[dns-operations] EDNS issue
Mark Andrews
marka at isc.org
Fri Feb 25 05:00:57 UTC 2011
In message <000b01cbd4a6$0740d4a0$15c27de0$@iname.com>, "Frank Bulk" writes:
> Mark:
>
> Our borders routers blog fragments:
>
> Edge1#sh run | inc frag
> access-list 101 deny tcp any any log fragments
> access-list 101 deny udp any any log fragments
> access-list 101 deny icmp any any log fragments
> access-list 101 deny ip any any log fragments
> Edge1#
>
> Not sure if that's the same kind of fragments as you're talking about.
>
> The first query failed, the second didn't. Do I need to be making some
> changes to our border routers?
Yes. You need to permit, as a minimum, fragmented UDP packets
(determined by looking at the next header field of the IP header).
There is this security myth that you can run a IP network without
letting through fragmented IP packets. This has never been the
case. There is also a security myth that fragmented IP packets are
dangerous. They aren't. This is much the same as the security
myth that ICMP packets are bad. ICMP is essential to the good
running of a IP network.
> root at nagios:/etc/cron.hourly# dig @140.172.17.237 +dnssec
> forecast.weather.gov
>
> ; <<>> DiG 9.5.1-P3 <<>> @140.172.17.237 +dnssec forecast.weather.gov
> ; (1 server found)
> ;; global options: printcmd
> ;; connection timed out; no servers could be reached
> root at nagios:/etc/cron.hourly# dig @140.172.17.237 +dnssec
> forecast.weather.gov +bufsize=1400
>
> ; <<>> DiG 9.5.1-P3 <<>> @140.172.17.237 +dnssec forecast.weather.gov
> +bufsize=1400
> ; (1 server found)
> ;; global options: printcmd
> ;; Got answer:
> ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 12832
> ;; flags: qr aa rd; QUERY: 1, ANSWER: 8, AUTHORITY: 4, ADDITIONAL: 4
> ;; WARNING: recursion requested but not available
>
> ;; OPT PSEUDOSECTION:
> ; EDNS: version: 0, flags: do; udp: 4096
> ;; QUESTION SECTION:
> ;forecast.weather.gov. IN A
>
> ;; ANSWER SECTION:
> forecast.weather.gov. 5 IN CNAME edge-ext.lb.noaa.gov.
> forecast.weather.gov. 5 IN RRSIG CNAME 5 3 5 20110303213142
> 20110224213142 17808 weather.gov.
> B/ga+/E+QUWvvGxAbCqcekDsZj0H0cCnYtB3n4/SPiRaGQZyLTbKHAFr
> U2wsBQdecrAwtcbMA1eIHpqVw1c15H6L6m2931fUJ0uUXk9ahBiBIf5h
> ztst05qoFrbotqFiZjO4sYTOK02YxSnmSWv0RpFIYzMGd9vYL4mpC7EF
> mM0/97QBJTMI51dZPU2tLuLXYc7ZX3psKM145r90vp3HMZU4h+dCkl6S
> QcVq23qy/3UHvw50G1N3HHwIp0asExGQ2dJilWDk/1/jsAAV87GzA+sg
> +0pjPnd45Rdd/HC1thj/Bq4KK6FOLzzWFAey5HpWvxt1o5Mnh7c8rPeK V8puqA==
> edge-ext.lb.noaa.gov. 30 IN A 129.15.96.22
> edge-ext.lb.noaa.gov. 30 IN A 140.90.33.21
> edge-ext.lb.noaa.gov. 30 IN A 140.90.33.22
> edge-ext.lb.noaa.gov. 30 IN A 140.90.200.22
> edge-ext.lb.noaa.gov. 30 IN A 140.172.17.22
> edge-ext.lb.noaa.gov. 30 IN RRSIG A 5 4 30 20110304033622
> 20110225033622 38565 lb.noaa.gov.
