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2021 Jan 400-101 ccie routing and switching written exam fee:
Q371. You are tasked with configuring a router on an OSPF domain to import routes from an EIGRP domain and summarize the routes to 192.168.64.0.
Which statement configures the summarized route and provides equal-path route redundancy?
A. area 32 range 192.168.64.0 255.255.192.0 cost 100
B. area 32 range 192.168.64.0 255.255.63.0 cost 100
C. area 32 range 192.168.64.0 255.255.64.0 cost 100
D. area 32 range 192.168.64.0 255.255.192.0 multi-path
Answer: A
Explanation:
area range
To consolidate and summarize routes at an area boundary, use the area range command in router configuration mode. To disable this function, use the no form of this command.
Syntax Description
area-id
Identifier of the area about which routes are to be summarized. It can be specified as either a decimal value or as an IP address.
ip-address
IP address.
mask
IP address mask.
advertise
(Optional) Sets the address range status to advertise and generates a Type 3 summary link-state advertisement (LSA).
not-advertise
(Optional) Sets the address range status to DoNotAdvertise. The Type 3 summary LSA is suppressed, and the component networks remain hidden from other networks.
cost cost
(Optional) Metric or cost for this summary route, which is used during OSPF SPF calculation to determine the shortest paths to the destination. The value can be 0 to 16777215.
Reference: http://www.cisco.com/c/en/us/td/docs/ios/12_2/iproute/command/reference/fiprrp_r/1rfospf. html#wp1017596
Q372. Which three statements about the default behaviour of eBGP sessions are true? (Choose three.)
A. eBGP sessions between sub-ASs in different confederations transmit the next hop unchanged.
B. The next hop in an eBGP peering is the IP address of the neighbor that announced the route.
C. When a route reflector reflects a route to a client, it transmits the next hop unchanged.
D. The next hop in an eBGP peering is the loopback address of the interface that originated the route.
E. The next hop in an eBGP peering is the loopback address of the neighbor that announced the route.
F. When a route reflector reflects a route to a client, it changes the next hop to its own address.
Answer: A,B,C
Q373. Which two mechanisms can be used to eliminate Cisco Express Forwarding polarization? (Choose two.)
A. alternating cost links
B. the unique-ID/universal-ID algorithm
C. Cisco Express Forwarding antipolarization
D. different hashing inputs at each layer of the network
Answer: B,D
Explanation:
This document describes how Cisco Express Forwarding (CEF) polarization can cause suboptimal use of redundant paths to a destination network. CEF polarization is the effect when a hash algorithm chooses a particular path and the redundant paths remain completely unused.
How to Avoid CEF Polarization
. Alternate between default (SIP and DIP) and full (SIP + DIP + Layer4 ports) hashing inputs configuration at each layer of the network.
. Alternate between an even and odd number of ECMP links at each layer of the network.The CEF load-balancing does not depend on how the protocol routes are inserted in the routing table. Therefore, the OSPF routes exhibit the same behavior as EIGRP. In a hierarchical network where there are several routers that perform load-sharing in a row, they all use same algorithm to load-share.
The hash algorithm load-balances this way by default:
1: 1
2: 7-8
3: 1-1-1
4: 1-1-1-2
5: 1-1-1-1-1
6: 1-2-2-2-2-2
7: 1-1-1-1-1-1-1
8: 1-1-1-2-2-2-2-2
The number before the colon represents the number of equal-cost paths. The number after the colon represents the proportion of traffic which is forwarded per path.
This means that:
For two equal cost paths, load-sharing is 46.666%-53.333%, not 50%-50%.
For three equal cost paths, load-sharing is 33.33%-33.33%-33.33% (as expected).
For four equal cost paths, load-sharing is 20%-20%-20%-40% and not 25%-25%-25%-25%.
This illustrates that, when there is even number of ECMP links, the traffic is not load-balanced.
.Cisco IOS introduced a concept called unique-ID/universal-ID which helps avoid CEF polarization. This algorithm, called the universal algorithm (the default in current Cisco IOS versions), adds a 32-bit router-specific value to the hash function (called the universal ID - this is a randomly generated value at the time of the switch boot up that can can be manually controlled). This seeds the hash function on each router with a unique ID, which ensures that the same source/destination pair hash into a different value on different routers along the path. This process provides a better network-wide load-sharing and circumvents the polarization issue. This unique -ID concept does not work for an even number of equal-cost paths due to a hardware limitation, but it works perfectly for an odd number of equal-cost paths. In order to overcome this problem, Cisco IOS adds one link to the hardware adjacency table when there is an even number of equal-cost paths in order to make the system believe that there is an odd number of equal-cost links.
