[strongSwan] weird cisco behaviour - how to work around?

Noel Kuntze noel.kuntze+strongswan-users-ml at thermi.consulting
Fri Jun 12 10:18:12 CEST 2020

Hi Volodymyr,

I'd configure your RADIUS server to use DAE and allow new connections, thus simply disconnecting existing clients with the same account when a client authenticates as that account.

Kind regards


Am 11.06.20 um 22:41 schrieb Volodymyr Litovka:
> Colleagues, hi,
> as always, the most magic things happens with those, who claims the best security solutions in the Universe :-\
> Faced a very strange behaviour when using IPSec between Strongswan (server) and Cisco (client). On Cisco I'm using the tunnel configuration:
>> interface Tunnel1
>>  ip address negotiated
>>  ip mtu 1400
>>  ip tcp adjust-mss 1360
>>  tunnel source GigabitEthernet1
>>  tunnel mode ipsec ipv4
>>  tunnel destination y.y.y.y
>>  tunnel protection ipsec profile NEW-tun
> and things are ok to some degree: when I shutting down the tunnel, Cisco IOS clears all states inside (both ike sa and ike session), while sending to the peer only request to close Child SA:
>> Jun 11 21:48:58 newton charon-systemd[3040]: received DELETE for ESP CHILD_SA with SPI fb709251
> causing Strongswan to delete Child SA but to keep IKE SA active:
>> root at newton:/etc/strongswan.d# swanctl --list-sas
>> ikev2-eap-mschapv2: #1, ESTABLISHED, IKEv2, 865999d54ba73a0c_i 63a1831a36835a29_r*
>>   local  'newton.sq' @ y.y.y.y[4500]
>>   remote '' @ x.x.x.x[4500] EAP: 'doka.ua at gmail.com' []
>>   AES_GCM_16-256/PRF_HMAC_SHA2_256/MODP_2048
>>   established 246s ago, rekeying in 10188s
>>   active:  IKE_DPD
> I'm using Radius to authenticate users and manage simultaneous use of sessions with same id. Thus, the problem with this issue is that Strongswan don't send Accounting-Stop record until DPD will find it finally closed and during this period connection looks as active, preventing reconnection.
> Even after I reduced dpd_delay to 10s, full cleanup happens in about 3 minutes after Child SA was closed:
>> 21:48:58 newton: 09[IKE] <ikev2-eap-mschapv2|1> received DELETE for ESP CHILD_SA with SPI fb709251
>> 21:48:58 newton: 09[IKE] <ikev2-eap-mschapv2|1> closing CHILD_SA carlo{1} with SPIs cfd87900_i [...]
>> 21:48:58 newton: 09[IKE] <ikev2-eap-mschapv2|1> sending DELETE for ESP CHILD_SA with SPI cfd87900
>> 21:48:58 newton: 09[CHD] <ikev2-eap-mschapv2|1> CHILD_SA carlo{1} state change: INSTALLED => DELETING
>> 21:48:58 newton: 09[IKE] <ikev2-eap-mschapv2|1> CHILD_SA closed
>> 21:48:58 newton: 09[CHD] <ikev2-eap-mschapv2|1> CHILD_SA carlo{1} state change: DELETING => DESTROYING
>> 21:49:22 newton: 16[IKE] <ikev2-eap-mschapv2|1> sending DPD request
>> 21:49:22 newton: 16[IKE] <ikev2-eap-mschapv2|1> queueing IKE_DPD task
>> 21:49:22 newton: 16[IKE] <ikev2-eap-mschapv2|1>   activating IKE_DPD task
>> 21:49:26 newton: 05[IKE] <ikev2-eap-mschapv2|1> retransmit 1 of request with message ID 8
>> 21:49:34 newton: 09[IKE] <ikev2-eap-mschapv2|1> retransmit 2 of request with message ID 8
>> 21:49:47 newton: 12[IKE] <ikev2-eap-mschapv2|1> retransmit 3 of request with message ID 8
>> 21:50:10 newton: 05[IKE] <ikev2-eap-mschapv2|1> retransmit 4 of request with message ID 8
>> 21:50:52 newton: 07[IKE] <ikev2-eap-mschapv2|1> retransmit 5 of request with message ID 8
>> 21:52:07 newton: 06[IKE] <ikev2-eap-mschapv2|1> giving up after 5 retransmits
>> 21:52:07 newton: 06[CFG] <ikev2-eap-mschapv2|1> sending RADIUS Accounting-Request to server ''
>> 21:52:08 newton: 06[CFG] <ikev2-eap-mschapv2|1> received RADIUS Accounting-Response from server ''
>> 21:52:08 newton: 06[IKE] <ikev2-eap-mschapv2|1> IKE_SA ikev2-eap-mschapv2[1] state change: ESTABLISHED => DESTROYING
> So, the question is: are there ways to be more aggressive in detecting closed connections, e.g. :
> - is it possible to destroy IKE SA if there are no Child SAs anymore?
> - or, may be, change parameters of DPD messages retransmission? - qty of messages, fixed delay between messages, smth else?
> Any other ways to work around this problem?
> Thank you.
> --
> Volodymyr Litovka
>   "Vision without Execution is Hallucination." -- Thomas Edison

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