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Re: Redboot responds to ICMP echo when it shouldn't.


On 2011-03-21, Gary Thomas <gary@mlbassoc.com> wrote:

>>> How are those packets even being received?
>>
>> The "pinging" host's ARP cache still has RedBoot's MAC address
>> associated with the IP address bing pinged.
>>
>>> Are they going to a broadcast address (IP or ESA)?
>>
>> Unicast Ethernet MAC, unicast IP.
>
> This is happening because of a stale ARP cache on your host.

Right.

>>> Normally incoming packets are filtered by ESA by the network driver
>>> before they get pushed up the stack and processed.
>>
>> Right.  And then the IP layer should filter them by IP address, right?
>>
>>> You might find that RedBoot replies to [some, maybe all] packets
>>> which somehow match it's ESA, but not IP address as well.
>>
>> That appears to be the case.
>>
>> I assumed that devices shouldn't respond to ICMP ping requests that
>> don't match their IP address.  Am I wrong?
>
> No, I think you are correct.  The IP code may match if the local IP
> address is set to IPANY (i.e. 0.0.0.0).

But doesn't Redboot use 0.0.0.0 as a sentinel value meaning "I don't
have an IP address" rather than "my address is IP_ANY"?

>> The DHCP server (which is sending the ICMP echo request before
>> offering an IP address) appears to be ignoring the reply from IP
>> address 0.0.0.0, but I can imagine somewhat contrived situations
>> where it might cause problems.
>
> This seems to be a pretty rare condition, caused by a stale ARP
> cache.

Agreed.

-- 
Grant Edwards               grant.b.edwards        Yow! I feel like a wet
                                  at               parking meter on Darvon!
                              gmail.com            


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