ng Quang Minh, CCIE#11897 Trung tm tin hc VnPro 149/1D Ung Vn Khim Phng 25, Q. Bnh Thnh TPHCM Giao thc ICMP, phn 1: Gii thiu Giao thc ICMP (Internetwork Control Message Protocol) cho php vic th nghim v khc phc cc s c ca giao thc TCP/IP. ICMP nh ngha cc cc thng ip c dng xc nh khi no mt h thng mng c th phn phi cc gi tin. Tht ra, ICMP l mt thnh phn bt buc ca mi hin thc IP. Trong mt vi trng hp, mt gateway hoc mt my ch s cn giao tip vi my ngun bo co li cc li xy ra trong qu trnh x l gi tin. Trong trng hp , ICMP s c dng. ICMP s dng IP nh th n (ICMP) nm mt mc cao hn. ARP khng phi l mt giao thc lp network. N l mt ng dng c vit trc tip trn lp Datalink. C mt cch thc khc chia cc loi thng ip ny l control plane, management plane v data plane. i khi gi tin ping cn c gi l ICMP echo request v ICMP echo replies, nhng tht ra, ICMP bao gm nhiu loi thng ip khc nhau. Ping thng c dng kim tra kt ni gia cc thit b. y l mt giao thc rt ph bin kim tra s tn ti ca mt my. Ping cng c th c dng khc phc nhng vn phc tp hn trong mng. Phn ln cc hin thc ca lnh ping cho php bn thay i kch thc ca gi tin. Bng di y m t mt vi thng k v kch thc gi tin ping trong Cisco IOS v cc thit b switch Catalyst. bng: Kch thc gi tin ping Device Cisco IOS Cisco Catalyst Minimum Packet Size 36 bytes 56 bytes Maximum Packet Size 18024 bytes 472 bytes Default Packet Size 100 bytes 64 bytes

Phn ln cc hin thc ca lnh ping trn cc my gi tng gi tin mi giy. Cisco IOS cho php bn gi cc gi tin nhanh hay chm ty thuc vo kh nng ca CPU v cc thit b mng c th truyn n nh th no.

C vi vn bn cn phi nhn bit khi dng lnh ping. Ping c to ra v c tr li bi CPU ca cc thit b Cisco. Mc d lnh ping khng c chim nhiu thi gian CPU, bn phi cn thn khi dng cc thit b c ti ln tr li hoc to ra lnh ping. Trn cc thit b Cisco, tc v ping c gn u tin rt thp. V vy, c th mt thit b ang bn rn khng th tr li lnh ping. Nu mt thit b m bn ang ping khng c trong bng ARP, gi tin ping u tin thng b time-out. Do , phn ln cc ng dng mng dng ping s gi ra vi gi tin ping trc khi thc s thng bo l b mt kt ni. Cng tng t, bn phi rt cn thn khi dng lnh ping xc nh tr hay thng lng ca mt h thng mng bi v bn ang o lng ICMP performance ca cc u cui ch khng phi o hiu nng thc s ca h thng mng. Bng di y lit k cc loi thng ip ICMP quan trng nht:

Loi thng ip ICMP Destination Unreachable Time Exceed Source Quench Redirect Echo Address/mask request/reply Router Advertisement and Selection

Mc ch Thng bo cho my ngun l c mt vn trong phn phi gi tin Thi gian chuyn mt gi tin l qu ln. Gi tin b loi b. My ngun ang gi d liu mc nhanh hn m my ch c th x l. Thng ip ny yu cu my gi gi chm li. c dng bi mt router thng bo cho mt host dng mt a ch router khc tt hn cho nhng ln gi khc sp ti. c dng bi lnh ping kim tra kt ni. c dng hc v truy vn a ch IP/ mask c dng. c dng cho php cc host hc a ch IP ca cc router gn vo subnet.

Mi thng ip ICMP cha mt trng Type v trng Code. Trng type ch ra loi thng ip trong bng trn. Trng code ngm nh mt loi kiu con. V d, nhiu ngi hay m t lnh ping nh l ICMP Echo request v ICMP Echo reply nhng trong thc t, hai loi thng ip trn c cng kiu Echo nhng khc Code (request v reply).

Di qu , vit ra lu v chc kh hiu hn... tui thy my bi ny kh hay .... c th tham kho Ping, vit tt ca Packet Internet Grouper (Groper), l mt cng c cho mng my tnh s dng trn cc mng TCP/IP (chng hn nh Internet) kim tra xem c th kt ni ti mt my ch c th no hay khng, v c lng khong thi gian tr trn vng gi gi d liu cng nh t l cc gi d liu c th b mt gia hai my. Cng c ny thc hin nhim v trn bng cch gi mt s gi tin ICMP n my kia v lng nghe tr li. Tc gi ca cng c ny l ng Mike Muuss. Kt xut ca ping thng thng bao gm kch c gi d liu, a ch host truy vn, dy s ICMP, thi gian sng (time to live), thi gian tr trn vng (round-trip time), n v thi gian l miligiy (1/1000 ca giy), v thi gian di 10 giy thng c chnh xc thp. Ping l mt tin ch i k m trong I , Internet v c c h thng mng CP IP. iv h u ht c c h i u hnh mng m y t nh hin nay u h tr CP IP, trong cng ao gm tin t ch Ping. Ping tng ng vi mt ting la trong h m n i v lng nghe ting vng li ca n. n ping mt m y ch kh c tr n h thng mng em host c th tin n c t host ca n hay khng. Cu lnh c dng ping ipaddress, y ipaddress l a ch IP ca host m n mun li n lc. Ping s dng giao th c ICMP Internet Control Message Protocol iao th c i u khin thng o tr n Internet) gii quyt cng vic ca n. i mt c ch c th, n gi i mt thng o kiu ting vang ICMP n host c ch nh. u c th tin n thit trc khi ht khong thi gian cho ph p, host ca n s nh n c mt ting vang ICMP thng o p li. Ping c th c s dng nh mt cng c gii quyt c c s c v truy n thng. ic u ti n phi lm l ping a ch ca h thng n ang lm vic. i u n y chc rng ph n m m mng m y t nh ca n ang lm vic. n, ping n h thng ch. u n khng thy mt tr li no, h y th ping n mt h thng kh c em h thng n y c th tin n c khng. u h thng kh c p ng li, h thng ca n c l l tt ri c n mng hay host ch c th l c vn . u c th, n h y n h thng ch v ping vo m y em h thng li n kt mng ca n c ang hot ng hay khng. u khng, h y kim tra li cu h nh ci t, c c ni kt v ngay c i vi c c card giao tip mng. mc li n quan ICMP (Internet Control Message Protocol); IP (Internet Protocol) Vo cmd g lnh : ipconfig /? ping /? Ipconfig dng xem v chnh sa a ch IP Ping : kim tra s khai thng ca cc my tnh trong mng thy nhau cha?) hng th dng : ipconfig all xem ton b thng tin ping : th d hn nhi u, nh p th m a ch IP ho c tn my, ho c domain (tn mi n) c n kim tra s khai thng l c. V d IP ca bn l 192.168.1.100 bn mun kim tra

my 19 (tn my tnh l may19, IP l 192.168.1.19) th bn g nh sau ping may19 ho c : ping 192.168.1.19 Nu thng bo Reply th thy nhau trong mng