OpenBSD + GRE + IPSec

Setting up GRE+IPSec is easy... right?!

OpenBSD + GRE + IPSec

I started this activity thinking that it would be a quick afternoon and I would have things working.  How wrong I was.  I'm writing this so that I can remember what I did to make this work.  Hopefully it helps someone else.


Now one thing I am doing here that is probably lead to most of my issues is I wanted to use rdomain(4)s for the private side of the connections.  So let's start from the beginning... it's a good place to start.  Step 1 is getting the communication between vm1 and vm2 working with straight GRE. Step 2 will encapsulate the GRE in IPSec.  Why would someone do this?  Why not just use straight IPSec?  Enter the need for the rdomains.  I want to logically separate functions/customers/etc from one another.  Using rdomains I can accomplish this. But once I go over a WAN/Internet I need some way to tag the traffic to a specific rdomain so I can keep it separate.  GRE allows this tagging through use of the vnetid.  So my tunnels keep stuff separate and and IPSec keeps things secure.

Step 1:  GRE

Enable sysctl values to allow forwarding and GRE.

# /etc/sysctl.conf
# enable GRE
# enable forwarding
# probably not needed but it will save some hair if you do
# enable ESP... should already be enabled

After the sysctl.conf is updated enable the settings.  Here a quick way to enable without restartinglll

for c in $(cat /etc/sysctl.conf | egrep -v "^#"); do sysctl $c; done

Now let's update the interface(s)

# vm1 gre0 interface
rdomain 10
tunneldomain 0
vnetid 11
tunnel inet
# vm1 vio0 interface
# vm2 gre0 interface
rdomain 10
tunneldomain 0
vnetid 11
tunnel inet
# vm2 vio0 interface
It would be awesome if we could specify an interface to use instead of the IP address of that interface, but until I can write better code... I'll have to dream.

That should be it.  To enable the interfaces without rebooting use the /etc/netstart command.  This also insures the hostname file will be process correctly during reboot.

vm1# /bin/sh /etc/netstart gre0 # or whatever interface you want.

Quick check of the interfaces should show similar

vm1# ifconfig vio0
        lladdr fe:e1:bb:d1:e8:ec
        index 1 priority 0 llprio 3
        media: Ethernet autoselect
        status: active
        inet netmask 0xffffff00 broadcast

vm1# ifconfig gre0
gre0: flags=8051<UP,POINTOPOINT,RUNNING,MULTICAST> rdomain 10 mtu 1476
        index 4 priority 0 llprio 6
        encap: vnetid 11 txprio payload rxprio packet
        groups: gre
        tunnel: inet -> ttl 64 nodf ecn rdomain 0
        inet --> netmask 0xffffff00

Now lets test.

vm1# ping
PING ( 56 data bytes
ping: sendmsg: No route to host
ping: wrote 64 chars, ret=-1
ping: sendmsg: No route to host
ping: wrote 64 chars, ret=-1
ping: sendmsg: No route to host
ping: wrote 64 chars, ret=-1
--- ping statistics ---
3 packets transmitted, 0 packets received, 100.0% packet loss

Why did it fail?  Well as stated above, I wanted to make my life hard err... I wanted to have the private side in a different rdomain.  Because of this I need to run the ping from within the correct rdomain like this

vm1# route -T 10 exec ping
PING ( 56 data bytes
64 bytes from icmp_seq=0 ttl=255 time=20.050 ms
64 bytes from icmp_seq=1 ttl=255 time=208.008 ms
64 bytes from icmp_seq=2 ttl=255 time=1.804 ms
--- ping statistics ---
3 packets transmitted, 3 packets received, 0.0% packet loss
round-trip min/avg/max/std-dev = 1.804/76.621/208.008/93.203 ms

Now that looks better!


Here we begin what must be the ultimate test in frustration, we need to enable IKED.  We could manually configure the IPSec SA, but that is not realistic and very manual...  (maybe after we have configured IKED the manual IPSec begins to look good.).

To start we need to distribute the key on each system to the other systems.  The key is located in /etc/iked/

vm1# scp /etc/iked/
Distribute vm1 to vm2
vm2# scp /etc/iked/
Distribute vm2 to vm1

Now let's configure iked.conf. For no particular reason at all we will make vm1 the initiator by specifying active. Make sure the the file has permission of '0600' so that iked doesn't complain.  We also set the mode to transport instead of the default tunneled.  Since the networks behind the rdomain are already encapsulated, the only thing that IPSec sees is the GRE packet.

# vm1 /etc/iked.conf

ikev2 active transport esp proto gre \
        from $vm1_ip to $vm2_ip \
        peer $vm2_ip
# vm2 /etc/iked.conf

ikev2 transport esp proto gre \
        from $vm2_ip to $vm1_ip \
        peer $vm1_ip

To test that the configuration files are correct use...

vm1# iked -nvf /etc/iked.conf 
ikev2 "policy1" active transport esp proto gre inet from to local any peer ikesa enc aes-128-gcm,aes-256-gcm prf hmac-sha2-256,hmac-sha2-384,hmac-sha2-512,hmac-sha1 group curve25519,ecp521,ecp384,ecp256,modp4096,modp3072,modp2048,modp1536,modp1024 ikesa enc aes-256,aes-192,aes-128,3des prf hmac-sha2-256,hmac-sha2-384,hmac-sha2-512,hmac-sha1 auth hmac-sha2-256,hmac-sha2-384,hmac-sha2-512,hmac-sha1 group curve25519,ecp521,ecp384,ecp256,modp4096,modp3072,modp2048,modp1536,modp1024 childsa enc aes-128-gcm,aes-256-gcm esn,noesn childsa enc aes-256,aes-192,aes-128 auth hmac-sha2-256,hmac-sha2-384,hmac-sha2-512,hmac-sha1 esn,noesn lifetime 10800 bytes 536870912 signature
configuration OK

If all is well you'll see "Configuration OK".

