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

Noel Kuntze noel.kuntze+strongswan-users-ml at thermi.consulting
Fri Jun 12 11:59:16 CEST 2020

Hi Volodymyr,

I disagree. That "prevention" enables a better user experience during network or software failures on the client side, as described before and by yourself already.

In IKEv2, every packet exchange is used for dead peer detection, so you need to change the IKEv2 timeout in strongswan.conf to tweak that.

Kind regards


Am 12.06.20 um 11:55 schrieb Volodymyr Litovka:
> 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.
> Thanks.
> 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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