this is for routers, but creation of the dynamic peer entires should be similar to what you want to do.
YMMV
In order to configure a LAN-to-LAN Virtual Private Network (VPN) tunnel between two routers with dynamic IP addresses, complete these steps apart from the basic configuration:
You can built an Ipsec VPN tunnel between Cisco routers, both on Dynamic IP addresses
In order to configure a LAN-to-LAN Virtual Private Network (VPN) tunnel between two routers with dynamic IP addresses, complete these steps apart from the basic configuration:
Configure the set peer dynamic command on one side of the tunnel with the use of the static crypto map.
On the remote router, configure the dynamic crypto map without the use of the peer statement.
With the use of the set peer dynamic command, the host name of the IP Security (IPsec) peer is resolved through a domain name server (DNS) lookup before the router establishes the IPsec tunnel.
Note:
1. Only a router with a static crypto map can initiate the tunnel with the dynamic DNS resolution of the peer statement.
2. This works on Cisco IOS router code 12.3 and above
Examples
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The following example shows a crypto map configuration when IKE will be used to establish the security associations (SAs). In this example, an SA could be set up to either the IPSec peer at 10.0.0.1 or the peer at 10.0.0.2.
Code:
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crypto map mymap 10 ipsec-isakmp
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match address 101
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set transform-set my_t_set1
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set peer 10.0.0.1
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set peer 10.0.0.2
#
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The following example shows how to configure a router to perform real-time Domain Name System (DNS) resolution with a remote IPSec peer; that is, the host name of peer is resolved via a DNS lookup right before the router establishes a connection (an IPSec tunnel) with the peer.
Code:
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crypto map secure_b 10 ipsec-isakmp
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match address 140
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set peer b.cisco.com dynamic
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set transform-set xset
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interface serial1
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ip address 30.0.0.1
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crypto map secure_b
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access-list 140 permit ...
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The following example shows that the first peer, at IP address 1.1.1.1, is the default peer.
Code:
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crypto map tohub 1 ipsec-isakmp
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set peer 1.1.1.1 default
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set peer 2.2.2.2
#
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The following example shows that the peer with the host name fred is the default peer.
Code:
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crypto map tohub 2 ipsec-isakmp
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set peer fred dynamic default
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set peer barney dynamic
ref:
https://supportforums.cisco.com/thread/343363