Hi Nischal,

Thank you for the info. Is there anyway to override the ".2 for DNS"
behavior or should I consider opening a feature request? When creating an
external network with public IP's losing even 1 of these to an unused
service is a bit tough to swallow considering the state of IP availability
on the Internet. We're not currently planning to use any of the DNS or DHCP
functionality within Contrail; in fact I would like to operate without any
concept of IPAM if at all possible :)

-Dan



On Sat, Oct 17, 2015 at 12:34 PM, Nischal Sheth <[email protected]> wrote:

>
> Hi Dan,
>
> The .2 address is set aside for use as DNS server at the TSN, irrespective
> of whether DNS is enabled or not.
>
> I think you should be able to control assignment of the MX irb addresses
> by creating an allocation pool. The pool could have the first 4 addresses
> in your case. The rest of the addresses in the subnet can be owned by your
> DHCP server.
>
> -Nischal
>
> Sent from my iPhone
>
> On Oct 17, 2015, at 9:25 AM, Dan Houtz <[email protected]> wrote:
>
> Hi fellow Contrailers,
>
> The 2.21 release adds functionality to configure redundant MX gateways
> using the virtual-gateway-address knob. Is anyone able to explain the logic
> of the per router IP assignments? Are these able to be set in a
> deterministic way or must we rely on Contrail to choose them at random from
> the subnet?
>
> For example, I created a network using 10.10.10.0/24 with .1 as the
> gateway. Contrail configured mx1 with and address of .3 and mx2 with an
> address of .4.
>
> I don't quite understand why .2 is skipped. At least in our environment
> where we'll probably only have 2 MX's for a VN, we would prefer that the
> first 3 usable IP addresses in the subnet ALWAYS be used for each router
> and the virtual gateway address.
>
> I'm also concerned about what happens if you remove a physical router
> temporarily. In my case above, I removed mx1 and then re-added it to the
> VN. When doing this, mx1 was then assigned a new IP address - this time .7.
> So if seems like, over, time it will cycle through the entire IP block.
> What happens if it chooses an IP that a host is already using?
>
> Again, I would much prefer if I could control this assignment so I can
> make sure it gets the same IP address. Removing/Adding a physical router to
> a VN might not be super common but I could see it happening for testing,
> troubleshooting, and maintenance .
>
> Thanks!
> Dan
>
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