Red Hat Bugzilla – Bug 230770
Mutiple DNS queries use same DNS transaction ID
Last modified: 2012-06-20 12:12:12 EDT
Description of problem:
Redhat clients make multiple DNS requests under the same Transaction ID number.
This is agains RFCs and our Cisco firewall is stomping on the second request if
the initial query was already responded too.
Version-Release number of selected component (if applicable):
RHEL4 update 4
We use PAM and nss_ldap for LDAP based authentication. If nscd is not running
(we have found it to be unreliable in the past), then the login process triggers
multiple queries for the IP address of our LDAP servers. These queries use
duplicate transaction IDs, causing them to be dropped by our firewall. The
duplicate transaction ID bug should be visible without a firewall, but the login
delays and timeouts caused by dropped queries would not.
Steps to Reproduce:
1.Configure client to use PAM and nss_ldap
3.start packet capture of DNS traffic
4.log in to client
5.stop packet capture
(see attache packet capture)
Packet 307 uses a transaction id of 0x5bd4, and packet 308 is the response with
the same transaction id. Then in packet 361, there is another request with the
same transaction id of 0x5bd4, which the firewall denies since the response was
issued in packet 308. Once the client times out (~5sec) it repeates the query
to the alternate DNS host.
Subsequent DNS queries should use different transaction IDs.
Created attachment 149140 [details]
packet capture showing duplicate DNS transaction ID numbers on repeated queries
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