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

Grant Edwards grant.b.edwards@gmail.com
Tue Mar 22 11:16:00 GMT 2011

On 2011-03-21, Gary Thomas <gary@mlbassoc.com> wrote:
> On 03/21/2011 02:21 PM, Grant Edwards wrote:
>> While testing my rewrite of Redboot DHCP support, I've noticed that
>> Redboots "ping" support is also broken.  Redboot responds to ICMP echo
>> requests that it shouldn't.
>> Redboot will respond to ICMP echo requests _before_ it has received an
>> IP address from the BOOTP/DHCP server.  The destination IP address in
>> the ICMP echo packet _does_not_match_ Redboot's IP address, but it
>> responds anyway with a source IP address of
>> Is this behavior intentional?
> Not as far as I know.
> 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.

> 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?

The DHCP server (which is sending the ICMP echo request before
offering an IP address) appears to be ignoring the reply from IP
address, but I can imagine somewhat contrived situations where
it might cause problems.

Grant Edwards               grant.b.edwards        Yow! Let's all show human
                                  at               CONCERN for REVERAND MOON's
                              gmail.com            legal difficulties!!

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