Bug 997271 - ipcalc does not understand RFC3021
ipcalc does not understand RFC3021
Product: Red Hat Enterprise Linux 6
Classification: Red Hat
Component: initscripts (Show other bugs)
All Linux
unspecified Severity low
: rc
: ---
Assigned To: Lukáš Nykrýn
Jan Ščotka
Depends On:
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Reported: 2013-08-15 02:44 EDT by Telford Tendys
Modified: 2016-11-25 07:56 EST (History)
3 users (show)

See Also:
Fixed In Version: initscripts-9.03.47-1.el6
Doc Type: Bug Fix
Doc Text:
Cause: ipcalc did not know about rfc3021 Consequence: Broadcast address was not computed correctly Fix: We have taught ipcalc that rfc3021 exists. Result: Broadcast address should be now correct.
Story Points: ---
Clone Of:
Last Closed: 2015-07-22 03:18:18 EDT
Type: Bug
Regression: ---
Mount Type: ---
Documentation: ---
Verified Versions:
Category: ---
oVirt Team: ---
RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: ---

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Description Telford Tendys 2013-08-15 02:44:43 EDT
Description of problem:

Broadcast address is wrong for /31 networks, this will cause misconfiguration of ethernet devices.

Version-Release number of selected component (if applicable):


How reproducible: Always

Steps to Reproduce:

ipcalc -b

Actual results:


Expected results:


Additional info:

[root@fmc ~]# cat /etc/sysconfig/network-scripts/ifcfg-eth1

Note that "BROADCAST=" needs to be manually inserted if you want your ethernet configured correctly, actually it should not require that because the correct result is well defined already.

[root@fmc ~]# strace -o /tmp/fff -f  /sbin/ifup  eth1
[root@fmc ~]# fgrep ipcalc /tmp/fff
9100  execve("/bin/ipcalc", ["/bin/ipcalc", "--prefix", "", ""], [/* 18 vars */]) = 0
9101  execve("/bin/ipcalc", ["/bin/ipcalc", "--broadcast", "", ""], [/* 18 vars */]) = 0
9106  execve("/bin/ipcalc", ["/bin/ipcalc", "--network", "", ""], [/* 18 vars */]) = 0

You can see the script depends on ipcalc to get the answer right... and so it should get the answer right.
Comment 1 Telford Tendys 2013-08-15 02:45:54 EDT
Comment 3 Lukáš Nykrýn 2013-08-26 06:43:48 EDT
Can you please try this patch:
diff --git a/src/ipcalc.c b/src/ipcalc.c
index 7316f05..416180b 100644
--- a/src/ipcalc.c
+++ b/src/ipcalc.c
@@ -141,7 +141,11 @@ struct in_addr calc_broadcast(struct in_addr addr, int prefix)
     struct in_addr broadcast;
     memset(&broadcast, 0, sizeof(broadcast));
-    broadcast.s_addr = (addr.s_addr & mask.s_addr) | ~mask.s_addr;
+    if (mask.s_addr ==  htonl(0xFFFFFFFE))
+        broadcast.s_addr = htonl(0xFFFFFFFF);
+    else
+        broadcast.s_addr = (addr.s_addr & mask.s_addr) | ~mask.s_addr;
     return broadcast;
Comment 4 Telford Tendys 2013-09-02 01:28:37 EDT
I replied to the Bugzilla email, but does not seem to have updated...

Yes the above patch worked for me (I tested by rebuilding SRPM). May I suggest a one-line comment in the source code mentioning RFC3021 (so people can find a reference explaining why it works that way, also in case anyone in future greps out the code looking for the RFC number) ?
Comment 10 errata-xmlrpc 2015-07-22 03:18:18 EDT
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.


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