Tempos limite para pares de VPN ASA

Eu configurei um site remoto com dois endereços IP para pares de VPN de data center - um primário (1.1.1.1) e um backup (2.2.2.2). Quando o ponto principal falha, o site remoto detecta a falha usando o DPD (após cerca de 15 segundos). Ele destrói as SAs e, em seguida, tenta se conectar novamente ao ponto principal! Após cerca de 30 segundos sem resposta, ele finalmente tenta o ponto de backup e se conecta imediatamente. Alguém mais viu isso e existe alguma maneira de evitar essa desnecessária espera de 30 segundos ?!

(A versão do código é 8.2 (5), configurações abaixo)

FIREWALL DE SITE REMOTO:

crypto ipsec transform-set L2L-VPN-TRANSFORM esp-3des esp-sha-hmac 
crypto ipsec security-association lifetime seconds 28800
crypto ipsec security-association lifetime kilobytes 4608000
!
tunnel-group 1.1.1.1 type ipsec-l2l
tunnel-group 1.1.1.1 general-attributes
 default-group-policy L2L-VPN-POLICY
tunnel-group 1.1.1.1 ipsec-attributes
 pre-shared-key *****
tunnel-group 2.2.2.2 type ipsec-l2l
tunnel-group 2.2.2.2 general-attributes
 default-group-policy L2L-VPN-POLICY
tunnel-group 2.2.2.2 ipsec-attributes
 pre-shared-key *****
!
crypto map OUTSIDE-MAP 1 match address ATOS-DC-ENCRYPTION-DOMAIN
crypto map OUTSIDE-MAP 1 set pfs 
crypto map OUTSIDE-MAP 1 set peer 1.1.1.1 2.2.2.2 
crypto map OUTSIDE-MAP 1 set transform-set L2L-VPN-TRANSFORM
crypto map OUTSIDE-MAP 1 set security-association lifetime seconds 3600
crypto map OUTSIDE-MAP 1 set security-association lifetime kilobytes 4608000
crypto map OUTSIDE-MAP interface OUTSIDE
crypto isakmp enable OUTSIDE
crypto isakmp policy 1
 authentication pre-share
 encryption 3des
 hash sha
 group 2
 lifetime 86400

FIREWALLS DC (AMBOS OS MESMOS):

crypto ipsec transform-set L2L-VPN-TRANSFORM esp-3des esp-sha-hmac 
crypto ipsec security-association lifetime seconds 28800
crypto ipsec security-association lifetime kilobytes 4608000
!
tunnel-group DefaultL2LGroup general-attributes
 default-group-policy L2L-VPN-POLICY
tunnel-group DefaultL2LGroup ipsec-attributes
 pre-shared-key *****
!
crypto dynamic-map REMOTE-DYNMAP 1 set pfs 
crypto dynamic-map REMOTE-DYNMAP 1 set transform-set L2L-VPN-TRANSFORM
crypto dynamic-map REMOTE-DYNMAP 1 set security-association lifetime seconds 3600
crypto dynamic-map REMOTE-DYNMAP 1 set security-association lifetime kilobytes 4608000
crypto dynamic-map REMOTE-DYNMAP 1 set reverse-route
crypto map OUTSIDE-MAP 1 ipsec-isakmp dynamic REMOTE-DYNMAP
crypto map OUTSIDE-MAP interface OUTSIDE
crypto isakmp enable OUTSIDE
crypto isakmp policy 1
 authentication pre-share
 encryption 3des
 hash sha
 group 2
 lifetime 86400

Logs mostrando a falha e o atraso:

