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From: moriko@hh.iij4u.or.jp
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References: <20011205.231421.74752105.moriko@mizuki.noe.mcu.or.jp>
	<20011212013038.9704.MARKUN@onohara.to>
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Date: 12 Dec 2001 09:47:18 +0900
In-Reply-To: <20011212013038.9704.MARKUN@onohara.to> (TERAMOTO Masahiro's message of "Wed, 12 Dec 2001 01:52:41 +0900")
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$B?9$G$9!#;{K\$5$s%U%)%m!<$"$j$,$H$&$4$6$$$^$9!#(B

TERAMOTO Masahiro <markun@onohara.to> writes:

> NetBSD $B$,Ej$2$h$&$H$7$F$$$k(B IP datagram $B$N%5%$%:$O!"(BEthereal 
> $B$G8+$?$H$3$m(B
> 
> MSS 1414 + TCP header 32 + IP header 20 = 1466

$B$=$&$G$9$h$M!#:rHU$O(B timestamp $B$,%*%W%7%g%s$GF~$C$F$$$k$3$H$r(B
$BK:$l$?>e$K!"(BTCP $B%X%C%@D9$NFI$`2U=j$r4V0c$($F$^$7$?!#(B

> $B$$$:$l$K$;$h!"(BMTU $B$,(B 1454 $B$G$"$kDL?.O)$G(B fragment $B$rH/@8$5$;(B
> $B$J$/$9$k$K$O!"(BMSS $B$r(B 1414 $B$K$9$k$@$1$G$OITB-$G$"$k$3$H$O3N$+(B
> $B$@$H;W$$$^$9!#(B

$B9+$GA{$,$l$F$$$k(B path MTU discovery $B0JA0$NLdBj$H$7$F!"(B
$BC<E@$N(B MTU $B$+$i7W;;$7$?(B MSS $B$NCM$rDLCN$7$"$C$F>/$J$/$H$b$=$l$r1[$($J$$(B
$B$h$&$K$9$k$H$$$&$N$,$"$j$^$9$+$i(B (ppp(8) $B$N(B mssfixup $B$O(B TCP $B%Q%1%C%H$N(B
mss $B%*%W%7%g%s$NCM$r=q$-49$($FC<E@$N(B mss $B$N?6$j$r$9$k(B)
$B$3$l$,Bg$-$9$.$k$H0UL#$J$$$G$9!#(B

$B$H$$$&$3$H$G(B [FreeBSD-net-jp 3485] $B$G=q$$$?$3$H$GBgBN$"$C$F$k$H;W$&$N$G(B
$B;n$7$F$_$^$7$?!#(B

usr.sbin/ppp $B$N(B tcpmss.c $B$r0J2<$N$h$&$K=$@5$7!"(Bppp(8) $B$,=q$-49$($k(B
mss $B$NCM$r>/$J$a$K$7$^$9!#(B($B$H$j$"$($:(B 12 $B$K$7$^$7$?$,!"$b$&>/$7(B
$BM>M58+$?J}$,$$$$$G$7$g$&(B)

--- tcpmss.c    2001/07/19 11:39:54     1.1.4.3
+++ tcpmss.c    2001/12/12 00:10:44
@@ -67,7 +67,7 @@
  * We are in a liberal position about MSS
  * (RFC 879, section 7).
  */
-#define MAXMSS(mtu) (mtu - sizeof(struct ip) - sizeof(struct tcphdr)) 
+#define MAXMSS(mtu) (mtu - sizeof(struct ip) - sizeof(struct tcphdr) - 12) 
 
 
 /*-

$B0J2<$O<B9T7k2L$G$9!#(B
$BDLCN$9$k(B mss $B$O(B MTU 1454 $B$KBP$7$F(B 1402 (= 1454 - 20 - 20 - 12) $B$H$J$C$F$*$j!"(B
$B1~Ez$N%;%0%a%s%H%5%$%:$b(B 1402 $B$KD4@0$5$l$F%U%i%0%a%s%H2=$5$l$F$$$J$$$3$H$,(B
$B3NG'$G$-$^$9!#(B

09:38:24.207511 PPPoE  [ses 0x1395] IP 62: xxx.xxx.xxx.xxx.4826 > 204.152.186.171.80: S 3329176101:3329176101(0) win 16384 <mss 1402,nop,wscale 0,nop,nop,timestamp 33339458 0> (DF)

09:38:24.542333 PPPoE  [ses 0x1395] IP 1456: 204.152.186.171.80 > xxx.xxx.xxx.xxx.4826: . 1:1403(1402) ack 192 win 33580 <nop,nop,timestamp 2964938 33339474>

-- 
$B?9(B $B9@Fs(B	(MORI Kouji)
E-mail: moriko@hh.iij4u.or.jp
