This is our old Q&A Site. Please post any new questions and answers at

Hi, I know what the M, V and P stand for and how they work. What I don't quite understand is meaning of "MUST", "MUST NOT", "SHOULD"... There are only 2 possible values for each bit (0 and 1) but more then one value of MUST, MUST NOT... I've been googling quite a lot (unsuccessfully) to find the solution for setting these in the vendor specific dictionary I'm working on. In 3GPP specs, there's always a neat table with bits and their values. However, the spec for the VSA I'm working on, has only these values provided: alt text

So, the question is, how should I set mandatory, vendot-bit, protected and encryption values in the dictionary? How does wireshark use these values when dissecting the packet?


asked 13 Nov '15, 06:27

Aliniel's gravatar image

accept rate: 100%

The MUST, MUST NOT, and SHOULD are telling you whether the bit should be set or not. The meanings of those key words come from RFC 2119. Basically: if some bit MUST be set then you really, really better set it to 1. If it SHOULD be set then you probably should set it to 1 but you don't have to (you won't risk interoperability by leaving it 0).

It appears that VzW doesn't use those terms but simply tells you what you MUST set the values to (M=0, V=1, P=0 in your example).

Wireshark doesn't currently do anything with the bit fields (e.g., may-encrypt="no"). I suppose it might in the future so it's probably Better to fill them in correctly.

permanent link

answered 13 Nov '15, 07:19

JeffMorriss's gravatar image

JeffMorriss ♦
accept rate: 27%

Or, you SHOULD fill them in. :)

(14 Nov '15, 14:34) Quadratic
Your answer
toggle preview

Follow this question

By Email:

Once you sign in you will be able to subscribe for any updates here



Answers and Comments

Markdown Basics

  • *italic* or _italic_
  • **bold** or __bold__
  • link:[text]( "title")
  • image?![alt text](/path/img.jpg "title")
  • numbered list: 1. Foo 2. Bar
  • to add a line break simply add two spaces to where you would like the new line to be.
  • basic HTML tags are also supported

Question tags:


question asked: 13 Nov '15, 06:27

question was seen: 1,863 times

last updated: 14 Nov '15, 14:34

p​o​w​e​r​e​d by O​S​Q​A