Catalyst switch copy file ! . O meaning

[lightda]

Hi Community,

I'm copy file from tftp to flash, it shows like this:

I know that ! means packet transfer success, but what does O and . meaning?

Thanks!

[Torbjørn]

"O" means retrying and "." means data dropped

EDIT: @liviu.gheorghe is right. See the following documentation: https://www.cisco.com/c/en/us/td/docs/routers/ios/config/17-x/syst-mgmt/b-system-management/m_ifs-file-trans-0.html#GUID-C36D6A22-BAA3-4975-A3BC-AFCC08B0B30B:~:text=%5Bok%5D%0AServer%23-,Troubleshooting,-Troubleshooting 

[liviu.gheorghe · Accepted solution]

Hello @lightda ,

the O means the packet was received out of sequence and the . means the respective packet timed out.

Hope this helps.

[shambhu.kumar]

This link may help to understand

https://community.cisco.com/t5/switching/tftp-image-file-tranfer-out-of-sequence/td-p/1986184

[Joseph W. Doherty]

As a side note, I confess I haven't previously gone down the TFTP rabbit hole, but quickly reviewing the protocol, it's unclear how you would obtain an out of sequence packet.  This because TFTP uses a "lockstep" approach.  I.e., only one packet is ever sent and it must be acknowledged before another is sent.

Can anyone explain?

PS:

Oh, I see one of the latter TFTP RFCs, do support windowing, possibly the answer lies there.

[Joseph W. Doherty]

Just skimmed the TFTP window size. RFC.  Unclear, that would the specific out of sequence error, but its example of dealing with lost packets, I suspect, reveals what an out of sequence error actually is.

When TFTP sends a packet it expects an ACK.  If it doesn't receive the ACK, a TFTP packet has been lost.  However, which TFTP packet has been lost, the data packet or its corresponding ACK?

I suspect, the latter, lost of an ACK, causes the out of sequence error as the receiver receives a duplicate retransmitted packet, rather than the next packet, as expected.

If the forgoing is correct, you would be able to tell in which direction packets are being lost.

[vishalbhandari · Accepted solution]

@lightda 

• . (Dot): Means a timeout occurred while waiting for a response from the TFTP server. This could be due to temporary network latency or issues.

• O (Letter O): Indicates a packet was retransmitted due to a timeout or an acknowledgment failure. This typically happens when the device does not receive confirmation from the server in time.