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Re: [libvirt] [PATCH] Add support for DNS TXT records



[snip]
> It would be great to:
>
> 1) add <user-class> and <vendor-class> tags inside <dhcp> that allow
> filtering according to user/vendor classes

Well, I didn't know this is supported by DNSMasq but it seems to be
(according to the manpage at least):

       -U, --dhcp-vendorclass=<network-id>,<vendor-class>
              Map from a vendor-class string to a network id tag. Most
DHCP clients provide a "vendor class" which represents, in some sense,
the type of host. This option maps ven‐
              dor classes to tags, so that DHCP options may be
selectively delivered to different classes of hosts. For example 
dhcp-vendorclass=printers,Hewlett-Packard  JetDirect
              will  allow  options to be set only for HP printers like
so: --dhcp-option=printers,3,192.168.4.4 The vendor-class string is
substring matched against the vendor-class
              supplied by the client, to allow fuzzy matching.

       -j, --dhcp-userclass=<network-id>,<user-class>
              Map from a user-class string to a network id tag (with
substring matching, like vendor classes). Most DHCP clients provide a
"user class" which is  configurable.  This
              option  maps  user  classes to tags, so that DHCP options
may be selectively delivered to different classes of hosts. It is
possible, for instance to use this to set a
              different printer server for hosts in the class "accounts"
than for hosts in the class "engineering".

There's also MAC mapping:


       -4, --dhcp-mac=<network-id>,<MAC address>
              Map from a MAC address to a network-id tag. The MAC
address may include wildcards. For example
--dhcp-mac=3com,01:34:23:*:*:* will set the  tag  "3com"  for  any  host
              whose MAC address matches the pattern.

> 2) allow to specify <bootp> inside those as well as inside <range>
> or <host> elements.

Right, there's bootp option:

       -M,
--dhcp-boot=[net:<network-id>,]<filename>,[<servername>[,<server address>]]
              Set  BOOTP options to be returned by the DHCP server.
Server name and address are optional: if not provided, the name is left
empty, and the address set to the address
              of the machine running dnsmasq. If dnsmasq is providing a
TFTP service (see --enable-tftp ) then only the filename is required
here to enable network booting.  If  the
              optional network-id(s) are given, they must match for this
configuration to be sent. Note that network-ids are prefixed by "net:"
to distinguish them.

> 3) add support for DHCP options besides bootp, with a tag like <option
> force="yes|no" name="..." value="...">.
>
> For example, my router's DHCP configuration would look like this:
>
> <dhcp>
>   <range ...>
>   <user-class prefix="iPXE">
>     <bootp file="http://playground.usersys.redhat.com/pxe/boot.ipxe";>
>   </user-class>
>   <bootp file="undionly.kpxe">
> </dhcp>
>


That's not a bad idea at all and I think it's worth it however
originally my patch was about DNS and not DHCP. I have to admit that DNS
TXT record only patch was not the right thing to be implemented since I
should have implemented all the DNS records supported (mentioned in this
thread but from what I recall it would be support for PTR, TXT, SRV,
NAPTR and CNAME records to support all of the DNS records).

> It must be possible to use record values containing a space.
>
> $ dig TXT gmail.com
> [...]
>
> ;; QUESTION SECTION:
> ;gmail.com.		IN	TXT
>
> ;; ANSWER SECTION:
> gmail.com.	300	IN	TXT	"v=spf1 redirect=_spf.google.com"

Well, I've been investigating a little more and it's possible to have it
in the value of the record for this but not the name of the record.

I tried following invocations of dnsmasq (I tried it on port 52 instead
not to mess up with my current networking):

first-term# dnsmasq --strict-order --bind-interfaces
--pid-file=/var/run/libvirt/network/default.pid --conf-file=
--except-interface lo --listen-address 192.168.122.1 --dhcp-range
192.168.122.2,192.168.122.254
--dhcp-leasefile=/var/lib/libvirt/dnsmasq/default.leases
--dhcp-lease-max=253 --dhcp-no-override --no-daemon -p 52
--txt-record="some name","some value"

second-term$ dig TXT some name @192.168.122.1 -p 52
connection timed out; no servers could be reached

second-term$ dig TXT "some name" @192.168.122.1 -p 52
;; ANSWER SECTION:
some\032name.           0       IN      TXT     "some value"

first-term# dnsmasq --strict-order --bind-interfaces
--pid-file=/var/run/libvirt/network/default.pid --conf-file=
--except-interface lo --listen-address 192.168.122.1 --dhcp-range
192.168.122.2,192.168.122.254
--dhcp-leasefile=/var/lib/libvirt/dnsmasq/default.leases
--dhcp-lease-max=253 --dhcp-no-override --no-daemon -p 52
--txt-record=some-name,"some value"

$ dig TXT some-name @192.168.122.1 -p 52
;; ANSWER SECTION:
some-name.              0       IN      TXT     "some value"

So I guess we should disable the spaces in the name since it's being
interpreted like \032 characters as can be seen in the dig output - we
should either disable such a definition entirely or change spaces (' ')
to dashes ('-'). But escaping the value of the record to the quotes is a
good thing since this is working fine.

So what do you think about this? Also, do you think we should implement
everything connected to DNSMasq mentioned there (i.e. both DNS and DHCP
stuff) in one commit, just few separate patches (e.g. one for DNS and
second for DHCP/BOOTP) ?

Thanks,
Michal

-- 
Michal Novotny <minovotn redhat com>, RHCE
Virtualization Team (xen userspace), Red Hat


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