how to config class

[Simon Hobson]

Julie Xu wrote:
>how to write match if A and not B??

Two bits of netiquette :

1) Please keep the subject line, "dhcp-users Digest, Vol 61, Issue 24" is not a useful subject line.
2) Please trim what you quote - ie don't include the entire days digest as quoted text.

The second of those is a natural thing that comes from (IMO) your third mistake which is to top post. When you just hit reply and top post, you are oblivious to how much (often irrelevant) text you are quoting. If you bottom post, apart from making the flow of dialogue make sense, you realise just how much text you've quoted.
A: Because it messes up the order in which people normally read text.
Q: Why is top-posting such a bad thing?
A: Top-posting.
Q: What is the most annoying thing in e-mail?

Back to your question. First, I suggest you refer to "mandhcp-eval"
You'll see that to combine two tests, you use the form "boolean-expression-1 and boolean-expression-2", to negate a test you use the form "not boolean-expression". To use both together you use the form"boolean-expression-1 and not boolean-expression-2". So you'll be needing something like :
substring( option vendor-class-identifier, 0, 9 ) = "PXEClient" and not binary-to-ascii(10,8, ".", packet(24,4)) = "10.2.2.1"