Copyright (C) 1999-2001, 2004, 2016 Internet Systems Consortium, Inc. ("ISC")

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$Id: search,v 1.10 2004/03/05 05:04:47 marka Exp $

What follows is pseudocode for the zone and cache lookup algorithms, as they

will work in the RBT DB.

Note: These algorithms differ in some respects from those discussed in

the RFCs and drafts. I believe these algorithms provide better

answers in some cases.

Preliminary Stuff

BIND 9 zone databases are versioned, and every search is done in the

context of some version. There are a number of ways of implementing

versioning. The method that's going to be used in the RBT DB is to

store a serial number with every rdataset. All rdatasets added as the

result of a single database update have the same serial number. This

serial number is not related to the SOA serial, since the SOA serial

is under user control and can do weird things. The database serial

number is a monotonically increasing value. When you go to retrieve

an rdataset, you may encounter many rdatasets of that type at any

given node. The correct one to return, called the "active rdataset",

has the greatest serial number less than or equal to the serial number

used for the search. The version whose serial number is being used in

the search is the "target version".

Cache databases are not versioned. A search will always return the

most recent value.

DKZC == Deepest Known Zone Cut. This is the zone cut closest to the

desired name. In a zone, it's either a delegation out of authoritative

data, or it's the top of the zone.

ZC == "zone cut", a node not at the zone top which has an active NS

rdataset, or a node (including the zone top) with an active DNAME

rdataset.

Zone Search Algorithm

Inputs:

Search name

Search rdata type (including ANY)

Search options

The search options parameter is a flags variable. Current

flags are

Glue OK If set, then the caller is

wants best match results for

the search name, even if it's

glue. If not set, the caller

will get a delegation if the

search name is glue.

Glue Validation Section 7.18 of RFC 2136

requires that certain data that

is not in the zone and is not

glue remain stored in the zone.

A search can never return this

data, but there might be glue

mixed in with it. Telling glue

from non glue involves some

work, especially since the

database is versioned. Often,

however, the caller will know

the name it's looking for is

glue, so validation isn't

required.

Outputs:

result code

a node

the name of the node

rdataset (not bound if querying for ANY)

Note: The node, name, and rdataset are optional. If the

caller doesn't care about them, they won't be set.

Note: there is no EDNS1 "longest match" support in the algorithm yet,

though I know how to do it.

cname_ok = yes

search_must_succeed = no

Search down from the root of the tree. If, while going down, we

encounter a zone cut node, then search the rdatasets at the zone

cut for active DNAME or NS rdatasets. Note that if we find both

an active DNAME rdataset and an active NS rdataset, then the DNAME

rdataset has precedence.

If we found an active DNAME rdataset, the search ends here.

result = DNS_R_DNAME

foundname = name of this node

*nodep = this node

rdataset is the DNAME

return

If we found an active NS rdataset

If finding glue is not OK, or we're not searching for

a glue type, then the search ends here.

result = DNS_R_DELEGATION

foundname = name of this node

*nodep = this node

rdataset = NS

return

Else

We remember that this node is the ZC.

We remember this node's name.

We'll ignore any zone cuts found further down

the tree.

Continue the search down.

Partial_Match:

If we don't have an exact match to the name

If we're below a zone cut, then we need to return a referral.

result = DNS_R_DELEGATION;

foundname = ZC name

*nodep = ZC

rdataset = NS

return

Else If this zone has any wildcards, then

Go looking for a wildcard match for this name.

If we found one,

result = DNS_R_WILDCARD

foundname = wildcard node name

Fall through to searching the wildcard node

for the desired type.

Else

NXDOMAIN (finally!)

If this is a secure zone then

Find the greatest predecessor to this node

that has at least one active rdataset.

Change the type we're search for to NXT

cname_ok = no

search_must_succeed = yes

Else

result = DNS_R_NXDOMAIN

foundname = <empty>

rdataset = <unbound>

*nodep = NULL

return

If we're here, then we've got a node and are now trying to find

an active rdataset of the desired type, or, in the case of an ANY

query, any active rdataset.

If we're beneath a zone cut

cname_ok = no

If the caller wants us to validate glue, then see if the

current name is a valid glue name for the ZC.

If not,

result = DNS_R_DELEGATION;

foundname = ZC name

*nodep = ZC

rdataset = NS

return

If the desired type is KEY, SIG, or NXT, then

cname_ok = no

foundname = current node name

*nodep = current node;

Search the rdataset list for the desired type. If cname_ok, also

look for a CNAME rdataset. While searching, remember the active NXT

rdataset if we come across it. We must also determine if there are

any active rdatasets at the node.

If there are no active rdatasets at the node, then we've got an

exact name match, but the name doesn't exist in the desired version.

This means we really have a partial match. Goto Partial_Match.

If we didn't find the type we were looking for (including a failed

ANY search)

If (search_must_succeed), then

The database is bad, e.g. missing NXT records.

result = DNS_R_BADDB

*nodep = NULL

foundname = <empty>

Else if we're beneath a zone cut

result = DNS_R_DELEGATION

foundname = ZC name

*nodep = ZC

rdataset = NS

Else

result = DNS_R_NXRDATASET

If this is a secure zone then

If we found an active NXT rdataset

rdataset = NXT rdataset

Else

result = DNS_R_BADDB

*nodep = NULL

foundname = <empty>

Else

rdataset = <unbound>

return

We have found the type we were looking for or we've found a CNAME.

If we're not doing any ANY query, didn't find the type we were looking

for, but did find a CNAME

result = DNS_R_CNAME

rdataset = CNAME

Else If we're beneath a zone cut

result = DNS_R_GLUE

Else

result = DNS_R_SUCCESS

If type is ANY

rdataset = <unbound>

else

rdataset = the type we were looking for

XXX This is now old XXX

Now for the cache lookup algorithm, which is a little different. The

cache algorithm takes an optional "zone DKZC". Say a server is

authoritative for vix.com but not rc.vix.com. When it looks up

bb.rc.vix.com it will search vix.com and discover the delegation to

rc.vix.com. We then want to look in the cache for bb.rc.vix.com, and

if we don't find it, the authoritative delegation might be the best

DKZC (since there might not be anything for rc.vix.com in the cache),

so that's why we allow it to be an argument to the cache search

algorithm. Of course, the cache might have data for rc.vix.com

cached, in which case we should use it and not the DKZC.

DKZC A is "better" than DKZC B if DKZC A is a proper subdomain of DKZC

B.

Cache Search Algorithm:

Go down as far as possible remembering every parent node.

Remember the predecessor too.

If some rdataset for name exists

Look for desired type or CNAME

If found

If negative cache entry

Indicate this and return.

If CNAME?

Indicate it and return.

Return.

Else

Indicate we know nothing about this type at this

node.

Return.

Else

(Peek at predecessor to see if it has an NXT for the same

zone and which covers the QNAME. If so, return it.)

Go up until we find a node with a DNAME or a zone cut.

XXX DNAME draft says go up until you prove that there are no

ancestor DNAMEs at all XXX

If there's a DNAME

Return a DNAME result with the dname node and node name

XXX what if the zone DKZC is better (i.e. deeper)? XXX

We know nothing about this name.

XXX DNAME draft says that if we have a zone DKZC, we should

use it now. I say use the best DKZC you've got. XXX

If we get all the way to '.' and we don't even have the

root NS records

If we have a DKZC from authoritative data

Return it.

Else

Return NO_KNOWN_AUTHORITY

(this will cause priming of root servers or,

perhaps, forwarding)

If we have a zone DKZC and it's better than the one we found

in the cache

Return it (node and name).

Return the cache DKZC (node and name).