paradigm(paradigm:reboot)

.硬件类型:硬件地址类型，该字段值一般为ARPHRD_ETHER，表示以太网。.协议类型:表示三层地址使用的协议，该字段值一般为ETH_P_IP

 

从ip_finish_output2到dev_queue_xmit路径：

arping命令：http://www.bluestep.cc/linux%e5%91%bd%e4%bb%a4arping-%e7%bd%91%e7%bb%9c%e7%ae%a1%e7%90%86-%e9%80%9a%e8%bf%87%e5%8f%91%e9%80%81arp%e5%8d%8f%e8%ae%ae%e6%8a%a5%e6%96%87%e6%b5%8b%e8%af%95%e7%bd%91%e7%bb%9c/

arp协议：

arp报文结构：

(1).硬件类型：硬件地址类型，该字段值一般为ARPHRD_ETHER，表示以太网F:\company\Linux\linux-4.1.45\linux-4.1.45\include\uapi\linux\if_arp.h 。

/* ARP protocol HARDWARE identifiers. */#define ARPHRD_NETROM 0 /* from KA9Q: NET/ROM pseudo */#define

ARPHRD_ETHER 1 /* Ethernet 10Mbps */#define ARPHRD_EETHER 2 /* Experimental Ethernet */#define ARPHRD_AX25 3

/* AX.25 Level 2 */#define ARPHRD_PRONET 4 /* PROnet token ring */#define ARPHRD_CHAOS 5 /* Chaosnet */

#define ARPHRD_IEEE802 6 /* IEEE 802.2 Ethernet/TR/TB */#define ARPHRD_ARCNET 7 /* ARCnet */#define

ARPHRD_APPLETLK 8 /* APPLEtalk */#define ARPHRD_DLCI 15 /* Frame Relay DLCI */#define ARPHRD_ATM 19

/* ATM */ ...(2).协议类型：表示三层地址使用的协议，该字段值一般为ETH_P_IP，表示IP协议F:\company\Linux\linux-4.1.45\linux-4.1.45

\include\uapi\linux\if_ether.h #define ETH_P_LOOP 0x0060 /* Ethernet Loopback packet */#define ETH_P_PUP 0x0200

/* Xerox PUP packet */#define ETH_P_PUPAT 0x0201 /* Xerox PUP Addr Trans packet */#define ETH_P_IP 0x0800

/* Internet Protocol packet */#define ETH_P_X25 0x0805 /* CCITT X.25 */#define ETH_P_ARP 0x0806 /* Address Resolution packet */

...(3)硬件地址长度，以太网MAC地址就是6；(4)协议地址长度，IP地址就是4；(5)操作码常见的有四种，arp请求，arp相应，rarp请求，rarp相应F:\company\Linux\linux。

-4.1.45\linux-4.1.45\include\uapi\linux\if_arp.h /* ARP protocol opcodes. */#define ARPOP_REQUEST 1

/* ARP request */#define ARPOP_REPLY 2 /* ARP reply */#define ARPOP_RREQUEST 3 /* RARP request */

#define ARPOP_RREPLY 4 /* RARP reply */#define ARPOP_InREQUEST 8 /* InARP request */#define ARPOP_InREPLY 9

/* InARP reply */#define ARPOP_NAK 10 /* (ATM)ARP NAK */(6)发送方硬件地址与IP地址，(7)目标硬件地址与目标IP地址arp头数据结构：。

F:\company\Linux\linux-4.1.45\linux-4.1.45\include\uapi\linux\if_arp.h /* * This structure defines an ethernet arp header. */

structarphdr { __be16 ar_hrd; /* format of hardware address */ __be16 ar_pro; /* format of protocol address */

unsignedchar ar_hln; /* length of hardware address */unsignedchar ar_pln; /* length of protocol address */

__be16 ar_op; /* ARP opcode (command) */#if 0/* * Ethernet looks like this : This bit is variable sized however... */

unsignedchar ar_sha[ETH_ALEN]; /* sender hardware address */unsignedchar ar_sip[4]; /* sender IP address */

unsignedchar ar_tha[ETH_ALEN]; /* target hardware address */unsignedchar ar_tip[4]; /* target IP address */

#endif }; 1. arp_init()arp模块的初始化函数为arp_init()，这个函数在ipv4协议栈的初始化函数inet_init()中被调用1.初始化arp表arp_tbl;2.注册arp协议类型；。

3.建立arp相关proc文件，/proc/net/arp；4.注册通知事件F:\company\Linux\linux-4.1.45\linux-4.1.45\net\ipv4\arp.c void __

init arp_init(void){ neigh_table_init(NEIGH_ARP_TABLE, &arp_tbl);//初始化arp协议的邻居表 dev_add_pack(&arp_packet_type);

//在协议栈中注册arp协议 arp_proc_init();//建立proc对象#ifdef CONFIG_SYSCTL neigh_sysctl_register(NULL, &arp_tbl.parms,

NULL); #endif register_netdevice_notifier(&arp_netdev_notifier);//注册通知事件 } arp邻居项函数指针表：F:\company\Linux\linux

-4.1.45\linux-4.1.45\net\ipv4\arp.c staticconststructneigh_opsarp_generic_ops = { .family = AF_INET, .solicit = arp_solicit, .error_report = arp_error_report, .output = neigh_resolve_output, .connected_output = neigh_connected_output, };

staticconststructneigh_opsarp_hh_ops = { .family = AF_INET, .solicit = arp_solicit, .error_report = arp_error_report, .output = neigh_resolve_output, .connected_output = neigh_resolve_output, };

staticconststructneigh_opsarp_direct_ops = { .family = AF_INET, .output = neigh_direct_output, .connected_output = neigh_direct_output, };

neigh_table:一个neigh_table对应一种邻居协议，IPv4就是arp协议用来存储于邻居协议相关的参数、功能函数、邻居项散列表等structneigh_table {int family;。

/*地址族，arp为AF_INET*//*邻居项结构大小：sizeof(neighbour+4),因为neighbour结构最后一个成员0长数组，用于存储4字节长IP地址*/int entry_size; 。

/*hash函数所使用的键值长度，就是IP地址长度，为4*/int key_len; /*ETH_P_IP*/ __be16 protocol; /*hash函数，arp_hash*/ __u32 (*hash)(

constvoid *pkey, const struct net_device *dev, __u32 *hash_rnd); bool (*key_eq)(const struct neighbour *,

constvoid *pkey); /*邻居表项初始化函数，用于初始化neighbour结构实例，即arp_constructor，在neigh_create中被调用*/int (*constructor)(struct neighbour *);

/*创建和释放一个代理项时被调用，代理先不管*/int (*pconstructor)(struct pneigh_entry *); void (*pdestructor)(struct pneigh_entry *);

/*用来处理在proxy_queue缓存队列中的代理arp报文*/void (*proxy_redo)(struct sk_buff *skb); /*用来分配neighbour结构实例的缓存区名，即arp_cache。

*/char *id; /*存储一些与协议相关的可调节参数，如超时重传时间，proxy_queue队列长度等*/structneigh_parmsparms;structlist_headparms_list

;int gc_interval; int gc_thresh1; int gc_thresh2; int gc_thresh3; unsignedlong last_flush;

structdelayed_workgc_work;/*处理proxy_queue的定时器*/structtimer_listproxy_timer;/*对于接收到的需要进行代理的arp报文，先缓存到proxy_queue,在定时器处理函数中再对其进行处理。