Jun 18 2013 00:52:46: %ASA-5-111008: User 'enable_15' executed the 'clear logging buffer' command.
Jun 18 2013 00:54:37: %ASA-3-713123: Group = 1.1.1.1, IP = 1.1.1.1, IKE lost contact with remote peer, deleting connection (keepalive type: DPD)
Jun 18 2013 00:54:37: %ASA-5-713259: Group = 1.1.1.1, IP = 1.1.1.1, Session is being torn down. Reason: Lost Service
Jun 18 2013 00:54:37: %ASA-4-113019: Group = 1.1.1.1, Username = 1.1.1.1, IP = 1.1.1.1, Session disconnected. Session Type: IPsec, Duration: 0h:03m:00s, Bytes xmt: 480192, Bytes rcv: 478992, Reason: Lost Service
Jun 18 2013 00:54:37: %ASA-5-713041: IP = 1.1.1.1, IKE Initiator: New Phase 1, Intf OUTSIDE, IKE Peer 1.1.1.1  local Proxy Address 10.233.224.4, remote Proxy Address 1.1.1.1,  Crypto map (OUTSIDE-MAP)
Jun 18 2013 00:54:39: %ASA-3-713042: IKE Initiator unable to find policy: Intf INSIDE-TRANSIT, Src: 10.60.1.1, Dst: 10.250.1.1
Jun 18 2013 00:54:41: %ASA-3-713042: IKE Initiator unable to find policy: Intf INSIDE-TRANSIT, Src: 10.60.1.1, Dst: 10.250.1.1
Jun 18 2013 00:54:43: %ASA-3-713042: IKE Initiator unable to find policy: Intf INSIDE-TRANSIT, Src: 10.60.1.1, Dst: 10.250.1.1
Jun 18 2013 00:54:45: %ASA-3-713042: IKE Initiator unable to find policy: Intf INSIDE-TRANSIT, Src: 10.60.1.1, Dst: 10.250.1.1
Jun 18 2013 00:54:47: %ASA-3-713042: IKE Initiator unable to find policy: Intf INSIDE-TRANSIT, Src: 10.60.1.1, Dst: 10.250.1.1
Jun 18 2013 00:54:48: %ASA-3-713042: IKE Initiator unable to find policy: Intf INSIDE-TRANSIT, Src: 10.60.1.1, Dst: 10.250.1.1
Jun 18 2013 00:54:49: %ASA-3-713042: IKE Initiator unable to find policy: Intf INSIDE-TRANSIT, Src: 10.60.1.1, Dst: 10.250.1.1
Jun 18 2013 00:54:51: %ASA-3-713042: IKE Initiator unable to find policy: Intf INSIDE-TRANSIT, Src: 10.60.1.1, Dst: 10.250.1.1
Jun 18 2013 00:54:53: %ASA-3-713042: IKE Initiator unable to find policy: Intf INSIDE-TRANSIT, Src: 10.60.1.1, Dst: 10.250.1.1
Jun 18 2013 00:54:55: %ASA-3-713042: IKE Initiator unable to find policy: Intf INSIDE-TRANSIT, Src: 10.60.1.1, Dst: 10.250.1.1
Jun 18 2013 00:54:57: %ASA-3-713042: IKE Initiator unable to find policy: Intf INSIDE-TRANSIT, Src: 10.60.1.1, Dst: 10.250.1.1
Jun 18 2013 00:54:59: %ASA-3-713042: IKE Initiator unable to find policy: Intf INSIDE-TRANSIT, Src: 10.60.1.1, Dst: 10.250.1.1
Jun 18 2013 00:55:01: %ASA-3-713042: IKE Initiator unable to find policy: Intf INSIDE-TRANSIT, Src: 10.60.1.1, Dst: 10.250.1.1
Jun 18 2013 00:55:03: %ASA-3-713042: IKE Initiator unable to find policy: Intf INSIDE-TRANSIT, Src: 10.60.1.1, Dst: 10.250.1.1
Jun 18 2013 00:55:05: %ASA-3-713042: IKE Initiator unable to find policy: Intf INSIDE-TRANSIT, Src: 10.60.1.1, Dst: 10.250.1.1
Jun 18 2013 00:55:07: %ASA-3-713042: IKE Initiator unable to find policy: Intf INSIDE-TRANSIT, Src: 10.60.1.1, Dst: 10.250.1.1
Jun 18 2013 00:55:09: %ASA-5-713041: IP = 2.2.2.2, IKE Initiator: New Phase 1, Intf OUTSIDE, IKE Peer 2.2.2.2  local Proxy Address 10.233.224.4, remote Proxy Address 2.2.2.2,  Crypto map (OUTSIDE-MAP)
Jun 18 2013 00:55:09: %ASA-5-713119: Group = 2.2.2.2, IP = 2.2.2.2, PHASE 1 COMPLETED
Jun 18 2013 00:55:09: %ASA-5-713049: Group = 2.2.2.2, IP = 2.2.2.2, Security negotiation complete for LAN-to-LAN Group (2.2.2.2)  Initiator, Inbound SPI = 0xd21ad657, Outbound SPI = 0xd7d9c25a
Jun 18 2013 00:55:09: %ASA-5-713120: Group = 2.2.2.2, IP = 2.2.2.2, PHASE 2 COMPLETED (msgid=1949f878)
Jun 18 2013 00:55:09: %ASA-5-713041: Group = 2.2.2.2, IP = 2.2.2.2, IKE Initiator: New Phase 2, Intf INSIDE-TRANSIT, IKE Peer 2.2.2.2  local Proxy Address 10.60.0.0, remote Proxy Address 10.0.0.0,  Crypto map (OUTSIDE-MAP)
Jun 18 2013 00:55:09: %ASA-5-713049: Group = 2.2.2.2, IP = 2.2.2.2, Security negotiation complete for LAN-to-LAN Group (2.2.2.2)  Initiator, Inbound SPI = 0xd4218cd3, Outbound SPI = 0xf9a8108b
Jun 18 2013 00:55:09: %ASA-5-713120: Group = 2.2.2.2, IP = 2.2.2.2, PHASE 2 COMPLETED (msgid=c0a82858)

O ASA não tem um mecanismo para marcar pares como acima ou abaixo. Quando o DPD detecta que um par não está mais disponível, qualquer SA com esse par é derrubada. Quando o "tráfego interessante" exige uma nova SA, o ASA passa pelo processo normal da fase 1, o que significa começar com o primeiro ponto no seu mapa de criptografia e, se uma conexão não puder ser estabelecida, tentar o segundo.

Os 30 segundos de atraso são uma questão de tempo, enquanto o ASA "resolve as coisas" por assim dizer. Você tem tráfego acionando uma nova SA, enquanto o DPD está derrubando a SA existente para o mesmo ponto, o que cria um pouco de uma condição de corrida que acaba sendo resolvida.

Se um failover mais rápido é desejado, geralmente envolve a manutenção de ambos os túneis simultaneamente e o uso de GRE e roteamento dinâmico para mover o tráfego quando um túnel falha. No entanto, isso exigiria o uso de roteadores em vez dos ASAs, já que os ASAs não oferecem suporte ao GRE e apresentam algumas deficiências no roteamento dinâmico.