From: Huan Pham (pnhuan@yahoo.com)
Date: Sat Sep 06 2008 - 09:27:44 ART
Hi CCIE3000,
You did not miss anything. Instead, you have an extra command on the router
that works as DNS server. Please remove the "ip name-server" from the server,
and you should be fine.
Here's the working config, and scrolling down, you will see the debugging
message showing you why the router crashes. The DNS server router crashes only
when you try to send a query for an invalid hostname, which causes the server
to go into a loop.
Client R1#
----------
ip name-server 2.2.2.2
! ip domain-lookup is enabled by default
ip domain-lookup
Server R2#
----------
ip dns server
! ip domain-lookup is enabled by default
ip domain-lookup
ip host R2 2.2.2.2
ip host R1 1.1.1.1
! DO NOT point name-server to itself
! NO ip name-server 2.2.2.2
R1#ping R2
Translating "R2"...domain server (2.2.2.2) [OK]
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 155.1.0.5, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 56/58/60 ms
R1#
*Apr 7 11:35:07.163: Domain: query for R2 type 1 to 2.2.2.2
*Apr 7 11:35:07.195: DOM: dom2cache: hostname is R2, RR type=1, class=1,
ttl=1, n=4Reply received ok
R2#debug domain
Domain Name System debugging is on
R2#
*Apr 7 02:18:27.683: DNS: Incoming UDP query (id#2)
*Apr 7 02:18:27.683: DNS: Type 1 DNS query (id#2) for host 'R2' from
12.0.0.1(58198)
*Apr 7 02:18:27.683: DNS: Query for my own hostname: R2
*Apr 7 02:18:27.683: DNS: Spoofing reply to query (id#2)
*Apr 7 02:18:27.683: DNS: Finished processing query (id#2) in 0.004 secs
REPRODUCE ROUTER CRASH
----------------------
R2#c
Enter configuration commands, one per line. End with CNTL/Z.
R2(config)#ip name-server 2.2.2.2
R2(config)#
R2#
R2#
R2#
!
! The R2 successfully serves the DNS queuries
! for valid hostnames (When "ping R2" is issued on R1 router)
R1#ping R2
Translating "R2"...domain server (2.2.2.2) [OK]
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 155.1.0.5, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 56/58/60 ms
*Apr 7 11:35:58.539: Domain: query for R2 type 1 to 2.2.2.2
*Apr 7 11:35:58.571: DOM: dom2cache: hostname is R2, RR type=1, class=1,
ttl=1, n=4Reply received ok
R2#
*Apr 7 02:19:19.059: DNS: Incoming UDP query (id#3)
*Apr 7 02:19:19.059: DNS: Type 1 DNS query (id#3) for host 'R2' from
12.0.0.1(54174)
*Apr 7 02:19:19.059: DNS: Query for my own hostname: R2
*Apr 7 02:19:19.059: DNS: Spoofing reply to query (id#3)
*Apr 7 02:19:19.059: DNS: Finished processing query (id#3) in 0.000 secs
R2#
R2#
! The R2 crashes when "ping R3" is issued on R1)
R1#ping R3
Translating "R3"...domain server (2.2.2.2)
*Apr 7 11:36:22.991: Domain: query for R3 type 1 to 2.2.2.2
% Unrecognized host or address, or protocol not running.
timed out
*Apr 7 11:36:55.459: %LINEPROTO-5-UPDOWN: Line protocol on Interface
Serial0/1, changed state to down
*Apr 7 11:36:55.459: %OSPF-5-ADJCHG: Process 1, Nbr 12.0.0.2 on Serial0/1
from FULL to DOWN, Neighbor Down: Interface down or detached
! As R2 cannot resolve IP for hostname R3, it tries to forward the queury to
! the next DNS server with IP address of itself. And the request keeps looping
within R2.
!
!
