[gentoo-user] resolving names of local hosts locally

[gentoo-user] resolving names of local hosts locally

[lee]

Hi,

is there a way to configure bind so that the names of local hosts,
i. e. the ones bind is authoritative for, can be resolved without a
connection to the internet?

I don't like it at all that when the internet connection goes out, no
name resolution at all is possible.  Since the information about the
local hosts is known to bind from its configuration files, why can't it
just resolve them?

Re: [gentoo-user] resolving names of local hosts locally

[Alan McKinnon]

On 02/12/2015 21:37, lee wrote:
> Hi,
> 
> is there a way to configure bind so that the names of local hosts,
> i. e. the ones bind is authoritative for, can be resolved without a
> connection to the internet?
> 
> I don't like it at all that when the internet connection goes out, no
> name resolution at all is possible.  Since the information about the
> local hosts is known to bind from its configuration files, why can't it
> just resolve them?
> 


There are several problems with your idea. First, the configured
namservers in resolv.conf are caching servers, not authoritative
servers. You never configure an auth server to act as a cache. Yes, it
can be done. No, it's an awful idea and things break horribly.

Secondly, nothing else on your network can know your auth server is
authoritative without first being informed so by the delegating server.
Or in other words, if you own example.com and an auth server for
example.com is on your network, you have to first go via .com to know
that. Weird, but that's how it works.

DNS was designed to need a network connection because most of the DNS is
out there somewhere else

What you should do, is run your own caching server on the local network
and set the TTL for your own zones to something sane i.e. 1 day (as
opposed to the current idiotic fad of making it 10 minutes). The query
your cache for your entire zone once a day. Unless your internet
connection goes out for more than a day, you're good.



-- 
Alan McKinnon
alan.mckinnon@gmail.com

Re: [gentoo-user] resolving names of local hosts locally

[Mike Gilbert]

On Wed, Dec 2, 2015 at 2:52 PM, Alan McKinnon <alan.mckinnon@gmail.com> wrote:
> On 02/12/2015 21:37, lee wrote:
>> Hi,
>>
>> is there a way to configure bind so that the names of local hosts,
>> i. e. the ones bind is authoritative for, can be resolved without a
>> connection to the internet?

I am surprised to hear that bind does not do this by default. I can't
see any reason it would recursively resolve a query that it already
has the answer to.

Maybe there is a config setting or something, because I seem to recall
it working that way previously.

>> I don't like it at all that when the internet connection goes out, no
>> name resolution at all is possible.  Since the information about the
>> local hosts is known to bind from its configuration files, why can't it
>> just resolve them?
>>
>
>
> There are several problems with your idea. First, the configured
> namservers in resolv.conf are caching servers, not authoritative
> servers. You never configure an auth server to act as a cache. Yes, it
> can be done. No, it's an awful idea and things break horribly.

For small private networks, it is quite common to set up a name server
that is both authoritative for some zones, and recursively resolves
others. This is especially common with Active Directory, where the
domain for AD is not made public.

> Secondly, nothing else on your network can know your auth server is
> authoritative without first being informed so by the delegating server.
> Or in other words, if you own example.com and an auth server for
> example.com is on your network, you have to first go via .com to know
> that. Weird, but that's how it works.

You have described how a recursive resolver works. Most devices use a
sub resolver that simply passes queries to a single name server which
then resolves the query as you describe.

Re: [gentoo-user] resolving names of local hosts locally

[Peter Humphrey]

On Wednesday 02 December 2015 20:37:34 lee wrote:
> Hi,
> 
> is there a way to configure bind so that the names of local hosts,
> i. e. the ones bind is authoritative for, can be resolved without a
> connection to the internet?
> 
> I don't like it at all that when the internet connection goes out, no
> name resolution at all is possible.  Since the information about the
> local hosts is known to bind from its configuration files, why can't it
> just resolve them?

Have you looked into net-dns/dnsmasq?

-- 
Rgds
Peter

Re: [gentoo-user] resolving names of local hosts locally

[lee]

Peter Humphrey <peter@prh.myzen.co.uk> writes:

> On Wednesday 02 December 2015 20:37:34 lee wrote:
>> Hi,
>> 
>> is there a way to configure bind so that the names of local hosts,
>> i. e. the ones bind is authoritative for, can be resolved without a
>> connection to the internet?
>> 
>> I don't like it at all that when the internet connection goes out, no
>> name resolution at all is possible.  Since the information about the
>> local hosts is known to bind from its configuration files, why can't it
>> just resolve them?
>
> Have you looked into net-dns/dnsmasq?

"Small forwarding DNS server"?  Why would I want a forwarding one?

Re: [gentoo-user] resolving names of local hosts locally

[lee]

Alan McKinnon <alan.mckinnon@gmail.com> writes:

> On 02/12/2015 21:37, lee wrote:
>> Hi,
>> 
>> is there a way to configure bind so that the names of local hosts,
>> i. e. the ones bind is authoritative for, can be resolved without a
>> connection to the internet?
>> 
>> I don't like it at all that when the internet connection goes out, no
>> name resolution at all is possible.  Since the information about the
>> local hosts is known to bind from its configuration files, why can't it
>> just resolve them?
>> 
>
>
> There are several problems with your idea. First, the configured
> namservers in resolv.conf are caching servers, not authoritative
> servers. You never configure an auth server to act as a cache. Yes, it
> can be done. No, it's an awful idea and things break horribly.

I thought it was caching anyway.  What's the point of forgetting the
answers to queries right away after answering them?

> Secondly, nothing else on your network can know your auth server is
> authoritative without first being informed so by the delegating server.

The name server itself knows this from its configuration, and it's the
only thing that needs to know this because it's the only thing
everything on the network is asking.

> Or in other words, if you own example.com and an auth server for
> example.com is on your network, you have to first go via .com to know
> that. Weird, but that's how it works.

