Try Cisco 642-885 Exam Questions – Updated 2018

By | January 11, 2018

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642-885 exam questions, 642-885 PDF dumps; 642-885 exam dumps:: https://www.dumpsschool.com/642-885-exam-dumps.html (131 Q&A) (New Questions Are 100% Available! Also Free Practice Test Software!)

Latest and Most Accurate Cisco 642-885 Dumps Exam Questions and Answers:

Question: 21

Which three statements regarding NAT64 operations are correct? (Choose three.)

A. With stateful NAT64, many IPv6 address can be translated into one IPv4 address, thus IPv4 address conservation is achieved
B. Stateful NAT64 requires the use of static translation slots so IPv6 hosts and initiate connections to IPv4 hosts.
C. With stateless NAT64, the source and destination IPv4 addresses are embedded in the IPv6 addresses
D. NAT64 works in conjunction with DNS64
E. Both the stateful and stateless NAT64 methods will conserve IPv4 address usage

Answer: A, C, D

Explanation:
Stateful NAT64-Network Address and Protocol Translation from IPv6 Clients to IPv4 Servers
Stateful NAT64 multiplexes many IPv6 devices into a single IPv4 address. It can be assumed that this technology will be used mainly where IPv6-only networks and clients (ie. Mobile handsets, IPv6 only wireless, etc…) need access to the IPv4 internet and its services.
The big difference with stateful NAT64 is the elimination of the algorithmic binding between the IPv6 address and the IPv4 address. In exchange, state is created in the NAT64 device for every flow. Additionally, NAT64 only supports IPv6-initiated flows. Unlike stateless NAT64, stateful NAT64 does `not’ consume a single IPv4 address for each IPv6 device that wants to communicate to the IPv4 Internet. More practically this means that many IPv6-only users consume only single IPv4 address in similar manner as IPv4-to-IPv4 network address and port translation works. This works very well if the connectivity request is initiated from the IPv6 towards the IPv4 Internet. If an IPv4-only device wants to speak to an IPv6-only server for example, manual configuration of the translation slot will be required, making this mechanism less attractive to provide IPv6 services towards the IPv4 Internet. DNS64 is usually also necessary with a stateful NAT64, and works the same with both stateless and stateful NAT64
Stateless NAT64-Stateless translation between IPv4 and IPv6 RFC6145 (IP/ICMP Translation Algorithm) replaces RFC2765 (Stateless IP/ICMP Translation Algorithm (SIIT)) and provides a stateless mechanism to translate a IPv4 header into an IPv6 header and vice versa. Due to the stateless character this mechanism is very effective and highly fail safe because more as a single-or multiple translators in parallel can be deployed and work all in parallel without a need to synchronize between the translation devices.
The key to the stateless translation is in the fact that the IPv4 address is directly embedded in the IPv6 address. A limitation of stateless NAT64 translation is that it directly translates only the IPv4 options that have direct IPv6 counterparts, and that it does not translate any IPv6 extension headers beyond the fragmentation extension header; however, these limitations are not significant in practice.
With a stateless NAT64, a specific IPv6 address range will represent IPv4 systems within the IPv6 world. This range needs to be manually configured on the translation device. Within the IPv4 world all the IPv6 systems have directly correlated IPv4 addresses that can be algorithmically mapped to a subset of the service provider’s IPv4 addresses. By means of this direct mapping algorithm there is no need to keep state for any translation slot between IPv4 and IPv6. This mapping algorithm requires the IPv6 hosts be assigned specific IPv6 addresses, using manual configuration or DHCPv6.
Stateless NAT64 will work very successful as proven in some of the largest networks, however it suffers from some an important side-effect: Stateless NAT64 translation will give an IPv6-only host access to the IPv4 world and vice versa, however it consumes an IPv4 address for each IPv6-only device that desires translation — exactly the same as a dual-stack deployment. Consequentially, stateless NAT64 is no solution to address the ongoing IPv4 address depletion. Stateless NAT64 is a good tool to provide Internet servers with an accessible IP address for both IPv4 and IPv6 on the global Internet. To aggregate many IPv6 users into a single IPv4 address, stateful NAT64 is required. NAT64 are usually deployed in conjunction with a DNS64. This functions similar to, but different than, DNS-ALG that was part of NAT-PT. DNS64 is not an ALG; instead, packets are sent directly to and received from the DNS64’s IP address. DNS64 can also work with DNSSEC (whereas DNS-ALG could not).

Question: 22

Which type of DNS record is used for IPv6 forward lookups?

A. A records
B. AAAA records
C. PTR records
D. MX records

Answer: B

Explanation:

Question: 23

Which two BGP mechanisms are used to prevent routing loops when using a design with redundant route reflectors? (Choose two.)

