I've gotten these ?'s over the years and always wondered what they were. I would occassionally look it up and find the documentation says "Unknown Packet" but that's it. Nothing else. Nothing about what caused the error or what ICMP error code it stood for. Many people on forums will answer you that it means "unknown packet" like that means something without more explanation.
Well I got sick of it so I checked Cisco's docs again and found 'unknown packet' unhelpfully listed as Cisco's answer again. Then I went to the IETF RFC for ICMP and looked for "unknown packet". Wouldn't you know: It's not in there. There is no such code. I read all of the codes and none of them seem to resemble something like "unknown packet".
After thinking about it my guess is that the '?/Unknown packet' message is IOS code for: We have not programmed a symbol for this ICMP type/code combination. Each possible ICMP response message has a type and a code. Depending on these the response might mean host unreachable, net unreachable, etc etc. There are many type/codes and Cisco doesn't seem to have a symbol for all of them (only like 5-7 or so). So literally, the ? means this ICMP packet (or type/code combination) is unknown to IOS.
If anyone has a better or definitive answer on this subject I would love to hear it.
Roger: In my experience a ? can be anything but is usually a problem with the host. But if my above argument is true obviously my experience means nothing with this code. So I would just check end to end connectivity. If that seems good than work on the host itsself. This may be a time for debug/packet sniffing/capturing if you don't figure it out quickly. Anything that could flap obviously may be involved too from your output.
Question We run asr9001 with XR 6.1.3, and we have a very long delay to
login w/ SSH 1 or 2 to the device compare to IOS device. After
investigation, the there is 1s delay between the client KEXDH_INIT and
the server (XR) KEXDH_REPLY. After debug ssh serv...
Introduction The purpose of this document is to demonstrate the Open
Shortest Path First (OSPF) behavior when the V-bit (Virtual-link bit) is
present in a non-backbone area. The V-bit is signaled in Type-1 LSA only
if the router is the endpoint of one or ...
Hi, I am seeing quite a few issues with patch install and wanted to
share my experience and workaround to this. Login to admin via CLI, then
access root with the “shell” command Issue “df –h” and you’ll probably
see the following directory full or nearly ...