The name server doesn't know what domains it's supposed to give answers
for without asking others first?

> DNS was designed to need a network connection because most of the DNS is
> out there somewhere else

Then how do you solve the problem of being unable to even resolve the
names of hosts on the LAN when the connection goes down?

> What you should do, is run your own caching server on the local network
> and set the TTL for your own zones to something sane i.e. 1 day (as
> opposed to the current idiotic fad of making it 10 minutes). The query
> your cache for your entire zone once a day. Unless your internet
> connection goes out for more than a day, you're good.

Hm, I just tried that, and it seems to work.  It didn't before I made
some small changes last night, that's why I'm asking.  Weird ...

Re: [gentoo-user] resolving names of local hosts locally

[Alec Ten Harmsel]

On 2015-12-03 17:20, lee wrote:
> Alan McKinnon <alan.mckinnon@gmail.com> writes:
>> Secondly, nothing else on your network can know your auth server is
>> authoritative without first being informed so by the delegating server.
> The name server itself knows this from its configuration, and it's the
> only thing that needs to know this because it's the only thing
> everything on the network is asking.
>
>> Or in other words, if you own example.com and an auth server for
>> example.com is on your network, you have to first go via .com to know
>> that. Weird, but that's how it works.
> The name server doesn't know what domains it's supposed to give answers
> for without asking others first?

If you have a DNS server that is serving DNS info for example.com, it 
*does* know that. However,
what Alan is saying is that none of the resolvers (not even the resolver 
running on your
example.com DNS server) knows which DNS server serves records for 
example.com without
a few more queries.

Assume a resolver (for example, the resolver in glibc) that has no 
cached knowledge. To
look up www.example.com, it first queries for '.com' from the root DNS 
servers. Next, it
queries for 'example' from the '.com' DNS servers. Finally, from the 
'example.com' DNS
server, it can get the IP for www.example.com.

>
>> DNS was designed to need a network connection because most of the DNS is
>> out there somewhere else
> Then how do you solve the problem of being unable to even resolve the
> names of hosts on the LAN when the connection goes down?

Ideally, your caching name server has cached the record for your domain 
by the time
your connection goes down.

Alec

Re: [gentoo-user] resolving names of local hosts locally

[waltdnes]

On Thu, Dec 03, 2015 at 11:20:57PM +0100, lee wrote

> Then how do you solve the problem of being unable to even resolve the
> names of hosts on the LAN when the connection goes down?

  Do the machines on the LAN have static IP addresses?  If so, try hosts
files on the LAN machines (No, my initials are not "apk").  If they get
random addresses via dhcp, that won't work.

-- 
Walter Dnes <waltdnes@waltdnes.org>
I don't run "desktop environments"; I run useful applications

Re: [gentoo-user] resolving names of local hosts locally

[Peter Humphrey]

[-- Attachment #1: Type: text/plain, Size: 414 bytes --]

On Thursday 03 December 2015 23:01:27 lee wrote:
> Peter Humphrey <peter@prh.myzen.co.uk> writes:
> > Have you looked into net-dns/dnsmasq?
> 
> "Small forwarding DNS server"?  Why would I want a forwarding one?

Because it only forwards queries that it can't answer itself - see lines 72 
- 74 in the attached config file. (My resolv.conf points to localhost and 
resolv.dnsmasq points upstream.)

-- 
Rgds
Peter

[-- Attachment #2: dnsmasq.conf --]
[-- Type: text/plain, Size: 25874 bytes --]

# Configuration file for dnsmasq.
#
# Format is one option per line, legal options are the same
# as the long options legal on the command line. See
# "/usr/sbin/dnsmasq --help" or "man 8 dnsmasq" for details.

# Listen on this specific port instead of the standard DNS port
# (53). Setting this to zero completely disables DNS function,
# leaving only DHCP and/or TFTP.
#port=5353

# The following two options make you a better netizen, since they
# tell dnsmasq to filter out queries which the public DNS cannot
# answer, and which load the servers (especially the root servers)
# unnecessarily. If you have a dial-on-demand link they also stop
# these requests from bringing up the link unnecessarily.

# Never forward plain names (without a dot or domain part)
domain-needed
# Never forward addresses in the non-routed address spaces.
bogus-priv

# Uncomment these to enable DNSSEC validation and caching:
# (Requires dnsmasq to be built with DNSSEC option.)
#conf-file=/usr/share/dnsmasq/trust-anchors.conf
#dnssec

# Replies which are not DNSSEC signed may be legitimate, because the domain
# is unsigned, or may be forgeries. Setting this option tells dnsmasq to
# check that an unsigned reply is OK, by finding a secure proof that a DS 
# record somewhere between the root and the domain does not exist. 
# The cost of setting this is that even queries in unsigned domains will need
# one or more extra DNS queries to verify.
#dnssec-check-unsigned

# Uncomment this to filter useless windows-originated DNS requests
# which can trigger dial-on-demand links needlessly.
# Note that (amongst other things) this blocks all SRV requests,
# so don't use it if you use eg Kerberos, SIP, XMMP or Google-talk.
# This option only affects forwarding, SRV records originating for
# dnsmasq (via srv-host= lines) are not suppressed by it.
filterwin2k

# Change this line if you want dns to get its upstream servers from
# somewhere other that /etc/resolv.conf
resolv-file=/etc/resolv.dnsmasq

# By  default,  dnsmasq  will  send queries to any of the upstream
# servers it knows about and tries to favour servers to are  known
# to  be  up.  Uncommenting this forces dnsmasq to try each query
# with  each  server  strictly  in  the  order  they   appear   in
# /etc/resolv.conf
#strict-order

# If you don't want dnsmasq to read /etc/resolv.conf or any other
# file, getting its servers from this file instead (see below), then
# uncomment this.
#no-resolv

# If you don't want dnsmasq to poll /etc/resolv.conf or other resolv
# files for changes and re-read them then uncomment this.
#no-poll

