Re: newbie question about tcp three-way handshaking

[Jaap Keuter <jaap.keuter () xs4all nl>]

On 01/22/2013 07:08 AM, 温金超 wrote:
> Thanks. and I add comments inline.
>
>
> On Jan 21, 2013, at 6:41 PM, 温金超 <wenjinchao0418@xxxxxxxxx> wrote:
>
> > Is should be three-way handshaking or not when trying to establishe a new connection?
> > but I tcpdump following:
> >  
> > 19:23:12.688758 IP 10.1.164.64.51350 > 10.13.220.4.80: S 3779651860:3779651860(0) win 8192 <mss 1260,nop,wscale 
> > 8,nop,nop,sackOK>
> > 19:23:12.688776 IP 10.13.220.4.80 > 10.1.164.64.51350: S4133937230:4133937230(0) ack 3779651861 win 5840 <mss 
> > 1460,nop,nop,sackOK,nop,wscale 9>
> > 19:23:12.688779 IP 10.13.220.4.80 > 10.1.164.64.51350: S4133937230:4133937230(0) ack 3779651861 win 5840 <mss 
> > 1460,nop,nop,sackOK,nop,wscale 9>
> > 19:23:12.689716 IP 10.1.164.64.51350 > 10.13.220.4.80: . ack 1 win 260
> >
> > 10.13.220.4 ack twice for syn. any idea ?
>
> > Are you sniffing on the machine that's sending the two SYN+ACK packets (i.e., >sniffing on 10.13.220.4), on the 
> > machine to which they're being sent (i.e., sniffing on >10.1.164.64), or on some other machine (passively sniffing)?
>
>
>
> I'm sniffing on machine 10.13.220.4.
>
>
> > Do the two SYN+ACK packets have the same IP packet ID value?  Perhaps it's >getting retransmitted, either at the link 
> > layer or the TCP layer, for some reason.  If it's at the >link layer, they'll probably have the same IP ID value; if 
> > it's at the TCP layer, they probably will >have different IP ID values.  For tcpdump, use the -v flag to get the IP 
> > ID printed.
>
>
>
> Confirm that they have the same IP ID value.
>
>
> And I sniffing again both on client(10.1.164.64) side  and server(10.13.220.4) side, get followings:
>
>
>
> On client(10.1.164.64) side, it's normal three-way handshaking.
>
>
>
>
>
> and on server side(10.13.220.4)
>
>
>
> 13:57:39.659310 IP (tos 0x0, ttl 124, id 27852, offset 0, flags [DF], proto: TCP (6), length: 52) 10.1.164.64.59211 > 
> 10.13.220.4.80: S, cksum 0xc08c (correct), 563933632:563933632(0) win 8192 <mss 1260,nop,wscale 8,nop,nop,sackOK>
> 13:57:39.659389 IP (tos 0x0, ttl  64,* id 0*, offset 0, flags [DF], proto: TCP (6), length: 52) 10.13.220.4.80 > 
> 10.1.164.64.59211: S, cksum 0x8bf2 (correct), 3096740955:3096740955(0) ack 563933633 win 5840 <mss 
> 1460,nop,nop,sackOK,nop,wscale 9>
> 13:57:39.659413 IP (tos 0x0, ttl  64, *id 0*, offset 0, flags [DF], proto: TCP (6), length: 52) 10.13.220.4.80 > 
> 10.1.164.64.59211: S, cksum 0x8bf2 (correct), 3096740955:3096740955(0) ack 563933633 win 5840 <mss 
> 1460,nop,nop,sackOK,nop,wscale 9>
>
> 13:57:39.660220 IP (tos 0x0, ttl 124, id 27853, offset 0, flags [DF], proto: TCP (6), length: 40) 10.1.164.64.59211 > 
> 10.13.220.4.80: ., cksum 0xe292 (correct), 1:1(0) ack 1 win 260 
>
>
>
>
> Both SYN+ACK have the same IP id 0.
> Why the sniffing result is different between client side and server side?


Hi,

It would be interesting to know what kind of network interface is installed on
the server 10.13.220.4. Is there some kind of bonding interface? On what
interface is this server capture taken?

Thanks,
Jaap


___________________________________________________________________________
Sent via:    Wireshark-users mailing list <wireshark-users () wireshark org>
Archives:    http://www.wireshark.org/lists/wireshark-users
Unsubscribe: https://wireshark.org/mailman/options/wireshark-users
             mailto:wireshark-users-request () wireshark org?subject=unsubscribe