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Old 8th November 2010
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jggimi jggimi is offline
More noise than signal
 
Join Date: May 2008
Location: USA
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Quote:
Originally Posted by SlyM View Post
I am trying to use only 1 NIC...and ISP1's IP assigned to the NIC as the primary IP and the IP of ISP2 aliased onto the same NIC
Alias IP addresses are not designed for routing. They merely give the NIC multiple IP addresses to respond to. But they will always respond with their "real" address as the origination.

That will -usually- work with stateful connection protocols like TCP, as there are TCP sequence numbers, but will of course fail with any stateless connections -- UDP and ICMP being the two that come immediately to mind.

(I discovered this with UDP on some aliased addresses years ago.)

Add another NIC, and use two separate subnets for Multipath routing. Avoid alias IP addresses except for TCP-only activity, such as web servers. FAQ 6.14 shows an example of equal cost routing -- using two interfaces.
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