1 dst-address=0.0.0.0/0 sa-src-address=1.1.1.1 protocol=udp src-port=1701 tunnel=yes action=discard

Now router will drop any L2TP unencrypted incoming traffic, but after a successful L2TP/IPsec connection dynamic policy is created with higher priority than it is on default static rule, and packets matching that dynamic rule can be forwarded.

[admin@rack2_10g1] /ip ipsec policy> print
Flags: T - template, X - disabled, D - dynamic, I - inactive, * - default
0 T * group=default src-address=::/0 dst-address=::/0 protocol=all
proposal=default template=yes

1 D src-address=1.1.1.1/32 src-port=1701 dst-address=10.5.130.71/32
dst-port=any protocol=udp action=encrypt level=require
ipsec-protocols=esp tunnel=no sa-src-address=1.1.1.1
sa-dst-address=10.5.130.71

2 src-address=1.1.1.1/32 src-port=1701 dst-address=0.0.0.0/0
dst-port=any protocol=udp action=discard level=unique
ipsec-protocols=esp tunnel=yes sa-src-address=1.1.1.1
sa-dst-address=0.0.0.0 proposal=default manual-sa=none

Manually specifying local-address parameter under Peer configuration

Using different routing table

IPsec, as any other service in RouterOS, uses the main routing table regardless of what local-address parameter is used for Peer configuration. It is necessary to apply routing marks to both IKE and IPSec traffic.

Consider the following example. There are two default routes - one in the main routing table and another in the routing table "backup". It is necessary to use the backup link for the IPsec site to site tunnel.

[admin@pair_r1] > /ip route print detail 
Flags: X - disabled, A - active, D - dynamic, C - connect, S - static, r - rip, b - bgp, o - ospf, m - mme, B - blackhole, U - unreachable, P - prohibit 
0 A S dst-address=0.0.0.0/0 gateway=10.155.107.1 gateway-status=10.155.107.1 reachable via ether1 distance=1 scope=30 target-scope=10 routing-mark=backup 

1 A S dst-address=0.0.0.0/0 gateway=172.22.2.115 gateway-status=172.22.2.115 reachable via ether2 distance=1 scope=30 target-scope=10 

2 ADC dst-address=10.155.107.0/25 pref-src=10.155.107.8 gateway=ether1 gateway-status=ether1 reachable distance=0 scope=10 

3 ADC dst-address=172.22.2.0/24 pref-src=172.22.2.114 gateway=ether2 gateway-status=ether2 reachable distance=0 scope=10 

4 ADC dst-address=192.168.1.0/24 pref-src=192.168.1.1 gateway=bridge-local gateway-status=ether2 reachable distance=0 scope=10 

[admin@pair_r1] > /ip firewall nat print 
Flags: X - disabled, I - invalid, D - dynamic 
0 chain=srcnat action=masquerade out-interface=ether1 log=no log-prefix="" 

1 chain=srcnat action=masquerade out-interface=ether2 log=no log-prefix="" 

IPsec peer and policy configurations are created using the backup link's source address, as well as the NAT bypass rule for IPsec tunnel traffic.

/ip ipsec peer
add address=10.155.130.136/32 local-address=10.155.107.8 secret=test
/ip ipsec policy
add sa-src-address=10.155.107.8 src-address=192.168.1.0/24 dst-address=172.16.0.0/24 sa-dst-address=10.155.130.136 tunnel=yes
/ip firewall nat
add action=accept chain=srcnat src-address=192.168.1.0/24 dst-address=172.16.0.0/24 place-before=0

Currently, we see "phase1 negotiation failed due to time up" errors in the log. It is because IPsec tries to reach the remote peer using the main routing table with an incorrect source address. It is necessary to mark UDP/500, UDP/4500, and ipsec-esp packets using Mangle:

/ip firewall mangle
add action=mark-connection chain=output connection-mark=no-mark dst-address=10.155.130.136 dst-port=500,4500 new-connection-mark=ipsec passthrough=yes protocol=udp
add action=mark-connection chain=output connection-mark=no-mark dst-address=10.155.130.136 new-connection-mark=ipsec passthrough=yes protocol=ipsec-esp
add action=mark-routing chain=output connection-mark=ipsec new-routing-mark=backup passthrough=no

Using the same routing table with multiple IP addresses

Consider the following example. There are multiple IP addresses from the same subnet on the public interface. Masquerade rule is configured on out-interface. It is necessary to use one of the IP addresses explicitly.

