ARP

NAME
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IOCTLS
SYSCTLS
BUGS
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NAME

arp - LinuxçARPæ ¸å¿æ¨¡å

æè¿°

è¿ä¸ªæ ¸å¿å议模åå®ç°RFC826ä¸å®ä¹ç Address Resolution Protocol [è¯æ³¨ï¼å³TCP/IPç第ä¸å±å°ç¬¬ä¸å±çå°å转æ¢åè®®]ï¼ ç¨äºå¨ç´æ¥ç¸è¿çç½ç»ä¸æ¢ç¬¬äºå±ç¡¬ä»¶å°åå Ipv4 åè®®å°åä¹é´ç转æ¢ã ç¨æ·é¤éæ³å¯¹å¶è¿è¡éç½®ï¼å¦åä¸è¬ä¸ä¼ç´æ¥æä½è¿ä¸ªæ¨¡åã

å®éä¸ï¼å®æä¾å¯¹æ ¸å¿ä¸å¶å®åè®®çæå¡ã

ç¨æ·è¿ç¨å¯ä»¥ä½¿ç¨ packet(7) ç socketsï¼æ¶å° ARP åï¼è¯æ³¨ï¼ä¸è¯åç»ï¼ã è¿æä¸ç§æºå¶æ¯ä½¿ç¨ netlink(7) socketsï¼å¨ç¨æ·ç©ºé´ç®¡ç ARP ç¼åçæºå¶ã æ们ä¹å¯ä»¥éè¿ ioctl (2) æ§å¶ä»»æ PF_INET socketä¸ç ARP 表

ARP 模åç»´æ¤ä¸ä¸ªç¡¬ä»¶å°åå°åè®®å°åæ å°çç¼åãè¿ä¸ªç¼åæ大å°éå¶ï¼æ以 ä¸å¸¸ç¨çåæ§çè®°å½ï¼Entryï¼å°è¢«åå¾æ¶éå¨æ¸é¤ï¼garbage-collectedï¼ï¼ åå¾æ¶éå¨æ°¸è¿ä¸è½å é¤æ为永ä¹çè®°å½ãæ们å¯ä»¥ä½¿ç¨ioctlsç´æ¥æ纵ç¼å²ï¼ 并ä¸å¶æ§ç¶å¯ä»¥ç¨ä¸é¢å®ä¹ç sysctl è°èã

å¦æå¨éå®çæ¶é´ï¼è§ä¸é¢çsysctlï¼åï¼ä¸æ¡ç°åæ å°æ²¡æè¯å®åé¦æ¶ï¼ å认为ç¸é»å±çç¼åè®°å½å¤±æã 为äºå次åç®æ åéæ°æ®ï¼ARPå°é¦åè¯ç询é®æ¬å°arpè¿ç¨ app_solicit 次ï¼è·åæ´æ°äºç MACï¼ä»è´¨è®¿é®æ§å¶ï¼å°åã å¦æ失败ï¼å¹¶ä¸æ§çMACå°åæ¯å·²ç¥çï¼ååé ucast_solicit 次ç unicast probeãå¦æä»ç¶å¤±è´¥ï¼åå°åç½ç»å¹¿æä¸ä¸ªæ°çARP请æ±,æ¤æ¶è¦ æå¾åéæ°æ®çéå

å¦æ Linux æ¥å°ä¸ä¸ªå°å请æ±ï¼èä¸è¯¥å°åæå Linux 转åçå°åï¼ å¹¶ä¸æ¥æ¶æ¥å£æå¼äºä»£ç arp æ¶ï¼Linux å°èªå¨æ·»å ä¸æ¡éæ°¸ä¹ç 代ç arp è®°å½ï¼å¦æåå¨æç»å°ç®æ çè·¯ç±ï¼åä¸æ·»å ä»£ç arp è®°å½ã

IOCTLS

æä¸ä¸ª ioctl å¯ä»¥ç¨äºææ PF_INET ç sockets ä¸ãå®ä»¬ä»¥ä¸ä¸ªæå struct arpreq çæéä½ä¸ºå®ä»¬çåæ°ã

struct arpreq
{
struct sockaddr arp_pa; /* åè®®å°å(protocol address)*/
struct sockaddr arp_ha; /* 硬件å°å(hardware address) */
int arp_flags; /* æ å¿(flags) */
struct sockaddr arp_netmask;
/* åè®®å°åçç½ç»æ©ç (netmask of protocol address)*/
char arp_dev[16];
};

