From: CCIE3000 (ccie3000@googlemail.com)
Date: Sat Sep 06 2008 - 10:19:25 ART
Thanks very much Huan,
That's really helpful, it's been driving me crazy as it's one of those
simple things but has a massive impact if not correct.
Thanks again,
Si.
On Sat, Sep 6, 2008 at 3:27 PM, <huan@huanlan.com> wrote:
> 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.
>
>
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This archive was generated by hypermail 2.1.4 : Sat Oct 04 2008 - 09:26:17 ART