[admin@pair_r1] > /ip address print 
Flags: X - disabled, I - invalid, D - dynamic 
# ADDRESS NETWORK INTERFACE
0 192.168.1.1/24 192.168.1.0 bridge-local
1 172.22.2.1/24 172.22.2.0 ether1
2 172.22.2.2/24 172.22.2.0 ether1
3 172.22.2.3/24 172.22.2.0 ether1

[admin@pair_r1] > /ip route print 
Flags: X - disabled, A - active, D - dynamic, C - connect, S - static, r - rip, b - bgp, o - ospf, m - mme, B - blackhole, U - unreachable, P - prohibit 
# DST-ADDRESS PREF-SRC GATEWAY DISTANCE
1 A S 0.0.0.0/0 172.22.2.115 1
3 ADC 172.22.2.0/24 172.22.2.1 ether1 0
4 ADC 192.168.1.0/24 192.168.1.1 bridge-local 0

[admin@pair_r1] /ip firewall nat> print 
Flags: X - disabled, I - invalid, D - dynamic 
0 chain=srcnat action=masquerade out-interface=ether1 log=no log-prefix="" 

IPsec peer and policy configuration is created using one of the public IP addresses.

/ip ipsec peer
add address=10.155.130.136/32 local-address=172.22.2.3 secret=test
/ip ipsec policy
add sa-src-address=172.22.2.3 src-address=192.168.1.0/24 dst-address=172.16.0.0/24 sa-dst-address=10.155.130.136 tunnel=yes
/ip firewall nat
add action=accept chain=srcnat src-address=192.168.1.0/24 dst-address=172.16.0.0/24 place-before=0

Currently, the phase 1 connection uses a different source address than we specified, and "phase1 negotiation failed due to time up" errors are shown in the logs. This is because masquerade is changing the source address of the connection to match the pref-src address of the connected route. The solution is to exclude connections from the public IP address from being masqueraded.

/ip firewall nat
add action=accept chain=srcnat protocol=udp src-port=500,4500 place-before=0

Application examples

Site to Site IPsec tunnel

Consider setup as illustrated below. Two remote office routers are connected to the internet and office workstations are behind NAT. Each office has its own local subnet, 10.1.202.0/24 for Office1 and 10.1.101.0/24 for Office2. Both remote offices need secure tunnels to local networks behind routers.

Site 1 configuration

Start off by creating a new Phase 1profileand Phase 2proposalentries using stronger or weaker encryption parameters that suit your needs. It is advised to create separate entries for each menu so that they are unique for each peer in case it is necessary to adjust any of the settings in the future. These parameters must match between the sites or else the connection will not establish.

/ip ipsec profile
add dh-group=modp2048 enc-algorithm=aes-128 name=ike1-site2
/ip ipsec proposal
add enc-algorithms=aes-128-cbc name=ike1-site2 pfs-group=modp2048

Continue by configuring a peer. Specify the address of the remote router. This address should be reachable through UDP/500 and UDP/4500 ports, so make sure appropriate actions are taken regarding the router's firewall. Specify the name for this peer as well as the newly created profile.

/ip ipsec peer
add address=192.168.80.1/32 name=ike1-site2 profile=ike1-site2

The next step is to create an identity. For a basic pre-shared key secured tunnel, there is nothing much to set except for a strong secret and the peer to which this identity applies.

