you can easly configure the VPN between Cisco router and Juniper netscreen
just follow the instruction of junper site to site given and give remote IP of cisco router
http://www.fir3net.com/Netscreen/netscreen-creating-a-route-based-vpn.html
or
http://kb.juniper.net/InfoCenter/index?page=content&id=KB14330
and for cisco config check the link and give the ip of juniper
http://www.firewall.cx/cisco-technical-knowledgebase/cisco-routers/867-cisco-router-site-to-site-ipsec-vpn.html
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