On Thu, Oct 06, 2016 at 03:53:12AM -0700, Gurucharan Shetty wrote:
> OVN currently supports multiple gateway routers (residing on
> different chassis) connected to the same logical topology.
>
> When external traffic enters the logical topology, they can enter
> from any gateway routers and reach its eventual destination. This
> is achieved with proper static routes configured on the gateway
> routers.
>
> But when traffic is initiated in the logical space by a logical
> port, we do not have a good way to distribute that traffic across
> multiple gateway routers.
>
> This commit introduces one particular way to do it. Based on the
> source IP address or source IP network of the packet, we can now
> jump to a specific gateway router.
>
> This is very useful for a specific use case of Kubernetes.
> When traffic is initiated inside a container heading to outside world,
> we want to be able to send such traffic outside the gateway router
> residing in the same host as that of the container. Since each
> host gets a specific subnet, we can use source IP address based
> policy routing to decide on the gateway router.
>
> Rationale for using the same routing table for both source and
> destination IP address based routing:
>
> Some hardware network vendors support policy routing in a different table
> on arbitrary "match". And when a packet enters, if there is a match
> in policy based routing table, the default routing table is not
> consulted at all. In case of OVN, we mainly want policy based routing
> for north-south traffic. We want east-west traffic to flow as-is. Creating
> a separate table for policy based routing complicates the configuration
> quite a bit. For e.g., if we have a source IP network based rule added,
> to decide a particular gateway router as a next hop, we should add rules at
> a higher priority for all the connected routes to make sure that east-west
> traffic is not effected in the policy based routing table itself.
>
> Signed-off-by: Gurucharan Shetty <g...@ovn.org>
Thank you!
Acked-by: Ben Pfaff <b...@ovn.org>
I kind of like this better since it doesn't talk about priorities, which
seem like a lower level concept:
diff --git a/ovn/ovn-nb.xml b/ovn/ovn-nb.xml
index 3646e55..7626551 100644
--- a/ovn/ovn-nb.xml
+++ b/ovn/ovn-nb.xml
@@ -1083,6 +1083,12 @@
Each record represents a static route.
</p>
+ <p>
+ When multiple routes match a packet, the longest-prefix match is chosen.
+ For a given prefix length, a <code>dst-ip</code> route is preferred over
+ a <code>src-ip</code> route.
+ </p>
+
<column name="ip_prefix">
<p>
IP prefix of this route (e.g. 192.168.100.0/24).
@@ -1098,16 +1104,12 @@
<li>
<code>src-ip</code>: This policy sends the packet to the
<ref column="nexthop"/> when the packet's source IP address matches
- <ref column="ip_prefix"/>. If the <ref column="ip_prefix"/> has
- a mask length of <code>n</code>, then this record gets an implicit
- priority of <code>2*n</code>.
+ <ref column="ip_prefix"/>.
</li>
<li>
<code>dst-ip</code>: This policy sends the packet to the
<ref column="nexthop"/> when the packet's destination IP address
- matches <ref column="ip_prefix"/>. If the <ref column="ip_prefix"/>
- has a mask length of <code>n</code>, then this record gets an
- implicit priority of <code>2*n + 1</code>.
+ matches <ref column="ip_prefix"/>.
</li>
</ul>
<p>
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