/ip ipsec identity
add peer=ike1-site2 secret=thisisnotasecurepsk

Lastly, create a policy that controls the networks/hosts between whom traffic should be encrypted.

/ip ipsec policy
add src-address=10.1.202.0/24 src-port=any dst-address=10.1.101.0/24 dst-port=any tunnel=yes action=encrypt proposal=ike1-site2 peer=ike1-site2

Site 2 configuration

Office 2 configuration is almost identical to Office 1 with proper IP address configuration. Start off by creating a new Phase 1 profile and Phase 2 proposal entries:

/ip ipsec profile
add dh-group=modp2048 enc-algorithm=aes-128 name=ike1-site1
/ip ipsec proposal
add enc-algorithms=aes-128-cbc name=ike1-site1 pfs-group=modp2048

Next is the peer and identity:

/ip ipsec peer
add address=192.168.90.1/32 name=ike1-site1 profile=ike1-site1
/ip ipsec identity
add peer=ike1-site1 secret=thisisnotasecurepsk

When it is done, create a policy:

/ip ipsec policy
add src-address=10.1.101.0/24 src-port=any dst-address=10.1.202.0/24 dst-port=any tunnel=yes action=encrypt proposal=ike1-site1 peer=ike1-site1

At this point, the tunnel should be established and two IPsec Security Associations should be created on both routers:

/ip ipsec
active-peers print
installed-sa print

NAT and Fasttrack Bypass

At this point if you try to send traffic over the IPsec tunnel, it will not work, packets will be lost. This is because both routers have NAT rules (masquerade) that are changing source addresses before a packet is encrypted. A router is unable to encrypt the packet because the source address does not match the address specified in the policy configuration. For more information see the IPsec packet flow example.

To fix this we need to set up IP/Firewall/NAT bypass rule.

Office 1 router:

/ip firewall nat
add chain=srcnat action=accept place-before=0 src-address=10.1.202.0/24 dst-address=10.1.101.0/24

Office 2 router:

/ip firewall nat
add chain=srcnat action=accept place-before=0 src-address=10.1.101.0/24 dst-address=10.1.202.0/24

It is very important that the bypass rule is placed at the top of all other NAT rules.

Another issue is if you have IP/Fasttrack enabled, the packet bypasses IPsec policies. So we need to add accept rule before FastTrack.

/ip firewall filter
add chain=forward action=accept place-before=1
src-address=10.1.101.0/24 dst-address=10.1.202.0/24 connection-state=established,related
add chain=forward action=accept place-before=1
src-address=10.1.202.0/24 dst-address=10.1.101.0/24 connection-state=established,related

However, this can add a significant load to the router's CPU if there is a fair amount of tunnels and significant traffic on each tunnel.

The solution is to use IP/Firewall/Raw to bypass connection tracking, that way eliminating the need for filter rules listed above and reducing the load on CPU by approximately 30%.

/ip firewall raw
add action=notrack chain=prerouting src-address=10.1.101.0/24 dst-address=10.1.202.0/24
add action=notrack chain=prerouting src-address=10.1.202.0/24 dst-address=10.1.101.0/24

Road Warrior setup using IKEv2 with RSA authentication

This example explains how to establish a secure IPsec connection between a device connected to the Internet (road warrior client) and a device running RouterOS acting as a server.

RouterOS server configuration

Before configuring IPsec, it is required to set up certificates. It is possible to use a separate Certificate Authority for certificate management, however in this example, self-signed certificates are generated in RouterOS System/Certificates menu. Some certificate requirements should be met to connect various devices to the server:

• Common name should contain IP or DNS name of the server;
• SAN (subject alternative name) should have IP or DNS of the server;
• EKU (extended key usage) tls-server and tls-client are required.

