openstack/neutron
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Add devref for supporting use floatingip cross scopes

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[1] has been merged for supporting use floating IP to cross scopes.
The devref should be updated for it, due to the discussion in [1].

[1] https://review.openstack.org/#/c/283134/

Change-Id: I5c330ba5d5446ec985b628d8bc3b37d65fa7d53d
Related-Bug: #1543885
This commit is contained in:
Hong Hui Xiao 2016-03-08 03:52:05 -05:00 committed by Brian Haley
parent 87cb9d8552
commit 36893a55bd
1 changed files with 32 additions and 5 deletions
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37
doc/source/devref/address_scopes.rst
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@ -100,12 +100,39 @@ Routing
The reference implementation honors address scopes. Within an address scope,
addresses route freely (barring any FW rules or other external restrictions).
Between scopes, routed is prevented unless address translation is used. For
now, floating IPs are the only place where traffic crosses scope boundaries.
The 1-1 NAT allows this to happen.
Between scopes, routing is prevented unless address translation is used.
.. TODO (Carl) Implement NAT for floating ips crossing scopes
.. TODO (Carl) Implement SNAT for crossing scopes
For now, floating IPs are the only place where traffic crosses scope
boundaries. When a floating IP is associated to a fixed IP, the fixed IP is
allowed to access the address scope of the floating IP by way of a 1:1 NAT
rule. That means the fixed IP can access not only the external network, but
also any internal networks that are in the same address scope as the external
network. This is diagrammed as follows::
+----------------------+ +---------------------------+
| address scope 1 | | address scope 2 |
| | | |
| +------------------+ | | +------------------+ |
| | internal network | | | | external network | |
| +-------------+----+ | | +--------+---------+ |
| | | | | |
| +-------+--+ | | +------+------+ |
| | fixed ip +----------------+ floating IP | |
| +----------+ | | +--+--------+-+ |
+----------------------+ | | | |
| +------+---+ +--+-------+ |
| | internal | | internal | |
| +----------+ +----------+ |
+---------------------------+
Due to the asymmetric route in DVR, and the fact that DVR local routers do not
know the information of the floating IPs that reside in other hosts,
there is a limitation in the DVR multiple hosts scenario. With DVR in
multiple hosts, when the destination of traffic is an internal fixed IP
in a different host, the fixed IP with a floating IP associated can't cross
the scope boundary to access the internal networks that are in the same
address scope of the external network.
See https://bugs.launchpad.net/neutron/+bug/1682228
RPC
~~~