# Add other name servers here, with domain specs if they are for
# non-public domains.
#server=/localnet/192.168.1.1

# Example of routing PTR queries to nameservers: this will send all
# address->name queries for 192.168.3/24 to nameserver 10.1.2.3
#server=/3.168.192.in-addr.arpa/10.1.2.3

# Add local-only domains here, queries in these domains are answered
# from /etc/hosts or DHCP only.
local=/prhnet/

# Add domains which you want to force to an IP address here.
# The example below send any host in double-click.net to a local
# web-server.
#address=/double-click.net/127.0.0.1

# --address (and --server) work with IPv6 addresses too.
#address=/www.thekelleys.org.uk/fe80::20d:60ff:fe36:f83

# Add the IPs of all queries to yahoo.com, google.com, and their
# subdomains to the vpn and search ipsets:
#ipset=/yahoo.com/google.com/vpn,search

# You can control how dnsmasq talks to a server: this forces
# queries to 10.1.2.3 to be routed via eth1
# server=10.1.2.3@eth1

# and this sets the source (ie local) address used to talk to
# 10.1.2.3 to 192.168.1.1 port 55 (there must be a interface with that
# IP on the machine, obviously).
# server=10.1.2.3@192.168.1.1#55

# If you want dnsmasq to change uid and gid to something other
# than the default, edit the following lines.
#user=
#group=

# If you want dnsmasq to listen for DHCP and DNS requests only on
# specified interfaces (and the loopback) give the name of the
# interface (eg eth0) here.
# Repeat the line for more than one interface.
#interface=
# Or you can specify which interface _not_ to listen on
#except-interface=
# Or which to listen on by address (remember to include 127.0.0.1 if
# you use this.)
#listen-address=
# If you want dnsmasq to provide only DNS service on an interface,
# configure it as shown above, and then use the following line to
# disable DHCP and TFTP on it.
#no-dhcp-interface=

# On systems which support it, dnsmasq binds the wildcard address,
# even when it is listening on only some interfaces. It then discards
# requests that it shouldn't reply to. This has the advantage of
# working even when interfaces come and go and change address. If you
# want dnsmasq to really bind only the interfaces it is listening on,
# uncomment this option. About the only time you may need this is when
# running another nameserver on the same machine.
#bind-interfaces

# If you don't want dnsmasq to read /etc/hosts, uncomment the
# following line.
#no-hosts
# or if you want it to read another file, as well as /etc/hosts, use
# this.
#addn-hosts=/etc/banner_add_hosts

# Set this (and domain: see below) if you want to have a domain
# automatically added to simple names in a hosts-file.
#expand-hosts

# Set the domain for dnsmasq. this is optional, but if it is set, it
# does the following things.
# 1) Allows DHCP hosts to have fully qualified domain names, as long
#     as the domain part matches this setting.
# 2) Sets the "domain" DHCP option thereby potentially setting the
#    domain of all systems configured by DHCP
# 3) Provides the domain part for "expand-hosts"
#domain=thekelleys.org.uk

# Set a different domain for a particular subnet
#domain=wireless.thekelleys.org.uk,192.168.2.0/24

# Same idea, but range rather then subnet
#domain=reserved.thekelleys.org.uk,192.68.3.100,192.168.3.200

# Uncomment this to enable the integrated DHCP server, you need
# to supply the range of addresses available for lease and optionally
# a lease time. If you have more than one network, you will need to
# repeat this for each network on which you want to supply DHCP
# service.
#dhcp-range=192.168.1.50,192.168.1.150,12h
#dhcp-range=192.168.1.32,192.168.1.48,12h

# This is an example of a DHCP range where the netmask is given. This
# is needed for networks we reach the dnsmasq DHCP server via a relay
# agent. If you don't know what a DHCP relay agent is, you probably
# don't need to worry about this.
#dhcp-range=192.168.1.50,192.168.1.150,255.255.255.0,12h

# This is an example of a DHCP range which sets a tag, so that
# some DHCP options may be set only for this network.
#dhcp-range=set:red,192.168.1.50,192.168.1.150

# Use this DHCP range only when the tag "green" is set.
#dhcp-range=tag:green,192.168.1.50,192.168.1.150,12h

# Specify a subnet which can't be used for dynamic address allocation,
# is available for hosts with matching --dhcp-host lines. Note that
# dhcp-host declarations will be ignored unless there is a dhcp-range
# of some type for the subnet in question.
# In this case the netmask is implied (it comes from the network
# configuration on the machine running dnsmasq) it is possible to give
# an explicit netmask instead.
#dhcp-range=192.168.1.0,static

# Enable DHCPv6. Note that the prefix-length does not need to be specified
# and defaults to 64 if missing/
#dhcp-range=1234::2, 1234::500, 64, 12h

# Do Router Advertisements, BUT NOT DHCP for this subnet.
#dhcp-range=1234::, ra-only 

# Do Router Advertisements, BUT NOT DHCP for this subnet, also try and
# add names to the DNS for the IPv6 address of SLAAC-configured dual-stack 
# hosts. Use the DHCPv4 lease to derive the name, network segment and 
# MAC address and assume that the host will also have an
# IPv6 address calculated using the SLAAC alogrithm.
#dhcp-range=1234::, ra-names

# Do Router Advertisements, BUT NOT DHCP for this subnet.
# Set the lifetime to 46 hours. (Note: minimum lifetime is 2 hours.)
#dhcp-range=1234::, ra-only, 48h

# Do DHCP and Router Advertisements for this subnet. Set the A bit in the RA
# so that clients can use SLAAC addresses as well as DHCP ones.
#dhcp-range=1234::2, 1234::500, slaac

# Do Router Advertisements and stateless DHCP for this subnet. Clients will
# not get addresses from DHCP, but they will get other configuration information.
# They will use SLAAC for addresses.
#dhcp-range=1234::, ra-stateless

# Do stateless DHCP, SLAAC, and generate DNS names for SLAAC addresses
# from DHCPv4 leases.
#dhcp-range=1234::, ra-stateless, ra-names

# Do router advertisements for all subnets where we're doing DHCPv6
# Unless overriden by ra-stateless, ra-names, et al, the router 
# advertisements will have the M and O bits set, so that the clients
# get addresses and configuration from DHCPv6, and the A bit reset, so the 
# clients don't use SLAAC addresses.
#enable-ra

# Supply parameters for specified hosts using DHCP. There are lots
# of valid alternatives, so we will give examples of each. Note that
# IP addresses DO NOT have to be in the range given above, they just
# need to be on the same network. The order of the parameters in these
# do not matter, it's permissible to give name, address and MAC in any
# order.

