From: Michael Bredel Date: Wed, 2 Apr 2014 09:26:59 +0000 (+0200) Subject: Added a comment that briefly describes the ArpHander service and explains some design... X-Git-Tag: autorelease-tag-v20140601202136_82eb3f9~287 X-Git-Url: https://git.opendaylight.org/gerrit/gitweb?p=controller.git;a=commitdiff_plain;h=ce8b227502448c0a18e3dc22362e4b42e589ef35 Added a comment that briefly describes the ArpHander service and explains some design decisions. Change-Id: I2dd3877e5a12ad59f4c5057de09ecab2b4e9f768 Signed-off-by: Michael Bredel --- diff --git a/opendaylight/arphandler/src/main/java/org/opendaylight/controller/arphandler/internal/ArpHandler.java b/opendaylight/arphandler/src/main/java/org/opendaylight/controller/arphandler/internal/ArpHandler.java index 083e2ed0e9..e549182439 100644 --- a/opendaylight/arphandler/src/main/java/org/opendaylight/controller/arphandler/internal/ArpHandler.java +++ b/opendaylight/arphandler/src/main/java/org/opendaylight/controller/arphandler/internal/ArpHandler.java @@ -64,6 +64,31 @@ import org.opendaylight.controller.topologymanager.ITopologyManager; import org.slf4j.Logger; import org.slf4j.LoggerFactory; +/** + * The ArpHandler offers services to react on ARP requests and replies + * sent by network hosts. Moreover it allows for creating ARP messages + * by the controller itself. + * + * The ARP Handler on ODL doesn't use the requester MAC address in + * order to avoid to have to build a spanning tree where to forward + * ARP Requests. The ARP requests are broadcast packets so in order to + * reach everywhere need to be flooded, when you flood in a network + * that is not a tree (all the networks has some level of redundancy) + * that would create forwarding loops without a spanning tree. Given + * the need is only to send out the ARP requests toward all the hosts + * we actually don't need to implement a flooding mechanism in software + * (which would be expensive) we just send out the ARP request toward + * all the ports that are suspected to be host ports on all the + * switches (from the controller). Now the condition for which a port + * is marked as host port could potentially be incorrect so when the + * controller sends out the ARP Request that could come back to the + * controller and could cause another request not needed. So changing + * the source MAC address of the request to be the one of the controller, + * controller can protect itself from honoring twice the same request. + * This enables an ARP handler resolution, without the need of spanning + * tree and limiting software flooding to the minimum required. + */ + public class ArpHandler implements IHostFinder, IListenDataPacket, ICacheUpdateAware { private static final Logger log = LoggerFactory.getLogger(ArpHandler.class); static final String ARP_EVENT_CACHE_NAME = "arphandler.arpRequestReplyEvent";