[ILUG] Bizarre networking problem

[Niall O Broin]

On 29 Feb 2008, at 13:49, paul at clubi.ie wrote:

> On Fri, 29 Feb 2008, Niall O Broin wrote:
>
>> Any ideas welcomed, because I'm stumped.
>
> Dump on both sides at same time.
>
> Is the S8B box receiving the same packets as the S2.5.1 box is  
> sending?

The problem wasn't with the s251 box, but with the s8a box. However,  
I have dumped on both sides,
and there IS a difference. Here are the first couple of syns sent, as  
seen by snoop on s8A:

s8A -> s8B        TCP D=22 S=32858 Syn Seq=3908249784 Len=0 Win=24820  
Options=<nop,nop,sackOK,mss 1460>
s8A -> s8B        TCP D=22 S=32858 Syn Seq=3908249784 Len=0 Win=24820  
Options=<nop,nop,sackOK,mss 1460>

and here they are as seen by snoop on s8B:

s8A -> s8B        TCP D=22 S=32858 Syn Seq=3908249784 Len=0 Win=24820  
Options=<mss 1460,sack 16843778-2895157918|>
s8A -> s8B        TCP D=22 S=32858 Syn Seq=3908249784 Len=0 Win=24820  
Options=<mss 1460,sack 16843778-1767550315|>


so it would seem that the ISDN router is mangling the packets from  
s8A, which frankly isn't ALL that surprising, considering that the  
same router randomly lost its configuration. However, I'm left  
wondering why it only mangles the packets from s8A.

The solution to my immediate need (i.e. make it work Niall, NOW !)  
was to turn off selective acknowledgment on TCP connections initiated  
by s8A (thanks again, Gavin !) [ see http://lists.samba.org/archive/ 
rsync/2003-May/006091.html ]


Niall