# Always allocate the host with Ethernet address 11:22:33:44:55:66
# The IP address 192.168.1.60
#dhcp-host=11:22:33:44:55:66,192.168.1.60

# Always set the name of the host with hardware address
# 11:22:33:44:55:66 to be "fred"
#dhcp-host=11:22:33:44:55:66,fred

# Always give the host with Ethernet address 11:22:33:44:55:66
# the name fred and IP address 192.168.1.60 and lease time 45 minutes
#dhcp-host=11:22:33:44:55:66,fred,192.168.1.60,45m

# Give a host with Ethernet address 11:22:33:44:55:66 or
# 12:34:56:78:90:12 the IP address 192.168.1.60. Dnsmasq will assume
# that these two Ethernet interfaces will never be in use at the same
# time, and give the IP address to the second, even if it is already
# in use by the first. Useful for laptops with wired and wireless
# addresses.
#dhcp-host=11:22:33:44:55:66,12:34:56:78:90:12,192.168.1.60

# Give the machine which says its name is "bert" IP address
# 192.168.1.70 and an infinite lease
#dhcp-host=bert,192.168.1.70,infinite

# Always give the host with client identifier 01:02:02:04
# the IP address 192.168.1.60
#dhcp-host=id:01:02:02:04,192.168.1.60

# Always give the host with client identifier "marjorie"
# the IP address 192.168.1.60
#dhcp-host=id:marjorie,192.168.1.60

# Enable the address given for "judge" in /etc/hosts
# to be given to a machine presenting the name "judge" when
# it asks for a DHCP lease.
#dhcp-host=judge

# Never offer DHCP service to a machine whose Ethernet
# address is 11:22:33:44:55:66
#dhcp-host=11:22:33:44:55:66,ignore

# Ignore any client-id presented by the machine with Ethernet
# address 11:22:33:44:55:66. This is useful to prevent a machine
# being treated differently when running under different OS's or
# between PXE boot and OS boot.
#dhcp-host=11:22:33:44:55:66,id:*

# Send extra options which are tagged as "red" to
# the machine with Ethernet address 11:22:33:44:55:66
#dhcp-host=11:22:33:44:55:66,set:red

# Send extra options which are tagged as "red" to
# any machine with Ethernet address starting 11:22:33:
#dhcp-host=11:22:33:*:*:*,set:red

# Give a fixed IPv6 address and name to client with 
# DUID 00:01:00:01:16:d2:83:fc:92:d4:19:e2:d8:b2
# Note the MAC addresses CANNOT be used to identify DHCPv6 clients.
# Note also the they [] around the IPv6 address are obilgatory.
#dhcp-host=id:00:01:00:01:16:d2:83:fc:92:d4:19:e2:d8:b2, fred, [1234::5] 

# Ignore any clients which are not specified in dhcp-host lines
# or /etc/ethers. Equivalent to ISC "deny unknown-clients".
# This relies on the special "known" tag which is set when
# a host is matched.
#dhcp-ignore=tag:!known

# Send extra options which are tagged as "red" to any machine whose
# DHCP vendorclass string includes the substring "Linux"
#dhcp-vendorclass=set:red,Linux

# Send extra options which are tagged as "red" to any machine one
# of whose DHCP userclass strings includes the substring "accounts"
#dhcp-userclass=set:red,accounts

# Send extra options which are tagged as "red" to any machine whose
# MAC address matches the pattern.
#dhcp-mac=set:red,00:60:8C:*:*:*

# If this line is uncommented, dnsmasq will read /etc/ethers and act
# on the ethernet-address/IP pairs found there just as if they had
# been given as --dhcp-host options. Useful if you keep
# MAC-address/host mappings there for other purposes.
#read-ethers

# Send options to hosts which ask for a DHCP lease.
# See RFC 2132 for details of available options.
# Common options can be given to dnsmasq by name:
# run "dnsmasq --help dhcp" to get a list.
# Note that all the common settings, such as netmask and
# broadcast address, DNS server and default route, are given
# sane defaults by dnsmasq. You very likely will not need
# any dhcp-options. If you use Windows clients and Samba, there
# are some options which are recommended, they are detailed at the
# end of this section.

# Override the default route supplied by dnsmasq, which assumes the
# router is the same machine as the one running dnsmasq.
#dhcp-option=3,1.2.3.4

# Do the same thing, but using the option name
#dhcp-option=option:router,1.2.3.4

# Override the default route supplied by dnsmasq and send no default
# route at all. Note that this only works for the options sent by
# default (1, 3, 6, 12, 28) the same line will send a zero-length option
# for all other option numbers.
#dhcp-option=3

# Set the NTP time server addresses to 192.168.1.4 and 10.10.0.5
#dhcp-option=option:ntp-server,192.168.1.4,10.10.0.5

# Send DHCPv6 option. Note [] around IPv6 addresses.
#dhcp-option=option6:dns-server,[1234::77],[1234::88]

# Send DHCPv6 option for namservers as the machine running 
# dnsmasq and another.
#dhcp-option=option6:dns-server,[::],[1234::88]

