Re: SMB problems when ICMP is blocked?

[ronnie sahlberg <ronniesahlberg () gmail com>]

Blocking ICMP will usually break TCP completely.
Things like path mtu discovery will no longer work,
routing loops can no longer be detected, etc etc.
This leads to tcp connections hanging indefinitely and other bad things.


Please tell the person blocking icmp in the firewall he is
"misinformed" (better than saying he is stupid) and should stop
blocking icmp if he wants the network to work.

Dont block icmp. icmp is a vital part of the ip stack and blocking it
will break things.


ronnie



On Fri, Mar 5, 2010 at 9:25 AM, Feeny, Michael (GWMT-TASCS)
<michael_feeny () ml com> wrote:
> Hello,
>
>
>
> I’m troubleshooting a problem where a Windows XP user has problems with a
> certain mapped drive (file share).  Specifically, after mapping, a file copy
> from the mapped drive fails, after 10-15 seconds, with a ““The specified
> network name is no longer available” message.
>
>
>
> As I have dug into this, I was told that ICMP has been blocked between the
> user’s site and the site of the remote  file share.
>
>
>
> Then, after capturing packets, I found that, in addition to the SMB packets
> between the 2 endpoints, the user’s workstation was sending PINGs to the
> remote site.  Due to the blocking of ICMP these PINGs are never answered.
>
>
>
> My suspicion is that, when the PINGs are unanswered, the file system decides
> that the remote file share host is unavailable, and the file copy is
> terminated.  (In reality, the file copy seemed to be proceeding just fine.)
>
>
>
> So…  My questions are…
>
>
>
> 1)      Has anyone else run into this?
>
> 2)      Assuming that allowing ICMP between these sites is not an option,
> does anyone know if one can disable this PING mechanism, so that file
> sharing operations can proceed successfully?
>
>
>
> Thx,
>
> Michael
>
>
>
> Michael Feeny
> Bank of America / Merrill Lynch
>
> Global Wealth Management Technology
> Technology Architecture, Strategy & Core Services
>
> Application Infrastructure Services
>
> Office: 609-274-2761
> Mobile:  484-995-1745
> AOL IM: feenyman99
>
>
>
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