Q1. DRAG DROP
Drag each MPLS term on the left to the matching statement on the right.
Answer:
Q2. Which two options are reasons to manipulate the delay metric instead of the bandwidth metric for EIGRP routing? (Choose two.)
A. Because the delay metric provides better handling for bursty traffic
B. Because manipulating the bandwidth metric can also affect QoS
C. Because manipulating the bandwidth affects only a particular path
D. Because changes to the delay metric are propagated to all neighbors on a segment
Answer: B,D
Explanation:
Using the bandwidth to influence EIGRP paths is discouraged for two reasons:
. Changing the bandwidth can have impact beyond affecting the EIGRP metrics. For example, quality of service (QoS) also looks at the bandwidth on an interface.
. EIGRP throttles to use 50 percent of the configured bandwidth. Lowering the bandwidth can cause problems like staving EIGRP neighbors from getting hello packets because of the throttling back.
Because changes to the delay metric are propagated to all downstream routers, changing the interface delay parameter is the preferred method of influencing path selection
Reference: http://www.cisco.com/c/en/us/support/docs/ip/enhanced-interior-gateway-routing-protocol-eigrp/13673-14.html
Q3. Which two options are BGP attributes that are updated when router sends an update to its eBGP peer? (Choose two.)
A. weight
B. local preference
C. AS_path
D. next-hop
Answer: C,D
Explanation:
AS_Path describes the inter-AS path taken to reach a destination. It gives a list of AS Numbers traversed when reaching to a destination. Every BGP speaker when advertising a route to a peer will include its own AS number in the NLRI. The subsequent BGP speakers who advertise this route will add their own AS number to the AS_Path, the subsequent AS numbers get prepended to the list. The end result is the AS_Path attribute is able to describe all the autonomous systems it has traversed, beginning with the most recent AS and ending with the originating AS.
NEXT_HOP Attribute specifies the next hop IP address to reach the destination advertised in the NLRI. NEXT_HOP is a well-known mandatory attribute that is included in every eBGP update.
Reference: http://netcerts.net/bgp-path-attributes-and-the-decision-process/
Q4. Which statement about the overload bit in IS-IS is true?
A. The IS-IS adjacencies on the links for which the overload bit is set are brought down.
B. Routers running SPF ignore LSPs with the overload bit set and hence avoid blackholing traffic.
C. A router setting the overload bit becomes unreachable to all other routers in the IS-IS area.
D. The overload bit in IS-IS is used only for external prefixes.
Answer: B
Explanation:
The OL bit is used to prevent unintentional blackholing of packets in BGP transit networks. Due to the nature of these protocols, IS-IS and OSPF converge must faster than BGP. Thus there is a possibility that while the IGP has converged, IBGP is still learning the routes. In that case if other IBGP routers start sending traffic towards this IBGP router that has not yet completely converged it will start dropping traffic. This is because it isnt yet aware of the complete BGP routes. OL bit comes handy in such situations. When a new IBGP neighbor is added or a router restarts, the IS-IS OL bit is set. Since directly connected (including loopbacks) addresses on an “overloaded” router are considered by other routers, IBGP can be bought up and can begin exchanging routes. Other routers will not use this router for transit traffic and will route the packets out through an alternate path. Once BGP has converged, the OL bit is cleared and this router can begin forwarding transit traffic.
Reference: https://routingfreak.wordpress.com/category/ospf-vs-is-is/
Q5. 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: D
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/
Q6. Which two statements about packet fragmentation on an IPv6 network are true? (Choose two.)
A. The fragment header is 64 bits long.
B. The identification field is 32 bits long.
C. The fragment header is 32 bits long.
D. The identification field is 64 bits long.
E. The MTU must be a minimum of 1280 bytes.
F. The fragment header is 48 bits long.
Answer: A,B
Explanation:
The fragment header is shown below, being 64 bits total with a 32 bit identification field:
Reference: http://www.openwall.com/presentations/IPv6/img24.html
Q7. Refer to the exhibit.
Video Source S is sending interactive video traffic to Video Receiver R. Router R1 has multiple routing table entries for destination R. Which load-balancing mechanism on R1 can cause out-of-order video traffic to be received by destination R?
A. per-flow load balancing on R1 for destination R
B. per-source-destination pair load balancing on R1 for destination R
C. CEF load balancing on R1 for destination R
D. per-packet load balancing on R1 for destination R
Answer: D
Explanation:
Per-packet load balancing guarantees equal load across all links, however potentially the packets may arrive out-of-order at the destination as differential delay may exist within the network.
Reference: http://www.cisco.com/en/US/products/hw/modules/ps2033/prod_technical_reference09186 a00800afeb7.html
Q8. DRAG DROP
Drag and drop each EIGRP element on the left to the corresponding definition on the right.
Answer:
Q9. Which two statements are true about IS-IS? (Choose two.)
A. IS-IS DIS election is nondeterministic.
B. IS-IS SPF calculation is performed in three phases.
C. IS-IS works over the data link layer, which does not provide for fragmentation and reassembly.
D. IS-IS can never be routed beyond the immediate next hop.
Answer: C,D
Explanation:
IS-IS runs directly over the data link alongside IP. On Ethernet, IS-IS packets are always 802.3 frames, with LSAPs 0xFEFE while IP packets are either Ethernet II frames or SNAP frames identified with the protocol number 0x800. OSPF runs over IP as protocol number 89.
IS-IS runs directly over layer 2 and hence:
-cannot support virtual links unless some explicit tunneling is implemented
-packets are kept small so that they don't require hop-by-hop fragmentation
-uses ATM/SNAP encapsulation on ATM but there are hacks to make it use VcMux encapsulation
-some operating systems that support IP networking have been implemented to differentiate Layer 3 packets in kernel. Such Oss require a lot of kernel modifications to support IS-IS for IP routing.
-can never be routed beyond the immediate next hop and hence shielded from IP spoofing and similar Denial of Service attacks.
Reference: https://tools.ietf.org/html/draft-bhatia-manral-diff-isis-ospf-00
Q10. Which two statements about BPDU guard are true? (Choose two.)
A. The global configuration command spanning-tree portfast bpduguard default shuts down interfaces that are in the PortFast-operational state when a BPDU is received on that port.
B. The interface configuration command spanning-tree portfast bpduguard enable shuts down only interfaces with PortFast enabled when a BPDU is received.
C. BPDU guard can be used to prevent an access port from participating in the spanning tree in the service provider environment.
D. BPDU guard can be used to protect the root port.
E. BPDU guard can be used to prevent an invalid BPDU from propagating throughout the network.
Answer: A,C