# Ask client to poll for option changes every six hours. (RFC4242)
#dhcp-option=option6:information-refresh-time,6h

# Set the NTP time server address to be the same machine as
# is running dnsmasq
#dhcp-option=42,0.0.0.0

# Set the NIS domain name to "welly"
#dhcp-option=40,welly

# Set the default time-to-live to 50
#dhcp-option=23,50

# Set the "all subnets are local" flag
#dhcp-option=27,1

# Send the etherboot magic flag and then etherboot options (a string).
#dhcp-option=128,e4:45:74:68:00:00
#dhcp-option=129,NIC=eepro100

# Specify an option which will only be sent to the "red" network
# (see dhcp-range for the declaration of the "red" network)
# Note that the tag: part must precede the option: part.
#dhcp-option = tag:red, option:ntp-server, 192.168.1.1

# The following DHCP options set up dnsmasq in the same way as is specified
# for the ISC dhcpcd in
# http://www.samba.org/samba/ftp/docs/textdocs/DHCP-Server-Configuration.txt
# adapted for a typical dnsmasq installation where the host running
# dnsmasq is also the host running samba.
# you may want to uncomment some or all of them if you use
# Windows clients and Samba.
#dhcp-option=19,0           # option ip-forwarding off
#dhcp-option=44,0.0.0.0     # set netbios-over-TCP/IP nameserver(s) aka WINS server(s)
#dhcp-option=45,0.0.0.0     # netbios datagram distribution server
#dhcp-option=46,8           # netbios node type

# Send an empty WPAD option. This may be REQUIRED to get windows 7 to behave.
#dhcp-option=252,"\n"

# Send RFC-3397 DNS domain search DHCP option. WARNING: Your DHCP client
# probably doesn't support this......
#dhcp-option=option:domain-search,eng.apple.com,marketing.apple.com

# Send RFC-3442 classless static routes (note the netmask encoding)
#dhcp-option=121,192.168.1.0/24,1.2.3.4,10.0.0.0/8,5.6.7.8

# Send vendor-class specific options encapsulated in DHCP option 43.
# The meaning of the options is defined by the vendor-class so
# options are sent only when the client supplied vendor class
# matches the class given here. (A substring match is OK, so "MSFT"
# matches "MSFT" and "MSFT 5.0"). This example sets the
# mtftp address to 0.0.0.0 for PXEClients.
#dhcp-option=vendor:PXEClient,1,0.0.0.0

# Send microsoft-specific option to tell windows to release the DHCP lease
# when it shuts down. Note the "i" flag, to tell dnsmasq to send the
# value as a four-byte integer - that's what microsoft wants. See
# http://technet2.microsoft.com/WindowsServer/en/library/a70f1bb7-d2d4-49f0-96d6-4b7414ecfaae1033.mspx?mfr=true
#dhcp-option=vendor:MSFT,2,1i

# Send the Encapsulated-vendor-class ID needed by some configurations of
# Etherboot to allow is to recognise the DHCP server.
#dhcp-option=vendor:Etherboot,60,"Etherboot"

# Send options to PXELinux. Note that we need to send the options even
# though they don't appear in the parameter request list, so we need
# to use dhcp-option-force here.
# See http://syslinux.zytor.com/pxe.php#special for details.
# Magic number - needed before anything else is recognised
#dhcp-option-force=208,f1:00:74:7e
# Configuration file name
#dhcp-option-force=209,configs/common
# Path prefix
#dhcp-option-force=210,/tftpboot/pxelinux/files/
# Reboot time. (Note 'i' to send 32-bit value)
#dhcp-option-force=211,30i

# Set the boot filename for netboot/PXE. You will only need
# this is you want to boot machines over the network and you will need
# a TFTP server; either dnsmasq's built in TFTP server or an
# external one. (See below for how to enable the TFTP server.)
#dhcp-boot=pxelinux.0

# The same as above, but use custom tftp-server instead machine running dnsmasq
#dhcp-boot=pxelinux,server.name,192.168.1.100

# Boot for Etherboot gPXE. The idea is to send two different
# filenames, the first loads gPXE, and the second tells gPXE what to
# load. The dhcp-match sets the gpxe tag for requests from gPXE.
#dhcp-match=set:gpxe,175 # gPXE sends a 175 option.
#dhcp-boot=tag:!gpxe,undionly.kpxe
#dhcp-boot=mybootimage

# Encapsulated options for Etherboot gPXE. All the options are
# encapsulated within option 175
#dhcp-option=encap:175, 1, 5b         # priority code
#dhcp-option=encap:175, 176, 1b       # no-proxydhcp
#dhcp-option=encap:175, 177, string   # bus-id
#dhcp-option=encap:175, 189, 1b       # BIOS drive code
#dhcp-option=encap:175, 190, user     # iSCSI username
#dhcp-option=encap:175, 191, pass     # iSCSI password

# Test for the architecture of a netboot client. PXE clients are
# supposed to send their architecture as option 93. (See RFC 4578)
#dhcp-match=peecees, option:client-arch, 0 #x86-32
#dhcp-match=itanics, option:client-arch, 2 #IA64
#dhcp-match=hammers, option:client-arch, 6 #x86-64
#dhcp-match=mactels, option:client-arch, 7 #EFI x86-64

# Do real PXE, rather than just booting a single file, this is an
# alternative to dhcp-boot.
#pxe-prompt="What system shall I netboot?"
# or with timeout before first available action is taken:
#pxe-prompt="Press F8 for menu.", 60

# Available boot services. for PXE.
#pxe-service=x86PC, "Boot from local disk"

# Loads <tftp-root>/pxelinux.0 from dnsmasq TFTP server.
#pxe-service=x86PC, "Install Linux", pxelinux

# Loads <tftp-root>/pxelinux.0 from TFTP server at 1.2.3.4.
# Beware this fails on old PXE ROMS.
#pxe-service=x86PC, "Install Linux", pxelinux, 1.2.3.4

