Red Hat Bugzilla – Bug 981751
[RFE] No option to specify IPv6 or IPv4 explicitly must be used
Last modified: 2016-08-16 07:32:07 EDT
telnet is a very useful low level utility for debugging connections to mail or webservers or other such plain text services.
A lot of services such as ping and traceroute offer means of forcing either IPv4 or IPv6. EG with traceroute you can add a -4 for explicit IPv4 or -6 or explicit IPv6 against a host. Or you can use traceroute6
Telnet doesn't offer that option so if I wanted to test to see if a mail server was working correctly with IPv6 there is no way I can force it to use IPv6.
EG: I want to test the if the MX for the skymesh.com.au domain are accepting mail on IPv6 I would do the following:
$ dig skymesh.com.au mx
And get a list of MX records:
;; ANSWER SECTION:
skymesh.com.au. 70 IN MX 500 mx1.skymesh.com.au.
skymesh.com.au. 70 IN MX 500 mx1.skymesh.net.au.
skymesh.com.au. 70 IN MX 500 mx2.skymesh.com.au.
skymesh.com.au. 70 IN MX 500 mx2.skymesh.net.au.
skymesh.com.au. 70 IN MX 500 mx3.skymesh.com.au.
skymesh.com.au. 70 IN MX 500 mx3.skymesh.net.au.
skymesh.com.au. 70 IN MX 500 mx4.skymesh.com.au.
skymesh.com.au. 70 IN MX 500 mx4.skymesh.net.au.
skymesh.com.au. 70 IN MX 500 mx5.skymesh.com.au.
And we find that mx1, mx2 and mx3 have IPv6 records
;; ADDITIONAL SECTION:
mx2.skymesh.com.au. 71 IN A 18.104.22.168
mx2.skymesh.com.au. 73 IN AAAA 2401:a400:100:dead::cafe:2
mx3.skymesh.com.au. 74 IN A 22.214.171.124
mx3.skymesh.com.au. 74 IN AAAA 2401:a400:100:dead::cafe:3
mx4.skymesh.com.au. 76 IN A 126.96.36.199
mx5.skymesh.com.au. 81 IN A 188.8.131.52
mx1.skymesh.com.au. 81 IN A 184.108.40.206
mx1.skymesh.com.au. 82 IN AAAA 2401:a400:100:dead::cafe:1
But I can't force IPv6:
$ telnet mx2.skymesh.com.au 25
Connected to mx2.skymesh.com.au.
Escape character is '^]'.
220 mx2.skymesh.com.au ESMTP (Debian/GNU)
I could try the IPv6 address directly:
$ telnet 2401:a400:100:dead::cafe:2 25
telnet: connect to address 2401:a400:100:dead::cafe:2: Network is unreachable
but in the case of testing something like a virtual http host we need to be able to actually specify the proper FQDN.
This request was evaluated by Red Hat Product Management for
inclusion in the current release of Red Hat Enterprise Linux.
Because the affected component is not scheduled to be updated
in the current release, Red Hat is unable to address this
request at this time.
Red Hat invites you to ask your support representative to
propose this request, if appropriate, in the next release of
Red Hat Enterprise Linux.
Cloning against Fedora. Let's resolve it there first and then we can consider backporting for RHEL.
Red Hat Enterprise Linux version 6 is entering the Production 2 phase of its
lifetime and this bug doesn't meet the criteria for it, i.e. only high severity
issues will be fixed. Please see
https://access.redhat.com/support/policy/updates/errata/ for further
This issue is tracked as a bug #1367415 in Red Hat
Enterprise Linux version 7.