Answer: A 

Explanation: 

Open Shortest Path First http://en.wikipedia.org/wiki/Open_Shortest_Path_First 

The configuration of R1 shows "router ospf 1" however, the diagram also shows that both routers should be in the backbone OSPF Area of "0". When routers are in different OSPF areas they will not form a neighbor relationship. Neighbor relationships As a link state routing protocol, OSPF establishes and maintains neighbor relationships in order to exchange routing updates with other routers. The neighbor relationship table is called an adjacency database in OSPF. Provided that OSPF is configured correctly, OSPF forms neighbor relationships only with the routers directly connected to it. In order to form a neighbor relationship between two routers, the interfaces used to form the relationship must be in the same area. Generally an interface is only configured in a single area, however you can configure an interface to belong to multiple areas. In the second area, such an interface must be configured as a secondary interface. (A neighbor state simulation shows how neighbor state changes from Down to Full Adjacency progressively with exchanging Hello, DD, Request, Update, and Ack packets). 

Answer: C 

Explanation: 

In this question, we only care about the Access Layer switches (Switch3 & 4). Switch 3 has a lower bridge ID than Switch 4 (because the MAC of Switch3 is smaller than that of Switch4) so both ports of Switch3 will be in forwarding state. The alternative port will surely belong to Switch4. Switch4 will need to block one of its ports to avoid a bridging loop between the two switches. But how does Switch4 select its blocked port? Well, the answer is based on the BPDUs it receives from Switch3. A BPDU is superior than another if it has: 

1. A lower Root Bridge ID2. A lower path cost to the Root3. A lower Sending Bridge ID4. A lower Sending Port ID 

These four parameters are examined in order. In this specific case, all the BPDUs sent by Switch3 have the same Root Bridge ID, the same path cost to the Root and the same Sending Bridge ID. The only parameter left to select the best one is the Sending Port ID (Port ID = port priority + port index). In this case the port priorities are equal because they use the default value, so Switch4 will compare port index values, which are unique to each port on the switch, and because Fa0/12 is inferior to Fa0/1, Switch4 will select the port connected with Fa0/1 (of Switch3) as its root port and block the other port -> Port fa0/11 of Switch4 will be blocked (discarding role) 

Answer: A,B,F 

Explanation: 

The question says "no other configuration changes have been made" so we can 

understand these switches have the same bridge priority. SwitchC has lowest MAC 

address so, it will become root bridge and 2 of its ports (Fa0/1 & Fa0/2) will be designated 

ports (DP). Because SwitchC is the root bridge the 2 ports nearest SwitchC on SwitchA 

(Fa0/1) and SwitchD (Gi0/2) will be root ports (RP) -> B and F are correct. 

SwitchB must have a root port so which port will it choose? To answer this question we 

need to know about STP cost and port cost. 

In general, "cost" is calculated based on bandwidth of the link. The higher the bandwidth on 

a link, the lower the value of its cost. Below are the cost values you should memorize: 

Link speed Cost SwitchB will choose the interface with lower cost to the root bridge as the root port so we must calculate the cost on interface Gi0/1 & Gi0/2 of SwitchB to the root bridge. This can be calculated from the "cost to the root bridge" of each switch because a switch always advertises its cost to the root bridge in its BPDU. The receiving switch will add its local port cost value to the cost in the BPDU. SwitchC advertises its cost to the root bridge with a value of 0. Switch D adds 4 (the cost value of 1Gbps link) and advertises this value (4) to SwitchB. SwitchB adds another 4 and learns that it can reach SwitchC via Gi0/1 port with a total cost of 8. The same process happens for SwitchA and SwitchB learns that it can reach SwitchC via Gi0/2 with a total cost of 23 -> Switch B chooses Gi0/1 as its root port. Now our last task is to identify the port roles of the ports between SwitchA & SwitchB. It is rather easy as the MAC address of SwitchA is lower than that of SwitchB so Fa0/2 of SwitchA will be designated port while Gi0/2 of SwitchB will be alternative port. 

Answer: C 

Explanation: 

DLCI 16 and DLCI 19 need to act like a point-to-point link and will therefore need to be on the same network as will DLCI 17 and DLCI 28. With this information we can see that option "B" is the only option that has the corresponding DLCI's on the same network based on the ip addresses and subnetmask. Option "D" is incorrect because, this would put the same network on both interfaces of the R2 router. Option "A" is similar. 

