North American Network Operators Group

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  • From: william
  • Date: Tue Aug 18 06:22:58 1998

Hi all!

Just wondering if the following is possible:


Corporate intranet is currently connected to 2 separate ISPs using 2
different set of IP addresses.  When one is down, the network has to be
reconfigured for access via the 2nd ISP.

Required Result:

Corporate intranet connects to 2 ISPs.  When one is down or unavailable,
traffic will automatically shift to the other connection.  DNS server and
mail server remains inside the intranet.  The DNS and mail servers should
not be reconfigured during any problems and should keep on working.

Proposed Solution:

The 7010 router will be connected to the 2 ISPs.  The 7010 will be upgraded
to an IOS that supports NAT; all IP address behind the 7010 will be treated
as internal IP addresses (to reduce reconfiguration).  IP address subnets
from both ISPs will be NAT-mapped to internal IP addresses over the 7010,
including the DNS server and the mail server.

The DNS will be configured to use their DNS as the primary name server.
The 2 ISPs' name servers will be used as secondary name servers.

The mail server will be configured to have 2 IP address, one actual and one
virtual IP address using the network card.  The DNS will have an MX 10 and
an MX 20, each pointing to one IP addresses for the network card.

Is this solution possible?  Will it work?  Did I forget anything?  Any tips?