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New Member

BroadCast MAC problem

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

1 ACCEPTED SOLUTION

Accepted Solutions
New Member

BroadCast MAC problem

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

2 REPLIES
Cisco Employee

BroadCast MAC problem

can you post the debug results?

New Member

BroadCast MAC problem

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

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