*/structsk_buff_headproxy_queue;/*邻居项条目数，在neigh_alloc()、neigh_destroy()中更新*/atomic_t entries; rwlock_t

lock; unsignedlong last_rand; /*记录邻居表中有关邻居项的各类统计数据*/structneigh_statistics __percpu *stats;/*存储邻居项的散列表：hash表，用来存储邻居项*/

structneigh_hash_table __rcu *nht;/*存储arp代理三层协议地址的散列表*/structpneigh_entry **phash_buckets; };neighbour

一个neighbour对应一个邻居项，就是一个arp条目structneighbour {structneighbour __rcu *next;structneigh_table *tbl;/*指向arp_tbl*/

structneigh_parms *parms;unsignedlong confirmed; unsignedlong updated; rwlock_t lock; atomic_t refcnt;

/*引用计数*/structsk_buff_headarp_queue;/*用来缓存待发送的报文*/unsignedint arp_queue_len_bytes; structtimer_list

timer;/*定时器*/unsignedlong used; atomic_t probes; __u8 flags; __u8 nud_state;/*邻居项状态*/ __u8 type;

/*邻居地址类型，例如单播、组播、广播等*//*生存标志，为1时，表示该邻居项正在被删除，最终通过垃圾回收将其删除*/ __u8 dead; seqlock_t ha_lock; /*邻居项MAC地址*/

unsignedchar ha[ALIGN(MAX_ADDR_LEN, sizeof(unsignedlong))]; /*缓存二层报头，包括目的MAC地址*/structhh_cachehh;/*输出函数，用来将报文输出到该邻居*/

int (*output)(struct neighbour *, struct sk_buff *); /*邻居项函数指针*/conststructneigh_ops *ops;structrcu_head

rcu;structnet_device *dev;/*通过该设备访问邻居项*/ u8 primary_key[0];/*存储IP地址*/ };邻居项函数指针表，实现三层和二层的dev_queue_xmit()之间的跳转。

structneigh_ops { int family;//AF_INET/*发送arp报文*/ void (*solicit)(structneighbour *, structsk_buff

*); /*向三层报告错误*/ void (*error_report)(structneighbour *, structsk_buff *); /*通用的输出函数，实现了完整的输出过程，存在较多的操作。

*/ int (*output)(structneighbour *, structsk_buff *); /*确定邻居可达，即状态为NUD_CONNETCTE时的输出函数，由于所有输出所需要的信息都已具备， 该函数只是简单地添加二层首部，发送*/

int (*connected_output)(structneighbour *, structsk_buff *); };neigh_statistics用来存储统计信息，一个结构实例对应一个网络设备上的一种邻居协议。

structneigh_statistics {unsignedlong allocs; /* number of allocated neighs */unsignedlong destroys;

/* number of destroyed neighs */unsignedlong hash_grows; /* number of hash resizes */unsignedlong res_failed;

/* number of failed resolutions */unsignedlong lookups; /* number of lookups */unsignedlong hits; /* number of hits (among lookups) */

unsignedlong rcv_probes_mcast; /* number of received mcast ipv6 */unsignedlong rcv_probes_ucast; /* number of received ucast ipv6 */

unsignedlong periodic_gc_runs; /* number of periodic GC runs */unsignedlong forced_gc_runs; /* number of forced GC runs */

unsignedlong unres_discards; /* number of unresolved drops */ };arp表结构：arp_tblF:\company\Linux\linux-4.1.45\linux-4.1.45\net\ipv4\arp.c

structneigh_tablearp_tbl={.family=AF_INET,.key_len=4,.protocol=cpu_to_be16(ETH_P_IP),.hash=arp_hash,.key_eq

=arp_key_eq,.constructor=arp_constructor,.proxy_redo=parp_redo,.id="arp_cache",.parms={.tbl=&arp_tbl,

.reachable_time=30*HZ,.data={[NEIGH_VAR_MCAST_PROBES]=3,[NEIGH_VAR_UCAST_PROBES]=3,[NEIGH_VAR_RETRANS_TIME]

=1*HZ,[NEIGH_VAR_BASE_REACHABLE_TIME]=30*HZ,[NEIGH_VAR_DELAY_PROBE_TIME]=5*HZ,[NEIGH_VAR_GC_STALETIME]

=60*HZ,[NEIGH_VAR_QUEUE_LEN_BYTES]=64*1024,[NEIGH_VAR_PROXY_QLEN]=64,[NEIGH_VAR_ANYCAST_DELAY]=1*HZ,[NEIGH_VAR_PROXY_DELAY]

=(8*HZ)/10,[NEIGH_VAR_LOCKTIME]=1*HZ,},},.gc_interval=30*HZ,.gc_thresh1=128,.gc_thresh2=512,.gc_thresh3

=1024,};dev_add_pack()注册arp报文类型：dev_add_pack(&arp_packet_type);就是把arp_packet_type添加到ptype_base哈希表中void dev_add_pack(。

struct packet_type *pt) { struct list_head *head = ptype_head(pt); spin_lock(&ptype_lock); list_add_rcu(&pt->list, head); spin_unlock(&ptype_lock); } static inline

struct list_head *ptype_head(conststruct packet_type *pt) { if (pt->type == htons(ETH_P_ALL)) return

pt->dev ? &pt->dev->ptype_all : &ptype_all; elsereturn pt->dev ? &pt->dev->ptype_specific : &ptype_base[ntohs(pt->

type) & PTYPE_HASH_MASK]; } struct list_head ptype_base[PTYPE_HASH_SIZE] __read_mostly; static struct

packet_type arp_packet_type __read_mostly = { .type = cpu_to_be16(ETH_P_ARP), .func = arp_rcv, };

struct packet_type { __be16 type; /* This is really htons(ether_type). */struct net_device *dev; /* NULL is wildcarded here */

int (*func) (struct sk_buff *, struct net_device *, struct packet_type *, struct net_device *)

;bool (*id_match)(struct packet_type *ptype, struct sock *sk); void *af_packet_priv; struct

list_head list; }; register_netdevice_notifier注册新通知事件的时候，在已经注册和UP的设备上，会调用一次这个通知事件/** * register_netdevice_notifier - register a network notifier block * @nb: notifier * * Register a notifier to be called when network device events occur. * The notifier passed is linked into the kernel structures and must * not be reused until it has been unregistered. A negative errno code * is returned on a failure. * * When registered all registration and up events are replayed * to the new notifier to allow device to have a race free * view of the network device list. */。

intregister_netdevice_notifier(struct notifier_block *nb){ structnet_device *dev;structnet_device *last

;structnet *net;int err; rtnl_lock(); /*新事件注册到netdev_chain通知链上*/ err = raw_notifier_chain_register(&netdev_chain, nb);

if (err) goto unlock; if (dev_boot_phase) goto unlock; for_each_net(net) { for_each_netdev(net, dev) {

