Implementing and Operating Cisco Enterprise Network Core Technologies (ENCOR) Free Sample Questions

Debug conditions are combined with an OR logic. When multiple debug conditions are configured (interface serial 0/0, interface serial 0/1, and username RouterB), the debug output will display messages that match ANY of these conditions. The debug ppp authentication command will show messages that contain the RouterB username OR arrive on either Serial 0/0 OR Serial 0/1 interface. The other options are incorrect because they suggest only one specific condition would be met, ignoring the OR logic of multiple debug conditions.

The IPv4 do-not-fragment bit (DF bit) is essential for MTU discovery because it prevents fragmentation of the ping packets. When the DF bit is set and a packet is too large for a link, an ICMP "fragmentation needed" message is returned, allowing you to determine the maximum transmission unit size. The other options are incorrect: increasing ping count, datagram size, or timeout values do not directly help determine MTU size - you need the DF bit to force MTU discovery through fragmentation prevention.

Based on the image showing debug output, the debug condition has been met on the Serial 0/1 interface. The debug output displays PPP authentication messages specifically from the Serial 0/1 connection to RouterC, indicating that this interface condition triggered the debug display. The other options are incorrect because the output specifically shows Serial 0/1 interface activity, not Serial 0/0, username-based conditions, or all/no conditions being met.

When a ping with DF bit set fails because the datagram is too large (1501 bytes), you should issue the command with a lower size parameter value to find the maximum MTU. This process of gradually reducing the size until pings succeed determines the largest unfragmented packet size the path supports. The other options are incorrect: removing the dfbit parameter defeats MTU discovery purpose, removing size parameter uses default small size, and removing both parameters provides no MTU information.

You should issue the debug condition interface serial 0/1 command on RouterA to receive Point-to-Point Protocol (PPP) authentication debug output from both RouterB and RouterC with the least administrative effort. The debug condition interface command filters debug output to show only messages from the specified interface. Since both routers connect through different serial interfaces, adding the Serial 0/1 condition will enable debug output from both connections. The other options either disable debugging entirely or use incorrect syntax for interface conditions.

The pings were sent to the destination in a fragmented fashion. Since the default system MTU on Cisco devices is typically 1500 bytes and the ping size is 1600 bytes, the packets exceed the MTU and must be fragmented to succeed. Without the DF bit set, fragmentation is allowed and the pings succeed. The other options are incorrect: MTU of 1600 is not default, DF bit prevents fragmentation (would cause failure), and 1600 bytes exceeds default MTU values.

Most likely, the Generic Routing Encapsulation (GRE) tunnel MTU is 1476 bytes. GRE tunneling adds 24 bytes of overhead to packets (20-byte IP header + 4-byte GRE header). With a standard Ethernet MTU of 1500 bytes, the effective tunnel MTU becomes 1476 bytes. Since the ping size is 1500 bytes with DF bit set, it exceeds the tunnel MTU and cannot be fragmented, causing the ping to fail. The other options are incorrect as they do not account for GRE tunneling overhead.

Only routing updates are tunneled in OSPF virtual links. Virtual links are logical connections that carry OSPF routing information between areas when a non-backbone area cannot directly connect to Area 0. Unlike GRE tunnels, virtual links do not encapsulate all traffic - they only tunnel OSPF routing updates and LSA exchanges. The other options are incorrect: virtual links do not encapsulate regular traffic, do not add tunnel headers to data packets, and the transit area cannot be a stub area (stub areas cannot have virtual links).

Down/up is not a valid GRE tunnel state on Cisco devices. The valid GRE tunnel states are: Up/up (tunnel is operational), Up/down (tunnel interface is up but line protocol is down), Administratively down/down (tunnel is shutdown), and Reset/down (tunnel is being reset). The Down/up state does not exist because if the interface is down, the line protocol cannot be up. The other options are all legitimate tunnel states that can occur during tunnel operations.

Traffic is encapsulated and decapsulated by tunnel endpoints when using OSPF over GRE tunnels. GRE tunneling encapsulates the original packets (including OSPF traffic) with GRE and IP headers at the source endpoint, then decapsulates them at the destination endpoint. This allows OSPF to operate over networks that do not natively support multicast or direct connectivity. The other options are incorrect: tunnel headers do create overhead, transit areas can be stub areas in regular OSPF, and all traffic (not just routing updates) is tunneled in GRE.