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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, 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 * wrote: > > From: CCIE3000 > Subject: Router acting as DNS server > To: “Cisco certification” > 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 > > _______________________________________________________________________ > Subscription information may be found at: http://www.groupstudy.com/list/CCIELab.html
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