Answer: C 

Explanation: 

First we should grasp the concept of BECN & FECN through an example: 

Suppose Router A wants to send data to Router B through a Frame Relay network. If the network is congested, Switch 1 (a DCE device) will set the FECN bit value of that frame to 1, indicating that frame experienced congestion in the path from source to destination. This frame is forwarded to Switch 2 and to Router B (with the FECN bit = 1). Switch 1 knows that the network is congesting so it also sends frames back to Router A with BECN bit set to 1 to inform that path through the network is congested. 

In general, BECN is used on frames traveling away from the congested area to warn source devices that congestion has occurred on that path while FECN is used to alert receiving devices if the frame experiences congestion. 

BECN also informs the transmitting devices to slow down the traffic a bit until the network returns to normal state. The question asks “which output value indicates to the local router that traffic sent to the corporate site is experiencing congestion” which means it asks about the returned parameter which indicates congestion ->BECN. 

Answer: B,D Explanation: 

Here is a list of the differences between OSPFv2 and OSPFv3: 

They use different address families (OSPFv2 is for IPv4-only, OSPFv3 can be used for IPv6-only or both protocols OSPFv3 introduces new LSA types OSPFv3 has different packet format OSPFv3 uses different flooding scope bits (U/S2/S1) OSPFv3 adjacencies are formed over link-local IPv6 communications OSPFv3 runs per-link rather than per-subnet OSPFv3 supports multiple instances on a single link, Interfaces can have multiple IPv6 addresses OSPFv3 uses multicast addresses FF02::5 (all OSPF routers), FF02::6 (all OSPF DRs) OSPFv3 Neighbor Authentication done with IPsec (AH) OSPFv2 Router ID (RID) must be manually configured, still a 32-bit number 

Reference: http://www.networkworld.com/article/2225270/cisco-subnet/ospfv3-for-ipv4-and-ipv6.html 

Answer: A 

Explanation: 

Spanning Tree Protocol convergence (Layer 2 convergence) happens when bridges and switches have transitioned to either the forwarding or blocking state. When layer 2 is converged, root bridge is elected and all port roles (Root, Designated and Non-Designated) in all switches are selected. 

Answer: A,C,E 

Explanation: 

From the output, we see that all ports are in Designated role (forwarding state) -> A and E 

are correct. 

The command “show spanning-tree vlan 30 only shows us information about VLAN 30. We 

don’t know how many VLAN exists in this switch -> B is not correct. 

The bridge priority of this switch is 24606 which is lower than the default value bridge 

priority 32768 -> C is correct. 

All three interfaces on this switch have the connection type “p2p”, which means Point-to-point environment – not a shared media -> D is not correct. 

The only thing we can specify is this switch is the root bridge for VLAN 3o but we can not 

guarantee it is also the root bridge for other VLANs -> F is not correct. 

Answer: B 

Explanation: 

High-Level Data Link Control (HDLC) - HDLC is the default encapsulation type on point-to-point, dedicated links, and circuit-switched connections. It is used typically when communicating between two Cisco devices. It is a bit-oriented synchronous data link layer protocol. Point-to-Point Protocol (PPP) - Provides router-to-router and host-to network connections over synchronous and asynchronous circuits. PPP was designed to work with several network layer protocols, such as IP, and IPX. PPP also has built in security mechanisms such as PAP and CHAP X.25/Link Access Procedure, Balanced (LAPB) - ITU-T standard that defines how connections between DTE and DCE are maintained for remote terminal access and computer communications in public data networks. X.25 specifies LAPB, a data line layer protocol. X.25 is a predecessor to Frame Relay. Frame Relay - Industry standard, switched data link layer protocol that handles multiple virtual circuits. It is a next-generation to X.25 that is streamlined to eliminate some of the time-consuming processes (such as error correction and flow control) that were employed in X.25. 

Answer: C 

Explanation: http://www.ciscopress.com/articles/article.asp?p=174107&seqNum=3 

RIPv1, RIPv2, IGRP, and EIGRP all auto-summarize classful boundaries by default (OSPF does not).To make discontiguous networks work, meaning you don't want classful boundries to summarize, you need to turn off auto-summary.