# Use bootserver on network, found my multicast or broadcast.
#pxe-service=x86PC, "Install windows from RIS server", 1

# Use bootserver at a known IP address.
#pxe-service=x86PC, "Install windows from RIS server", 1, 1.2.3.4

# If you have multicast-FTP available,
# information for that can be passed in a similar way using options 1
# to 5. See page 19 of
# http://download.intel.com/design/archives/wfm/downloads/pxespec.pdf


# Enable dnsmasq's built-in TFTP server
#enable-tftp

# Set the root directory for files available via FTP.
#tftp-root=/var/ftpd

# Make the TFTP server more secure: with this set, only files owned by
# the user dnsmasq is running as will be send over the net.
#tftp-secure

# This option stops dnsmasq from negotiating a larger blocksize for TFTP
# transfers. It will slow things down, but may rescue some broken TFTP
# clients.
#tftp-no-blocksize

# Set the boot file name only when the "red" tag is set.
#dhcp-boot=tag:red,pxelinux.red-net

# An example of dhcp-boot with an external TFTP server: the name and IP
# address of the server are given after the filename.
# Can fail with old PXE ROMS. Overridden by --pxe-service.
#dhcp-boot=/var/ftpd/pxelinux.0,boothost,192.168.1.3

# If there are multiple external tftp servers having a same name
# (using /etc/hosts) then that name can be specified as the
# tftp_servername (the third option to dhcp-boot) and in that
# case dnsmasq resolves this name and returns the resultant IP
# addresses in round robin fasion. This facility can be used to
# load balance the tftp load among a set of servers.
#dhcp-boot=/var/ftpd/pxelinux.0,boothost,tftp_server_name

# Set the limit on DHCP leases, the default is 150
#dhcp-lease-max=150

# The DHCP server needs somewhere on disk to keep its lease database.
# This defaults to a sane location, but if you want to change it, use
# the line below.
#dhcp-leasefile=/var/lib/misc/dnsmasq.leases

# Set the DHCP server to authoritative mode. In this mode it will barge in
# and take over the lease for any client which broadcasts on the network,
# whether it has a record of the lease or not. This avoids long timeouts
# when a machine wakes up on a new network. DO NOT enable this if there's
# the slightest chance that you might end up accidentally configuring a DHCP
# server for your campus/company accidentally. The ISC server uses
# the same option, and this URL provides more information:
# http://www.isc.org/files/auth.html
#dhcp-authoritative

# Run an executable when a DHCP lease is created or destroyed.
# The arguments sent to the script are "add" or "del",
# then the MAC address, the IP address and finally the hostname
# if there is one.
#dhcp-script=/bin/echo

# Set the cachesize here.
#cache-size=150

# If you want to disable negative caching, uncomment this.
#no-negcache

# Normally responses which come from /etc/hosts and the DHCP lease
# file have Time-To-Live set as zero, which conventionally means
# do not cache further. If you are happy to trade lower load on the
# server for potentially stale date, you can set a time-to-live (in
# seconds) here.
local-ttl=86400

# If you want dnsmasq to detect attempts by Verisign to send queries
# to unregistered .com and .net hosts to its sitefinder service and
# have dnsmasq instead return the correct NXDOMAIN response, uncomment
# this line. You can add similar lines to do the same for other
# registries which have implemented wildcard A records.
bogus-nxdomain=64.94.110.11

# If you want to fix up DNS results from upstream servers, use the
# alias option. This only works for IPv4.
# This alias makes a result of 1.2.3.4 appear as 5.6.7.8
#alias=1.2.3.4,5.6.7.8
# and this maps 1.2.3.x to 5.6.7.x
#alias=1.2.3.0,5.6.7.0,255.255.255.0
# and this maps 192.168.1.10->192.168.1.40 to 10.0.0.10->10.0.0.40
#alias=192.168.1.10-192.168.1.40,10.0.0.0,255.255.255.0

# Change these lines if you want dnsmasq to serve MX records.

# Return an MX record named "maildomain.com" with target
# servermachine.com and preference 50
#mx-host=maildomain.com,servermachine.com,50

# Set the default target for MX records created using the localmx option.
#mx-target=servermachine.com

# Return an MX record pointing to the mx-target for all local
# machines.
#localmx

# Return an MX record pointing to itself for all local machines.
#selfmx

# Change the following lines if you want dnsmasq to serve SRV
# records.  These are useful if you want to serve ldap requests for
# Active Directory and other windows-originated DNS requests.
# See RFC 2782.
# You may add multiple srv-host lines.
# The fields are <name>,<target>,<port>,<priority>,<weight>
# If the domain part if missing from the name (so that is just has the
# service and protocol sections) then the domain given by the domain=
# config option is used. (Note that expand-hosts does not need to be
# set for this to work.)

# A SRV record sending LDAP for the example.com domain to
# ldapserver.example.com port 389
#srv-host=_ldap._tcp.example.com,ldapserver.example.com,389

# A SRV record sending LDAP for the example.com domain to
# ldapserver.example.com port 389 (using domain=)
#domain=example.com
#srv-host=_ldap._tcp,ldapserver.example.com,389

# Two SRV records for LDAP, each with different priorities
#srv-host=_ldap._tcp.example.com,ldapserver.example.com,389,1
#srv-host=_ldap._tcp.example.com,ldapserver.example.com,389,2

# A SRV record indicating that there is no LDAP server for the domain
# example.com
#srv-host=_ldap._tcp.example.com

# The following line shows how to make dnsmasq serve an arbitrary PTR
# record. This is useful for DNS-SD. (Note that the
# domain-name expansion done for SRV records _does_not
# occur for PTR records.)
#ptr-record=_http._tcp.dns-sd-services,"New Employee Page._http._tcp.dns-sd-services"

# Change the following lines to enable dnsmasq to serve TXT records.
# These are used for things like SPF and zeroconf. (Note that the
# domain-name expansion done for SRV records _does_not
# occur for TXT records.)

