400 101 pdf : May 2021 Edition


The article at Testaimer.com going over http://www.testaimer.com/400-101-test is very comprehensive.

Q311. Refer to the exhibit. 

Which statement is true? 

A. BGP peer 10.1.2.3 is performing inbound filtering. 

B. BGP peer 10.1.2.3 is a route reflector. 

C. R1 is a route reflector, but BGP peer 10.1.2.3 is not a route reflector client. 

D. R1 still needs to send an update to the BGP peer 10.1.2.3. 

Answer:

Explanation: 

On R1 the routing table version (Tbl Ver) for 10.1.2.3 is 1, other routers have version 2, so it needs to send an update to the 10.1.2.3 peer. 


Q312. Refer to the exhibit. 

You are bringing a new MPLS router online and have configured only what is shown to bring LDP up. Assume that the peer has been configured in a similar manner. You verify the LDP peer state and see that there are no neighbors. What will the output of show mpls ldp discovery show? 

A. Interfaces: 

Ethernet0/0 (ldp): xmit 

B. Interfaces: 

Ethernet0/0 (ldp): xmit/recv 

LDP Id: 25.25.25.2:0; IP addr: 192.168.12.2 

C. Interfaces: 

Ethernet0/0 (ldp): xmit/recv 

LDP Id: 192.168.12.2:0; no route 

D. Interfaces: 

Ethernet0/0 (ldp): xmit/recv 

LDP Id: 25.25.25.2:0; no route 

Answer:


Q313. What is a cause for unicast flooding? 

A. Unicast flooding occurs when multicast traffic arrives on a Layer 2 switch that has directly connected multicast receivers. 

B. When PIM snooping is not enabled, unicast flooding occurs on the switch that interconnects the PIM-enabled routers. 

C. A man-in-the-middle attack can cause the ARP cache of an end host to have the wrong MAC address. Instead of having the MAC address of the default gateway, it has a MAC address of the man-in-the-middle. This causes all traffic to be unicast flooded through the man-in-the-middle, which can then sniff all packets. 

D. Forwarding table overflow prevents new MAC addresses from being learned, and packets destined to those MAC addresses are flooded until space becomes available in the forwarding table. 

Answer:

Explanation: 

Causes of Flooding The very cause of flooding is that destination MAC address of the packet is not in the L2 forwarding table of the switch. In this case the packet will be flooded out of all forwarding ports in its VLAN (except the port it was received on). Below case studies display most common reasons for destination MAC address not being known to the switch. 

Cause 1: Asymmetric Routing 

Large amounts of flooded traffic might saturate low-bandwidth links causing network performance issues or complete connectivity outage to devices connected across such low-bandwidth links 

Cause 2: Spanning-Tree Protocol Topology Changes 

Another common issue caused by flooding is Spanning-Tree Protocol (STP) Topology Change Notification (TCN). TCN is designed to correct forwarding tables after the forwarding topology has changed. This is necessary to avoid a connectivity outage, as after a topology change some destinations previously accessible via particular ports might become accessible via different ports. TCN operates by shortening the forwarding table aging time, such that if the address is not relearned, it will age out and flooding will occur 

Cause 3: Forwarding Table Overflow 

Another possible cause of flooding can be overflow of the switch forwarding table. In this case, new addresses cannot be learned and packets destined to such addresses are flooded until some space becomes available in the forwarding table. New addresses will then be learned. This is possible but rare, since most modern switches have large enough forwarding tables to accommodate MAC addresses for most designs. 

Reference: 

http://www.cisco.com/c/en/us/support/docs/switches/catalyst-6000-series-switches/23563-143.html 


Q314. RIPv2 is enabled on a router interface. The "neighbor" command is also configured with a specific IP address. Which statement describes the effect of this configuration? 

A. RIP stops sending multicast packets on that interface. 

B. RIP starts sending only unicast packets on that interface. 

C. RIP starts ignoring multicast packets on that interface. 

D. RIP starts sending unicast packets to the specified neighbor, in addition to multicast packets. 

Answer:


Q315. DRAG DROP 

Drag and drop each EIGRP element on the left to the corresponding definition on the right. 

