09-27-2012 07:03 AM - edited 03-07-2019 09:09 AM
Hi,
Here is an image of VTP summary advertisement packet format taken from
http://www.cisco.com/en/US/tech/tk389/tk689/technologies_tech_note09186a0080094c52.shtml#vtp_msg
We can see the MD5 digest field is 16 bytes.
Now here is a sample output of "show vtp status"
Notice the MD5 digest (highlighted). I know "0x" is just a prefix for hexadecimal numbers. One hexadecimal character equals to 4 bits, two hexadecimal characters equal to 8 bits (1 byte). There is only 16 hexadecimal characters there, so just 8 bytes in total is shown in the output. But the Cisco documentation states the MD5 digest is 16 bytes long. So why is there only 8 bytes shown in MD5 digest in "show vtp status"?
Regards,
Putra
Solved! Go to Solution.
09-27-2012 11:47 PM
Hi Amhar,
Alain said right option. I would like add some more detail,
Log:
03:51:51: VTP LOG RUNTIME: Transmit vtp summary, domain CCIE, rev 11, followers 0, tlv blk size 8 (inc #tlv field),
MD5 digest calculated = E1 92 86 29 E9 A5 D0 CC 6F 89 32 34 21 A0 C4 6D
Regards,
Aru
*** Please if this post is useful ***
09-27-2012 08:23 AM
Hi,
can you put wireshark into action and see how it is encoded in the advertisement ?
Regards.
Alain
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09-27-2012 11:47 PM
Hi Amhar,
Alain said right option. I would like add some more detail,
Log:
03:51:51: VTP LOG RUNTIME: Transmit vtp summary, domain CCIE, rev 11, followers 0, tlv blk size 8 (inc #tlv field),
MD5 digest calculated = E1 92 86 29 E9 A5 D0 CC 6F 89 32 34 21 A0 C4 6D
Regards,
Aru
*** Please if this post is useful ***
09-28-2012 02:16 AM
Hi Alain and Aru,
Thank you for your responses.
I put the Wireshark into action and here is the result:
The switch that I sniffed:
The result of wireshark sniff:
So apparently Cisco only show the first 8 bytes (out of 16 bytes) of MD5 digest from "show vtp status". But the actual length is really 16 bytes as shown in the Wireshark.
Furthermore, I just found out that on newer Catalyst IOS, "show vtp status" will show the whole 16 bytes of MD5 digest. Here is a sample:
Thank you Alain for leading me to use Wireshark.
Thank you Aru for further details and sample debug output.
Regards,
Putra
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