>
> Sao ko gia su la` ca'c ma'y trong LAN ko co' rule do'? Thu te
> thi` chuc nang ipforward default la` OFF. Trong truong hop ca'c ma'y
> trong LAN co' ca'i rule ky` qua'i a^'y, nghi~a la` cu+' nha^.n
> ddu+o+.c go'i co' di'ch la` 0.0.0.0 thi` send dde^'n gateway thi`
> gateway sau khi nhan duoc qua'i go'i na`y cu~ng discard luon because
> no machine on the world has that weird address. Da^'y la` gia? su+?
> go'i dda~ ddu+o+.c send di trong mang LAN. Tre^n thuc te khi may tinh
> send mo^.t ip packet se~ co' 2 tru+o+`ng ho+.p :
>
> 1. Di'ch la` mo^.t ma'y trong cu`ng subnet. Card ma.ng se~ du`ng ddia
> chi? MAC cua? ma'y di'ch de send go'i truc tiep de^'n ma'y ddi'ch.
>
> 2. Di'ch la` mot ma'y kha'c subnet. Card ma.ng se send goi nay den dia
> chi MAC cua default gateway. Gateway thay la dia chi ip dich cua goi
> ko phai la cua minh be`n look up trong ip routing table roi forward
> tiep ( day chinh la` ipforward) To'm lai trong qua' trinh forward go'i
> ip thi` chi dest MAC address thay doi from hop to hop, dest IP address
> does not.
>
Nhu+ng trong tru+o+`ng ho+.p cu?a mi`nh thi` di'ch 0.0.0.0 di ke`m vo+'i
subnet 0.0.0.0 cho tru+o+`ng ho+.p default route ... Ta^'t ca? ma'y trong
LAN de^� co' chung subnet`, chi? co' proxy server la` na(`m o+? 1 public
IP ... Du'ng la` ca'i gateway 0.0.0.0 thi` thu+.c su+. la` kho^ng bi't di
da^u nhu+ng mi`nh kie^?m tra la.i route lu'c tru+o+'c thi` no' ghi la`
Destination Gateway Genmask
10.2.0.0 0.0.0.0 255.255.240.0 (route cho ca'c ip di'ch
trong LAN)
ne^n mi`nh nghi~ ra(`ng gw 0.0.0.0 la` da`nh cho packet co' IP trong LAN.
> Tro lai truong hop ba'c ba?o ma'y ba'c send den dia chi? 0.0.0.0 thi`
> bi`nh thuong kernel se refuse to send such packet vi` no' chang biet
> du`ng MAC address na`o tuong ung cho ddia chi do' ca?\. Truong hop
> dda(.c bie^.t la` ba('c du`ng raw ip but that's a different story.
> layer packet co' MAC ddi'ch cua gateway
>
> > Trong tru+o+`ng ho+.p cu?a em thi` em da~
> > co^' ti`nh thay vi` forward qua 10.2.0.1 thi` em forward qua 1 ma'y ba^'t
> > ki` na`o do' tre^n LAN vo+'i gateway la` 0.0.0.0 ... The^' nhu+ng die^`u
> > la. la` ca'c packet de^`u bi. discard o+? da^u do' ... chu+' no' kho^ng
> > forward giu`m mi`nh sang 10.2.0.1 ... Mong ca'c ba'c gia?i thi'ch the^m
> > cho 'con tre?' die^`u ngo^. na`y !!! (Ca'i chuye^.n forward package la`
> > no' na(`m o+? lo+'p thu+' 3 cu?a OSI ... hoa(.c la` layer thu+' 2 cu?a
> > TCP/IP the^' thi` no' da^u di'nh gi` de^' App Layer tre^n ca'c ma'y PC
> > da^u tu+'c la` ne^'u ai do' xa`i ZoneAlarm hay set firewall thi` da^u
> > a?nh hu+o+?ng gi`)
> >
> >
> To'm la.i, khi mot may co' the ping cac may co`n lai trong lan ma`
> lai ko ping duoc mot ma'y khac (proxy server) thi` to+' ca' 10 an 1
> la` do dda(.t sai default gateway. Anyway, your solution for the
> problem is rather interesting.
>
Mi`ng cu~ng cha('c 1 a(n 1 la` default gateway hoa`n toa`n chi'nh xa'c ...
Ca'i tho+`i die^?m drop ma.ng thi` mi`nh co`n dang online ma` ... bo^~ng
du+ng no' drop ma.ng do^.t ngo^.t chu+' da^u pha?i ca^'u hi`nh la.i ma'y
ro^� no' mo+'i drop da^u ...
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