1841 DNS Updates from DHCP

Unanswered Question
Jan 20th, 2013

Hello,

I have an 1841 running Advanced Enterprise Services 12.4(22)T3 that is functioning as a DHCP server and DNS server.  What I am trying to figure out how to do is have the DNS service respond to queries about the clients of the dhcp service.  I have successfully enabled it as a caching server for other requests, like "google.com" and "cisco.com", but what about the hosts on the local LAN?

As an example, let's say a Windows computer connects to the network with the hostname "computer" and receives an IP address from the 1841 with the domain name "test.net".  I would like the 1841 to serve DNS queries for "computer.test.net" with the IP address that it assigned.  How can I get it to do this?

Thanks!

I have this problem too.
0 votes
  • 1
  • 2
  • 3
  • 4
  • 5
Average Rating: 0 (0 ratings)
jeffs7@sbcglobal.net Mon, 01/21/2013 - 12:41

Thanks for the suggestion, but unfortunately it does not accomplish what I am seeking.  I am running a test configuration, with excerpts pasted below.

hostname Router

!

boot-start-marker

boot-end-marker

!

logging message-counter syslog

!

no aaa new-model

dot11 syslog

ip source-route

!

!

ip dhcp excluded-address 192.168.0.1

!

ip dhcp pool Test

   network 192.168.0.0 255.255.255.0

   default-router 192.168.0.1

   dns-server 192.168.0.1

   domain-name test.net

!

!

ip cef

ip domain name test.net

no ipv6 cef

!

multilink bundle-name authenticated

!

!

!

interface FastEthernet0/0

ip address 192.168.0.1 255.255.255.0

duplex auto

speed auto

!

interface FastEthernet0/1

no ip address

shutdown

duplex auto

speed auto

!

!

ip forward-protocol nd

no ip http server

no ip http secure-server

!

!

ip dns server

ip dns primary test.net soa Router.test.net postmaster.test.net 21600 900 777600

0 86400

!

Looking with Wireshark, when I perform a dns lookup, Windows first attempts to do a reverse lookup on the router's address (192.168.0.1) to try to find the server name.  The router receives this query and then just relays it out via a broadcast to the rest of the network, rather than answering with its own hostname or FQDN.  When I try to do a forward lookup on the name of my test computer, the router give an immediate response of No Such Name.

If I manually enter these records with the command "ip host router.test.net 192.168.0.1", then the router will correctly return forward and reverse queries.  I would like the router to automatically add these entries for itself and every DHCP client.  Is this possible?

Jeff

jeffs7@sbcglobal.net Tue, 01/22/2013 - 13:37

I turned on DHCP and DNS debugging and saw the following when attempting to connect a computer:

*Jan 22 21:17:46.343: DYNUPD: SWIF comingup 'FastEthernet0/0'

*Jan 22 21:17:46.495: DHCPD: DHCPREQUEST received from client 0100.1742.8e62.a2.

*Jan 22 21:17:46.495: DHCPD: Sending notification of ASSIGNMENT:

                                   DHCPD: address 192.168.0.101 mask 255.255.255.0

                                   DHCPD: htype 1 chaddr 0017.428e.62a2

                                   DHCPD: lease time remaining (secs) = 3600

*Jan 22 21:17:46.499: DHCPD: Appending default domain from pool

*Jan 22 21:17:46.499: DHCPD: Using hostname 'computer.test.local.' for dynami

c update (from FQDN option)

*Jan 22 21:17:46.499: DHCPD: Doing dynamic update...

*Jan 22 21:17:46.499: DHCPD: Updating 'PTR' RR 192.168.0.101 -> 'computer.test.local.'

*Jan 22 21:17:46.499: DHCPD: Updating 'A' RR 'computer.test.local.' -> 192.168.0.101

*Jan 22 21:17:46.499: DDNS: Enqueuing new DDNS update 'computer.test.local.'<=> 192.168.0.101

*Jan 22 21:17:46.499: DHCPD: Sending DHCPACK to client 0100.1742.8e62.a2 (192.168.0.101).

*Jan 22 21:17:46.499: DHCPD: Including FQDN option name 'computer.test.local.' rcode1=255, rcode2=255 flags=0x3

*Jan 22 21:17:46.499: DHCPD: broadcasting BOOTREPLY to client 0017.428e.62a2.

*Jan 22 21:17:47.343: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/0, changed state to up

*Jan 22 21:17:55.503: DDNS: Can't find authoritative zone info for '101.0.168.192.in-addr.arpa.'

*Jan 22 21:18:04.503: DDNS: Can't find authoritative zone info for 'computer.test.local.'

*Jan 22 21:18:04.503: DDNS: Update of 'JeffStevens.test.local.' <=> 192.168.0.101 finished

I believe the problem is in the two lines marked above but I am not sure what command is needed to fix it.  I had configured "ip dns primary test.local soa router.test.local postmaster@test.local" and "ip host router.test.local 192.168.0.1" but for some reason it still does not realize that it is the authoritative dns for that zone.

Any ideas?  Anybody?

jeffs7@sbcglobal.net Tue, 01/22/2013 - 17:28

Thanks Paul, unfortunately that had not helped me get any closer.  That link talked about static entries in the configuration.  I want the DHCP server to update the DNS server dynamically as it assigns addresses.

I recognize that it is desirable to have an external server perfrom DNS, but this is for a small lan of perhaps 12 clients where DHCP must be used (since these are laptops that will be moving in and out) but would benefit from DNS for mapping drives and filesharing.  For this small LAN, a separate DNS server would seem to me to be overkill if the functionality could be provided directly by the 1841 IOS.

I have found a couple of other posts with people asking the same question and ultimately giving up, so I am wondering if it is something that IOS even supports.

Jeff

glen.j.lerner Thu, 02/14/2013 - 12:08

Jeff,

Were you able to get this working?  I'm in a similar situation where I have several small remote offices that use a 2901 for dhcp.  It prefer not to send all dns requests to hq dns box (windows).  Have you looked into creating dns views on your ios router?

jeffs7@sbcglobal.net Fri, 02/15/2013 - 00:40

Unfortunately Troy, I ended up giving up on the idea.  After many attempts and contacting everybody I could find, it seems that the IOS is not programmed to provide this feature.  The problem boils down to this: the dhcp server hands out an ip address and then goes to notify the dns server, so it looks up the name-server specified in the configuration and attempts to update that.  That is to say, it fails to notice that it is in fact the authoratitive name-server for that domain and instead attempts to update the upstream name-server.  I cannot get it to realize that it needs to update its own internal name cache.

It seems to me that this is a great oversight on the part of Cisco and this should be considered critical functionality for a device termed "Integrated Services" and marketed as an all-in-one solution for small branch offices.  I still cannot wrap my head around why a "professional" product cannot perform this rather simple task but the cheap 2wire residential gateway AT&T gives me at home can (this and why it cannot get its upstream dns servers from DHCP on one of the interfaces).

Sorry I was not of more help.  If you can find a way to make this work, please tell me because it has been a source of extreme frustration.

Actions

Login or Register to take actions

This Discussion

Posted January 20, 2013 at 4:31 PM
Stats:
Replies:7 Avg. Rating:
Views:821 Votes:0
Shares:0
Tags: dns, dhcp, 1841, ddns
+

Related Content

Discussions Leaderboard

Rank Username Points
1 15,007
2 8,150
3 7,725
4 7,083
5 6,742
Rank Username Points
165
82
69
65
55