How to debug intermittent name resolution failures on a Debian Stretch machine?
When it does not work: % dig +trace github.com ; <<>> DiG 9.10.3-P4-Debian <<>> +trace github.com ;; global options: +cmd ;; connection timed out; no servers could be reached When it works % dig +trace github.com ; <<>> DiG 9.10.3-P4-Debian <<>> +trace github.com ;; global options: +cmd . 139521 IN NS g.root-servers.net. . 139521 IN NS f.root-servers.net. . 139521 IN NS c.root-servers.net. . 139521 IN NS d.root-servers.net. . 139521 IN NS j.root-servers.net. . 139521 IN NS m.root-servers.net. . 139521 IN NS i.root-servers.net. . 139521 IN NS e.root-servers.net. . 139521 IN NS k.root-servers.net. . 139521 IN NS l.root-servers.net. . 139521 IN NS h.root-servers.net. . 139521 IN NS a.root-servers.net. . 139521 IN NS b.root-servers.net. . 139521 IN RRSIG NS 8 0 518400 20190108050000 20181226040000 2134 . FRQBGgylQysK4zZxEMLZPGakdSzurTVRPYbxqNMUOx/PgD6k6sCIQF1X Wy+VfUunSSrcI5zOA1uZYK+3Aji8dRqbXGZX/queVWSO3fa8+I5OjNHb SF44MNhHyw2+brYhc2ilM9LayT+KFDjIOwtx2ZOSem4XpBQoYqoJIUso FEsqEYrNEkCNdWEHaEZS+zbt9lScf1JPNGHcN/ySyVP0z2PEO3ciS5o8 lbhwtJvhkDCYtpMmZHkqpjZRWTIB+oONAS+Z6uVhujDHBVi8WU/uuGnL uduqu361+Z7bmQW+SpQ+qjkpZTbiwDlvx75PzHT0O5Ip0Vtnpvc9tMFr q4ShtA== ;; Received 525 bytes from 8.8.8.8#53(8.8.8.8) in 11 ms com. 172800 IN NS a.gtld-servers.net. com. 172800 IN NS b.gtld-servers.net. com. 172800 IN NS c.gtld-servers.net. com. 172800 IN NS d.gtld-servers.net. com. 172800 IN NS e.gtld-servers.net. com. 172800 IN NS f.gtld-servers.net. com. 172800 IN NS g.gtld-servers.net. com. 172800 IN NS h.gtld-servers.net. com. 172800 IN NS i.gtld-servers.net. com. 172800 IN NS j.gtld-servers.net. com. 172800 IN NS k.gtld-servers.net. com. 172800 IN NS l.gtld-servers.net. com. 172800 IN NS m.gtld-servers.net. com. 86400 IN DS 30909 8 2 E2D3C916F6DEEAC73294E8268FB5885044A833FC5459588F4A9184CF C41A5766 com. 86400 IN RRSIG DS 8 1 86400 20190109190000 20181227180000 2134 . VIX0wchjf73XwDh8x23kN2KTC0FxlPu0tEfNwpszCSvtf31FnvVdi8cx Jp8/GigmCX/vX3iytRZQtjM/SbZYDc9dQLr628IP6bEDG0iTzKZyYuuk ehoEYuIGKVZvPbQYxLtDK2dRZSbU88YcwJXVzpwLifc4vpZkvidq6PHM QXAnIayiejL5cxrfPWhei1tyW4OX1rTBQvtZ7CQ8Bd3GR3RAMwqZdDK4 vPdfHDv+NgNVOvP2+8+7LYMRUkl3+BfZvnLMbmM1wxn/kJ/tNmfdUKih jnyIziZX15MnrDpa4fiLyTpE351TO2ZNwXmddcGFHbmguaNCxZk6GSTj 1ANl5Q== ;; Received 1170 bytes from 199.7.83.42#53(l.root-servers.net) in 78 ms github.com. 172800 IN NS ns1.p16.dynect.net. github.com. 172800 IN NS ns3.p16.dynect.net. github.com. 172800 IN NS