SIOCSARP, SIOCDARP å SIOCGARP å¯åè´è®¾ç½®ãå é¤åè·å ARP æ å°ã设置åå é¤ ARP æ å°æ¯ç¹è®¸æä½ï¼ åªææ¥æ CAP_NET_ADMIN æéçè¿ç¨æææUID为0çè¿ç¨å¯ä»¥æ§è¡ã

arp_pa å¿é¡»æ¯ AF_INET socketï¼å¹¶ä¸ arp_ha å¿é¡»æå arp_dev. æå®ç设å¤ç¸åçç±»åã arp_dev æ¯ä¸ªä»¥nullç»æç设å¤åå符串ã

     

å¦æè®¾ç½®äº ATF_NETMASK æ å¿ï¼é£ä¹ arp_netmask å¿é¡»ææã Linux 2.2 ä¸æ¯æ代çç½ç» ARP è®°å½ï¼å æ¤ï¼è¦è®¾æ0xffffffffæè0ï¼ ä»¥å é¤ç°å- 代çarpè®°å½ãè¿éä¸ä½¿ç¨ ç°å代çarpè®°å½ã ATF_USETRAILERS å·²ç»è¿æ¶äºï¼ä¸åºè¯¥ç»§ç»ä½¿ç¨ã

SYSCTLS

ARP æ¯æä¸ä¸ª sysctl æ¥å£ï¼å¯ä»¥ç¨ä»¥éç½®å¨å±åæ°æé个ç½ç»æ¥å£å°è¿è¡éå¶ã 该 sysctl å¯ä»¥éè¿ /proc/sys/net/ipv4/neigh/*/* æ件æèä½¿ç¨ sysctl(2) æ¥å£æ¥è®¿é®ãç³»ç»ä¸æ¯ä¸ªæ¥å£é½å¨ /proc/sys/net/ipv4/neigh/. ä¸- æèªå·±çç®å½ã‘default’ç®å½ä¸ç设置ç¨äºæææ°å»ºç设å¤ã sysctl ç¸å³çæ¶é´æ¯ä»¥ç§ä¸ºåä½ï¼é¤éç¹å«å£°æè¿ï¼
anycast_delay

对 IPv6 ç¸é»è¯·æ±ä¿¡æ¯çåå¤çæ大延è¿æ¶é´ï¼ ç®åè¿ä¸æ¯æ anycastã缺çå¼ä¸º1ç§ã

app_solicit

è¿æ¯å¨ä½¿ç¨å¤è·¯å¹¿ææ¢æµ(multicast probe)åï¼ ç»è¿ç½ç»è¿æ¥éå°ç¨æ·é´éARP端å£çæ§ç¨åºçæ¢æµï¼probeï¼ æ大æ°ç®(è§ mcast_solicit )ã 缺çå¼ä¸º0ã

base_reachable_time

ä¸æ¦åç°ç¸é»è®°å½ï¼è³å°å¨ä¸æ®µä»äº base_reachable_time/2å3*base_reachable_time/2 ä¹é´çéæºæ¶é´åï¼è¯¥è®°å½æ¯ææçãå¦ææ¶å°ä¸å±åè®®çè¯å®åé¦ï¼ é£ä¹è®°å½çæææå°å»¶é¿ã 缺çå¼æ¯30ç§ã

delay_first_probe_time

åç°æ个ç¸é»å±è®°å½æ æ(stale)åï¼ååºç¬¬ä¸ä¸ªæ¢æµè¦çå¾çæ¶é´ã 缺çå¼æ¯5ç§ã

gc_interval

æ¶éç¸é»å±è®°å½çæ ç¨è®°å½çåå¾æ¶éç¨åºçè¿è¡å¨æï¼ç¼ºç为30ç§ã

gc_stale_time

å³å®æ£æ¥ä¸æ¬¡ç¸é»å±è®°å½çæææ§çå¨æã å½ç¸é»å±è®°å½å¤±ææ¶ï¼å°å¨ç»å®åéæ°æ®åï¼å解æä¸æ¬¡ã 缺çå¼æ¯60ç§ã

gc_thresh1

åå¨äºARPé«éç¼åä¸çæå°å±æ°ï¼å¦æå°äºè¿ä¸ªæ°ï¼ åå¾æ¶éå¨å°ä¸ä¼è¿è¡ã缺çå¼æ¯128ã

gc_thresh2

ä¿åå¨ ARP é«éç¼åä¸çæå¤çè®°å½è½¯éå¶ã åå¾æ¶éå¨å¨å¼å§æ¶éåï¼å许记å½æ°è¶è¿è¿ä¸ªæ°å 5 ç§ã 缺çå¼æ¯ 512ã

gc_thresh3

ä¿åå¨ ARP é«éç¼åä¸çæå¤è®°å½ç硬éå¶ï¼ ä¸æ¦é«éç¼åä¸çæ°ç®é«äºæ¤ï¼ åå¾æ¶éå¨å°é©¬ä¸è¿è¡ã缺çå¼æ¯1024ã

