linux pppstats命令详解

Linux系统下pppstats命令用于显示PPP连线状态，下面是pppstats命令内容的具体介绍：

1、pppstats命令简介：

pppstats命令全称是point to point protocol status，用于显示PPP连线状态，可以得知PPP连接网络的相关信息。

2、语法：

pppstats [-adrv][-c][-w][网络界面]

3、参数说明：

-a：显示绝对统计值。

-c：设置回报状况的次数。

-d：显示相对统计值。

-r：显示数据包压缩比率的统计值。

-v：显示VJTCP文件头的压缩效率统计值。

-w：设置显示统计信息的间隔时间。

以上就是小编今天的分享了，希望可以帮助到大家。

linux下arping命令详解

Linux内核-arp协议

从ip_finish_output2到dev_queue_xmit路径：

arping命令：

http://www.bluestep.cc/linux命令arping-网络管理-通过发送arp协议报文测试网络/

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. */struct arphdr { __be16 ar_hrd; /* format of hardware address */ __be16 ar_pro; /* format of protocol address */ unsigned char ar_hln; /* length of hardware address */ unsigned char ar_pln; /* length of protocol address */ __be16 ar_op; /* ARP opcode (command) */#if 0 /* * Ethernet looks like this : This bit is variable sized however... */ unsigned char ar_sha[ETH_ALEN]; /* sender hardware address */ unsigned char ar_sip[4]; /* sender IP address */ unsigned char ar_tha[ETH_ALEN]; /* target hardware address */ unsigned char 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.cvoid __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.cstatic const struct neigh_ops arp_generic_ops = { .family = AF_INET, .solicit = arp_solicit, .error_report = arp_error_report, .output = neigh_resolve_output, .connected_output = neigh_connected_output,};static const struct neigh_ops arp_hh_ops = { .family = AF_INET, .solicit = arp_solicit, .error_report = arp_error_report, .output = neigh_resolve_output, .connected_output = neigh_resolve_output,};static const struct neigh_ops arp_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。

struct neigh_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)(const void *pkey, const struct net_device *dev, __u32 *hash_rnd); bool (*key_eq)(const struct neighbour *, const void *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*/ struct neigh_parms parms; struct list_head parms_list; int gc_interval; int gc_thresh1; int gc_thresh2; int gc_thresh3; unsigned long last_flush; struct delayed_work gc_work; /*处理proxy_queue的定时器*/ struct timer_list proxy_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。*/ struct sk_buff_head proxy_queue; /*邻居项条目数，在neigh_alloc()、neigh_destroy()中更新*/ atomic_t entries; rwlock_t lock; unsigned long last_rand; /*记录邻居表中有关邻居项的各类统计数据*/ struct neigh_statistics __percpu *stats; /*存储邻居项的散列表：hash表，用来存储邻居项*/ struct neigh_hash_table __rcu *nht; /*存储arp代理三层协议地址的散列表*/ struct pneigh_entry **phash_buckets;};neighbour

一个neighbour对应一个邻居项，就是一个arp条目

struct neighbour { struct neighbour __rcu *next; struct neigh_table *tbl;/*指向arp_tbl*/ struct neigh_parms *parms; unsigned long confirmed; unsigned long updated; rwlock_t lock; atomic_t refcnt;/*引用计数*/ struct sk_buff_head arp_queue;/*用来缓存待发送的报文*/ unsigned int arp_queue_len_bytes; struct timer_list timer;/*定时器*/ unsigned long 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*/ unsigned char ha[ALIGN(MAX_ADDR_LEN, sizeof(unsigned long))]; /*缓存二层报头，包括目的MAC地址*/ struct hh_cache hh; /*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*/ const struct neigh_ops *ops; struct rcu_head rcu; struct net_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。

struct neigh_ops { int family;//AF_INET /*发送arp报文*/ void (*solicit)(struct neighbour *, struct sk_buff *); /*向三层报告错误*/ void (*error_report)(struct neighbour *, struct sk_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)(struct neighbour *, struct sk_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)(struct neighbour *, struct sk_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。

struct neigh_statistics { unsigned long allocs; /* number of allocated neighs */ unsigned long destroys; /* number of destroyed neighs */ unsigned long hash_grows; /* number of hash resizes */ unsigned long res_failed; /* number of failed resolutions */ unsigned long lookups; /* number of lookups */ unsigned long hits; /* number of hits (among lookups) */ unsigned long rcv_probes_mcast; /* number of received mcast ipv6 */ unsigned long rcv_probes_ucast; /* number of received ucast ipv6 */ unsigned long periodic_gc_runs; /* number of periodic GC runs */ unsigned long forced_gc_runs; /* number of forced GC runs */ unsigned long unres_discards; /* number of unresolved drops */};arp表结构：arp_tbl

F:\company\Linux\linux-4.1.45\linux-4.1.45\net\ipv4\arp.cstruct neigh_table arp_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(const struct packet_type *pt){ if (pt->type == htons(ETH_P_ALL)) return pt->dev ? &pt->dev->ptype_all : &ptype_all; else return 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. */int register_netdevice_notifier(struct notifier_block *nb){ struct net_device *dev; struct net_device *last; struct net *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;}

static RAW_NOTIFIER_HEAD(netdev_chain);#define RAW_NOTIFIER_HEAD(name) \ struct raw_notifier_head name = \ RAW_NOTIFIER_INIT(name) struct raw_notifier_head { struct notifier_block __rcu *head;}; 搞了半天就是：struct raw_notifier_head netdev_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 can't 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：？？

struct neighbour *__neigh_create(struct neigh_table *tbl, const void *pkey, struct net_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); struct neigh_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) << 1); write_lock_bh(&tbl->lock); nht = rcu_dereference_protected(tbl->nht, lockdep_is_held(&tbl->lock)); /*hash扩容*/ if (atomic_read(&tbl->entries) > (1 << nht->hash_shift)) nht = neigh_hash_grow(tbl, nht->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

static struct neighbour *neigh_alloc(struct neigh_table *tbl, struct net_device *dev){ struct neighbour *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_constructor