ns2.p16.dynect.net. github.com. 172800 IN NS ns4.p16.dynect.net. github.com. 172800 IN NS ns-520.awsdns-01.net. github.com. 172800 IN NS ns-421.awsdns-52.com. github.com. 172800 IN NS ns-1707.awsdns-21.co.uk. github.com. 172800 IN NS ns-1283.awsdns-32.org. CK0POJMG874LJREF7EFN8430QVIT8BSM.com. 86400 IN NSEC3 1 1 0 - CK0Q1GIN43N1ARRC9OSM6QPQR81H5M9A NS SOA RRSIG DNSKEY NSEC3PARAM CK0POJMG874LJREF7EFN8430QVIT8BSM.com. 86400 IN RRSIG NSEC3 8 2 86400 20190103054632 20181227043632 37490 com. KdNZS7+gu74UyGr9N/WHOjxGk6lc5i8ENAJQfBEoWUVHWUyimNDVwhXf kWLP5KFYrtTD3ttkUZqi2SKHa342XgS0+ZuxYqomAXY8lZyDEvySKKY+ 09quOmPHqrv6PCo+mRsrR6wOHqiTD8G2E+wvxIUvZq/6WuliibnvVPLp SDg= 4KB3QDAGSO6KO9JK2O5F2FO8F4C5FTA2.com. 86400 IN NSEC3 1 1 0 - 4KB4PTQQ5CTA7POCTGM7RUFC8B1RKTEU NS DS RRSIG 4KB3QDAGSO6KO9JK2O5F2FO8F4C5FTA2.com. 86400 IN RRSIG NSEC3 8 2 86400 20181231051755 20181224040755 37490 com. RidH3Du0PQ8UJTkN4iKk3pI/iShNZywXuFeihaf4smZF8A4xQ29jfFeh ADpk5peLKDOBGjML0rLQlgB8u8+bMLRLBsBX9lEk6id159AQ+3kvnCXT 2Ds4FXJitUd2QtBw/BAiVzeVkLAKUL92yy73gZtn7el82r/YhNfHsJin YiU= ;; Received 840 bytes from 192.5.6.30#53(a.gtld-servers.net) in 199 ms github.com. 60 IN A 192.30.253.113 github.com. 60 IN A 192.30.253.112 github.com. 900 IN NS ns1.p16.dynect.net. github.com. 900 IN NS ns-421.awsdns-52.com. github.com. 900 IN NS ns-1283.awsdns-32.org. github.com. 900 IN NS ns4.p16.dynect.net. github.com. 900 IN NS ns-520.awsdns-01.net. github.com. 900 IN NS ns3.p16.dynect.net. github.com. 900 IN NS ns2.p16.dynect.net. github.com. 900 IN NS ns-1707.awsdns-21.co.uk. ;; Received 291 bytes from 204.13.250.16#53(ns2.p16.dynect.net) in 9 ms Machine configuration: % cat /etc/hosts 127.0.0.1 localhost ::1 localhost ip6-localhost ip6-loopback ff02::1 ip6-allnodes ff02::2 ip6-allrouters 127.0.1.1 mercury.localdomain mercury % cat /etc/nsswitch.conf # /etc/nsswitch.conf # # Example configuration of GNU Name Service Switch functionality. # If you have the `glibc-doc-reference' and `info' packages installed, try: # `info libc "Name Service Switch"' for information about this file. passwd: compat group: compat shadow: compat gshadow: files hosts: files dns networks: files protocols: db files services: db files ethers: db files rpc: db files netgroup: nis % uname -a Linux mercury 4.9.0-8-amd64 #1 SMP Debian 4.9.130-2 (2018-10-27) x86_64 GNU/Linux % cat /etc/resolv.conf nameserver 8.8.8.8 nameserver 8.8.4.4 Any ideas/suggestions/comments on how to debug this? thanks raju -- Kamaraju S Kusumanchi | http://raju.shoutwiki.com/wiki/Blog
