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NAT with ECMP / multiple default routes

Question asked by Markus Marquardt on Sep 5, 2017
Latest reply on Sep 7, 2017 by Markus Marquardt

Hi, in my scenario I have a Gateway with multiple (two) equal cost default routes. I am trying to get NAT properly done but I am running into issues.


As there are two equal cost default routes learned by OSPF, the external interfaces have different ip addresses in different subnets leading to internet routers to two different ISPs.


So the source ip address of packets going out on each external interface shoud get NATted to the interface's address, right?


From my understanding, it is not possible to use a static NAT rule in this scenario because we cannot configure ONE static address for hide nat, we have always take into account that we have TWO external interfaces. So I came up with just enabling the AUTO HIDE NAT by enabling it in the Gateway properties.


Unfortunately we have issues with it, as we are seeing packets going out on one external interface with the NATted source address of the other external interface (and vice versa). This leads to packets get dropped or irregular routing.


It happens on R77.30 as well as on R80.10 and is reproduceable also in a very basic setup.


Is there any other way to get this working? ECMP default routes from OSPF with hide nat? What is your experience?