locktime

ARP è®°å½ä¿åå¨é«éç¼ååçæçæ¶é´ï¼jiffyæ°ï¼ï¼ 以é²æ¢å- å¨å¤ä¸ªå¯è½çæ å°(potential mapping)æ¶ï¼ ARP é«éç¼åç³»ç»ç颠簸 (ç»å¸¸æ¯ç±äºç½ç»çé误éç½®èå¼èµ·)ã 缺çå¼æ¯ 1 ç§ã

mcast_solicit

å¨æè®°å½æ è®°ä¸ºä¸å¯æµè¾¾çä¹åï¼ ç¨å¤è·¯å¹¿æ/广æ- ï¼multicast/broadcastï¼æ¹å¼è§£æå°åçæ大次æ°ã 缺çå¼æ¯3ã

proxy_delay

å½æ¥æ¶å°æä¸ä¸ªè¯·æ±å·²ç¥ç代ç ARP å°åç ARP 请æ±æ¶ï¼ å¨ååºåå¯ä»¥å»¶è¿ç jiffyï¼æ¶é´åä½ï¼è§BUGï¼æ°ç®ã è¿æ ·ï¼ä»¥é²æ- ¢ç½ç»é£æ´ã缺çå¼æ¯0.8ç§ã

proxy_qlen

è½æ¾å¥ä»£ç ARP å°åéå(proxy-ARP addresses)çæ°æ®åæ大æ°ç®ã缺çå¼æ¯64ã

retrans_time

éåä¸ä¸ªè¯·æ±åççå¾ jiffyï¼æ¶é´åä½ï¼è§BUGï¼çæ°ç®ã缺çå¼æ¯1ç§ã

ucast_solicit

询é®ARP端å£çæ§ç¨åºåï¼è¯å¾åéåæ¢æµï¼unicast probeï¼ç次æ°ã (è§ app_solicit). 缺çå¼æ¯3ç§ã

unres_qlen

æ¯ä¸ªæ²¡æ被å¶å®ç½ç»å±è§£æçå°åï¼å¨éåä¸å¯åæ¾åçæ大æ°ç®ã缺çå¼æ¯3.

BUGS

æ¶é设置çæ¶é´åä½ jiffyï¼è·ç¡¬ä»¶ä½ç³»æå³ã å¨ Alpha ä¸ï¼ä¸ä¸ª jiffy æ¯ 1/1024 ç§ï¼èå¨å¶å®æºå¨ä¸ï¼æ¯ 1/100 ç§ã

ç®åè¿æ²¡æåæ³ä»ç¨æ·ç©ºé´åéè¯å®åé¦ã è¿æå³çå¨ç¨æ·ç©ºé´å®ç°çé¢åè¿æ¥çåè®® ï¼connection oriented protocolsï¼å°äº§ç大éç ARP é讯ã å ä¸ºndiscå°éæ°æ¢æµMACå°åãåæ ¸ NFS çå®ç°ä¹åå¨åæ ·çé®é¢ã

è¿ä¸ªæå页主è¦è®² IPv4 è§è并ä¸å±äº« IPv4 å IPv6 çåè½ï¼

çæ¬

Linux 2.0ä¸ç struct arpreqï¼ æ·»å äº arp_dev ï¼åæ¶ ioctl æ°ç®ä¹æ¹åäºãå¨ Linux 2.2 ä¸å°ä¸åæ¯ææ§çioctlã

å¨ Linux 2.2 ä¸ï¼åæ¶äºå¯¹ç½ç»ä»£ç arp è®°å½(ç½ç»æ©ç ä¸æ¯0xffffffff)çæ¯æã è¿ä¸ªåè½è¢«å核设置çä¸ä¸ªèªå¨ä»£ç arp å代ï¼è¿ä¸ªèªå¨ä»£ç arp ç¨äºææä½äº å¶å®æ¥ä¸çå¯å°è¾¾ç主æºï¼å¦æ该æ¥å£ç转åå代ç arp æå¼äºï¼ã

å¦è§

ip(7)

RFC826 äºè§£ ARP æè¿°ï¼
RFC2461 æè¿°äºIPv6使ç¨çè¿é»æ¥æ¾ä»¥ååºæ¬ç®æ³

[ä¸æçç»´æ¤äºº]

Alan Yao <Alan_Yao@163.net>

[ä¸æçææ°æ´æ°]

2000/10/23

ãä¸å½linux论åmanæå页翻è¯è®¡åã:

http://cmpp.linuxforum.net

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æ¬é¡µé¢ä¸æçç±ä¸æ man æå页计åæä¾ã
ä¸æ man æå页计åï¼https://github.com/man-pages-zh/manpages-zh

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