Strongswan: “received NO_PROPOSAL_CHOSEN error notify” while connecting to Cisco Router

Question

I'm trying to establish an ipsec connection from a raspberry pi with Strongswan (Linux strongSwan U5.5.1/K4.14.50+) to a Cisco Router.

This is the Strongswan output:

root@raspberrypi:~# ipsec up Ciscoios
initiating Main Mode IKE_SA Ciscoios[1] to x.x.x.138
generating ID_PROT request 0 [ SA V V V V V ]
sending packet: from x.x.x.118[500] to x.x.x.138[500] (180 bytes)
received packet: from x.x.x.138[500] to x.x.x.118[500] (104 bytes)
parsed ID_PROT response 0 [ SA V ]
received NAT-T (RFC 3947) vendor ID
generating ID_PROT request 0 [ KE No NAT-D NAT-D ]
sending packet: from x.x.x.118[500] to x.x.x.138[500] (244 bytes)
received packet: from x.x.x.138[500] to x.x.x.118[500] (304 bytes)
parsed ID_PROT response 0 [ KE No V V V V NAT-D NAT-D ]
received Cisco Unity vendor ID
received DPD vendor ID
received unknown vendor ID: d4:35:02:b0:57:db:41:f3:0a:fc:a9:73:1f:79:b2:e4
received XAuth vendor ID
generating ID_PROT request 0 [ ID HASH ]
sending packet: from x.x.x.118[500] to x.x.x.138[500] (84 bytes)
received packet: from x.x.x.138[500] to x.x.x.118[500] (68 bytes)
parsed ID_PROT response 0 [ ID HASH ]
IKE_SA Ciscoios[1] established between x.x.x.118[[email protected]]...x.x.x.138[x.x.x.138]
scheduling reauthentication in 86201s
maximum IKE_SA lifetime 86381s
generating QUICK_MODE request 3400625212 [ HASH SA No ID ID ]
sending packet: from x.x.x.118[500] to x.x.x.138[500] (172 bytes)
received packet: from x.x.x.138[500] to x.x.x.118[500] (84 bytes)
parsed INFORMATIONAL_V1 request 1129071936 [ HASH N(NO_PROP) ]
received NO_PROPOSAL_CHOSEN error notify
establishing connection 'Ciscoios' failed

This is the ipsec.conf:

ipsec.conf - strongSwan IPsec configuration file


config setup
    strictcrlpolicy=no
    #charondebug="ike 4, knl 4, cfg 2"    #useful debugs
    uniqueids = no



conn %default
    ikelifetime=1440m
    keylife=60m
    rekeymargin=3m
    keyingtries=1
    keyexchange=ikev1
    authby=secret

conn Ciscoios
    left=x.x.x.118
    leftid=fqdn:[email protected]
    leftsubnet=10.10.145.0/24
    leftfirewall=no
    right=x.x.x.138
    rightsubnet=x.x.x.138/32
    rightid=x.x.x.x.138
    rightauth=psk
    leftauth=psk
    auto=add
    ike=3des-sha1-modp1024!
    esp=3des-sha1!

On the Cisco I have configured this:

crypto isakmp policy 1
encr 3des
authentication pre-share
group 2

crypto ipsec transform-set ESP-3DES-MD5 esp-3des esp-md5-hmac
mode transport
crypto ipsec transform-set ESP-NULL-MD5 esp-null esp-md5-hmac
mode transport

crypto dynamic-map TEST
description ipsecTest
set transform-set ESP-NULL-MD5 ESP-3DES-MD5
set isakmp-profile Routing
match address IPSEC

I think I might have the wrong parameters set at ike and esp in the ipsec.conf. The ipsec config on the Cisco works fine with another Cisco router as a peer but not with the Raspberry Pi. Can anyone help?

Solution

The ESP proposal in the strongSwan config must match that of the Cisco box, so change it to esp=3des-md5!, or, alternatively, modify the Cisco config to use SHA-1 as integrity algorithm.

Be aware that these are all very weak algorithms.