[clue-tech] remote access to Windows network from Linux

[Jim Ockers]

David L. Willson wrote:
> Nate: Turning off ping responses ~does~ "add security", just like 
> running ssh on a non-default port, and not returning specific version 
> numbers for PHP, and other things of that sort. Not providing more 
> info/access than needed is part of a good security policy.  Turning 
> off ping responses ~might~ be appropriate, depending on the circumstances.
Well I have to challenge this because as a senior network engineer who 
troubleshoots strange problems that confuse everyone else, I find that a 
disproportionate share of incidents that land on my desk have to do with 
blocked ICMP.  I agree with Nate, in almost every case a sysadmin who 
blocks ICMP echo request or reply is a doofus.  They may be well meaning 
but if they actually do it (or if they aren't careful about it) then 
they are a doofus.

Blocking ICMP usually adds nearly nothing in security and serves only to 
create a lot of confusion.  ICMP is an important part of the IP 
protocols and people generally expect it to work, so when it doesn't 
people tend to make incorrect assumptions about what's not working.  
Also, those pesky insecurity-causing type 3 packets are absolutely 
critical to allow through from end to end if there is any chance there 
is a network connection somewhere along the line with a smaller MTU than 
what the sending system expects.  Over the years I have seen several 
weird application issues caused by ICMP type 3 blocking, so much so that 
based on the symptoms that might be one of the first things I check when 
I start troubleshooting.

Sure there used to be the old smurf etc. attacks based on incorrect ICMP 
handling, but I don't think there have been widespread issues with ICMP 
for years now.
>
> OTOH, once on the same IP subnet, an arp request is rarely (never) 
> declined, and so might make a better test.
I think ARP traffic wouldn't be forwarded through a VPN router, since I 
think it is on the ethernet segment only.
>
> Dennis: Are you sure the VPN needs to be up to get to the TS? There 
> are an increasing number of networks with TS available directly to the 
> Internet.
That might be a good idea and Dennis you could try suggest that to your 
sysadmin/IT people.

Jim

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