Ethernet over IP - How does it work ???

Unanswered Question
Jan 31st, 2008
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Hi All,


How does etherip work?


Lets say now that Host 1 sends a packet to Host 2 over the etherip tunnel (btw, they are on seperate LANs), how is the packet built and what does it look like?


Lets say a normal IP packet like the below :-


Frame 9 (614 on wire, 614 captured)

Arrival Time: Apr 10, 2003 20:44:41.831144000

Time delta from previous packet: 0.003858000 seconds

Time relative to first packet: 3.298858000 seconds

Frame Number: 9

Packet Length: 614 bytes

Capture Length: 614 bytes

Ethernet II

Destination: 00:08:02:53:01:a5 (SPLPW236206)

Source: 00:10:f6:a8:18:00 (Cisco_a8:18:00)

Type: IP (0x0800)

Internet Protocol, Src Addr: 192.168.69.1 (192.168.69.1), Dst Addr: SPLPW236206 (192.168.69.100)

Version: 4

Header length: 20 bytes

Differentiated Services Field: 0xc0 (DSCP 0x30: Class Selector 6; ECN: 0x00)

1100 00.. = Differentiated Services Codepoint: Class Selector 6 (0x30)

.... ..0. = ECN-Capable Transport (ECT): 0

.... ...0 = ECN-CE: 0

Total Length: 600

Identification: 0x0002

Flags: 0x00

.0.. = Don't fragment: Not set

..0. = More fragments: Not set

Fragment offset: 0

Time to live: 255

Protocol: TCP (0x06)

Header checksum: 0xad27 (correct)

Source: 192.168.69.1 (192.168.69.1)

Destination: SPLPW236206 (192.168.69.100)

Transmission Control Protocol, Src Port: telnet (23), Dst Port: 2416 (2416), Seq: 2889137939, Ack: 1790722200, Len: 560

Source port: telnet (23)

Destination port: 2416 (2416)

Sequence number: 2889137939

Next sequence number: 2889138499

Acknowledgement number: 1790722200

Header length: 20 bytes

Flags: 0x0010 (ACK)

0... .... = Congestion Window Reduced (CWR): Not set

.0.. .... = ECN-Echo: Not set

..0. .... = Urgent: Not set

...1 .... = Acknowledgment: Set

.... 0... = Push: Not set

.... .0.. = Reset: Not set

.... ..0. = Syn: Not set

.... ...0 = Fin: Not set

Window size: 4128

Checksum: 0xc63c (correct)

Telnet

Data: \r\n

Data: \r\n

Data: Arsenal are the best team in the World



Now, if it was encap'd in etherip, would it take the entire packet, and put another IP header on it AND new ethernet header?


Does anyone have an etherip packet decode I can look at or a good dosument to show exactly what happens?


Many thx indeed,

Ken

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Jon Marshall Thu, 01/31/2008 - 06:23
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Ken


Slightly off topic.


Arsenal are not the best team in the World - that would be Man U :)


Jon

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