linux网桥中stp分析,linux网桥中stp分析

STP(Spanning Tree Protocol)是一个二层管理生成树协议。在一个扩展的局域网中参与STP的所有交换机之间通过交换桥协议数据单元bpdu(bridge protocol data unit)来实现；为稳定的生成树拓扑结构选择一个根桥；为每个交换网段选择一台指定交换机；将冗余路径上的交换机置为blocking，来消除网络中的环路.其标准在IEEE 802.1d定义,提供网络的动态冗余切换机制.

rSTP(rapid spanning tree protocol)是STP的扩展，其主要特点是增加了端口状态快速切换的机制，能够实现网络拓扑的快速转换.

STP通过阻塞一个或多个冗余端口，维护一个无回路的网络(IEEE802.1d)

2 代码分析

1) 软中断网桥接收数据

int netif_receive_skb(struct sk_buff *skb)

{

...

skb_reset_network_header(skb);

skb_reset_transport_header(skb);

skb->mac_len = skb->network_header - skb->mac_header;

...

/* 网桥处理 */

skb = handle_bridge(skb, &pt_prev, &ret, orig_dev);

if (!skb)

goto out;

...

type = skb->protocol;

list_for_each_entry_rcu(ptype,

&ptype_base[ntohs(type) & PTYPE_HASH_MASK], list) {

if (ptype->type == type &&

(ptype->dev == null_or_orig || ptype->dev == skb->dev ||

ptype->dev == orig_dev)) {

if (pt_prev)

ret = deliver_skb(skb, pt_prev, orig_dev);

pt_prev = ptype;

}

}

if (pt_prev) {

ret = pt_prev->func(skb, skb->dev, pt_prev, orig_dev);

} else {

kfree_skb(skb);

ret = NET_RX_DROP;

}

out:

rcu_read_unlock();

return ret;

}

static inline struct sk_buff *handle_bridge(struct sk_buff *skb,

struct packet_type **pt_prev, int *ret,

struct net_device *orig_dev)

{

struct net_bridge_port *port;

/* 非网桥数据, 交给后面的网络层来处理 */

if (skb->pkt_type == PACKET_LOOPBACK ||

(port = rcu_dereference(skb->dev->br_port)) == NULL)

return skb;

if (*pt_prev) {

*ret = deliver_skb(skb, *pt_prev, orig_dev);

*pt_prev = NULL;

}

/* 网桥处理 */

return br_handle_frame_hook(port, skb);

}

static int __init br_init(void)

{

...

/* 网桥HOOK点注册 */

err = br_netfilter_init();

if (err)

goto err_out1;

...

/* 网桥处理接口 */

br_handle_frame_hook = br_handle_frame;

...

}

int __init br_netfilter_init(void)

{

int ret;

ret = nf_register_hooks(br_nf_ops, ARRAY_SIZE(br_nf_ops));

...

return 0;

}

static struct nf_hook_ops br_nf_ops[] __read_mostly = {

{ .hook = br_nf_pre_routing,

.owner = THIS_MODULE,

.pf = PF_BRIDGE,

.hooknum = NF_BR_PRE_ROUTING,

.priority = NF_BR_PRI_BRNF, },

{ .hook = br_nf_local_in,

.owner = THIS_MODULE,

.pf = PF_BRIDGE,

.hooknum = NF_BR_LOCAL_IN,

.priority = NF_BR_PRI_BRNF, },

{ .hook = br_nf_forward_ip,

.owner = THIS_MODULE,

.pf = PF_BRIDGE,

.hooknum = NF_BR_FORWARD,

.priority = NF_BR_PRI_BRNF - 1, },

{ .hook = br_nf_forward_arp,

.owner = THIS_MODULE,

.pf = PF_BRIDGE,

.hooknum = NF_BR_FORWARD,

.priority = NF_BR_PRI_BRNF, },

{ .hook = br_nf_local_out,

.owner = THIS_MODULE,

.pf = PF_BRIDGE,

.hooknum = NF_BR_LOCAL_OUT,

.priority = NF_BR_PRI_FIRST, },

{ .hook = br_nf_post_routing,

.owner = THIS_MODULE,

.pf = PF_BRIDGE,

.hooknum = NF_BR_POST_ROUTING,

.priority = NF_BR_PRI_LAST, },

{ .hook = ip_sabotage_in,

.owner = THIS_MODULE,

.pf = PF_INET,

.hooknum = NF_INET_PRE_ROUTING,

.priority = NF_IP_PRI_FIRST, },

{ .hook = i