/*在已经注册的设备上调用该事件*/ err = call_netdevice_notifier(nb, NETDEV_REGISTER, dev); err = notifier_to_errno(err);

if (err) goto rollback; if (!(dev->flags & IFF_UP)) continue; /*在UP的设备上调用该事件*/ call_netdevice_notifier(nb, NETDEV_UP, dev); } } unlock: rtnl_unlock();

return err; rollback: last = dev; for_each_net(net) { for_each_netdev(net, dev) { if (dev == last)

goto outroll; if (dev->flags & IFF_UP) { call_netdevice_notifier(nb, NETDEV_GOING_DOWN, dev); call_netdevice_notifier(nb, NETDEV_DOWN, dev); } call_netdevice_notifier(nb, NETDEV_UNREGISTER, dev); } } outroll: raw_notifier_chain_unregister(&netdev_chain, nb);

goto unlock; }staticRAW_NOTIFIER_HEAD(netdev_chain); #define RAW_NOTIFIER_HEAD(name) \ struct raw_notifier_head name = \ RAW_NOTIFIER_INIT(name)

structraw_notifier_head {structnotifier_block __rcu *head; }; 搞了半天就是： structraw_notifier_headnetdev_chain

= {.head = NULL }设备事件类型：/* netdevice notifier chain. Please remember to update the rtnetlink * notification exclusion list in rtnetlink_event() when adding new * types. */

#define NETDEV_UP 0x0001 /* For now you cant veto a device up/down */#define NETDEV_DOWN 0x0002#define

NETDEV_REBOOT 0x0003 /* Tell a protocol stack a network interface detected a hardware crash and restarted - we can use this eg to kick tcp sessions once done */

#define NETDEV_CHANGE 0x0004 /* Notify device state change */#define NETDEV_REGISTER 0x0005#define NETDEV_UNREGISTER 0x0006

#define NETDEV_CHANGEMTU 0x0007 /* notify after mtu change happened */#define NETDEV_CHANGEADDR 0x0008

#define NETDEV_GOING_DOWN 0x0009#define NETDEV_CHANGENAME 0x000A#define NETDEV_FEAT_CHANGE 0x000B#define

NETDEV_BONDING_FAILOVER 0x000C#define NETDEV_PRE_UP 0x000D#define NETDEV_PRE_TYPE_CHANGE 0x000E#define

NETDEV_POST_TYPE_CHANGE 0x000F#define NETDEV_POST_INIT 0x0010#define NETDEV_UNREGISTER_FINAL 0x0011#

define NETDEV_RELEASE 0x0012#define NETDEV_NOTIFY_PEERS 0x0013#define NETDEV_JOIN 0x0014#define NETDEV_CHANGEUPPER 0x0015

#define NETDEV_RESEND_IGMP 0x0016#define NETDEV_PRECHANGEMTU 0x0017 /* notify before mtu change happened */

#define NETDEV_CHANGEINFODATA 0x0018#define NETDEV_BONDING_INFO 0x0019

__neigh_create：创建一个邻居项，并将其添加到散列表上，返回指向该邻居项的指针tbl:待创建的邻居项所属的邻居表，即arp_tbl；pkey：三层协议地址(IP地址)dev：输出设备want_ref：？？。

structneighbour *__neigh_create(structneigh_table *tbl, const void *pkey, structnet_device *dev,

bool want_ref) { u32 hash_val; int key_len = tbl->key_len; int error; /*调用neigh_alloc创建邻居项*/struct

neighbour *n1, *rc, *n = neigh_alloc(tbl, dev); structneigh_hash_table *nht; if (!n) { rc = ERR_PTR(-ENOBUFS); goto out; }

/*设置邻居项的三层协议地址、输出设备*/ memcpy(n->primary_key, pkey, key_len); n->dev = dev; /*增加设备引用计数*/ dev_hold(dev);

/* Protocol specific setup. *//*执行邻居表的邻居项初始化函数，arp为arp_constructor完成*/if (tbl->constructor && (error = tbl->constructor(n)) <

0) { rc = ERR_PTR(error); goto out_neigh_release; } /*指向设备的邻居项初始化函数*/if (dev->netdev_ops->ndo_neigh_construct) { error = dev->netdev_ops->ndo_neigh_construct(n);

if (error < 0) { rc = ERR_PTR(error); goto out_neigh_release; } } /* Device specific setup. */

/*以太网设备neigh_setup为NULL*/if (n->parms->neigh_setup && (error = n->parms->neigh_setup(n)) < 0) { rc = ERR_PTR(error); goto out_neigh_release; }

/*初始化邻居项的确认时间*/ n->confirmed = jiffies - (NEIGH_VAR(n->parms, BASE_REACHABLE_TIME) nht, lockdep_is_held(&tbl->lock));

/*hash扩容*/if (atomic_read(&tbl->entries) > (1 hash_shift +

1); /*计算hash值*/ hash_val = tbl->hash(pkey, dev, nht->hash_rnd) >> (32 - nht->hash_shift); /*邻居项正在被删除*/

if (n->parms->dead) { rc = ERR_PTR(-EINVAL); goto out_tbl_unlock; } /*邻居项已经存在，递增其引用计数，释放新创建的邻居项*/

for (n1 = rcu_dereference_protected(nht->hash_buckets[hash_val], lockdep_is_held(&tbl->lock)); n1 != NULL; n1 = rcu_dereference_protected(n1->next, lockdep_is_held(&tbl->lock))) {

if (dev == n1->dev && !memcmp(n1->primary_key, pkey, key_len)) { if (want_ref) /*增加引用计数，#define neigh_hold(n) atomic_inc(&(n)->refcnt)*/

neigh_hold(n1); rc = n1; goto out_tbl_unlock; } } n->dead = 0; if (want_ref) neigh_hold(n);

/*不存在，添加邻居项到hash表中*/ rcu_assign_pointer(n->next, rcu_dereference_protected(nht->hash_buckets[hash_val], lockdep_is_held(&tbl->lock))); rcu_assign_pointer(nht->hash_buckets[hash_val], n); write_unlock_bh(&tbl->lock); neigh_dbg(

2, "neigh %p is created\n", n); rc = n; out: return rc; out_tbl_unlock: write_unlock_bh(&tbl->lock); out_neigh_release: neigh_release(n); goto out; }

neigh_alloc创建邻居项staticstructneighbour *neigh_alloc(structneigh_table *tbl, structnet_device *dev) {

structneighbour *n = NULL; unsigned long now = jiffies; int entries; /*递增邻居表中邻居项的条目，然后返回当前条目(递增前)*/

entries = atomic_inc_return(&tbl->entries) - 1; /*数目>=gc_thresh3,或者 >=gc_thresh2并且已超过5s未刷新，则必须立即刷新并强制垃圾回收*/

if (entries >= tbl->gc_thresh3 || (entries >= tbl->gc_thresh2 && time_after(now, tbl->last_flush +

5 * HZ))) { /*如果垃圾回收失败，并且数目>=gc_thresh3，则不分配邻居项*/if (!neigh_forced_gc(tbl) && entries >= tbl->gc_thresh3) goto out_entries; }

/*分配邻居项*/ n = kzalloc(tbl->entry_size + dev->neigh_priv_len, GFP_ATOMIC); if (!n) goto out_entries;

/*初始化neighbour成员*/ __skb_queue_head_init(&n->arp_queue); rwlock_init(&n->lock); seqlock_init(&n->ha_lock); n->updated = n->used = now; n->nud_state = NUD_NONE; n->output = neigh_blackhole; seqlock_init(&n->hh.hh_lock);

/*parms初始化为tbl->parms*/ n->parms = neigh_parms_clone(&tbl->parms); /*设置定时器*/ setup_timer(&n->timer, neigh_timer_handler, (unsigned long)n); NEIGH_CACHE_STAT_INC(tbl, allocs); n->tbl = tbl; atomic_set(&n->refcnt,

