BroadCast MAC problem

[pankaj kumar]

i have read in cisco press book that broadcast mac is ff:ff:ff:ff:ff:ff but when i apply debug in a router and ping to a network that is no directly connected i found mac as 0000.0000.0000.0000  i have applied static route.

is ff:ff:ff:ff:ff:ff is same as 0000.0000.0000.0000 or what please explain

[Furose M]

can you post the debug results?

[Pedro Lereno · Accepted solution]

Hi,

Are you seeing the destination mac address of the frame, or inside arp request payload?

Here an example:

Frame 1 (42 on wire, 42 captured)
    Arrival Time: Sep 11, 2013 08:33:53.295306000
    Frame Number: 1
    Packet Length: 42 bytes
    Capture Length: 42 bytes
Ethernet II
    Destination: ff:ff:ff:ff:ff:ff (ff:ff:ff:ff:ff:ff)
    Source: 00:01:02:48:52:18 (00:01:02:48:52:18)
    Type: ARP (0x0806)
Address Resolution Protocol (request)
    Hardware type: Ethernet (0x0001)
    Protocol type: IP (0x0800)
    Hardware size: 6
    Protocol size: 4
    Opcode: request (0x0001)
    Sender MAC address: 00:01:02:48:52:18 (00:01:02:48:52:18)
    Sender IP address: 172.16.1.169 (172.16.1.169)
    Target MAC address: 00:00:00:00:00:00 (00:00:00:00:00:00)
    Target IP address: 172.16.1.140 (172.16.1.140)

The “ Target MAC address” inside ARP request payload is 00, because it does not know the destination, but on the ethernet frame the destination is broadcast ff:ff:ff:ff:ff:ff.

If this is not the case send the logs.

Regards,

Pedro Lereno