On Wed, 6 Sep 2000, Nurarif Wibawa wrote:
> Hi,
>
> I need a solution for the configuration below:
>
> Internet
> | |
> | |
> ISP A ISP B
> | |
> | |
> Customer
> |
> ---------------------------- Web Server
>
> Web Server will has 2 IP addresses, one will be given by ISP A and the other one
>will be given by ISP B.
> Primary DNS server is on ISP A and secondary DNS server is on ISP B.
> The DNS server on ISP A has two records for customer's web server, for example :
> www a 10.0.0.1 (IP address given by ISP A)
> www a 20.0.0.1 (IP address given by ISP B)
> The goal is to use dual ISP for back-up purpose, so the web server will serve for 24
>hour / day.
> Since the DNS server only load balance between two same host records, how about if
>one link is broken ?
The right way: Use BGP.
Another right way: Put the server in a multi-homed co-lo facility.
An ugly DNS hack:
Internet
| |
| |
ISP A ISP B
| |
| |
DNS A DNS B
Customer
[NAT]
---------------------------- Web Server
Both DNS A and B are located at customer's premise and are authoritative.
Both have relatively short TTL, on the order of a few minutes. DNS A
advertises the address on ISP A's network, and B on B's.
In theory, if ISP A becomes unreachable, then DNS A will also not be
reachable and only the announcement by DNS B will propagate.
Drawback: sub-optimal routing. Suppose a web surfer on ISP A, using
perhaps even the same router as customer makes a DNS query. By random
chance, that session is directed to DNS B. This visitor will be passed
the IP address of B, and take the long way around the internet to get
to the server. Try to pick two ISPs which have good peering to each
other.
--
Jay Hennigan - Network Administration - [EMAIL PROTECTED]
NetLojix Communications, Inc. NASDAQ: NETX - http://www.netlojix.com/
WestNet: Connecting you to the planet. 805 884-6323
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