1); n->dead = 1;/*刚创建neighbour时，n->dead为1，在__neigh_create中被设置为0*/ out: return n; out_entries: atomic_dec(&tbl->entries); goto out; }

arp_constructor1.设置邻居项的类型2.设置邻居项的ops指针3.设置邻居项的output函数指针static int arp_constructor(struct neighbour *neigh) { __be32 addr = *(__be32 *)neigh->primary_key; struct net_device *dev = neigh->dev; struct in_device *in_dev; struct neigh_parms *parms; rcu_read_lock();

/*获取IP配置块*/ in_dev = __in_dev_get_rcu(dev); if (!in_dev) { rcu_read_unlock(); return -EINVAL; }

/*获取邻居项的类型*/ neigh->type = inet_addr_type(dev_net(dev), addr); /*neigh->parms在neigh_alloc函数中初始化为tbl->parms，在这里初始化为in_dev->arp_parms*/

parms = in_dev->arp_parms; __neigh_parms_put(neigh->parms); neigh->parms = neigh_parms_clone(parms); rcu_read_unlock();

/*对于以太网设备，其dev->header_ops为eth_header_ops*/if (!dev->header_ops) { neigh->nud_state = NUD_NOARP; neigh->ops = &arp_direct_ops; neigh->output = neigh_direct_output; }

else { /* Good devices (checked by reading texts, but only Ethernet is tested) ARPHRD_ETHER: (ethernet, apfddi) ARPHRD_FDDI: (fddi) ARPHRD_IEEE802: (tr) ARPHRD_METRICOM: (strip) ARPHRD_ARCNET: etc. etc. etc. ARPHRD_IPDDP will also work, if author repairs it. I did not it, because this driver does not work even in old paradigm. */

if (neigh->type == RTN_MULTICAST) { neigh->nud_state = NUD_NOARP; arp_mc_map(addr, neigh->ha, dev,

1); } elseif (dev->flags & (IFF_NOARP | IFF_LOOPBACK)) { neigh->nud_state = NUD_NOARP; memcpy(neigh->ha, dev->dev_addr, dev->addr_len); }

elseif (neigh->type == RTN_BROADCAST || (dev->flags & IFF_POINTOPOINT)) { neigh->nud_state = NUD_NOARP; memcpy(neigh->ha, dev->broadcast, dev->addr_len); }

/*对于以太网设备，其header_ops->cache为eth_header_cache，所以对于以太网设备其neighbour->ops为arp_hh_ops*/if (dev->header_ops->cache) neigh->ops = &arp_hh_ops;

else neigh->ops = &arp_generic_ops; /*对于邻居项状态为有效状态时，则将neigh->output设置为neigh->ops->connected_output*/

if (neigh->nud_state & NUD_VALID) neigh->output = neigh->ops->connected_output; else neigh->output = neigh->ops->output; }

return0; } dst_neigh_outputstatic inline int dst_neigh_output(structdst_entry *dst, structneighbour *n,

structsk_buff *skb) { conststructhh_cache *hh; if (dst->pending_confirm) { unsigned long now = jiffies; dst->pending_confirm =

0; /* avoid dirtying neighbour */if (n->confirmed != now) n->confirmed = now; } hh = &n->hh;

if ((n->nud_state & NUD_CONNECTED) && hh->hh_len) return neigh_hh_output(hh, skb); elsereturn n->output(n, skb); }

neigh_resolve_output/* Slow and careful. */ int neigh_resolve_output(structneighbour *neigh, structsk_buff

*skb) { int rc = 0; if (!neigh_event_send(neigh, skb)) { int err; structnet_device *dev = neigh->dev; unsigned int seq;

if (dev->header_ops->cache && !neigh->hh.hh_len) neigh_hh_init(neigh); do { __skb_pull(skb, skb_network_offset(skb)); seq = read_seqbegin(&neigh->ha_lock);

/*sbk添加二层头*/ err = dev_hard_header(skb, dev, ntohs(skb->protocol), neigh->ha, NULL, skb->len); }

while (read_seqretry(&neigh->ha_lock, seq)); if (err >= 0) /*发送skb*/ rc = dev_queue_xmit(skb);

else goto out_kfree_skb; } out: return rc; out_kfree_skb: rc = -EINVAL; kfree_skb(skb); goto out; }

neigh_event_sendstatic inline int neigh_event_send(structneighbour *neigh, structsk_buff *skb) { unsigned long now = jiffies;

/*更新最近一次使用时间*/if (neigh->used != now) neigh->used = now; /*此时状态为NUD_NONE*/if (!(neigh->nud_state&(NUD_CONNECTED|NUD_DELAY|NUD_PROBE)))

return __neigh_event_send(neigh, skb); return0; } __neigh_event_sendint __neigh_event_send(structneighbour

*neigh, structsk_buff *skb) { int rc; bool immediate_probe = false; write_lock_bh(&neigh->lock); rc =

0; if (neigh->nud_state & (NUD_CONNECTED | NUD_DELAY | NUD_PROBE)) goto out_unlock_bh; if (neigh->dead) goto out_dead;

if (!(neigh->nud_state & (NUD_STALE | NUD_INCOMPLETE))) { if (NEIGH_VAR(neigh->parms, MCAST_PROBES) + NEIGH_VAR(neigh->parms, APP_PROBES)) { unsigned long next, now = jiffies; atomic_set(&neigh->probes, NEIGH_VAR(neigh->parms, UCAST_PROBES));

/*设置邻居状态为NUD_INCOMPLETE*/ neigh->nud_state = NUD_INCOMPLETE; neigh->updated = now; next = now + max(NEIGH_VAR(neigh->parms, RETRANS_TIME), HZ/

2); /*添加定时器*/ neigh_add_timer(neigh, next); immediate_probe = true; } else { neigh->nud_state = NUD_FAILED; neigh->updated = jiffies; write_unlock_bh(&neigh->lock); kfree_skb(skb);

return1; } } elseif (neigh->nud_state & NUD_STALE) { neigh_dbg(2, "neigh %p is delayed\n", neigh); neigh->nud_state = NUD_DELAY; neigh->updated = jiffies; neigh_add_timer(neigh, jiffies + NEIGH_VAR(neigh->parms, DELAY_PROBE_TIME)); }

/*如果队列满了，把arp队列中前面几个skb删除*/if (neigh->nud_state == NUD_INCOMPLETE) { if (skb) { while (neigh->arp_queue_len_bytes + skb->truesize > NEIGH_VAR(neigh->parms, QUEUE_LEN_BYTES)) {

structsk_buff *buff; buff = __skb_dequeue(&neigh->arp_queue); if (!buff) break; neigh->arp_queue_len_bytes -= buff->truesize; kfree_skb(buff); NEIGH_CACHE_STAT_INC(neigh->tbl, unres_discards); } skb_dst_force(skb);

/*队列添加到arp队列*/ __skb_queue_tail(&neigh->arp_queue, skb); neigh->arp_queue_len_bytes += skb->truesize; } rc =