> qAGLlVt9kZbwvP9DGodd+a/IHX/l+jY/7Pkk7Pcss4nuaKEL01H5TmsF
> 37CPDz8oaSHSX0PnVz7aMh3LDAjyEupgF7Rcqh0eu+9bQQBy8D+/h4LI
> 7Zrqa+t2Km4Ummx6Xn3miHqHHFyheMlMvUKXzdQZRvwrMYYkAPHYDFU/
> RB23/jRb5ng5tHvyuFz2rp5TjL4j1wJbusHKkwa9EHJPEjmPPTufNz6/
> aVM69UN/sIjwhr/JMjonwLswk/5+PUu4FieOl6ot6d/8HPn9/x5uad+N
> uKY9v0RV7pDvqnUyR0rR+vWCHu5TGVc/8MKNRmdToNmGQNEFXGxxn1sB Fh6Djg==
>
> ;; AUTHORITY SECTION:
> lb.noaa.gov. 86400 IN NS ns-mw.noaa.gov.
> lb.noaa.gov. 86400 IN NS ns-nw.noaa.gov.
> lb.noaa.gov. 86400 IN NS ns-e.noaa.gov.
> lb.noaa.gov. 86400 IN RRSIG NS 5 3 86400 20110304033622
> 20110225033622 38565 lb.noaa.gov.
> MWFCzQO4u74tqr7lxAuzT5LEEZPl45BHabC5ftC96Ufd8GB7n/AqOppT
> kO01bwAZBt30FBGShq1R+wc0nPFlLzJE5flyvA5dJwlF6jDh5fL9xt80
> UFEwlGdS/ogPeKdgNKrIMQ+VlMn5sd3rhaff9+rfIH3Bx38B8pZiQt5q
> Ii+vll/ASbHiLO91G6b6Ht8XoWn2y/jwQVAhApCI8DMswISqUZcQVoix
> V9OllJowlvuEJx/lFZYHjMibnHEZsSLr+mccMvB0tt46fdm3u7aDsUHr
> OrTLG6bh60AnyYtb+zExc2odyzlEx+AE+U72HWn7fhHg7HRbiXzYvfcZ x5yrOw==
>
> ;; ADDITIONAL SECTION:
> ns-e.noaa.gov. 86400 IN A 140.90.33.237
> ns-mw.noaa.gov. 86400 IN A 140.172.17.237
> ns-nw.noaa.gov. 86400 IN A 161.55.32.2
>
> ;; Query time: 55 msec
> ;; SERVER: 140.172.17.237#53(140.172.17.237)
> ;; WHEN: Thu Feb 24 22:36:56 2011
> ;; MSG SIZE rcvd: 1164
>
> root at nagios:/etc/cron.hourly#
>
> -----Original Message-----
> From: Mark Andrews [mailto:marka at isc.org]
> Sent: Thursday, February 24, 2011 7:27 PM
> To: frnkblk at iname.com
> Cc: dns-operations at dns-oarc.net
> Subject: Re: [dns-operations] EDNS issue
>
>
> In message <006d01cbd482$d54e5a30$7feb0e90$@iname.com>, "Frank Bulk" writes:
> > Our ISP helpdesk has been receiving a lot of complaints about their
> > inability to check the weather weather.gov, specifically,
> > forecast.weather.gov. Some digs showed that queries were failing, and my
> > BIND logs show the same:
>
> Make sure you can receive fragmented UDP responses. The servers
> are sending good reponses.
>
> ;; Query time: 201 msec
> ;; SERVER: 140.172.17.237#53(ns-mw.noaa.gov)
> ;; WHEN: Fri Feb 25 12:17:01 2011
> ;; MSG SIZE rcvd: 2052
>
> Try the following two queries. The first response will be fragmented
> and the second shouldn't be fragmented.
