Bug 1953097 - CoreDNS resolution failure for external hostnames with "A: dns: overflow unpacking uint16"
Summary: CoreDNS resolution failure for external hostnames with "A: dns: overflow unpa...
Alias: None
Product: OpenShift Container Platform
Classification: Red Hat
Component: Networking
Version: 4.5
Hardware: x86_64
OS: Linux
Target Milestone: ---
: 4.7.z
Assignee: Stephen Greene
QA Contact: jechen
Depends On: 1949361
Blocks: 1955632
TreeView+ depends on / blocked
Reported: 2021-04-23 20:50 UTC by Stephen Greene
Modified: 2022-11-09 06:12 UTC (History)
12 users (show)

Fixed In Version:
Doc Type: Bug Fix
Doc Text:
Cause: Cluster upstream resolver returns DNS response that exceeds 512 bytes via UDP. Consequence: CoreDNS may return SERVFAIL and or log various error messages, sometimes forcing the client to retry over TCP. Fix: Enable the CoreDNS bufisze plugin with a UDP buffer size of 1232 bytes. Result: CoreDNS is less likely to return SERVFAIL or present any runtime errors when handling large DNS responses via UDP. Also, UDP packet fragmentation is less likely to occur.
Clone Of: 1949361
: 1955632 (view as bug list)
Last Closed: 2021-05-19 15:16:26 UTC
Target Upstream Version:

Attachments (Terms of Use)

System ID Private Priority Status Summary Last Updated
Github openshift cluster-dns-operator pull 267 0 None open [release-4.7] Bug 1953097: Corefile: Enable bufsize plugin for all servers 2021-04-26 13:36:57 UTC
Red Hat Product Errata RHBA-2021:1550 0 None None None 2021-05-19 15:16:49 UTC

Comment 4 jechen 2021-05-03 15:23:37 UTC
Verified in 4.7.0-0.nightly-2021-05-01-081439

$ oc get clusterversions.config.openshift.io 
NAME      VERSION                             AVAILABLE   PROGRESSING   SINCE   STATUS
version   4.7.0-0.nightly-2021-05-01-081439   True        False         2m26s   Cluster version is 4.7.0-0.nightly-2021-05-01-081439

# verified bufsize in default DNS
[jechen@jechen ~]$ oc -n openshift-dns get cm/dns-default -oyaml
apiVersion: v1
  Corefile: |
    .:5353 {
        bufsize 1232              <-- verified fix by https://github.com/openshift/cluster-dns-operator/pull/267
        health {
            lameduck 20s

# created a test pod as custom DNS server, added custom forwarding into coreDNS, verified bufsize in custom DNS
$ oc create -f https://raw.githubusercontent.com/lihongan/test-dnsmasq/master/test-dnsmasq.json 
pod/test-dnsmasq created

$ oc get pod -owide
NAME           READY   STATUS    RESTARTS   AGE   IP            NODE                                       NOMINATED NODE   READINESS GATES
test-dnsmasq   1/1     Running   0          58s   ci-ln-0bskzdt-f76d1-fptks-worker-b-rk66z   <none>           <none>

$ oc edit dns.operator/default 
  - forwardPlugin:
    name: test
    - mytest.ocp

$ oc get cm dns-default -n openshift-dns -o yaml
apiVersion: v1
  Corefile: |
    # test
    mytest.ocp:5353 {
        forward .
        bufsize 1232                    <-- verified fix by https://github.com/openshift/cluster-dns-operator/pull/267
    .:5353 {
        bufsize 1232                    <-- verified fix by https://github.com/openshift/cluster-dns-operator/pull/267
        health {
            lameduck 20s

Comment 5 Siddharth Sharma 2021-05-10 17:59:31 UTC
This bug will be shipped as part of next z-stream release 4.7.11 on May 19th, as 4.7.10 was dropped due to a blocker https://bugzilla.redhat.com/show_bug.cgi?id=1958518.

Comment 9 errata-xmlrpc 2021-05-19 15:16:26 UTC
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory (OpenShift Container Platform 4.7.11 bug fix update), and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.


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