-- (rebroadcast to dev community from prior unicast discussion) --

Hi Nir

Sorry if the description is misleading. Didn't want a large title, and hoped 
that the description would provide those additional details to clarify the real 
goal of what's included and what's not included.

#1. Yes, it's only the gateway port. With that said, there are a series of BP 
that are being worked to support the dual-stack use case (although not 
necessarily dependent on each other) across Neutron, including internal ports 
facing the tenant.
https://blueprints.launchpad.net/neutron/+spec/allow-multiple-subnets-on-gateway-port
https://blueprints.launchpad.net/neutron/+spec/dnsmasq-mode-keyword
https://blueprints.launchpad.net/neutron/+spec/neutronclient-support-dnsmasq-mode-keyword
https://blueprints.launchpad.net/neutron/+spec/dnsmasq-bind-into-qrouter-namespace
https://blueprints.launchpad.net/neutron/+spec/dnsmasq-ipv6-slaac
https://blueprints.launchpad.net/neutron/+spec/dnsmasq-ipv6-dhcpv6-relay-agent
https://blueprints.launchpad.net/neutron/+spec/dnsmasq-ipv6-dhcpv6-stateful
https://blueprints.launchpad.net/neutron/+spec/dnsmasq-ipv6-dhcpv6-stateless

I'd suggest popping into the ipv6-subteam's meetings [1] and having further 
discussions about this as well.  We've been working on address allocation for 
the most part, but routing and service integration will need to be the next 
step.



#2. Surely it's possible to have multiple v4 and v6 [global] addresses on the 
interface, but for the gateway port, I don't have a specific use case. To 
remain consistent with current feature capability (single v4 IP), I continue to 
restrict a single IP from each flavor. With that said, there's nothing 
technically preventing this. It can be done; however, the CLI and Horizon would 
likely need significant changes. Right now, the code is written such that it 
explicitly prevents it. As I mentioned before, I actually had to add code in to 
disallow multiple addresses of the same flavor and send back an error to the 
user. Of course, we can evolve it in the future if a use-case warrants it.

The use case is for networks that rely on IP allocations for security.  You may 
want a pair of separate routed blocks on the same network for, say, a public 
network for the web server to get through a policy to the Internet, but a 
separate address to get to an internal-only database cluster somewhere.  I'm 
not saying it's the greatest way to do things, but I am sure there are people 
running networks this way.  The alternative would be to spin up another port on 
another network and configure another gateway port as well.



Thanks
Randy



On Thu, Jan 9, 2014 at 4:16 AM, Nir Yechiel 
<[email protected]<mailto:[email protected]>> wrote:
Hi Randy,

I don't have a specific use case. I just wanted to understand the scope here as 
the name of this blueprint ("allow multiple subnets on gateway port for 
router") could be a bit misleading.

Two questions I have though:

1. Is this talking specifically about the gateway port to the provider's 
next-hop router or relevant for all ports in virtual routers as well?
2. There is a fundamental difference between v4 and v6 address assignment. With 
IPv4 I agree that one IP address per port is usually enough (there is the 
concept of secondary IP, but I am not sure it's really common). With IPv6 
however you can sure have more then one (global) IPv6 on an interface. 
Shouldn't we support this?


Thanks,
Nir

________________________________
From: "Randy Tuttle" <[email protected]<mailto:[email protected]>>
To: "OpenStack Development Mailing List (not for usage questions)" 
<[email protected]<mailto:[email protected]>>
Cc: [email protected]<mailto:[email protected]>
Sent: Tuesday, December 31, 2013 6:43:50 PM
Subject: Re: [openstack-dev] [Neutron] Allow multiple subnets on gateway port 
for router


Hi Nir

Good question. There's absolutely no reason not to allow more than 2 subnets, 
or even 2 of the same IP versions on the gateway port. In fact, in our POC we 
allowed this (or, more specifically, we did not disallow it). However, for the 
gateway port to the provider's next-hop router, we did not have a specific use 
case beyond an IPv4 and an IPv6. Moreover, in Neutron today, only a single 
subnet is allowed per interface (either v4 or v6). So all we are doing is 
opening up the gateway port to support what it does today (i.e., v4 or v6) plus 
allow IPv4 and IPv6 subnets to co-exist on the gateway port (and same 
network/vlan). Our principle use case is to enable IPv6 in an existing IPv4 
environment.

Do you have a specific use case requiring 2 or more of the same IP-versioned 
subnets on a gateway port?

Thanks
Randy


On Tue, Dec 31, 2013 at 4:59 AM, Nir Yechiel 
<[email protected]<mailto:[email protected]>> wrote:
Hi,

With regards to 
https://blueprints.launchpad.net/neutron/+spec/allow-multiple-subnets-on-gateway-port,
 can you please clarify this statement: "We will disallow more that two 
subnets, and exclude allowing 2 IPv4 or 2 IPv6 subnets".
The use case for dual-stack with one IPv4 and one IPv6 address associated to 
the same port is clear, but what is the reason to disallow more than two 
IPv4/IPv6 subnets to a port?

Thanks and happy holidays!
Nir



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-Anthony

[1] https://wiki.openstack.org/wiki/Meetings/Neutron-IPv6-Subteam
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