1.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); } else if (dev->flags & (IFF_NOARP | IFF_LOOPBACK)) { neigh->nud_state = NUD_NOARP; memcpy(neigh->ha, dev->dev_addr, dev->addr_len); } else if (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; } return 0;}dst_neigh_output

static inline int dst_neigh_output(struct dst_entry *dst, struct neighbour *n, struct sk_buff *skb){ const struct hh_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); else return n->output(n, skb);}neigh_resolve_output

/* Slow and careful. */int neigh_resolve_output(struct neighbour *neigh, struct sk_buff *skb){ int rc = 0; if (!neigh_event_send(neigh, skb)) { int err; struct net_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_send

static inline int neigh_event_send(struct neighbour *neigh, struct sk_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); return 0;}__neigh_event_send

int __neigh_event_send(struct neighbour *neigh, struct sk_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); return 1; } } else if (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)) { struct sk_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); return 1;}neigh_timer_handler

/* Called when a timer expires for a neighbour entry. */static void neigh_timer_handler(unsigned long arg){ unsigned long now, next; struct neighbour *neigh = (struct neighbour *)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; } else if (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; } } else if (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_probe

static void neigh_probe(struct neighbour *neigh) __releases(neigh->lock){ struct sk_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。

static void arp_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(struct neighbour *neigh, struct sk_buff *skb){ __be32 saddr = 0; u8 dst_ha[MAX_ADDR_LEN], *dst_hw = NULL; struct net_device *dev = neigh->dev; __be32 target = *(__be32 *)neigh->primary_key; int probes = atomic_read(&neigh->probes); struct in_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 < 0) { if (!(neigh->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 < 0) { neigh_app_ns(neigh); return; } } arp_send(ARPOP_REQUEST, ETH_P_ARP, target, dev, saddr, dst_hw, dev->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. */void arp_send(int type, int ptype, __be32 dest_ip, struct net_device *dev, __be32 src_ip, const unsigned char *dest_hw, const unsigned char *src_hw, const unsigned char *target_hw){ struct sk_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 unsigned char *dest_hw, const unsigned char *src_hw, const unsigned char *target_hw){ struct sk_buff *skb; struct arphdr *arp; unsigned char *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) return NULL; 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 = (unsigned char *)(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;#endif default: if (target_hw) memcpy(arp_ptr, target_hw, dev->addr_len); else memset(arp_ptr, 0, dev->addr_len); arp_ptr = dev->addr_len; } memcpy(arp_ptr, &dest_ip, 4); return skb;out: kfree_skb(skb); return NULL;}arp_xmit()

发送arp报文

/* * Send an arp packet. */void arp_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(struct sk_buff *skb, struct net_device *dev, struct packet_type *pt, struct net_device *orig_dev){ const struct arphdr *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(struct neighbour_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); return 0;freeskb: kfree_skb(skb);out_of_mem: return 0;}arp_process()

/* * Process an arp request. */static int arp_process(struct sock *sk, struct sk_buff *skb){ struct net_device *dev = skb->dev; struct in_device *in_dev = __in_dev_get_rcu(dev); struct arphdr *arp; unsigned char *arp_ptr; struct rtable *rt; unsigned char *sha; __be32 sip, tip; u16 dev_type = dev->type; int addr_type; struct neighbour *n; struct net *net = dev_net(dev); bool is_garp = false; /* arp_rcv below verifies the ARP header and verifies the device * is ARP'able. */ 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, we'll 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。*/ else if (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); return 0; } 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); return 0;}

neigh_event_ns

struct neighbour *neigh_event_ns(struct neigh_table *tbl, u8 *lladdr, void *saddr, struct net_device *dev){ /*创建neighbour*/ struct neighbour *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; } else if (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; } else goto 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_notify

static void neigh_update_notify(struct neighbour *neigh){ call_netevent_notifiers(NETEVENT_NEIGH_UPDATE, neigh); __neigh_notify(neigh, RTM_NEWNEIGH, 0);}arp_ignore()

static int arp_ignore(struct in_device *in_dev, __be32 sip, __be32 tip){ struct net *net = dev_net(in_dev->dev); int scope; switch (IN_DEV_ARP_IGNORE(in_dev)) { case 0: /* Reply, the tip is already validated */ return 0; case 1: /* Reply only if tip is configured on the incoming interface */ sip = 0; scope = RT_SCOPE_HOST; break; case 2: /* * Reply only if tip is configured on the incoming interface * and is in same subnet as sip */ scope = RT_SCOPE_HOST; break; case 3: /* Do not reply for scope host addresses */ sip = 0; scope = RT_SCOPE_LINK; in_dev = NULL; break; case 4: /* Reserved */ case 5: case 6: case 7: return 0; case 8: /* Do not reply */ return 1; default: return 0; } return !inet_confirm_addr(net, in_dev, sip, tip, scope);}arp_filter

static int arp_filter(__be32 sip, __be32 tip, struct net_device *dev){ struct rtable *rt; int flag = 0; /*unsigned long now; */ struct net *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MAC。

2.当目的IP和自己不再同一网段时，arp请求默认网关的MAC。

https://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。