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This document describes how to troubleshoot Linux Based Domain Name Service (DNS) for MediaSense server and other Voice Operating System (VOS) platforms.
Contributed by Mingze Yan, Cisco TAC Engineer.
Cisco recommends that you have knowledge of these topics:
Cisco VOS platform
CentOS used for Linux DNS server
In MediaSense OS admin page, DNS shows unreachable.
Step 1. Run this command utils diagnose test to verify system
Warning: When run this command, you can hit this defect https://bst.cloudapps.cisco.com/bugsearch/bug/CSCuu99832/?referring_site=bugquickviewredir and you must run this command as workaround utils diagnose module validate_network
Step 2. The result of this command shows reverse DNS failed
Starting diagnostic test(s)
test - validate_network : Reverse DNS lookup failed
Step 3. Verfiied Linux DNS setting. First coloum in Linux DNS reverse setting must be the last octet of the server’s IP address.
For example in this case, the IP address of MSA server is x.x.x.25. Reverse DNS entry for it must be
25 IN PTR MSA.Domain
This is original setting :
3 IN PTR CUCM10PUB.Domain.
4 IN PTR CUCM10SUB. Domain.
5 IN PTR CUPS10PUB.Domain.
6 IN PTR CUPS10SUB.Domain.
7 IN PTR UCCXA.Domain
8 IN PTR UCCXB.Domain
9 IN PTR MSA.Domain
10 IN PTR MSB.Domain
Step 4. Re-ran utils diagnose module validate_network, but still got the revese DNS failure
This time, packet capture from the MediaSense server.
run this command to packet capture utils network capture eth0 file newcap count 100000 size all
Run this command utils diagnose module validate_network
Wait until it finishes. Then, press Ctrl + C to stop the capture.
Run this command file list activelog platform/cli/*.cap to save the capture.
Step 5. Use this filter dns and ip.dst==10.66.75.140 or dns and ip.src==10.66.75.140 to find out the packets from DNS server.
In the answer filed, we can see DNS returns hostname + ‘in-addr.arpa’
This causes the reverse DNS fails
Step 6. In Linux DNS setting, after the FQDN, a dot ‘.’ was missed on the non-working entry. After add the dot and restart DNS service, the issue got fixed.
25 IN PTR MSA.Domain .