1; } out_unlock_bh: if (immediate_probe) neigh_probe(neigh); else write_unlock(&neigh->lock); local_bh_enable();

return rc; out_dead: if (neigh->nud_state & NUD_STALE) goto out_unlock_bh; write_unlock_bh(&neigh->lock); kfree_skb(skb);

return1; }neigh_timer_handler/* Called when a timer expires for a neighbour entry. */static void neigh_timer_handler(unsigned long arg) { unsigned long now, next;

structneighbour *neigh = (structneighbour *)arg; unsigned int state; int notify = 0; write_lock(&neigh->lock); state = neigh->nud_state; now = jiffies; next = now + HZ;

if (!(state & NUD_IN_TIMER)) goto out; if (state & NUD_REACHABLE) { if (time_before_eq(now, neigh->confirmed + neigh->parms->reachable_time)) { neigh_dbg(

2, "neigh %p is still alive\n", neigh); next = neigh->confirmed + neigh->parms->reachable_time; }

elseif (time_before_eq(now, neigh->used + NEIGH_VAR(neigh->parms, DELAY_PROBE_TIME))) { neigh_dbg(

2, "neigh %p is delayed\n", neigh); neigh->nud_state = NUD_DELAY; neigh->updated = jiffies; neigh_suspect(neigh); next = now + NEIGH_VAR(neigh->parms, DELAY_PROBE_TIME); }

else { neigh_dbg(2, "neigh %p is suspected\n", neigh); neigh->nud_state = NUD_STALE; neigh->updated = jiffies; neigh_suspect(neigh); notify =

1; } } elseif (state & NUD_DELAY) { if (time_before_eq(now, neigh->confirmed + NEIGH_VAR(neigh->parms, DELAY_PROBE_TIME))) { neigh_dbg(

2, "neigh %p is now reachable\n", neigh); neigh->nud_state = NUD_REACHABLE; neigh->updated = jiffies; neigh_connect(neigh); notify =

1; next = neigh->confirmed + neigh->parms->reachable_time; } else { neigh_dbg(2, "neigh %p is probed\n"

, neigh); neigh->nud_state = NUD_PROBE; neigh->updated = jiffies; atomic_set(&neigh->probes,

0); next = now + NEIGH_VAR(neigh->parms, RETRANS_TIME); } } else { /* NUD_PROBE|NUD_INCOMPLETE */

next = now + NEIGH_VAR(neigh->parms, RETRANS_TIME); } /*发送报文请求次数大于上限*/if ((neigh->nud_state & (NUD_INCOMPLETE | NUD_PROBE)) && atomic_read(&neigh->probes) >= neigh_max_probes(neigh)) { neigh->nud_state = NUD_FAILED; notify =

1; neigh_invalidate(neigh); goto out; } if (neigh->nud_state & NUD_IN_TIMER) { if (time_before(next, jiffies + HZ/

2)) next = jiffies + HZ/2; if (!mod_timer(&neigh->timer, next)) neigh_hold(neigh); } /*发送arp请求报文*/

if (neigh->nud_state & (NUD_INCOMPLETE | NUD_PROBE)) { neigh_probe(neigh); } else { out: write_unlock(&neigh->lock); }

if (notify) neigh_update_notify(neigh); neigh_release(neigh); }neigh_probestatic void neigh_probe(

structneighbour *neigh) __releases(neigh->lock) { structsk_buff *skb = skb_peek_tail(&neigh->arp_queue);

/* keep skb alive even if arp_queue overflows */if (skb) skb = skb_copy(skb, GFP_ATOMIC); write_unlock(&neigh->lock);

/*调用arp_solicit发送arp请求报文*/if (neigh->ops->solicit) neigh->ops->solicit(neigh, skb); atomic_inc(&neigh->probes); kfree_skb(skb); }

arp_error_report()调用dst_link_failure()函数向三层报告错误，当邻居项缓存中还有未发送的报文，而该邻居却无法访问时被调用不懂staticvoidarp_error_report。

(struct neighbour *neigh, struct sk_buff *skb) { dst_link_failure(skb); kfree_skb(skb); } arp_solicit()

用来发送arp请求，在邻居项状态定时器处理函数中被调用neigh：arp请求的目的邻居项skb：缓存在该邻居项中的待发送报文，用来获取该skb的源ip地址static void arp_solicit(。

structneighbour *neigh, structsk_buff *skb) { __be32 saddr = 0; u8 dst_ha[MAX_ADDR_LEN], *dst_hw = NULL;

structnet_device *dev = neigh->dev; __be32 target = *(__be32 *)neigh->primary_key; int probes = atomic_read(&neigh->probes);

structin_device *in_dev; rcu_read_lock(); in_dev = __in_dev_get_rcu(dev); if (!in_dev) { rcu_read_unlock();

return; } switch (IN_DEV_ARP_ANNOUNCE(in_dev)) { default: case 0: /* By default announce any local IP */

if (skb && inet_addr_type(dev_net(dev), ip_hdr(skb)->saddr) == RTN_LOCAL) saddr = ip_hdr(skb)->saddr;

break; case 1: /* Restrict announcements of saddr in same subnet */if (!skb) break; saddr = ip_hdr(skb)->saddr;

if (inet_addr_type(dev_net(dev), saddr) == RTN_LOCAL) { /* saddr should be known to target */if (inet_addr_onlink(in_dev, target, saddr))

break; } saddr = 0; break; case 2: /* Avoid secondary IPs, get a primary/preferred one */break

; } rcu_read_unlock(); if (!saddr) saddr = inet_select_addr(dev, target, RT_SCOPE_LINK); probes -= NEIGH_VAR(neigh->parms, UCAST_PROBES);

if (probes nud_state & NUD_VALID)) pr_debug("trying to ucast probe in NUD_INVALID\n"

); neigh_ha_snapshot(dst_ha, neigh, dev); dst_hw = dst_ha; } else { probes -= NEIGH_VAR(neigh->parms, APP_PROBES);

if (probes dev_addr, NULL); }

将得到的硬件源、目的地址，IP源、目的地址等作为参数，调用arp_send()函数创建一个arp报文并将其输出arp_send()创建及发送arp报文/* * Create and send an arp packet. */。

voidarp_send(int type, int ptype, __be32 dest_ip, struct net_device *dev, __be32 src_ip,

constunsignedchar *dest_hw, constunsignedchar *src_hw, constunsignedchar *target_hw){ structsk_buff

*skb;/* * No arp on this interface. */if (dev->flags&IFF_NOARP) return; skb = arp_create(type, ptype, dest_ip, dev, src_ip, dest_hw, src_hw, target_hw);

if (!skb) return; arp_xmit(skb); } arp_create()创建arp报文，填充字段/* * Interface to link layer: send routine and receive handler. */。

/* * Create an arp packet. If dest_hw is not set, we create a broadcast * message. */struct sk_buff *

arp_create(int type, int ptype, __be32 dest_ip, struct net_device *dev, __be32 src_ip, const

unsignedchar *dest_hw, constunsignedchar *src_hw, constunsignedchar *target_hw){ structsk_buff

*skb;structarphdr *arp;unsignedchar *arp_ptr; int hlen = LL_RESERVED_SPACE(dev); int tlen = dev->needed_tailroom;

/* * Allocate a buffer */ skb = alloc_skb(arp_hdr_len(dev) + hlen + tlen, GFP_ATOMIC); if (!skb)

returnNULL; skb_reserve(skb, hlen); skb_reset_network_header(skb); arp = (struct arphdr *) skb_put(skb, arp_hdr_len(dev)); skb->dev = dev; skb->protocol = htons(ETH_P_ARP);

if (!src_hw) src_hw = dev->dev_addr; /*目的MAC未知时，置1*/if (!dest_hw) dest_hw = dev->broadcast;