R2#
DNS: Re-sending DNS query (type 1, id#4) to 2.2.2.2
DNS: Incoming UDP query (id#4)
DNS: Type 1 DNS query (id#4) for host 'R3' from 2.2.2.2(53)
DNS: Re-sending DNS query (type 1, id#4) to 2.2.2.2
DNS: Incoming UDP query (id#4)
DNS: Type 1 DNS query (id#4) for host 'R3' from 2.2.2.2(53)
DNS: Re-sending DNS query (type 1, id#4) to 2.2.2.2
DNS: Incoming UDP query (id#4)
DNS: Type 1 DNS query (id#4) for host 'R3' from 2.2.2.2(53)
DNS: Re-sending DNS query (type 1, id#4) to 2.2.2.2
DNS: Incoming UDP query (id#4)
DNS: Type 1 DNS query (id#4) for host 'R3' from 2.2.2.2(53)
DNS: Re-sending DNS query (type 1, id#4) to 2.2.2.2
DNS: Incoming UDP query (id#4)
DNS: Type 1 DNS query (id#4) for host 'R3' from 2.2.2.2(53)
DNS: Re-sending DNS query (type 1, id#4) to 2.2.2.2
DNS: Incoming UDP query (id#4)
DNS: Type 1 DNS query (id#4) for host 'R3' from 2.2.2.2(53)
DNS: Re-sending DNS query (type 1, id#4) to 2.2.2.2
DNS: Incoming UDP query (id#4)
DNS: Type 1 DNS query (id#4) for host 'R3' from 2.2.2.2(53)
DNS: Re-sending DNS query (type 1, id#4) to 2.2.2.2
DNS: Incoming UDP query (id#4)
DNS: Type 1 DNS query (id#4) for host 'R3' from 2.2.2.2(53)
DNS: Re-sending DNS query (type 1, id#4) to 2.2.2.2
DNS: Incoming UDP query (id#4)
DNS: Type 1 DNS query (id#4) for host 'R3' from 2.2.2.2(53)
DNS: Re-sending DNS query (type 1, id#4) to 2.2.2.2
DNS: Incoming UDP query (id#4)
DNS: Type 1 DNS query (id#4) for host 'R3' from 2.2.2.2(53)
DNS: Re-sending DNS query (type 1, id#4) to 2.2.2.2
DNS: Incoming UDP query (id#4)
DNS: Type 1 DNS query (id#4) for host 'R3' from 12.0.0.1(49206)
DNS: Re-sending DNS query (type 1, id#4) to 2.2.2.2
DNS: Incoming UDP query (id#4)
DNS: Type 1 DNS query (id#4) for host 'R3' from 2.2.2.2(53)
DNS: Re-sending DNS query (type 1, id#4) to 2.2.2.2
DNS: Incoming UDP query (id#4)
DNS: Type 1 DNS query (id#4) for host 'R3' from 2.2.2.2(53)
DNS: Re-sending DNS query (type 1, id#4) to 2.2.2.2
DNS: Incoming UDP query (id#4)
DNS: Type 1 DNS query (id#4) for host 'R3' from 2.2.2.2(53)
DNS: Re-sending DNS query (type 1, id#4) to 2.2.2.2
DNS: Incoming UDP query (id#4)
DNS: Type 1 DNS query (id#4) for host 'R3' from 2.2.2.2(53)
DNS: Re-sending DNS query (type 1, id#4) to 2.2.2.2
DNS: Incoming UDP query (id#4)
DNS: Type 1 DNS query (id#4) for host 'R3' from 2.2.2.2(53)
DNS: Re-sending DNS query (type 1, id#4) to 2.2.2.2
DNS: Incoming UDP query (id#4)
DNS: Type 1 DNS query (id#4) for host 'R3' from 2.2.2.2(53)
DNS: Re-sending DNS query (type 1, id#4) to 2.2.2.2
DNS: Incoming UDP query (id#4)
DNS: Type 1 DNS query (id#4) for host 'R3' from 2.2.2.2(53)
DNS: Re-sending DNS query (type 1, id#4) to 2.2.2.2
DNS: Incoming UDP query (id#4)
DNS: Type 1 DNS query (id#4) for host 'R3' from 2.2.2.2(53)
DNS: Re-sending DNS query (type 1, id#4) to 2.2.2.2
--- On Sat, 9/6/08, CCIE3000 <ccie3000@googlemail.com> wrote:
From: CCIE3000 <ccie3000@googlemail.com>
Subject: Router acting as DNS server
To: "Cisco certification" <ccielab@groupstudy.com>
Date: Saturday, September 6, 2008, 1:42 AM
Hi Guys,
Am I missing something?? Whenever I try and configure a router to act as a
DNS server it always ends up crashing due to memory problems.
I configure
ip dns server
and then enter my ip host commands.
I also configure ip domain-name lookup and ip name-server commands on all
the routers.
Is there something else I'm missing that if I configured it would stop the
router dieing on me ?/
Thanks,
Si.
Blogs and organic groups at http://www.ccie.net
This archive was generated by hypermail 2.1.4 : Sat Oct 04 2008 - 09:26:17 ART