清華大學 計算機網路 第4週小考

(+5)	(5%) Assume a bridge B receives a frame from port x, with destination MAC address “D” and source MAC address “S”. Which of the following statements about frame forwarding and address learning is NOT correct ? ( 單選)
		(a) The bridge will forward the frame to port y, if D is found in the Filtering database and D belongs to port y.
		(b) The bridge will broadcast the frame to all ports belong to the spanning tree, except port x, if D is not found in the Filtering database.
		(c) The bridge will filter the frame if D is found in the Filtering database and D belongs to port x.
		(d) The bridge will filter the frame if D is not found in the Filtering database.
		(e) The bridge will learn that S belongs to port x.

(+10)	(10%)  Assume a bridge B receives a frame from port x, with destination MAC address “D” and source MAC address “S”. Let R = (MAC address, port, timer) be a record in the Filtering database, where timer (in seconds) is the duration this record existed (initially, timer = 0). Which of the following statements about “MAC address learning” are correct ?(多選)
		(a) The bridge will add a new record of R = (D,x,0) to the Filtering database if D is not found in the Filtering database.
		(b) The bridge will add a new record of R = (S,x,0) to the Filtering database if S is not found in the Filtering database.
		(c) If a record R = (S, y, 20) already existed in the Filtering database, then the bridge will update the record to (S, x, 0).
		(d) The bridge will add a new record of R = (S,y,0) to the Filtering database if S is not found in the Filtering database and D is found in the Filtering database with port y.
		(e) If a record R = (S, x, 20) already existed in the Filtering database, then the bridge will update the record to (S, x, 0).

(+15)	(15％) Consider the following BLAN configuration. Initially, assume the Filtering databases are empty. Fill in each entry (using an integer to present a port number) in the following table after the following five transmissions. Use integer “0” to indicate if a station is not learned in the corresponding filtering database. (1) Station A transmits a frame to station E (2) Station B transmits a frame to station C (3) Station C transmits a frame to station A (4) Station D transmits a frame to station B (5) Station E transmits a frame to station D Station Port Number of Filterning Database X Port Number of Filterning Database Y Port Number of Filterning Database Z A (A) (F) (K) B (B) (G) (L) C (C) (H) (M) D (D) (I) (N) E (E) (J) (O)
	(A)	ANS:1
	(B)	ANS:2
	(C)	ANS:2
	(D)	ANS:2
	(E)	ANS:0
	(F)	ANS:2
	(G)	ANS:2
	(H)	ANS:1
	(I)	ANS:3
	(J)	ANS:3
	(K)	ANS:1
	(L)	ANS:1
	(M)	ANS:0
	(N)	ANS:1
	(O)	ANS:2

(+10)	(10%)What is the major feature of the spanning tree constructed by the IEEE 802.1D spanning tree algorithm ?(單選)
		(a)It is a spanning tree that includes the minimum cost path of each pair of LANs
		(b)It is a spanning tree that includes the minimum cost path of each pair of bridges
		(c)It is a minimum delay spanning tree.
		(d)It is a minimum cost spanning tree. Thus, the summation of the cost of each link is minimized.
		(e)It is a spanning tree that includes the minimum cost path of each bridge/LAN to the root bridge

(+10)	(10％) The “root path cost” (RPC) of a bridge is defined as the summation of the transmission costs of the bridges along the path from the bridge to the root bridge. Consider the following BLAN configuration, the RPC of bridge 3 is __(A)__, and the RPC of bridge 4 is __(B)__.
	(A)	ANS:5
	(B)	ANS:10

(+10)	(10%)Consider the procedure to construct the spanning tree by using IEEE 802.1D spanning tree algorithm. When a bridge B (with root bridge ID = w, rpc = p) receives a BPDU (with root bridge ID = m, rpc =q) from port x (with a transmission cost of c). Assume w > m. Then what will happen for bridge B ? (多選)
		(a) port x will be selected as a new R port.
		(b) port x will be selected as a new D port.
		(c) A BPDU (with root bridge ID = m, rpc =q) will be forwarded to all the ports, except port x.
		(d) A BPDU (with root bridge ID = w, rpc =q＋c) will be forwarded to all the ports, except port x.
		(e) A BPDU (with root bridge ID = m, rpc =q＋c) will be forwarded to all the ports, except port x.

(+10)	(10%)Consider the procedure to maintain the spanning tree by using IEEE 802.1D spanning tree algorithm. For a bridge B with three ports x,y,z and root bridge ID = w, rpc = p. Assume port x is an R port, port y is a D port, port z is blocked and connected to a LAN M. Also assume port z has a transmission cost of c. What will happen if the hello BPDUs suppose to be received from port z are lost for a long time (a timeout event) ? (多選)
		(a) Port z is selected as a new R port.
		(b) Port z is selected as a D port.
		(c) A BPDU (with root bridge ID = w, rpc =p) is forwarded to port z
		(d) A BPDU (with root bridge ID = w, rpc = p＋c) is forwarded to port z.
		(e) A BPDU (with root bridge ID = w, rpc =p＋c) is forwarded to port y.

(+29)	(30％) For the following bridged network configuration. Assume the spanning tree is constructed according to the IEEE 802.1D spanning tree algorithm. Please fill in the table for the constructed spanning tree. Use integer “0” to indicate the root port number if it is the “root bridge”. Root port number Root path cost (RPC) Designated bridge ID (10,20,…) Designated path cost (DPC) Bridge 1 (A) (I) X X Bridge 2 (B) (J) X X Bridge 3 (C) (K) X X Bridge 4 (D) (L) X X Bridge 5 (E) (M) X X Bridge 6 (F) (N) X X Bridge 7 (G) (O) X X Bridge 8 (H) (P) X X LAN 1 X X (Q) (X) LAN 2 X X (R) (Y) LAN 3 X X (S) (Z) LAN 4 X X (T) (AA) LAN 5 X X (U) (AB) LAN 6 X X (V) (AC) LAN 7 X X (W) (AD)
	(A)	ANS:0
	(B)	ANS:2
	(C)	ANS:2
	(D)	ANS:1
	(E)	ANS:1
	(F)	ANS:2
	(G)	ANS:1
	(H)	ANS:2
	(I)	ANS:0
	(J)	ANS:20
	(K)	ANS:10
	(L)	ANS:15
	(M)	ANS:5
	(N)	ANS:15
	(O)	ANS:20
	(P)	ANS:10
	(Q)	ANS:20
	(R)	ANS:30
	(S)	ANS:10
	(T)	ANS:50
	(U)	ANS:80
	(V)	ANS:10
	(W)	ANS:60
	(X)	ANS:20
	(Y)	ANS:10
	(Z)	ANS:0
	(AA)	ANS:5
	(AB)	ANS:10
	(AC)	ANS:0
	(AD)	ANS:15