#Example SPF.
#txt-record=example.com,"v=spf1 a -all"

#Example zeroconf
#txt-record=_http._tcp.example.com,name=value,paper=A4

# Provide an alias for a "local" DNS name. Note that this _only_ works
# for targets which are names from DHCP or /etc/hosts. Give host
# "bert" another name, bertrand
#cname=bertand,bert

# For debugging purposes, log each DNS query as it passes through
# dnsmasq.
#log-queries

# Log lots of extra information about DHCP transactions.
#log-dhcp

# Include another lot of configuration options.
#conf-file=/etc/dnsmasq.more.conf
#conf-dir=/etc/dnsmasq.d

Re: [gentoo-user] resolving names of local hosts locally

[Adam Carter]

[-- Attachment #1: Type: text/plain, Size: 1375 bytes --]

There are several problems with your idea. First, the configured

> namservers in resolv.conf are caching servers, not authoritative
> servers. You never configure an auth server to act as a cache. Yes, it
> can be done. No, it's an awful idea and things break horribly.
>
>
Hi Alan,

What breaks if you have caching and auth on the same server? I have been
running my tiny home network this way for years. The local domain is
properly delegated, but if you just wont a local domain that's not
necessary.


> Secondly, nothing else on your network can know your auth server is
> authoritative without first being informed so by the delegating server.
> Or in other words, if you own example.com and an auth server for
> example.com is on your network, you have to first go via .com to know
> that. Weird, but that's how it works.
>

AFAIK clients simply request service from whatever's configured in their
/etc/resolv.conf (recursive query). They dont need to know whether the DNS
server is authoritative or not, and they dont need to know anything about
delegation status as they are not performing iterative queries.

As long as all caching servers on your network are also authoritative for
the zone, or have forwarders for that zone to an authoritative server, it
works. Right? Bind doesnt do iteration on zones its authoritative for - i
just tested with a dummy domain.

[-- Attachment #2: Type: text/html, Size: 2043 bytes --]

Re: [gentoo-user] resolving names of local hosts locally

[Alan McKinnon]

On 16/12/2015 05:01, Adam Carter wrote:
> There are several problems with your idea. First, the configured
> 
>     namservers in resolv.conf are caching servers, not authoritative
>     servers. You never configure an auth server to act as a cache. Yes, it
>     can be done. No, it's an awful idea and things break horribly.
> 
> 
> Hi Alan,
> 
> What breaks if you have caching and auth on the same server? I have been
> running my tiny home network this way for years. The local domain is
> properly delegated, but if you just wont a local domain that's not
> necessary.

Well first off I should explain where I'm coming from. I work at a large
ISP and the DNS infrastructure falls in my team's area. There are 1000s
of customers and nothing must break[1] so it's a very different POV from
having your own small instance serving just you.

>  
> 
>     Secondly, nothing else on your network can know your auth server is
>     authoritative without first being informed so by the delegating server.
>     Or in other words, if you own example.com <http://example.com> and
>     an auth server for
>     example.com <http://example.com> is on your network, you have to
>     first go via .com to know
>     that. Weird, but that's how it works.
> 
> 
> AFAIK clients simply request service from whatever's configured in their
> /etc/resolv.conf (recursive query). They dont need to know whether the
> DNS server is authoritative or not, and they dont need to know anything
> about delegation status as they are not performing iterative queries.
> 
> As long as all caching servers on your network are also authoritative
> for the zone, or have forwarders for that zone to an authoritative
> server, it works. Right? Bind doesnt do iteration on zones its
> authoritative for - i just tested with a dummy domain.

All large DNS providers' auth servers are full of outdated and orphaned
zones and RRs. It happens, and it happens a LOT more than one would
think. It's almost well-nigh impossible to keep things 100% straight for
these lame zones[2]

What happens when your auth server is also a recursive cache and a
client requests one of those lame zones? Your cache replies. If that
zone is something big and important (like a busy co.tLD) that zone just
broke for all your customers.

Technically, it's a case of domain poisoning and very very difficult to
find. You never run into this on your own network so you likely are
wondering what I'm on about. You don't have an auth zone for a
supermarket chain on your auth server that can be migrated away on a
whim :-)



[1] Yeah, I know - nothing must break. It can and it does because humans
ask for changes and humans implement them. We pretend these things never
happen in our advertising materials.

[2] It's really an exercise in garbage collection, the same as
interpreters have to do. The only reliable way to find all the garbage
is to walk the DNS for every zone hosted and see if they are still
legit. No-one ever really does this until their DNS management software
is migrated, and then eyeballs get very big indeed. I had the pleasure
once - it took 16 hours to fully validate 50,000 zones, and it took 6
attempts to write code for all errors.

-- 
Alan McKinnon
alan.mckinnon@gmail.com

Re: [gentoo-user] resolving names of local hosts locally

[Tom H]

On Wed, Dec 16, 2015 at 4:01 AM, Adam Carter <adamcarter3@gmail.com> wrote:
>>
>> There are several problems with your idea. First, the configured
>>
>> namservers in resolv.conf are caching servers, not authoritative
>> servers. You never configure an auth server to act as a cache. Yes, it
>> can be done. No, it's an awful idea and things break horribly.
>
> What breaks if you have caching and auth on the same server? I have been
> running my tiny home network this way for years. The local domain is
> properly delegated, but if you just wont a local domain that's not
> necessary.

The ISC recommends separating authoritative and caching bind servers.

The main reason that I can think of is that someone can poison the
cache of the domains for which a server's authoritative.

