Re: Ethernet Frame Header - Trailer (Variable Length)

kfarrington · ‎11-10-2005

All,

I have four frames below (captured using ethereal) and would like to know what the trailer in the L2 frame is?

Is it just to pad the packet to the minimum ethernet frame length?

Many kind regards in advance,

Ken

Trailer 6 bytes

Frame 102 (60 bytes on wire, 60 bytes captured)

Arrival Time: Jul 16, 2003 06:36:44.412671000

Time delta from previous packet: 0.139895000 seconds

Time since reference or first frame: 2.674510000 seconds

Frame Number: 102

Packet Length: 60 bytes

Capture Length: 60 bytes

Ethernet II, Src: 00:02:a5:34:03:86, Dst: 00:50:8b:fd:d7:54

Destination: 00:50:8b:fd:d7:54 (CompaqCo_fd:d7:54)

Source: 00:02:a5:34:03:86 (30.42.101.39)

Type: IP (0x0800)

Trailer: 000000000000

Internet Protocol,

Trailer (lots of bytes)

Frame 113 (60 bytes on wire, 60 bytes captured)

Arrival Time: Jul 16, 2003 06:36:44.689337000

Time delta from previous packet: 0.071447000 seconds

Time since reference or first frame: 2.951176000 seconds

Frame Number: 113

Packet Length: 60 bytes

Capture Length: 60 bytes

Ethernet II, Src: 00:02:a5:34:b2:33, Dst: ff:ff:ff:ff:ff:ff

Destination: ff:ff:ff:ff:ff:ff (Broadcast)

Source: 00:02:a5:34:b2:33 (30.42.101.43)

Type: ARP (0x0806)

Trailer: 00000000000000000000000000000000...

Address Resolution Protocol (request)

Trailer 3 bytes

Frame 139 (60 bytes on wire, 60 bytes captured)

Arrival Time: Jul 16, 2003 06:36:45.230010000

Time delta from previous packet: 0.007420000 seconds

Time since reference or first frame: 3.491849000 seconds

Frame Number: 139

Packet Length: 60 bytes

Capture Length: 60 bytes

Ethernet II, Src: 00:b0:c2:d1:b7:fc, Dst: 00:50:8b:fd:d7:54

Destination: 00:50:8b:fd:d7:54 (CompaqCo_fd:d7:54)

Source: 00:b0:c2:d1:b7:fc (Cisco_d1:b7:fc)

Type: IP (0x0800)

Trailer: 000000

Trailer 5 bytes

Frame 175 (60 bytes on wire, 60 bytes captured)

Arrival Time: Jul 16, 2003 06:36:46.134412000

Time delta from previous packet: 0.000769000 seconds

Time since reference or first frame: 4.396251000 seconds

Frame Number: 175

Packet Length: 60 bytes

Capture Length: 60 bytes

Ethernet II, Src: 00:b0:c2:d1:b7:fc, Dst: 00:50:8b:fd:d7:54

Destination: 00:50:8b:fd:d7:54 (CompaqCo_fd:d7:54)

Source: 00:b0:c2:d1:b7:fc (Cisco_d1:b7:fc)

Type: IP (0x0800)

Trailer: 0000000000

Internet Protocol,

wdrootz · ‎11-16-2005

Trailer is like a label negotiated between the routers for specific packet along with CRC and the Trailer will be different according to the packet size.

kfarrington · ‎11-17-2005

Thats great. Many thx for the info. I am just wondering is this protocol field and contents is documented anywhere?

Do you have any idea about this?

Many kind regards,

Ken