/* * Fill the device header for the ARP frame */if (dev_hard_header(skb, dev, ptype, dest_hw, src_hw, skb->len) <

0) goto out; /* * Fill out the arp protocol part. * * The arp hardware type should match the device type, except for FDDI, * which (according to RFC 1390) should always equal 1 (Ethernet). */

/* * Exceptions everywhere. AX.25 uses the AX.25 PID value not the * DIX code for the protocol. Make these device structure fields. */

switch (dev->type) { default: arp->ar_hrd = htons(dev->type); arp->ar_pro = htons(ETH_P_IP); break

; #if IS_ENABLED(CONFIG_AX25)case ARPHRD_AX25: arp->ar_hrd = htons(ARPHRD_AX25); arp->ar_pro = htons(AX25_P_IP);

break; #if IS_ENABLED(CONFIG_NETROM)case ARPHRD_NETROM: arp->ar_hrd = htons(ARPHRD_NETROM); arp->ar_pro = htons(AX25_P_IP);

break; #endif#endif#if IS_ENABLED(CONFIG_FDDI)case ARPHRD_FDDI: arp->ar_hrd = htons(ARPHRD_ETHER); arp->ar_pro = htons(ETH_P_IP);

break; #endif } arp->ar_hln = dev->addr_len; arp->ar_pln = 4; arp->ar_op = htons(type); arp_ptr = (

unsignedchar *)(arp + 1); memcpy(arp_ptr, src_hw, dev->addr_len); arp_ptr += dev->addr_len; memcpy

(arp_ptr, &src_ip, 4); arp_ptr += 4; switch (dev->type) { #if IS_ENABLED(CONFIG_FIREWIRE_NET)case ARPHRD_IEEE1394:

break; #endifdefault: if (target_hw) memcpy(arp_ptr, target_hw, dev->addr_len); elsememset(arp_ptr,

0, dev->addr_len); arp_ptr += dev->addr_len; } memcpy(arp_ptr, &dest_ip, 4); return skb; out: kfree_skb(skb);

returnNULL; } arp_xmit()发送arp报文/* * Send an arp packet. */voidarp_xmit(struct sk_buff *skb){ /* Send it off, maybe filter it using firewalling first. */

NF_HOOK(NFPROTO_ARP, NF_ARP_OUT, NULL, skb, NULL, skb->dev, dev_queue_xmit_sk); } arp报文的输入：arp_rcv()

用来从二层接收并处理一个arp报文。这个函数中就是做了一些参数检查，然后调用arp_process()函数。

/* * Receive an arp request from the device layer. */static int arp_rcv(structsk_buff *skb, structnet_device

*dev, structpacket_type *pt, structnet_device *orig_dev) { conststructarphdr *arp; /* do not tweak dropwatch on an ARP we will ignore */

if (dev->flags & IFF_NOARP || //网络设备知否支持arp协议 skb->pkt_type == PACKET_OTHERHOST || //arp报文是否是转发的包，表示这个包不应该由自己接收

skb->pkt_type == PACKET_LOOPBACK) //arp报文来自回环接口 goto consumeskb; skb = skb_share_check(skb, GFP_ATOMIC);

//如果skb是共享的，就复制一份if (!skb) goto out_of_mem; /* ARP header, plus 2 device addresses, plus 2 IP addresses. */

/*检测arp报文的完整性，其长度是否等于一个arp头部长度+两个硬件地址长度+两个IP地址长度*/if (!pskb_may_pull(skb, arp_hdr_len(dev))) goto freeskb; arp = arp_hdr(skb);

/*arp报文的硬件地址长度与网络设备的硬件地址长度是否匹配，arp报文的协议地址长度是否为4*/if (arp->ar_hln != dev->addr_len || arp->ar_pln != 4

) goto freeskb; memset(NEIGH_CB(skb), 0, sizeof(structneighbour_cb)); //#define NEIGH_CB(skb) ((struct neighbour_cb *)(skb)->cb)cb[]数组中存放的是每一协议层都可以自由使用的一段空间，一般用来存放控制指令和控制数据

return NF_HOOK(NFPROTO_ARP, NF_ARP_IN, NULL, skb, //netfilter arp hook函数 dev, NULL, arp_process); consumeskb: consume_skb(skb);

return0; freeskb: kfree_skb(skb); out_of_mem: return0; } arp_process()/* * Process an arp request. */

static int arp_process(structsock *sk, structsk_buff *skb) { structnet_device *dev = skb->dev; struct

in_device *in_dev = __in_dev_get_rcu(dev); structarphdr *arp; unsigned char *arp_ptr; structrtable

*rt; unsigned char *sha; __be32 sip, tip; u16 dev_type = dev->type; int addr_type; structneighbour

*n; structnet *net = dev_net(dev); bool is_garp = false; /* arp_rcv below verifies the ARP header and verifies the device * is ARPable. */

if (!in_dev)//输入网络设备的IP配置块 goto out; arp = arp_hdr(skb); //根据网络设备类型，检测arp报文中硬件类型与协议类型的有效性

switch (dev_type) { default: if (arp->ar_pro != htons(ETH_P_IP) || htons(dev_type) != arp->ar_hrd) goto out;

break; case ARPHRD_ETHER: case ARPHRD_FDDI: case ARPHRD_IEEE802: /* * ETHERNET, and Fibre Channel (which are IEEE 802 * devices, according to RFC 2625) devices will accept ARP * hardware types of either 1 (Ethernet) or 6 (IEEE 802.2). * This is the case also of FDDI, where the RFC 1390 says that * FDDI devices should accept ARP hardware of (1) Ethernet, * however, to be more robust, well accept both 1 (Ethernet) * or 6 (IEEE 802.2) */

if ((arp->ar_hrd != htons(ARPHRD_ETHER) && arp->ar_hrd != htons(ARPHRD_IEEE802)) || arp->ar_pro != htons(ETH_P_IP)) goto out;

break; case ARPHRD_AX25: if (arp->ar_pro != htons(AX25_P_IP) || arp->ar_hrd != htons(ARPHRD_AX25)) goto out;

break; case ARPHRD_NETROM: if (arp->ar_pro != htons(AX25_P_IP) || arp->ar_hrd != htons(ARPHRD_NETROM)) goto out;

break; } /* Understand only these message types */if (arp->ar_op != htons(ARPOP_REPLY) && arp->ar_op != htons(ARPOP_REQUEST)) goto out;

/* * Extract fields *///从arp报文中解析发送方MAC,IP，目的target IP arp_ptr = (unsigned char *)(arp + 1); sha = arp_ptr;。

//发送方硬件地址 arp_ptr += dev->addr_len; memcpy(&sip, arp_ptr, 4);//解析源IP arp_ptr += 4; switch (dev_type) { #

if IS_ENABLED(CONFIG_FIREWIRE_NET) case ARPHRD_IEEE1394: break; #endif default: arp_ptr += dev->addr_len; } memcpy(&tip, arp_ptr,

4);//解析目的IP/* * Check for bad requests for 127.x.x.x and requests for multicast * addresses. If this is one such, delete it. */

//丢弃ip地址为组播或互换地址的arp报文if (ipv4_is_multicast(tip) || (!IN_DEV_ROUTE_LOCALNET(in_dev) && ipv4_is_loopback(tip))) goto out;