>
> dig @140.172.17.237 +dnssec forecast.weather.gov
> dig @140.172.17.237 +dnssec forecast.weather.gov +bufsize=1400
>
> Mark
>
> > Feb 24 18:25:12 10.20.0.100 named[2603]: too many timeouts resolving
> > 'forecast.weather.gov/A' (in 'weather.gov'?): disabling EDNS
> > Feb 24 18:25:36 199.120.69.22 named[5289]: success resolving
> > 'forecast.weather.gov/A' (in 'weather.gov'?) after reducing the advertised
> > EDNS UDP packet size to 512 octets
> > Feb 24 18:25:37 10.20.0.200 named[2583]: success resolving
> > 'forecast.weather.gov/A' (in 'weather.gov'?) after reducing the advertised
> > EDNS UDP packet size to 512 octets
> > Feb 24 18:25:38 10.20.0.100 named[2603]: too many timeouts resolving
> > 'forecast.weather.gov/A' (in 'weather.gov'?): disabling EDNS
> > Feb 24 18:25:39 199.120.69.22 named[5289]: success resolving
> > 'radar.weather.gov/A' (in 'weather.gov'?) after reducing the advertised
> EDNS
> > UDP packet size to 512 octets
> > Feb 24 18:25:40 199.120.69.22 named[5289]: success resolving
> > 'www.weather.gov/A' (in 'weather.gov'?) after reducing the advertised EDNS
> > UDP packet size to 512 octets
> > Feb 24 18:25:42 10.20.0.200 named[2583]: success resolving
> > 'radar.weather.gov/A' (in 'weather.gov'?) after reducing the advertised
> EDNS
> > UDP packet size to 512 octets
> > Feb 24 18:25:42 10.20.0.100 named[2603]: too many timeouts resolving
> > 'radar.weather.gov/A' (in 'weather.gov'?): disabling EDNS
> >
> >
> > A quick check showed the following:
> >
> > mail1:~# dig -4 +short rs.dns-oarc.net txt
> > rst.x1002.rs.dns-oarc.net.
> > rst.x1994.x1002.rs.dns-oarc.net.
> > rst.x2495.x1994.x1002.rs.dns-oarc.net.
> > "Tested at 2011-02-25 00:20:31 UTC"
> > "2607:fe28:0:1003:223:7dff:fe9c:4aa5 sent EDNS buffer size 4096"
> > "2607:fe28:0:1003:223:7dff:fe9c:4aa5 DNS reply size limit is at
> > least 2495"
> > mail1:~#
> > mail1:~# dig forecast.weather.gov
> >
> > ; <<>> DiG 9.3.4-P1.1 <<>> forecast.weather.gov
> > ;; global options: printcmd
> > ;; connection timed out; no servers could be reached
> >
> > Does this make sense? EDNS of size 512 shouldn't be an issue, yet all 7
> > *nix DNS servers (the first one is above) running BIND complain. The
> first
> > four of the DNS servers are behind an old F5 BigIP, the others aren't.
> >
> > root at nagios:/var/log# dig -4 +short rs.dns-oarc.net txt
> > rst.x1002.rs.dns-oarc.net.
> > rst.x1222.x1002.rs.dns-oarc.net.
> > rst.x1403.x1222.x1002.rs.dns-oarc.net.
> > "96.31.0.5 DNS reply size limit is at least 1403"
> > "Tested at 2011-02-25 00:24:38 UTC"
> > "96.31.0.5 sent EDNS buffer size 4096"
> > root at nagios:/var/log#
> > root at nagios:/var/log# dig forecast.weather.gov
> >
> > ; <<>> DiG 9.5.1-P3 <<>> forecast.weather.gov
> > ;; global options: printcmd
> > ;; connection timed out; no servers could be reached
> > root at nagios:/var/log#
> >
> > Any ideas? Querying our corporate Microsoft DNS server, behind a Cisco
> ASA,
> > works fine!
> >
> > Frank Bulk
> >
> > _______________________________________________
> > dns-operations mailing list
> > dns-operations at lists.dns-oarc.net
> > https://lists.dns-oarc.net/mailman/listinfo/dns-operations
> --
> Mark Andrews, ISC
> 1 Seymour St., Dundas Valley, NSW 2117, Australia
> PHONE: +61 2 9871 4742 INTERNET: marka at isc.org
>
--
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742 INTERNET: marka at isc.org
More information about the dns-operations
mailing list