Considering all requirements above, generate CA and server certificates:

/certificate
add common-name=ca name=ca
sign ca ca-crl-host=2.2.2.2
add common-name=2.2.2.2 subject-alt-name=IP:2.2.2.2 key-usage=tls-server name=server1
sign server1 ca=ca

Now that valid certificates are created on the router, add a new Phase 1 profile and Phase 2 proposal entries with pfs-group=none:

/ip ipsec profile
add name=ike2
/ip ipsec proposal
add name=ike2 pfs-group=none

Mode config is used for address distribution from IP/Pools:

[admin@MikroTik] > /ip firewall nat print 
Flags: X - disabled, I - invalid, D - dynamic 
0 D ;;; ipsec mode-config
chain=srcnat action=src-nat to-addresses=192.168.77.254 src-address-list=local dst-address-list=!local

Since that the policy template must be adjusted to allow only specific network policies, it is advised to create a separate policy group and template.

/ip ipsec policy group
add name=ike2-policies
/ip ipsec policy
add dst-address=192.168.77.0/24 group=ike2-policies proposal=ike2 src-address=0.0.0.0/0 template=yes

Create a new IPsec peer entry that will listen to all incoming IKEv2 requests.

/ip ipsec peer
add exchange-mode=ike2 name=ike2 passive=yes profile=ike2

Identity configuration

The identity menu allows to match specific remote peers and assign different configurations for each one of them. First, create a default identity, that will accept all peers, but will verify the peer's identity with its certificate.

/ip ipsec identity
add auth-method=digital-signature certificate=server1 generate-policy=port-strict mode-config=ike2-conf peer=ike2 policy-template-group=ike2-policies

For example, we want to assign a different mode config for user "A", who uses certificate "rw-client1" to authenticate itself to the server. First of all, make sure a new mode config is created and ready to be applied for the specific user.

/ip ipsec mode-config
add address=192.168.66.2 address-prefix-length=32 name=usr_A split-include=192.168.55.0/24 system-dns=no

It is possible to apply this configuration for user "A" by using the match-by=certificate parameter and specifying his certificate with remote-certificate.

/ip ipsec identity
add auth-method=digital-signature certificate=server1 generate-policy=port-strict match-by=certificate mode-config=usr_A peer=ike2 policy-template-group=ike2-policies remote-certificate=rw-client1

Split tunnel configuration

Split tunneling is a method that allows road warrior clients to only access a specific secured network and at the same time send the rest of the traffic based on their internal routing table (as opposed to sending all traffic over the tunnel). To configure split tunneling, changes to mode config parameters are needed.

For example, we will allow our road warrior clients to only access the 10.5.8.0/24 network.

/ip ipsec mode-conf
set [find name="rw-conf"] split-include=10.5.8.0/24

It is also possible to send a specific DNS server for the client to use. By default, system-dns=yes is used, which sends DNS servers that are configured on the router itself in IP/DNS. We can force the client to use a different DNS server by using the static-dns parameter.

/ip ipsec mode-conf
set [find name="rw-conf"] system-dns=no static-dns=10.5.8.1

While it is possible to adjust the IPsec policy template to only allow road warrior clients to generate policies to network configured by split-include parameter, this can cause compatibility issues with different vendor implementations (see known limitations). Instead of adjusting the policy template, allow access to a secured network in IP/Firewall/Filter and drop everything else.

/ip firewall filter
add action=drop chain=forward src-address=192.168.77.0/24 dst-address=!10.5.8.0/24

Generating client certificates

To generate a new certificate for the client and sign it with a previously created CA.

/certificate
add common-name=rw-client1 name=rw-client1 key-usage=tls-client
sign rw-client1 ca=ca

PKCS12 format is accepted by most client implementations, so when exporting the certificate, make sure PKCS12 is specified.

/certificate
export-certificate rw-client1 export-passphrase=1234567890 type=pkcs12

A file named cert_export_rw-client1.p12 is now located in the routers System/File section. This file should be securely transported to the client's device.

