There has been enough confusion regarding arp responders in
ovn to warrant some additional comments; hence add a
general description regarding why they exist and document
the special cases.
Signed-off-by: Darrell Ball <dlu...@gmail.com>
---
ovn/northd/ovn-northd.8.xml | 25 ++++++++++++++++++++-----
1 file changed, 20 insertions(+), 5 deletions(-)
diff --git a/ovn/northd/ovn-northd.8.xml b/ovn/northd/ovn-northd.8.xml
index 77eb3d1..74ac5b3 100644
--- a/ovn/northd/ovn-northd.8.xml
+++ b/ovn/northd/ovn-northd.8.xml
@@ -415,14 +415,29 @@
<h3>Ingress Table 9: ARP/ND responder</h3>
<p>
- This table implements ARP/ND responder for known IPs. It contains these
- logical flows:
+ This table implements ARP/ND responder for known IPs. The advantage
+ of the arp responder flow is to limit arp broadcasts by locally
+ responding to arp requests without the need to send to other
+ hypervisors. One common case is when the inport is a logical
+ port associated with a VIF and the broadcast is responded to on the
+ local hypervisor rather than broadcast across the whole network and
+ responded to by the destination VM. It contains these logical flows:
</p>
<ul>
<li>
Priority-100 flows to skip ARP responder if inport is of type
- <code>localnet</code>, and advances directly to the next table.
+ <code>localnet</code> or <code>vtep</code> or <code>router</code>,
+ and advances directly to the next table. <code>localnet</code>
+ and <code>vtep</code> port types are skipped, otherwise the arp
+ request is received by multiple hypervisors, which all have the
+ same mac binding downloaded from northd, which will cause redundant
+ arp replies, confusing the originator of the arp request. If the
+ inport is of type <code>router</code>, we skip install since
+ there is no known valid use case. There is a special case:
+ north->south traffic using the l2gateway port will use an arp
+ responder on the l2 gateway chassis in the context of a logical
+ switch datapath.
</li>
<li>
@@ -446,8 +461,8 @@ output;
</pre>
<p>
- These flows are omitted for logical ports (other than router ports)
- that are down.
+ These flows are omitted for router type ports and other
+ logical ports that are down.
</p>
</li>
--
1.9.1
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