642-885 | Validated 642-885 Bundle 2021

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NEW QUESTION 1
Refer to the exhibit. R2cannot to learn RP information from XR3. Which issue is the source of the problem?
642-885 dumps exhibit

  • A. XR3 is not the DR.
  • B. Multicast routing is not enabled on the XR3 Giga0/0/0/0 interface.
  • C. R2 is learning the RP address via non-IGP routing protocol.
  • D. Multicast routing is not enabled on the XR3 Loopback0 interface.
  • E. BGP IPv4 MDT address family is not enabled on XR3.

Answer: D

NEW QUESTION 2
The following Cisco IOS-XR configuration command will globally enable which multicast process(es) on the router?
RP/0/RP0/CPU0:router(config)# multicast-routing

  • A. IGMP only
  • B. PIM only
  • C. IGMP and MLD only
  • D. PIM and IGMP only
  • E. PIM and IGMP and MLD

Answer: E

Explanation:
http://www.cisco.com/en/US/docs/ios_xr_sw/iosxr_r3.5/multicast/configuration/guide/mc35 mcst.html
Multicast-routing Configuration Submode
When you issue the multicast-routing ipv4 or multicast-routing ipv6 command, all default multicast components (PIM, IGMP, MLD, MFWD, and MRIB) are automatically started, and the CLI prompt changes to "config-mcastipv4" or "config-mcast-ipv6", indicating that you have entered multicast-routing configuration submode

NEW QUESTION 3
Which difference occurs between intradomain and interdomain routing technology?

  • A. PIM is used in intradomain routing technology and uses reverse path forwarding mechanism to implement optimize multicast data forwarding.
  • B. MSDP is used in intradomain routing technology to discover the multicast source.
  • C. Interdomain routing technology uses MSDP and M-BGP for exchanging multicast routing information.
  • D. RP is not needed in intradomain routing technology, but RP is needed in interdomain routing technology to receive multicast traffic.

Answer: A

NEW QUESTION 4
What are three BGP configuration characteristics of a multihomed customer that is connected to multiple service providers? (Choose three.)

  • A. The multihomed customer can use local preference to influence the return traffic from the service providers
  • B. The multihomed customer announces its assigned IP address space to its service providers through BGP
  • C. The multihomed customer has to decide whether to perform load sharing or use a primary/backup implementation
  • D. The multihomed customer must use private AS number
  • E. The multihomed customer configures outbound route filters to prevent itself from becoming a transit AS

Answer: BCE

NEW QUESTION 5
Which multicast routing protocol supports dense mode, sparse mode and bidirectional mode?

  • A. DVMRP
  • B. MOSPF
  • C. PIM
  • D. MP-BGP
  • E. MSDP

Answer: C

NEW QUESTION 6
Which statement is correct regarding using the TTL threshold to define the delivery boundaries of multicast traffic?

  • A. If a packet TTL is less than the specified TTL threshold, the packet is forwarded out of the interface
  • B. If a packet TTL is greater or equal to the specified TTL threshold, the packet is forwarded out of the interface
  • C. If a packet TTL is equal to the specified TTL threshold, the packet is dropped
  • D. When a multicast packet arrives, the TTL threshold value is decremented by 1. If the resulting TTL threshold value is greater than or equal to 0, the packet is dropped

Answer: B

NEW QUESTION 7
Which command set implements BGP support for NSF/SSO on Cisco IOS XE between a PE and a route reflector?

