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Encapsulation of the Ethernet bridge traffic ⇐ ПредыдущаяСтр 10 из 10
Let’s consider the trace of the encapsulated Ethernet traffic, transmitted through the bridges (Bridge Ethernet). As a first example (route 2) let’s present a detailed route of messages 7 and 8 of route 1 containing exchange of messages between the Ethernet bridges (it can be seen from the address source and message receiver).
Route 2 An example of the detailed route of Ethernet bridge traffic via Frame Relay (Sniffer Expert analyzer)
------------------------- Frame 7 -------------------------- DLC: – DLC Header – DLC: DLC: Frame 7 arrived at 17: 54: 38.7894; frame size is 34 bytes. DLC: This frame is dated 2 day(s) after capture started. DLC: Destination =DTE DLC: Source = DCE DLC: FRELAY: – Frame Relay – FRELAY: FRELAY: Address word = 0811 FRELAY: 0000 10.. 0001.... = DLCI 33 FRELAY:......0......... = Response FRELAY:............ 0... = No forward congestion FRELAY:.............0.. = No backward congestion FRELAY:..............0. = Not eligible for discard FRELAY: FRELAY: -- Multiprotocol over Frame Relay – FRELAY: FRELAY: Control, pad(s) = 0300 FRELAY: NLPID = 0x80 (SNAP) FRELAY: SNAP: -- SNAP Header – SNAP: Vendor ID - IEEE 802.1 SNAP: Type = 0007 (802.3/Ethernet) SNAP: ETHER: -- Ethernet Header – ETHER: ETHER: Destination = Station 000000218001 ETHER: Source = Station 000000218002 ETHER: 802.3 length = 10 ETHER: LLC: -- LLC Header – LLC: LLC: DSAP = AA, SSAP = AA, Command, Unnumbered frame: UI LLC: SNAP: -- SNAP Header – SNAP: SNAP: Type = 80FF (Unknown) SNAP: [2 byte s of data] ------------------------- Frame 8 -------------------------- DLC: --DLC Header- DLC: DLC: Frame 8 arrived at 17: 54: 38.9854; frame size is 34 bytes. DLC: This frame is dated 2 day(s) after capture started. DLC: Destination = DTE DLC: Source = DCE DLC: FRELAY: -- Frame Relay – FRELAY: FRELAY: Address word = 04E1 FRELAY: 0000 01.. 1110.... = DLC130 FRELAY:......0......... = Response FRELAY:............ 0... = No forward congestion FRELAY:.............0.. = No backward congestion FRELAY:..............0. = Not eligible for discard FRELAY: FRELAY: -- Multiprotocol over Frame Relay -- FRELAY: FRELAY: Control, pad(s) = 0300 FRELAY: NLPID = 0x80 (SNAP) FRELAY: SNAP: -- SNAP Header – SNAP: SNAP: Vendor ID = IEEE 802.1 SNAP: Type = 0007 (802.3/Ethernet) SNAP: ETHER: -- Ethernet Header -- ETHER: ETHER: Destination = Station 000000208501 ETHER: Source = Station 000000208502 ETHER: 802.3 length = 10 ETHER: LLC: -- LLC Header – LLC: LLC: DSAP = AA, SSAP = AA, Command, Unnumbered frame: UI LLC: SNAP: -- SNAP Header -- SNAP: SNAP: Type = 80FF (Unknown) SNAP: [2 byte(s) of data]
For traffic transmission we use a virtual connection with the DLCI = 33 address; for the encapsulation of traffic - the SNAP protocol with the identification of encapsulated traffic through the OUI (802.1 protocol) into the bridge traffic of Ethernet (full value of OUI = 00 80 C2 on the route is not represented). The value of PID = 00 07 indicates the transfer traffic of Ethernet IEEE 802.3 without the use of FCS (see Fig. 2.1 and 2.2). Decoding of message of a higher level protocol (the Ethernet protocol) shows the presence of a rather small IEEE 802.3 frame in the T1.618 frame. Encapsulated 802.3 frame contains the address of the source and receiver reports (6 octets each), 2 octet field of frame length and the message itself. The report begins with a message header of control of logical link of LLC (Logical Link Control) with the length of 3 octets, containing the addresses of access points to the service source and message receiver (Source Service Access Point Address - SSAP and Destination Service Access Point Address - DSAP, 1 octet each) and control field. Then the title of SNAP and two octets of data go. SNAP protocol is involved in the process of encapsulation twice: once directly to encapsulate and identify a process of encapsulation (NLPID), the second time - to identify information inside the encapsulated message.
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