Reference: http://www.cisco.com/c/en/us/support/docs/ip/express-forwarding-cef/116376-technote-cef-00.html
Q374. Refer to the exhibit.
A PE router is configured with a policy map that contains the policer shown. The policy map is configured in the inbound direction of an interface facing a CE router. If the PE router
receives 12Mb/s of traffic with the CoS value set to 7 on a 100-Mb/s interface from the CE router, what value of MPLS EXP is set when this traffic goes through the policer shown?
A. 0
B. 6
C. 7
D. 8
Answer: B
Explanation:
Here, the policer is set where the conforming traffic is set to 10 percent of the 100 Mbps interface, so anything more than 10 Mbps will be placed into the exceeding traffic class, the traffic EXP value will be changed from 7 to 6 per the configuration.
Q375. Which two statements about NetFlow are true? (Choose two.)
A. It must be configured on each router in a network.
B. It supports ATM LAN emulation.
C. The existing network is unaware that NetFlow is running.
D. It uses SIP to establish sessions between neighbors.
E. It provides resource utilization accounting.
Answer: C,E
Explanation:
NetFlow identifies packet flows for both ingress and egress IP packets. It does not involve any connection-setup protocol, either between routers or to any other networking device or end station. NetFlow does not require any change externally--either to the packets themselves or to any networking device. NetFlow is completely transparent to the existing network, including end stations and application software and network devices like LAN switches. Also, NetFlow capture and export are performed independently on each internetworking device; NetFlow need not be operational on each router in the network. NetFlow data provides fine-grained metering for highly flexible and detailed resource utilization accounting. For example, flow data includes details such as IP addresses, packet and byte counts, timestamps, type-of-service, and application ports. Service providers might utilize the information for billing based on time-of-day, bandwidth usage, application usage, or quality of service. Enterprise customers might utilize the information for departmental chargeback or cost allocation for resource utilization.
Reference: http://www.cisco.com/c/en/us/td/docs/ios-xml/ios/netflow/configuration/12-4t/nf-12-4t-book/ios-netflow-ov.html
Up to the immediate present ccie written exam:
Q376. Which two statements about the function of the stub feature in EIGRP are true? (Choose two.)
A. It stops the stub router from sending queries to peers.
B. It stops the hub router from sending queries to the stub router.
C. It stops the stub router from propagating dynamically learned EIGRP prefixes to the hub routers.
D. It stops the hub router from propagating dynamically learned EIGRP prefixes to the stub routers.
Answer: B,C
Explanation:
When using the EIGRP Stub Routing feature, you need to configure the distribution and remote routers to use EIGRP, and to configure only the remote router as a stub. Only specified routes are propagated from the remote (stub) router. The router responds to queries for summaries, connected routes, redistributed static routes, external routes, and internal routes with the message "inaccessible." A router that is configured as a stub will send a special peer information packet to all neighboring routers to report its status as a stub router. Without the stub feature, even after the routes that are sent from the distribution router to the remote router have been filtered or summarized, a problem might occur. If a route is lost somewhere in the corporate network, EIGRP could send a query to the distribution router, which in turn will send a query to the remote router even if routes are being summarized. If there is a problem communicating over the WAN link between the distribution router and the remote router, an EIGRP stuck in active (SIA) condition could occur and cause instability elsewhere in the network. The EIGRP Stub Routing feature allows a network administrator to prevent queries from being sent to the remote router.
Reference: http://www.cisco.com/c/en/us/td/docs/ios/12_0s/feature/guide/eigrpstb.html
Q377. Refer to the exhibit.
Your network is suffering excessive output drops. Which two actions can you take to resolve the problem? (Choose two.)
A. Install a switch with larger buffers.
B. Configure a different queue set.
C. Reconfigure the switch buffers.
D. Configure the server application to use TCP.
E. Update the server operating system.
Answer: A,B
Explanation:
Installing a switch with larger buffers and correctly configuring the buffers can solve output queue problems.
For each queue we need to configure the assigned buffers. The buffer is like the ‘storage’ space for the interface and we have to divide it among the different queues. This is how to do it:
mls qos queue-set output <queue set> buffers Q1 Q2 Q3 Q4
In this example, there is nothing hitting queue 2 or queue 3 so they are not being utilized.
Q378. DRAG DROP
Drag and drop the BGP attribute on the left to the correct category on the right.
Answer:
Q379. Which map is locally defined?
A. DSCP-to-DSCP-mutation
B. CoS-to-DSCP
C. IP-precedence-to-DSCP
D. DSCP-to-CoS
Answer: A
Q380. DRAG DROP
Drag and drop each step of the Unicast RPF process on the left into the correct order on the right.
Answer: