https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=252596
Bug ID: 252596
Summary: ping to 255.255.255.255 does not set broadcast MAC
Product: Base System
Version: CURRENT
Hardware: amd64
OS: Any
Status: New
Severity: Affects Many People
Priority: ---
Component: kern
Assignee: b...@freebsd.org
Reporter: jcap...@blackberry.com
Summary: When pinging the ip address 255.255.255.255, the MAC address should be
set to the broadcast address.
Description:
I narrowed this down to sys/netinet/ip_output.c where it looks like the
decision about whether to set M_BCAST is happening on line 505 for this case:
isbroadcast = in_ifaddr_broadcast(gw->sin_addr, ia);
It looks like in_ifaddr_broadcast is only checking whether the address is the
same as the interface broadcast (e.g. 192.168.122.255), but not
255.255.255.255.
If I ping 192.168.122.255, then I get the expected MAC broadcast address.
Actual results:
--------------
tcpdump -vvvv -xx -ni em0 icmp &
ping -nc 1 255.255.255.255
root@bsd-vbox:/home/jcaplan # tcpdump -vvvv -xx -ni em0 icmp &
[1] 5429
root@bsd-vbox:/home/jcaplan # tcpdump: listening on em0, link-type EN10MB
(Ethernet), capture size 262144 bytes
root@bsd-vbox:/home/jcaplan # ping -nc 1 255.255.255.255
PING 255.255.255.255 (255.255.255.255): 56 data bytes
02:01:55.895257 IP (tos 0x0, ttl 64, id 46687, offset 0, flags [none], proto
ICMP (1), length 84)
192.168.1.32 > 255.255.255.255: ICMP echo request, id 13845, seq 0, length
64
0x0000: 3c37 862c 1f63 0800 27b8 57c0 0800 4500
Note the first six bytes are not 0xff.
Expected Results:
----------------
root@bsd-vbox:/home/jcaplan # tcpdump -vvvv -xx -ni em0 icmp &
[1] 5429
root@bsd-vbox:/home/jcaplan # tcpdump: listening on em0, link-type EN10MB
(Ethernet), capture size 262144 bytes
root@bsd-vbox:/home/jcaplan # ping -nc 1 255.255.255.255
PING 255.255.255.255 (255.255.255.255): 56 data bytes
02:01:55.895257 IP (tos 0x0, ttl 64, id 46687, offset 0, flags [none], proto
ICMP (1), length 84)
192.168.1.32 > 255.255.255.255: ICMP echo request, id 13845, seq 0, length
64
0x0000: ffff ffff ffff 0800 27b8 57c0 0800 4500
Note the first 6 bytes are 0xff.
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