A. Cluster-list
B. AS-Path
C. Originator ID
D. Community
E. Origin

Answer: A, C

Explanation:
http://www.cisco.com/en/US/docs/ios_xr_sw/iosxr_r3.7/routing/configuration/guide/rc37bgp.html
As the iBGP learned routes are reflected, routing information may loop. The route reflector model has the following mechanisms to avoid routing loops:
•Originator ID is an optional, nontransitive BGP attribute. It is a 4-byte attributed created by a route reflector.
The attribute carries the router ID of the originator of the route in the local autonomous system. Therefore, if a misconfiguration causes routing information to come back to the originator, the information is ignored.
•Cluster-list is an optional, nontransitive BGP attribute. It is a sequence of cluster IDs that the route has passed. When a route reflector reflects a route from its clients to nonclient peers, and vice versa, it appends the local cluster ID to the cluster-list. If the cluster-list is empty, a new cluster-list is created. Using this attribute, a route reflector can identify if routing information is looped back to the same cluster due to misconfiguration. If the local cluster ID is found in the cluster-list, the advertisement is ignored.

Question: 24

Which two statements correctly describe the BGP ttl-security feature? (Choose two.)

A. This feature protects the BGP processes from CPU utilization-based attacks from EBGP neighbors which can be multiple hops away
B. This feature prevents IBGP sessions with non-directly connected IBGP neighbors
C. This feature will cause the EBGP updates from the router to be sent using a TTL of 1
D. This feature needs to be configured on each participating BGP router
E. This feature is used together with the ebgp-multihop command

Answer: A, D

Explanation:
http://packetlife.net/blog/2009/nov/23/understanding-bgp-ttl-security/

Question: 25

When implementing source-based remote-triggered black hole filtering, which two configurations are required on the edge routers that are not the signaling router? (Choose two.)

A. A static route to a prefix that is not used in the network with a next hop set to the Null0 interface
B. A static route pointing to the IP address of the attacker
C. uRPF on all external facing interfaces at the edge routers
D. Redistribution into BGP of the static route that points to the IP address of the attacker
E. A route policy to set the redistributed static routes with the no-export BGP community

Answer: A, C

Explanation:
Source-Based RTBH Filtering
With destination-based black holing, all traffic to a specific destination is dropped after the black hole has been activated, regardless of where it is coming from. Obviously, this could include legitimate traffic destined for the target. Source-based black holes provide the ability to drop traffic at the network edge based on a specific source address or range of source addresses.
If the source address (or range of addresses) of the attack can be identified (spoofed or not), it would be better to drop all traffic at the edge based on the source address, regardless of the destination address. This would permit legitimate traffic from other sources to reach the target. Implementation of source-based black hole filtering depends on Unicast Reverse Path Forwarding (uRPF), most often loose mode uRPF.
Loose mode uRPF checks the packet and forwards it if there is a route entry for the source IP of the incoming packet in the router forwarding information base (FIB). If the router does not have an FIB entry for the source IP address, or if the entry points to a null interface, the Reverse Path Forwarding (RPF) check fails and the packet is dropped, as shown in Figure 2. Because uRPF validates a source IP address against its FIB entry, dropping traffic from specific source addresses is accomplished by configuring loose mode uRPF on the external interface and ensuring the RPF check fails by inserting a route to the source with a next hop of Null0.
This can be done by using a trigger device to send IBGP updates. These updates set the next hop for the source IP to an unused IP address that has a static entry at the edge, setting it to null as shown in Figure 2.

Question: 26

Refer to the topology diagram shown in the exhibit and the partial configurations shown below.

Once the attack from 209.165.201.144/28 to 209.165.202.128/28 has been detected, which additional configurations are required on the P1 IOS-XR router to implement source-based remote-triggered black hole filtering?
!
router bgp 123
address-family ipv4 unicast
redistribute static route-policy test
!

A. router static
address-family ipv4 unicast
209.165.202.128/28 null0 tag 666
192.0.2.1/32 null0 tag 667
!
route-policy test
if tag is 666 then
set next-hop 192.0.2.1
endif
if tag is 667 then
set community (no-export)
endif
end-policy
!
B. router static
address-family ipv4 unicast
209.165.201.144/28 null0 tag 666
192.0.2.1/32 null0 tag 667
!
route-policy test
if tag is 666 then
set next-hop 192.0.2.1
endif
if tag is 667 then
set community (no-export)
endif
end-policy
!
C. router static
address-family ipv4 unicast
209.165.201.144/28 null0 tag 666
192.0.2.1/32 null0
!
route-policy test
if tag is 666 then
set next-hop 192.0.2.1
set community (no-export)
endif
end-policy
D. router static
address-family ipv4 unicast
209.165.202.128/28 null0 tag 666
192.0.2.1/32 null0
!
route-policy test
if tag is 666 then
set next-hop 192.0.2.1
set community (no-export)
endif
end-policy
!

Answer: C

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