/* * Special case: We must set Frame Relay source Q.922 address *///如果硬件类型为Q.922，则arp应答报文中目的硬件地址设置为网路设备的广播地址

if (dev_type == ARPHRD_DLCI) sha = dev->broadcast; /* * Process entry. The idea here is we want to send a reply if it is a * request for us or if it is a request for someone else that we hold * a proxy for. We want to add an entry to our cache if it is a reply * to us or if it is a request for our address. * (The assumption for this last is that if someone is requesting our * address, they are probably intending to talk to us, so it saves time * if we cache their address. Their address is also probably not in * our cache, since ours is not in their cache.) * * Putting this another way, we only care about replies if they are to * us, in which case we add them to the cache. For requests, we care * about those for us and those for our proxies. We reply to both, * and in the case of requests for us we add the requester to the arp * cache. */

/* Special case: IPv4 duplicate address detection packet (RFC2131) *///如果请求报文的源ip为0，则该arp报文是用来检测ipv4地址冲突的，因此在确定请求报文的目的IP为本地IP地址后，以该IP地址为源地址及目的地址发送arp响应报文。

if (sip == 0) { if (arp->ar_op == htons(ARPOP_REQUEST) && inet_addr_type(net, tip) == RTN_LOCAL && !arp_ignore(in_dev, sip, tip)) arp_send(ARPOP_REPLY, ETH_P_ARP, sip, dev, tip, sha, dev->dev_addr, sha); goto out; }

if (arp->ar_op == htons(ARPOP_REQUEST) && ip_route_input_noref(skb, tip, sip, 0, dev) == 0) { //找目的IP对应的路由

rt = skb_rtable(skb); addr_type = rt->rt_type; /*如果arp报文是发送给本机的，调用neigh_event_ns更新对应的邻居项，然后根据系统设置来决定是否过滤和丢弃arp报文，最后发送arp响应报文。

*/if (addr_type == RTN_LOCAL) { int dont_send; dont_send = arp_ignore(in_dev, sip, tip); if

(!dont_send && IN_DEV_ARPFILTER(in_dev)) dont_send = arp_filter(sip, tip, dev); if (!dont_send) { n = neigh_event_ns(&arp_tbl, sha, &sip, dev);

if (n) { arp_send(ARPOP_REPLY, ETH_P_ARP, sip, dev, tip, sha, dev->dev_addr, sha); neigh_release(n); } } goto out; }

/*对于不是发送给本机的arp请求报文，根据系统参数确定是否进行arp代理*/elseif (IN_DEV_FORWARD(in_dev)) { if (addr_type == RTN_UNICAST && (arp_fwd_proxy(in_dev, dev, rt) || arp_fwd_pvlan(in_dev, dev, rt, sip, tip) || (rt->dst.dev != dev && pneigh_lookup(&arp_tbl, net, &tip, dev, 。

0)))) { n = neigh_event_ns(&arp_tbl, sha, &sip, dev); if (n) neigh_release(n); if (NEIGH_CB(skb)->flags & LOCALLY_ENQUEUED || skb->pkt_type == PACKET_HOST || NEIGH_VAR(in_dev->arp_parms, PROXY_DELAY) ==

0) { arp_send(ARPOP_REPLY, ETH_P_ARP, sip, dev, tip, sha, dev->dev_addr, sha); }

else { pneigh_enqueue(&arp_tbl, in_dev->arp_parms, skb); return0; } goto out; } } }

/* Update our ARP tables *//*对于arp应答消息，或未处理的代理请求，则需要更新邻居表，因此现在邻居表中根据sip找到对应的邻居项*/ n = __neigh_lookup(&arp_tbl, &sip, dev,

0); /*对于那些并非由arp请求而接收到的arp应答，在系统允许接收的情况下，创建相应的邻居项*/if (IN_DEV_ARP_ACCEPT(in_dev)) { /* Unsolicited ARP is not accepted by default. It is possible, that this option should be enabled for some devices (strip is candidate) */

is_garp = arp->ar_op == htons(ARPOP_REQUEST) && tip == sip && inet_addr_type(net, sip) == RTN_UNICAST;

if (!n && ((arp->ar_op == htons(ARPOP_REPLY) && inet_addr_type(net, sip) == RTN_UNICAST) || is_garp)) n = __neigh_lookup(&arp_tbl, &sip, dev,

1); } /*更新或创建新的邻居项，首先确定邻居项的新状态，如果是发送给本机的arp应答报文，则对应邻居项状态应转变为NUD_REACHABLE，否则转到NUD_STALE然后调用neigh_update更新邻居项，如果其更新时间已超过locktime,则用覆盖的方式进行更新。

*/if (n) { int state = NUD_REACHABLE; int override; /* If several different ARP replies follows back-to-back, use the FIRST one. It is possible, if several proxy agents are active. Taking the first reply prevents arp trashing and chooses the fastest router. */

override = time_after(jiffies, n->updated + NEIGH_VAR(n->parms, LOCKTIME)) || is_garp;

/* Broadcast replies and request packets do not assert neighbour reachability. */if (arp->ar_op != htons(ARPOP_REPLY) || skb->pkt_type != PACKET_HOST) state = NUD_STALE; neigh_update(n, sha, state,

override ? NEIGH_UPDATE_F_OVERRIDE : 0); neigh_release(n); } out: consume_skb(skb); return0; }

neigh_event_nsstructneighbour *neigh_event_ns(structneigh_table *tbl, u8 *lladdr, void *saddr,

structnet_device *dev) { /*创建neighbour*/structneighbour *neigh = __neigh_lookup(tbl, saddr, dev, lladdr || !dev->addr_len);

if (neigh) neigh_update(neigh, lladdr, NUD_STALE, NEIGH_UPDATE_F_OVERRIDE); return neigh; }

neigh_update这个函数的作用就是更新邻居项硬件地址和状态分支比较多/* Generic update routine. -- lladdr is new lladdr or NULL, if it is not supplied. -- new is new state. -- flags NEIGH_UPDATE_F_OVERRIDE allows to override existing lladdr, if it is different. NEIGH_UPDATE_F_WEAK_OVERRIDE will suspect existing "connected" lladdr instead of overriding it if it is different. It also allows to retain current state if lladdr is unchanged. NEIGH_UPDATE_F_ADMIN means that the change is administrative. NEIGH_UPDATE_F_OVERRIDE_ISROUTER allows to override existing NTF_ROUTER flag. NEIGH_UPDATE_F_ISROUTER indicates if the neighbour is known as a router. Caller MUST hold reference count on the entry. */。

/*new：邻居项新状态，lladdr：邻居项新硬件地址*/ int neigh_update(struct neighbour *neigh, const u8 *lladdr, u8 new, u32 flags) { u8 old;

//邻居项老的状态 int err; int notify = 0;//是否通知该事件 struct net_device *dev; int update_isrouter = 0;//邻居项是否为路由器

write_lock_bh(&neigh->lock); dev = neigh->dev; old = neigh->nud_state; err = -EPERM;

/*case1:邻居项原先状态为NUD_NOARP或者NUD_PERMANENT时，标志位必须包含NEIGH_UPDATE_F_ADMIN 才允许更新，表示是管理员进行的操作，否则不允许更新*/if (!(flags & NEIGH_UPDATE_F_ADMIN) && (old & (NUD_NOARP | NUD_PERMANENT)))

goto out; if (neigh->dead) goto out; /*case2:新状态为无效状态，删除其定时器如果原先状态为NUD_CONNECTED状态，调用neigh_suspect 更新其输出函数；如果老状态为NUD_INCOMPLETE或者NUD_PROBE，新状态为NUD_FAILED，执行neigh_invalidate操作。

