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https://issues.apache.org/jira/browse/JCS-89?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13193556#comment-13193556
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Diego Rivera edited comment on JCS-89 at 1/26/12 5:22 AM:
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To clarify, the issue is that InetAddress.getLocalHost() may not always return
an externally-visible address. In particular, it may return a loopback
address. This means that under those circumstances, all caches in a
UDP-discovery cluster will invariably discover only themselves, and thus the
lateral cluster will be useless.
This patch addresses that by superseding the IP address from the
UDPDiscoveryMessage.host property with the IP Address (NOT hostname, for speed,
efficiency and certainty) from the actual UDP multicast packet that has just
been received, and is being responded to.
This ensures there will be no confusion when performing the back-connect.
was (Author: diego.rivera...@gmail.com):
To clarify, the issue is that InetAddress.getLocalHost() may not always
return an externally-visible address. In particular, it may return a loopback
address. This means that under those circumstances, all caches in a
UDP-discovery cluster will invariably discover only themselves, and thus the
lateral cluster will be useless.
This patch addresses that by superseding the IP address from the
UDPDiscoveryMessage.host property with the IP Address (NOT hostname, for speed,
efficiency and certainty) from the actual UDP multicast packet that is being
responded to.
This ensures there will be no confusion when performing the back-connect.
> UDP Discovery fails to report correct IP address to peers for back-connect
> when InetAddress.getLocalHost() fails to return an externally-visible address
> (i.e. returns a local address)
> ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
>
> Key: JCS-89
> URL: https://issues.apache.org/jira/browse/JCS-89
> Project: Commons JCS
> Issue Type: Bug
> Reporter: Diego Rivera
> Attachments: jcs-89-fix.patch
>
> Original Estimate: 1h
> Remaining Estimate: 1h
>
> On certain environments where reverse-lookup of the machine's IP address
> isn't available, or other IP configurations restrict the ability of the JVM
> to determine its own "canonical" local address, it's impossible to determine
> ahead of time what address should be sent into the UDP multicast in order for
> lateral peers to establish the back-connection.
> The fix for this is simple: when the packet is received with the discovery
> message, determine the source host address of the packet that was received
> and set that to the discovery message's host property
> (setHost(packet.getAddress().getHostAddress()). This way, it's 100% for
> certain we'll be back-connecting to the correct instance.
> A patch will be uploaded shortly.
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