tcpdump показывает такую вот картину:
01:08:43.009439 IP 192.168.0.2 > 192.168.0.1: ESP(spi=0x0009924f,seq=0x6)
01:08:43.010781 IP 192.168.0.1 > 192.168.0.2: icmp 40: echo reply seq 54784
01:08:44.544115 IP 192.168.0.2 > 192.168.0.1: ESP(spi=0x0009924f,seq=0x7)
01:08:44.544813 IP 192.168.0.1 > 192.168.0.2: icmp 40: echo reply seq 55040
01:08:46.034120 IP 192.168.0.2 > 192.168.0.1: ESP(spi=0x0009924f,seq=0x8)
01:08:46.034808 IP 192.168.0.1 > 192.168.0.2: icmp 40: echo reply seq 55296
естественно пакеты не проходят.