As we all know, ping is really an ICMP echo. There are many possible ICMP
replies. Now, Cisco could tell the user of the Cisco IOS ping command the
actual reply received, but instead they output a character code. (Wouldn't
want to make the product intuitive, now would we?) I'm trying to get more
data on the character codes.
This is not a newbie question. Don't send me the chart of ping reply codes.
I've already seen about 20 versions of the chart. I'm trying to figure out
what routers really display and why there are so many versions of the
chart. Putting together all versions of the chart (plus the A code that we
have all seen but is not listed in Cisco documentation, as far as I can
tell), I have developed this list:
! An ICMP echo reply was received.
. The sending router or switch timed out while waiting for a reply.
U A destination unreachable response was received.
N A network unreachable response was received.
H A host unreachable response was received.
P A protocol unreachable response was received.
M Fragmentation was needed and the don't fragment (DF) bit was set.
& A time-to-live exceeded message was received.
I The user interrupted the test.
A The ping was administratively prohibited (blocked by an access list
probably).
Q A source quench response was received.
? An unknown packet was received.
C A packet was received with the congestion-experienced bit set.**
Questions:
Has anyone ever seen N, H, or P? It seems to me that Cisco just outputs U
if the router receives network, host, or protocol unreachable.
Has anyone ever seen M? I couldn't get this to happen in my lab. Is M even
for real or was that an error in one of the versions of the documentation?
Has anyone every seen &? I couldn't get that one to happen either.
How about I? That doesn't happen on my routers. Plus one version of the
documentation said it was |, not I.
And how about the mysterious C? I found out that it's related to RFC 2481,
an experimental protocol that adds explicit congestion notification to IP.
Maybe some internal developer asked for this. Cisco clearly favors helping
developers troubleshoot over helping customers troubleshoot. (Sorry, but
this ping research has made me angry at Cisco.)
Thanks for your help.
Priscilla
________________________
Priscilla Oppenheimer
http://www.priscilla.com
Message Posted at:
http://www.groupstudy.com/form/read.php?f=7&i=10910&t=10910
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