Answer: 


Q316. Which three types of address-family configurations are supported in EIGRP named mode? (Choose three.) 

A. address-family ipv4 unicast 

B. address-family vpnv4 

C. address-family ipv6 unicast 

D. address-family ipv6 multicast 

E. address-family vpnv6 

F. address-family ipv4 multicast 

Answer: A,C,F 


Q317. Which regular expression will only allow prefixes that originated from AS 65000 and that are learned through AS 65001? 

A. ^65000_65001$ 

B. 65000_65001$ 

C. ^65000_65001 

D. ^65001_65000$ 

Answer:

Explanation: 

The following table lists the regular expressions and their meanings: 

+------------------------------------------------------+ 

| CHAR | USAGE | 

+------------------------------------------------------| 

| ^ | Start of string | 

|------|-----------------------------------------------| 

| $ | End of string | 

|------|-----------------------------------------------| 

| [] | Range of characters | 

|------|-----------------------------------------------| 

| - | Used to specify range ( i.e. [0-9] ) | 

|------|-----------------------------------------------| 

| ( ) | Logical grouping | 

|------|-----------------------------------------------| 

| . | Any single character | 

|------|-----------------------------------------------| 

| * | Zero or more instances | 

|------|-----------------------------------------------| 

| + | One or more instance | 

|------|-----------------------------------------------| 

| ? | Zero or one instance | 

|------|-----------------------------------------------| 

| _ | Comma, open or close brace, open or close | 

| | parentheses, start or end of string, or space | 

+------------------------------------------------------+ 

Some commonly used regular expressions include: 

+-------------+---------------------------+ 

| Expression | Meaning | 

|-------------+---------------------------| 

| .* | Anything | 

|-------------+---------------------------| 

| ^$ | Locally originated routes | 

|-------------+---------------------------| 

| ^100_ | Learned from AS 100 | 

|-------------+---------------------------| 

| _100$ | Originated in AS 100 | 

|-------------+---------------------------| 

| _100_ | Any instance of AS 100 | 

|-------------+---------------------------| 

| ^[0-9]+$ | Directly connected ASes | 

+-------------+---------------------------+ 

Reference: http://blog.ine.com/2008/01/06/understanding-bgp-regular-expressions/ 


Q318. In the DiffServ model, which class represents the lowest priority with the lowest drop probability? 

A. AF11 

B. AF13 

C. AF41 

D. AF43 

Answer:

Explanation: 

Assured Forwarding (AF) Behavior Group 

Class 1 

Class 2 

Class 3 

Class 4 

Low Drop 

AF11 (DSCP 10) 

AF21 (DSCP 18) 

AF31 (DSCP 26) 

AF41 (DSCP 34) 

Med Drop 

AF12 (DSCP 12) 

AF22 (DSCP 20) 

AF32 (DSCP 28) 

AF42 (DSCP 36) 

High Drop 

AF13 (DSCP 14) 

AF23 (DSCP 22) 

AF33 (DSCP 30) 

AF43 (DSCP 38) 

Reference: http://en.wikipedia.org/wiki/Differentiated_services 


Q319. A company has just opened two remote branch offices that need to be connected to the corporate network. Which interface configuration output can be applied to the corporate router to allow communication to the remote sites? 

A. interface Tunnel0 

bandwidth 1536 

ip address 209.165.200.230 255.255.255.224 

tunnel source Serial0/0 

tunnel mode gre multipoint 

B. interface fa0/0 

bandwidth 1536 

ip address 209.165.200.230 255.255.255.224 

tunnel mode gre multipoint 

C. interface Tunnel0 

bandwidth 1536 

ip address 209.165.200.231 255.255.255.224 

tunnel source 209.165.201.1 

tunnel-mode dynamic 

D. interface fa 0/0 

bandwidth 1536 

ip address 209.165.200.231 255.255.255.224 

tunnel source 192.168.161.2 

tunnel destination 209.165.201.1 

tunnel-mode dynamic 

Answer:


Q320. Which BGP feature prevents a router from installing an iBGP learned route in its routing table until the route is validated within the IGP? 

A. confederation 

B. aggregation 

C. advertise-map 

D. synchronization 

Answer: