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

Volodymyr Litovka doka.ua at gmx.com
Fri Jun 12 11:55:37 CEST 2020

Hi Noel,

may be it sounds a bit strange :-) but this is kind of
errors/misconfigurations prevention. Existing connection must not be
dropped if somebody else trying to connect with same credentials.


In such configuration, it leads to another problem - if a client's
Internet connection flapped, it will be able to reconnect in ~3m because
of described earlier behaviour.

While it's possible to manage conn.dpd_delay, is it possible to manage
delay pattern of DPD messages and/or their qty? If admin (e.g. me) knows
and understands what he is doing, this can solve an issue, shortening
time to detection of dead peer.


On 12.06.2020 11:18, Noel Kuntze wrote:
> 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
> Noel
> 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
Volodymyr Litovka
   "Vision without Execution is Hallucination." -- Thomas Edison

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