From: Bob Foxworth (rfoxwor1@tampabay.rr.com)
Date: Sun Dec 11 2005 - 20:59:28 EST
> > Seems to me you are mixing up osi-layer functionality.
> >
> > A MAC-address is a layer 2 (physical) address. This address only has
> > significance on the local broadcast domain. In ip-terms, your local
subnet.
> > Ping is a layer 4 protocol, used to check end-to-end connectivity
> > between ip-adresses. You can't use ping to ping a mac-address, since
the
> > protocol underlying ping (ICMP) won't understand it.
>
> I can't find it now, but THERE IS a ethernet "ping" and is a standard
> protocol , only some old NIC support it , but it does exist.
You state that ping is layer 4 but I believe it is at 3.
Ping is the echo-request and echo-reply portion
of ICMP (Internet Control Message Protocol)
This is part of the IP protocol to do error-handling,
since IP by itself is not guaranteed delivery. IP
is at layer 3, not 4, and TCP, which is at 4, supports
error-checking, reassembly of lost data etc.
Some of the tools now support a TCP "ping" so this of
course muddies the water. Pure ICMP is supposed
to be part of IP, when it hasn't been blocked by
FW rules.
What you say about layer 2 is true, MAC's do not
route past the local gateway. I remember in the
days of the old 8-bit full length ISA bus card from
3com, the 3c501, there came on the support floppy
some sort of test diag program which created an
ethernet frame to do a connectivity test.
Bob Foxworth CISSP
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