*/if (!(new & NUD_VALID)) { neigh_del_timer(neigh); if (old & NUD_CONNECTED) neigh_suspect(neigh); neigh->nud_state =

new; err = 0; notify = old & NUD_VALID; if ((old & (NUD_INCOMPLETE | NUD_PROBE)) && (new & NUD_FAILED)) { neigh_invalidate(neigh); notify =

1; } goto out; } /* Compare new lladdr with cached one */if (!dev->addr_len) { /* First case: device needs no address. */

lladdr = neigh->ha; } elseif (lladdr) { /* The second case: if something is already cached and a new address is proposed: - compare new & old - if they are different, check override flag */

if ((old & NUD_VALID) && !memcmp(lladdr, neigh->ha, dev->addr_len)) lladdr = neigh->ha; } else

{ /* No address is supplied; if we know something, use it, otherwise discard the request. */

err = -EINVAL; if (!(old & NUD_VALID)) goto out; lladdr = neigh->ha; } if (new & NUD_CONNECTED) neigh->confirmed = jiffies; neigh->updated = jiffies;

/* If entry was valid and address is not changed, do not change entry state, if new one is STALE. */

err = 0; update_isrouter = flags & NEIGH_UPDATE_F_OVERRIDE_ISROUTER; if (old & NUD_VALID) { /*前后地址不相同，并且没有NEIGH_UPDATE_F_OVERRIDE标志*/

if (lladdr != neigh->ha && !(flags & NEIGH_UPDATE_F_OVERRIDE)) { update_isrouter = 0; /*带有NEIGH_UPDATE_F_WEAK_OVERRIDE标志，并且老状态为NUD_CONNECTED*/

if ((flags & NEIGH_UPDATE_F_WEAK_OVERRIDE) && (old & NUD_CONNECTED)) { lladdr = neigh->ha;

new = NUD_STALE; } elsegoto out; } else { if (lladdr == neigh->ha && new == NUD_STALE && ((flags & NEIGH_UPDATE_F_WEAK_OVERRIDE) || (old & NUD_CONNECTED)) )

new = old; } } if (new != old) { neigh_del_timer(neigh); if (new & NUD_IN_TIMER) neigh_add_timer(neigh, (jiffies + ((

new & NUD_REACHABLE) ? neigh->parms->reachable_time : 0))); neigh->nud_state = new; notify =

1; } /*前后地址不相同，更新地址*/if (lladdr != neigh->ha) { write_seqlock(&neigh->ha_lock); memcpy(&neigh->ha, lladdr, dev->addr_len); write_sequnlock(&neigh->ha_lock); neigh_update_hhs(neigh);

if (!(new & NUD_CONNECTED)) neigh->confirmed = jiffies - (NEIGH_VAR(neigh->parms, BASE_REACHABLE_TIME) <<

1); notify = 1; } if (new == old) goto out; if (new & NUD_CONNECTED) neigh_connect(neigh);//更新output函数

else neigh_suspect(neigh);//更新output函数/*如果邻居项是无效状态变为有效状态，则便利arp_queue,将缓存在队列中的报文逐个发出*/if (!(old & NUD_VALID)) { struct sk_buff *skb; 。

/* Again: avoid dead loop if something went wrong */while (neigh->nud_state & NUD_VALID && (skb = __skb_dequeue(&neigh->arp_queue)) !=

NULL) { struct dst_entry *dst = skb_dst(skb); struct neighbour *n2, *n1 = neigh; write_unlock_bh(&neigh->lock); rcu_read_lock();

/* Why not just use neigh as-is? The problem is that * things such as shaper, eql, and sch_teql can end up * using alternative, different, neigh objects to output * the packet in the output path. So what we need to do * here is re-lookup the top-level neigh in the path so * we can reinject the packet there. */

n2 = NULL; if (dst) { n2 = dst_neigh_lookup_skb(dst, skb); if (n2) n1 = n2; } n1->output(n1, skb);

if (n2) neigh_release(n2); rcu_read_unlock(); write_lock_bh(&neigh->lock); } __skb_queue_purge(&neigh->arp_queue); neigh->arp_queue_len_bytes =

0; } out: if (update_isrouter) { neigh->flags = (flags & NEIGH_UPDATE_F_ISROUTER) ? (neigh->flags | NTF_ROUTER) : (neigh->flags & ~NTF_ROUTER); } write_unlock_bh(&neigh->lock);

/*发送通知事件*/if (notify) neigh_update_notify(neigh); return err; }neigh_update_notifystaticvoidneigh_update_notify

(struct neighbour *neigh) { call_netevent_notifiers(NETEVENT_NEIGH_UPDATE, neigh); __neigh_notify(neigh, RTM_NEWNEIGH,

0); }arp_ignore()staticintarp_ignore(struct in_device *in_dev, __be32 sip, __be32 tip){ structnet *net

= dev_net(in_dev->dev);int scope; switch (IN_DEV_ARP_IGNORE(in_dev)) { case0: /* Reply, the tip is already validated */

return0; case1: /* Reply only if tip is configured on the incoming interface */ sip = 0; scope = RT_SCOPE_HOST;

break; case2: /* * Reply only if tip is configured on the incoming interface * and is in same subnet as sip */

scope = RT_SCOPE_HOST; break; case3: /* Do not reply for scope host addresses */ sip = 0; scope = RT_SCOPE_LINK; in_dev =

NULL; break; case4: /* Reserved */case5: case6: case7: return0; case8: /* Do not reply */return

1; default: return0; } return !inet_confirm_addr(net, in_dev, sip, tip, scope); } arp_filterstatic

intarp_filter(__be32 sip, __be32 tip, struct net_device *dev){ structrtable *rt;int flag = 0; /*unsigned long now; */

structnet *net = dev_net(dev); rt = ip_route_output(net, sip, tip, 0, 0); if (IS_ERR(rt)) return

1; if (rt->dst.dev != dev) { NET_INC_STATS_BH(net, LINUX_MIB_ARPFILTER); flag = 1; } ip_rt_put(rt);

return flag; } arp代理代理arp（proxy arp），通常像路由器这样的设备才使用，用来代替处于另一个网段的主机回答本网段主机的arp请求感觉代码ARP好像没啥用呀网络主机发包的一般过程：。

1.当目的IP和自己在同一网段时，直接arp请求该目的IP的MAC2.当目的IP和自己不再同一网段时，arp请求默认网关的MAChttps://www.cnblogs.com/taitai139/p/12336554.html。

https://www.cnblogs.com/Widesky/p/10489514.html当主机没有默认网关的时候，arp请求别的网段的报文，到达路由器后，本来路由器是要隔离广播的，把这个arp请求报文给丢弃，这样就没法通信了。

当路由器开启arp proxy后，路由器发现请求的目的IP在其他网段，就自己给主机回复一个arp响应报文，这样源主机就把路由器的MAC当成目的IP主机对应的MAC，可以通信了这样可能会造成主机arp表中，多个IP地址都对应于路由器的同一个MAC地址。

可以使用arping命令发送指定IP的arp请求报文。

写完了发现这个老妹写的arp代理文章蛮好的，不过她好像是转载的。

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