  • A. On RR:router bgp 300no synchronizationbgp log-neighbor-changesbgp graceful-restart restart-time 120 bgp graceful-restart stalepath-time 360 bgp graceful-restartneighbor 10.20.20.2 remote-as 200neighbor 10.20.20.2 update-source Loopback0 no auto-summary!address-family vpnv4 neighbor 10.20.20.2 activateneighbor 10.20.20.2 send-community both neighbor 10.20.20.2 route-reflector-client exit-address-familyOn PE:router bgp 300no synchronizationbgp log-neighbor-changesbgp graceful-restart restart-time 120 bgp graceful-restart stalepath-time 360 bgp graceful-restartneighbor 10.20.20.1 remote-as 300neighbor 10.20.20.1 update-source Loopback0 no auto-summary!address-family vpnv4 neighbor 10.20.20.1 activateneighbor 10.20.20.1 send-community both exit-address-family!
  • B. On RR:router bgp 300no synchronizationbgp log-neighbor-changesbgp graceful-restart restart-time 120 bgp graceful-restart stalepath-time 360 bgp graceful-restartneighbor 10.20.20.2 remote-as 200neighbor 10.20.20.2 update-source Loopback0 no auto-summary!address-family vpnv4 neighbor 10.20.20.2 activateneighbor 10.20.20.2 send-community both neighbor 10.20.20.2 route-reflector-client exit-address-familyOn PE:router bgp 300no synchronizationbgp log-neighbor-changes neighbor 10.20.02.1 remote-as 300neighbor 10.20.20.1 update-source Loopback0 no auto-summary!address-family vpnv4 neighbor 10.20.20.1 activateneighbor 10.20.20.1 send-community both exit-address-family!
  • C. On RR:router bgp 300no synchronizationbgp log-neighbor-changesbgp graceful-restart restart-time 120 bgp graceful-restart stalepath-time 360 bgp graceful-restartneighbor 10.20.20.2 remote-as 200neighbor 10.20.20.2 update-source Loopback0 no auto-summary!address-family vpnv4 neighbor 10.20.20.2 activateneighbor 10.20.20.2 send-community both neighbor 10.20.20.2 route-reflector-client exit-address-familyOn PE:router bgp 300no synchronizationbgp log-neighbor-changes neighbor 10.20.20.1 remote-as 300neighbor 10.20.20.1 update-source Loopback0 neighbor 10.20.20.1 ha-mode ssono auto-summary!address-family vpnv4 neighbor 10.20.20.1 activateneighbor 10.20.20.1 send-community both exit-address-family!
  • D. On RR:router bgp 300no synchronizationbgp log-neighbor-changes neighbor 10.20.20.2 remote-as 200neighbor 10.20.20.2 update-source Loopback0 neighbor 10.20.20.2 ha-mode ssono auto-summary!address-family vpnv4 neighbor 10.20.20.2 activateneighbor 10.20.20.2 send-community both neighbor 10.20.20.2 route-reflector-client exit-address-familyOn PE:router bgp 300no synchronizationbgp log-neighbor-changes neighbor 10.20.20.1 remote-as 300neighbor 10.20.20.1 update-source Loopback0 neighbor 10.20.20.1 ha-mode ssono auto-summary!address-family vpnv4 neighbor 10.20.20.1 activateneighbor 10.20.20.1 send-community both exit-address-family!
  • E. On RR:router bgp 300no synchronizationbgp log-neighbor-changesneighbor 10.20.20.2 remote-as 200neighbor 10.20.20.2 update-source Loopback0 no auto-summary!address-family vpnv4 neighbor 10.20.20.2 activateneighbor 10.20.20.2 send-community both neighbor 10.20.20.2 route-reflector-client exit-address-familyOn PE:router bgp 300no synchronizationbgp log-neighbor-changesbgp graceful-restart restart-time 120 bgp graceful-restart stalepath-time 360 bgp graceful-restartneighbor 10.20.20.1 remote-as 300neighbor 10.20.20.1 update-source Loopback0 no auto-summary!address-family vpnv4 neighbor 10.20.20.1 activateneighbor 10.20.20.1 send-community both exit-address-family!

Answer: A

NEW QUESTION 8
Which command set should be used for a 6to4 tunnel in a Cisco IOS XE router, considering the border interface with IPv4 address of 209.165.201.2?

  • A. interface Tunnel2002 ipv6 enableipv6 address 2002:D1A5:C902::1/128 tunnel source Ethernet0/0tunnel mode ipv6ip 6to4
  • B. interface Tunnel2002 ipv6 enableipv6 address 2002:D1A5:D902::1/128 tunnel source Ethernet0/0tunnel mode ipv6ip 6to4
  • C. interface Tunnel2002 ipv6 enableipv6 address 2002:D1A5:D902::1/128 tunnel source Ethernet0/0tunnel mode ipv6ip
  • D. interface Tunnel2002 ipv6 enableipv6 address 2002:D1A5:C902::1/128 tunnel source Ethernet0/0tunnel mode ipv6ip auto-tunnel
  • E. interface Tunnel2002ipv6 enableipv6 address 2002:D1A5:D902::1/128 tunnel source Ethernet0/0tunnel mode ipv6ip auto-tunnel

Answer: B

NEW QUESTION 9
An engineer is providing DNS for IPv6 over a currently working IPv4 domain. Which three changes are needed to offer DNS functionality for IPv6? (Choose three.)