Typically PKCS12 bundle contains also a CA certificate, but some vendors may not install this CA, so a self-signed CA certificate must be exported separately using PEM format.

/certificate
export-certificate ca type=pem

A file named cert_export_ca.crt is now located in the routers System/File section. This file should also be securely transported to the client's device.

PEM is another certificate format for use in client software that does not support PKCS12. The principle is pretty much the same.

/certificate
export-certificate ca
export-certificate rw-client1 export-passphrase=1234567890

Three files are now located in the routers Files section: cert_export_ca.crt, cert_export_rw-client1.crt and cert_export_rw-client1.key which should be securely transported to the client device.

Known limitations

Here is a list of known limitations by popular client software IKEv2 implementations.

• Windows will always ignore networks received by split-include and request policy with destination 0.0.0.0/0 (TSr). When IPsec-SA is generated, Windows requests DHCP option 249 to which RouterOS will respond with configured split-include networks automatically.

• Both Apple macOS and iOS will only accept the first split-include network.

• Both Apple macOS and iOS will use the DNS servers from system-dns and static-dns parameters only when 0.0.0.0/0 split-include is used.

• While some implementations can make use of different PFS group for phase 2, it is advised to use pfs-group=none under proposals to avoid any compatibility issues.

RouterOS client configuration

Import a PKCS12 format certificate in RouterOS.

/certificate import file-name=cert_export_RouterOS_client.p12 passphrase=1234567890

There should now be the self-signed CA certificate and the client certificate in the Certificate menu. Find out the name of the client certificate.

/certificate print

cert_export_RouterOS_client.p12_0 is the client certificate.

It is advised to create a separate Phase 1 profile and Phase 2 proposal configurations to not interfere with any existing IPsec configuration.

/ip ipsec profile
add name=ike2-rw
/ip ipsec proposal
add name=ike2-rw pfs-group=none

While it is possible to use the default policy template for policy generation, it is better to create a new policy group and template to separate this configuration from any other IPsec configuration.

/ip ipsec policy group
add name=ike2-rw
/ip ipsec policy
add group=ike2-rw proposal=ike2-rw template=yes

Create a new mode config entry with responder=no that will request configuration parameters from the server.

/ip ipsec mode-config
add name=ike2-rw responder=no

Lastly, create peer and identity configurations.

/ip ipsec peer
add address=2.2.2.2/32 exchange-mode=ike2 name=ike2-rw-client
/ip ipsec identity
add auth-method=digital-signature certificate=cert_export_RouterOS_client.p12_0 generate-policy=port-strict mode-config=ike2-rw peer=ike2-rw-client policy-template-group=ike2-rw

Verify that the connection is successfully established.

/ip ipsec
active-peers print
installed-sa print

Enabling dynamic source NAT rule generation

If we look at the generated dynamic policies, we see that only traffic with a specific (received by mode config) source address will be sent through the tunnel. But a router in most cases will need to route a specific device or network through the tunnel. In such case, we can use source NAT to change the source address of packets to match the mode config address. Since the mode config address is dynamic, it is impossible to create a static source NAT rule. In RouterOS, it is possible to generate dynamic source NAT rules for mode config clients.

For example, we have a local network 192.168.88.0/24 behind the router and we want all traffic from this network to be sent over the tunnel. First of all, we have to make a new IP/Firewall/Address list which consists of our local network

/ip firewall address-list
add address=192.168.88.0/24 list=local

When it is done, we can assign the newly created IP/Firewall/Address list to the mode config configuration.

/ip ipsec mode-config
set [ find name=ike2-rw ] src-address-list=local

Verify correct source NAT rule is dynamically generated when the tunnel is established.

[admin@MikroTik] > /ip firewall nat print 
Flags: X - disabled, I - invalid, D - dynamic 
0 D ;;; ipsec mode-config
chain=srcnat action=src-nat to-addresses=192.168.77.254 src-address-list=local dst-address-list=!local