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我有一个胖树拓扑，我正在使用 Mininet、OpenFlow 1.3、Ryu 控制器来模拟基于 ECMP 的路由。我正在使用组和流表来执行此操作。例如，s2 和 s3 连接到聚合交换机的端口 1 和 2，例如 as1，其中安装了以下规则：

组表定义

        # Create two actions that forwards packets to ports 1 and 2 that are connected to two core switches
        action1 = sw.ofproto_parser.OFPActionOutput(1)
        action2 = sw.ofproto_parser.OFPActionOutput(2)

        # Specify two action sets (buckets), each with one action
        bucket1 = sw.ofproto_parser.OFPBucket(weight=1, actions=[action1])
        bucket2 = sw.ofproto_parser.OFPBucket(weight=1, actions=[action2])
        
        # OFPGT_SELECT chooses between bucket1 and bucket2 based on
        # some logic implemented in the switch, typically, round-robin?!
        group_mod = sw.ofproto_parser.OFPGroupMod(
            datapath=sw, command=ofp.OFPGC_ADD,
            type_=ofp.OFPGT_SELECT, group_id=1,
            buckets=[bucket1, bucket2])
        sw.send_msg(group_mod)

在流表中安装组表操作

        match = sw.ofproto_parser.OFPMatch(eth_type = \
                    0x0800)
        action = sw.ofproto_parser.OFPActionGroup(1)


        inst = [ofp_parser.OFPInstructionActions(
                ofp.OFPIT_APPLY_ACTIONS, [action])]
        mod = sw.ofproto_parser.OFPFlowMod(
            datapath=sw, match=match, cookie=0, command=ofp.OFPFC_ADD,
            idle_timeout=0, hard_timeout=0, priority=100,
            flags=ofp.OFPFF_SEND_FLOW_REM, instructions=inst)

   # Other flow entries rules are added here ...

我使用dpctl dump-flowsMininet 中的命令确认了这一点。请注意，对于核心交换机 s2，n_packets = n_bytes = 0，而对于其他核心交换机 s3，情况并非如此：

*** s2 ------------------------------------------------------------------------
OFPST_FLOW reply (OF1.3) (xid=0x2):
 cookie=0x0, duration=71.556s, table=0, n_packets=0, n_bytes=0, send_flow_rem priority=1200,ip,nw_dst=10.0.0.1 actions=output:1
 cookie=0x0, duration=71.556s, table=0, n_packets=0, n_bytes=0, send_flow_rem priority=1200,ip,nw_dst=10.0.0.2 actions=output:1
 cookie=0x0, duration=71.556s, table=0, n_packets=0, n_bytes=0, send_flow_rem priority=1200,ip,nw_dst=10.0.0.3 actions=output:1
 cookie=0x0, duration=71.556s, table=0, n_packets=0, n_bytes=0, send_flow_rem priority=1200,ip,nw_dst=10.0.0.4 actions=output:1
 cookie=0x0, duration=71.556s, table=0, n_packets=0, n_bytes=0, send_flow_rem priority=1200,ip,nw_dst=10.0.0.5 actions=output:2

.....对于核心交换机s3：

*** s3 ------------------------------------------------------------------------
OFPST_FLOW reply (OF1.3) (xid=0x2):
 cookie=0x0, duration=71.582s, table=0, n_packets=4436, n_bytes=12043732, send_flow_rem priority=1200,ip,nw_dst=10.0.0.1 actions=output:1
 cookie=0x0, duration=71.582s, table=0, n_packets=6306, n_bytes=11448184, send_flow_rem priority=1200,ip,nw_dst=10.0.0.2 actions=output:1
 cookie=0x0, duration=71.582s, table=0, n_packets=870, n_bytes=1157688, send_flow_rem priority=1200,ip,nw_dst=10.0.0.3 actions=output:1
 cookie=0x0, duration=71.582s, table=0, n_packets=674, n_bytes=644616, send_flow_rem priority=1200,ip,nw_dst=10.0.0.4 actions=output:1
 cookie=0x0, duration=71.582s, table=0, n_packets=4475, n_bytes=11918478, send_flow_rem priority=1200,ip,nw_dst=10.0.0.5 actions=output:2

就像我在上面的评论中提到的那样，我相信 OFPGT_SELECT 基于交换机中实现的一些逻辑在 bucket1 和 bucket2 之间进行选择，比如循环？这似乎在拓扑中的较低级别交换机中运行良好，即，两个桶以相等的权重交替选择。但在顶部聚合交换机的情况下，始终只选择一条到核心交换机的路径（存储桶）。通常，所有数据包只选择第一个桶（端口）或最后一个桶（端口），但不会在两个桶之间交替！

但是，当给两个桶赋予不相等的权重（1 和 2）时，它确实有效。不确定权重相同的问题是什么。

任何帮助将不胜感激。谢谢！

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