Re: [gentoo-user] resolving names of local hosts locally

[Alan McKinnon]

On 16/12/2015 11:09, Tom H wrote:
> On Wed, Dec 16, 2015 at 4:01 AM, Adam Carter <adamcarter3@gmail.com> wrote:
>>>
>>> There are several problems with your idea. First, the configured
>>>
>>> namservers in resolv.conf are caching servers, not authoritative
>>> servers. You never configure an auth server to act as a cache. Yes, it
>>> can be done. No, it's an awful idea and things break horribly.
>>
>> What breaks if you have caching and auth on the same server? I have been
>> running my tiny home network this way for years. The local domain is
>> properly delegated, but if you just wont a local domain that's not
>> necessary.
> 
> The ISC recommends separating authoritative and caching bind servers.
> 
> The main reason that I can think of is that someone can poison the
> cache of the domains for which a server's authoritative.
> 


If I were a serious Cyber Kriminal, here's the avenue I'd be looking for:

Find some vendor of low or medium end equipment (some, small business
kit) that "helpfully" provides a combined DNS cache and auth server on
the border router and just as helpfully announces this to the internal
network. We all know how bad security on that stuff really is (think
factory default user admin pass admin, and never changed).

Find an exploit for these things and load lame zone files for some major
banks and other juicy target pointing at my malware. The owners of this
kit will never notice I did this. The router's DNS cache will trust the
authoritative zone it has loaded even though it's orphaned.

Awesome thanks. I just 0wned the internet for that entire business. And
9 out of 10 of those businesses will never find it.

Solution: obey best practice. Never run auth and cache on the same
address. On the same machine is fine, they are different daemons.

-- 
Alan McKinnon
alan.mckinnon@gmail.com

Re: [gentoo-user] resolving names of local hosts locally

[Rich Freeman]

On Wed, Dec 16, 2015 at 4:26 AM, Alan McKinnon <alan.mckinnon@gmail.com> wrote:
>
> Solution: obey best practice. Never run auth and cache on the same
> address. On the same machine is fine, they are different daemons.
>

Which one listens on port 53?  Also, how do you point the caching
daemon at the authoritative daemon for internal servers/domains/etc?
My authoritative server for doubleclick.net is not the same as the one
you'll find in the .net servers.  Also, for the domains I use
internally the DNS server and resolution is different within my LAN
from what you'd see on the internet.  I know that at my employer
internal DNS resolution is not the same as what you'd find outside the
organization, so this isn't an issue unique to small setups.

One of the reasons I run auth and cache on the same host is that it
greatly simplifies dependencies.  If I want to run them on separate
containers then they'll either need static addresses, or need to use
DHCP, which means the DHCP server has a potential circular dependency
with the DNS servers.  Plus most of my containers are going to need
DNS so these containers need to be running before other containers get
started.

For a large-scale datacenter the separated approach makes a lot of
sense.  If you're running 5000 hosts having two (or likely 10 counting
various backups/etc) that you start first isn't a big deal, and
neither is dedicating a bit of hardware to DNS/DHCP.  If you're
running all your services on one host, it can get a bit messy when you
start having multiple DNS servers all running on different IPs on the
same host.  It can of course still be done.

I just use BIND for both.  It isn't the best solution, but it is adequate.

-- 
Rich

Re: [gentoo-user] resolving names of local hosts locally

[Alan McKinnon]

On 16/12/2015 14:52, Rich Freeman wrote:
> On Wed, Dec 16, 2015 at 4:26 AM, Alan McKinnon <alan.mckinnon@gmail.com> wrote:
>>
>> Solution: obey best practice. Never run auth and cache on the same
>> address. On the same machine is fine, they are different daemons.
>>
> 
> Which one listens on port 53?  

I think you answered too quickly. The answer in in the phrase "same
address" and the following sentence which logically follows on.

Also, how do you point the caching
> daemon at the authoritative daemon for internal servers/domains/etc?
> My authoritative server for doubleclick.net is not the same as the one
> you'll find in the .net servers.  Also, for the domains I use
> internally the DNS server and resolution is different within my LAN
> from what you'd see on the internet.  I know that at my employer
> internal DNS resolution is not the same as what you'd find outside the
> organization, so this isn't an issue unique to small setups.
> 
> One of the reasons I run auth and cache on the same host is that it
> greatly simplifies dependencies.  If I want to run them on separate
> containers then they'll either need static addresses, or need to use
> DHCP, which means the DHCP server has a potential circular dependency
> with the DNS servers.  Plus most of my containers are going to need
> DNS so these containers need to be running before other containers get
> started.
> 
> For a large-scale datacenter the separated approach makes a lot of
> sense.  If you're running 5000 hosts having two (or likely 10 counting
> various backups/etc) that you start first isn't a big deal, and
> neither is dedicating a bit of hardware to DNS/DHCP.  If you're
> running all your services on one host, it can get a bit messy when you
> start having multiple DNS servers all running on different IPs on the
> same host.  It can of course still be done.
> 
> I just use BIND for both.  It isn't the best solution, but it is adequate.
> 


-- 
Alan McKinnon
alan.mckinnon@gmail.com

Re: [gentoo-user] resolving names of local hosts locally

[Tom H]

On Wed, Dec 16, 2015 at 1:52 PM, Rich Freeman <rich0@gentoo.org> wrote:
> On Wed, Dec 16, 2015 at 4:26 AM, Alan McKinnon <alan.mckinnon@gmail.com> wrote:
>>
>> Solution: obey best practice. Never run auth and cache on the same
>> address. On the same machine is fine, they are different daemons.
>
> Which one listens on port 53?

# ss -ntl | grep :53
LISTEN     0      10     192.168.1.222:53                       *:*
LISTEN     0      10     192.168.1.221:53                       *:*
# ps ax | grep [na]med
  791 ?        Ssl    0:00 /usr/sbin/named -f -4 -c
/var/named1/named.conf -u named
  799 ?        Ssl    0:00 /usr/sbin/named -f -4 -c
/var/named2/named.conf -u named
#