Why nslookup doesn't use mdns while ping do?

In dnsmasq.conf:

address=/local/127.0.0.1

In resolv.conf:

# Generated by NetworkManager
domain example.com
search example.com
nameserver 127.0.0.1
nameserver 10.66.127.17
nameserver 10.68.5.26

I can use nslookup:

# nslookup www.local
Server:     127.0.0.1
Address:    127.0.0.1#53

Name:   www.local
Address: 127.0.0.1

But I can't use ping:

# ping www.local
ping: unknown host www.local

I use tcpdump to capture lo while pinging www.local, no packets, while packets like

# tcpdump -i em1 -n | grep local

tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on em1, link-type EN10MB (Ethernet), capture size 65535 bytes
20:14:38.189335 IP 10.66.65.188.mdns > 224.0.0.251.mdns: 0 A (QM)? www.local. (27)
20:14:39.190700 IP 10.66.65.188.mdns > 224.0.0.251.mdns: 0 A (QM)? www.local. (27)
20:14:41.192979 IP 10.66.65.188.mdns > 224.0.0.251.mdns: 0 A (QM)? www.local. (27)

appeared from physical interface.

Which means ping is using mdns, but why nslookup doesn't use mdns? Why ping won't use normal dns when mdns doesn't return useful falue?

Thanks.

Solution 1:

ping use glibc's name resolution system, called Name Service Switch. This uses the /etc/nsswitch.conf file to know where to look for in order to resolve a name to an IP. The hosts: line in this file represents an order of preference for each service. For exemple, files represent the local /etc/hosts file, dns uses the /etc/resolv.conf file to contact a DNS server, and mdns uses mdns.

However, nslookup doesn't use it. It talks directly to the DNS server specified in /etc/resolv.conf and so can't use mdns.

But I can't answer your last question. If you have both mdns and dns in /etc/nsswitch.conf, even with mdns first, it should firstly try to resolve the name with mdns, then if no answer use dns.

Solution 2:

It's very simple - nslookup is specifically a DNS tool - it's part of the BIND tools.

It simply doesn't know about the other name services that library calls such as gethostbyname can access via NSS because nslookup doesn't use gethostbyname, etc.