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Posted to common-issues@hadoop.apache.org by GitBox <gi...@apache.org> on 2022/01/27 03:23:27 UTC
[GitHub] [hadoop] eubnara commented on pull request #3935: HADOOP-18087. fix bugs when looking up record from upstream DNS servers.
eubnara commented on pull request #3935:
URL: https://github.com/apache/hadoop/pull/3935#issuecomment-1022811323
It fixes:
- add missing chained CNAME records
- e.g. when querying `repo.maven.apache.org.` for A record, chained CNAME records should be in answer section.
```
❯ dig @8.8.8.8 repo.maven.apache.org
; <<>> DiG 9.16.1-Ubuntu <<>> @8.8.8.8 repo.maven.apache.org
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 65465
;; flags: qr rd ra; QUERY: 1, ANSWER: 4, AUTHORITY: 0, ADDITIONAL: 1
;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 512
;; QUESTION SECTION:
;repo.maven.apache.org. IN A
;; ANSWER SECTION:
repo.maven.apache.org. 20102 IN CNAME repo.apache.maven.org.
repo.apache.maven.org. 21178 IN CNAME maven.map.fastly.net.
maven.map.fastly.net. 4 IN A 199.232.192.215
maven.map.fastly.net. 4 IN A 199.232.196.215
;; Query time: 148 msec
;; SERVER: 8.8.8.8#53(8.8.8.8)
;; WHEN: 목 1월 27 12:18:39 KST 2022
;; MSG SIZE rcvd: 148
```
- distinguish between NXDOMAIN and NOERROR + empty answer from upstream DNS server
- e.g. when querying `repo.maven.apache.org.` for AAAA record, it should respond `NOERROR` with empty answer not `NXDOMAIN` because A record exists even though AAAA record does not exist.
- Please note that `status: NOERROR` in result of `dig` command.
```
❯ dig @8.8.8.8 repo.maven.apache.org AAAA
; <<>> DiG 9.16.1-Ubuntu <<>> @8.8.8.8 repo.maven.apache.org AAAA
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 5782
;; flags: qr rd ra; QUERY: 1, ANSWER: 2, AUTHORITY: 1, ADDITIONAL: 1
;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 512
;; QUESTION SECTION:
;repo.maven.apache.org. IN AAAA
;; ANSWER SECTION:
repo.maven.apache.org. 21161 IN CNAME repo.apache.maven.org.
repo.apache.maven.org. 20107 IN CNAME maven.map.fastly.net.
;; AUTHORITY SECTION:
fastly.net. 30 IN SOA ns1.fastly.net. hostmaster.fastly.com. 2017052201 3600 600 604800 30
;; Query time: 164 msec
;; SERVER: 8.8.8.8#53(8.8.8.8)
;; WHEN: 목 1월 27 12:20:47 KST 2022
;; MSG SIZE rcvd: 177
```
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