configuring isdn on cisco routers 1

[yankeenica]

I have been tasked to design a VPN with a site in Europe. The site has contracted with their ISP for 8 IP addresses and an ISDN line. Correct me if I'm wrong but doesn't ISDN require ISDN modems dialing into each other based on 'interesting traffic'? Further if this is true is there a method to keep the lines open all the time? Please point me to the cisco documentation regarding this if you can.

Thanks.

Tim Manville
manvilleti@state.gov

 

[talisker]

http://www.cisco.com/cgi-bin/Support/PSP/psp_view.pl?p=Internetworking:ISDN

(TAC access required)

or

http://www.cisco.com/univercd/cc/td/doc/cisintwk/idg4/nd2011.htm

(no TAC access required)

I hope this helps!

 

[yankeenica]

the 2nd link was quite helpful. So if you are using pri the link is always up. you access the internet via a csu/dsu configured for isdn?

tim manville
manvilleti@state.gov

 

[talisker]

ISDN is a dial-up line regardless of whether its BRI or PRI. When data wants to go across the line, a session is established, the data is transfered, the session is closed. If you want the link up all the time you could use keepalives, but it would cost big time (you pay by the minute).

If you want a link that is always up it is more cost-efficient to use a point-to-point T1 or frame-relay (depending on the distance to the router on the other end of the circuit). These have a flat monthly charge that doesn't change with the amount of data you put across it.

Yes, you need a specfic type of DSU/CSU that works with ISDN. I don't think a regular T1 DSU would work - but it may depend on the type of ISDN interface you have in the router: some have intergrated NT1/CSUs.

 

[rjdscs]

If you are planning to use VPN I am assuming you are going over the internet, so where does Cisco ISDN Routers come into play? Surely the way to go would be to have some form of leased line connection to the internet for both sites. Now is the VPN connections going to be always originate from the same site? If so all that is needed is a VPN aware firewall at the destination side and appropriate VPN client software installed on the originating site. If both sites can start a VPN session then place a VPN aware firewall at both sites.

If you are connecting the two sites directly using ISDN without going over the internet then again your requirements vary depending on if both sites can start a connection, or whether it is always one site that establishes the connection. If either site can start a session then you can have a ISDN Router at each end. If it is always one site that starts the session, then that site should have an ISDN Router and you could connect to the other site either via another router or via a RAS server.