Now we can start iked with the -dv flag to see the debug information.  This will show us if something fails.  tmux(1) makes it easy to run this command in one pane and have a shell to continue to work on in another.  Now we can check that the iked daemons are communicating using the ikectl command

vm1# ikectl show sa

iked_sas: 0xdd25d63a7d0 rspi 0x19dbcab84fda1041 ispi 0x9c7b6e03c5247505><FQDN/vm2>[] ESTABLISHED r udpecap nexti 0x0 pol 0xdd205f67000
.1:500-><FQDN/vm2>[] ESTABLISHED r udpecap nexti 0x0 pol 0xdd205f6(LA) B=0x0 P=0xdd20d731600 @0xdd25d63a7d0
  sa_childsas: 0xdd210366100 ESP 0x8b2cd3f1 in -> dd25d63a7d0
(LA) B=0x0 P=0xdd20d731600 @0xdd25d63a7d0
  sa_childsas: 0xdd20d731600 ESP 0x40b143ea out -> (L) B=0x0 P=0xdd210366100 @0xdd25d63a7d0
 (L) B=0x0 P=0xdd210366100 @0xdd25d63a7d0
  sa_flows: 0xdd24e75bc00 ESP out -> [47]@-1 (L) @0xd25d63a7d0
  sa_flows: 0xdd1fa4b1c00 ESP in -> [47]@-1 (L) @0xd
iked_activesas: 0xdd20d731600 ESP 0x40b143ea out ->
0 (L) B=0x0 P=0xdd210366100 @0xdd25d63a7d0
iked_activesas: 0xdd210366100 ESP 0x8b2cd3f1 in ->
 (LA) B=0x0 P=0xdd20d731600 @0xdd25d63a7d0
iked_flows: 0xdd1fa4b1c00 ESP in -> [47]@-1 (L) @0xd
iked_flows: 0xdd24e75bc00 ESP out -> [47]@-1 (L) @0xdd25d63a7d0

If you have similar output you can now use the ipsecctl command to see the IPSec SAs

vm1# ipsecctl -sall
flow esp in proto gre from to peer srcid FQDN/v
m1 dstid FQDN/vm2 type require
flow esp out proto gre from to peer srcid FQDN/
vm1 dstid FQDN/vm2 type require

esp transport from to spi 0x40b143ea enc aes-128-gcm
esp transport from to spi 0x8b2cd3f1 enc aes-128-gcm

If things are not working check the the iked pane and look for any errors.  I have listed some errors I saw below.

Last we need to enable the enc interface


Run the netstart command like was done previously.

Some may ask why we don't put this interface into the rdomain 10 like the GRE interfaces.  This took me longer than I would like to admit to figure out.  let me try to explain. The traffic first hits gre0 interface and is encapsulated and the encapsulated packet is placed in rdomain 0 (the default domain). From there the packet is then intercepted by IPSec and encrypted before being sent out the interface.

Let's test again.  From vm2 we will run a tcpdump on the vio0 interface.

vm2# tcpdump -i vio0 -nvv proto 50 or proto 47

This will show us if the traffic is ESP or GRE.  From vm1 we run the ping again (and we won't forget to do it from the correct rdomain? Right ;)

vm1# route -T 10 exec ping
PING ( 56 data bytes
64 bytes from icmp_seq=0 ttl=255 time=0.760 ms
64 bytes from icmp_seq=1 ttl=255 time=1.535 ms
--- ping statistics ---
2 packets transmitted, 2 packets received, 0.0% packet loss
round-trip min/avg/max/std-dev = 0.760/1.148/1.535/0.388 ms

and the output from tcpdump should look similar

vm2# tcpdump -i vio0 -nvv proto 50 or proto 47
tcpdump: listening on vio0, link-type EN10MB

22:28:29.832670 > esp spi 0x40b143ea seq 2 len 128 (ttl 64, id 16207, len 148)
22:28:29.832850 > esp spi 0x8b2cd3f1 seq 2 len 128 (ttl 64, id 27150, len 148)
22:28:31.849452 > esp spi 0x40b143ea seq 3 len 128 (ttl 64, id 14054, len 148)
22:28:31.849804 > esp spi 0x8b2cd3f1 seq 3 len 128 (ttl 64, id 52498, len 148)

With everything working we can stop the debug session with iked and start them like proper services.

rcctl enable iked
rcctl start iked


Below are some error you are likely to see if the keys are not distributed correctly

ca_getreq: no valid local certificate found for FQDN/vm1
ca_validate_pubkey: could not open public key pubkeys/fqdn/vm2
ikev2_dispatch_cert: peer certificate is invalid
ikev2_send_auth_failed: authentication failed for FQDN/vm2
sa_free: authentication failed notification from peer