Re: Why unidirectional ping in LAN?

In article <11ed5ub1f7nate0@xxxxxxxxxxxxxxxxxx>, "Chris Shearer
Cooper" <chrisnews@xxxxxxx> wrote:
>"Steve Winograd [MVP]" <winograd@xxxxxxxxx> wrote in message
>>>My LAN looks something like this, with R1 = normal router and R2 =
>>>wireless router :
>>>
>>>Internet ----- R ----- Desktop
>>> 1 --+
>>> |
>>>Nothing ------ R --+
>>> 2 ----- Laptop
>>>
>>>The problem I'm trying to figure out, is why the laptop can ping the
>>>desktop but not vice-versa.
>>>
>>>I'm imagining the ping from the laptop hits R2 who notices the destination
>>>address is inside the subnet, so he repeats that packet on all his LAN
>>>ports, one of which is R1. R1 sees the ping, notices the destination
>>>address is inside the subnet, so he repeats the packet on all his LAN
>>>ports, one of which is the desktop.
>>>
>>>So why doesn't it work the other direction? Is the fact that the laptop
>>>is connecting wirelessly relevant somehow?
>>>
>>>Thanks!
>>>Chris
>>
>> You don't say how you've connected the routers to each other. I'm
>> assuming that you've connected the WAN (Internet) port of R2 to a LAN
>> port of R1.
>>
>> In that configuration, R2 blocks pings from the desktop to the laptop.
>> From the router's point of view, the desktop is part of the Internet,
>> not part of the local area network, so it drops the ping request.
>>
>> The laptop can ping the desktop because R2's WAN (Internet) interface
>> has an IP address in the same LAN as the desktop.
>>
>> If you want the desktop and laptop to be in the same LAN, use R2 as a
>> wireless access point only, bypassing its routing capabilities:
>>
>> 1. Disable its DHCP server.
>>
>> 2. Assign its LAN interface an IP address in the same subnet that R1
>> uses.
>>
>> 3. Connect a LAN port of R2 to a LAN port of R1.
>>
>> 4. Don't connect anything to the WAN (Internet) port of R2.
>>
>> or:
>>
>> Remove R1 from the network and just use R2.

>I've got nothing connected to the WAN port of R2 ... I've got a cable
>running from a LAN port on R1 to a LAN port on R2.
>
>I can't get rid of R1 'cuz it's got my VPN and firewall.
>
>Thanks!
>Chris

Please answer these questions to help other people understand the
situation:

1. What is the IP address of each router's LAN interface?

2. What is the IP address of each computer?

3. Are you pinging the laptop from the desktop by computer name or by
IP address?

4. What exactly happens when you do it? If there's an error message,
what does it say?

5. Is DHCP enabled on R2's LAN interface?
--
Best Wishes,
Steve Winograd, MS-MVP (Windows Networking)

Please post any reply as a follow-up message in the news group
for everyone to see. I'm sorry, but I don't answer questions
addressed directly to me in E-mail or news groups.

Microsoft Most Valuable Professional Program
http://mvp.support.microsoft.com
.

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