  • A. Define a new record that stores the 128-bit IPv6 address.
  • B. Expand the existing IP address record to allow for 128 bits.
  • C. Define the IPv6 equivalent of the in-addr.arpa.com domain of the IPv4 PTR.
  • D. Modify the in-addr.arpa.com domain of the IPv4 PTR.
  • E. Change the query messages.
  • F. Transport IPv6 query messages by using UDP.
  • G. Transport IPv6 query messages by using TCP.

Answer: ACE

NEW QUESTION 10
After configuring the tunnel interface as shown in the exhibit, no IPv6 traffic is passed over the IPv4 network.
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Which additional configuration is required to pass the IPv6 traffic over the IPv4 network?

  • A. Configure an IPv4 address on the tunnel0 interface
  • B. Configure an IPv6 static route to send the required IPv6 traffic over the tunnel0 interface
  • C. The tunnel destination should be pointing to an IPv6 address instead of an IPv4 address
  • D. The tunnel0 interface IPv6 address must use the 2002:://16 prefix

Answer: B

NEW QUESTION 11
Which two commands can be used to implement a valid Cisco IOS XE IPv6 static tunnel configuration? (Choose two.)

  • A. interface Tunnel100 ipv6 enableipv6 address 2001:DB8::1/128 tunnel destination 209.165.201.2 tunnel mode ipv6ip 6to4
  • B. interface Tunnel100 ipv6 enableipv6 address 2001:DB8::1/128 tunnel source Ethernet 0/1 tunnel destination 209.165.201.2 tunnel mode gre ip
  • C. interface Tunnel 100 ipv6 enableip address 209.165.201.2 tunnel source Loopback 0 tunnel mode ipv6ip 6to4
  • D. interface Tunnel100 ipv6 enableipv6 address 2001:DB8::1/128 tunnel source Ethernet 0/1 tunnel destination 209.165.201.2 tunnel mode isatap
  • E. interface Tunnel100 ipv6 enableipv6 address 2001:DB8::1/128 tunnel source Ethernet 0/1 tunnel destination 209.165.201.2 tunnel mode auto-tunnel
  • F. interface Tunnel100 ipv6 enableipv6 address 2001:DB8::1/128 tunnel source Ethernet 0/1 tunnel destination 209.165.201.2tunnel mode ipv6ip

Answer: BF

NEW QUESTION 12
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: ACD

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).

NEW QUESTION 13
Refer to the exhibit.
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On the PE5 router, which statementis correct regarding the learned BGP prefixes?

  • A. The 209.165.201.0/27 prefix is received from the 10.0.1.1 IBGP peer which is a route reflector
  • B. The 172.16.66.0/24 prefix BGP next-hop points to the route reflector
  • C. All prefixes learned on PE5 has the default local preference value
  • D. The 209.165.202.128/27 prefix is originated by the 10.0.1.1 IBGP peer

Answer: C

Explanation:
#show ip bgp -- check i tag for PE5

NEW QUESTION 14
Refer to the exhibit.
642-885 dumps exhibit
Based on the output of two eBGP adjacent neighbors, which command can be used to set up the default BGP timers?

  • A. RP/0/0/CPU0:R1(config-bgp)#timers bgp 60 30
  • B. RP/0/0/CPU0:R2(config-bgp)#timers bgp 30 60
  • C. RP/0/0/CPU0:R2(config-bgp-nbr)#timers bgp 180 60
  • D. RP/0/0/CPU0:R2(config-bgp)#timers bgp 60 180
  • E. RP/0/0/CPU0:R1(config-bgp)#timers bgp 60 180

Answer: D

NEW QUESTION 15
Refer to the exhibit.
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Which three statements regarding the BGP operations are correct? (Choose three)

  • A. PE5 is the route reflector with P1 and PE6 as its client
  • B. PE5 is using the IS-IS route to reach the BGP next-hop for the 172.16.66.0/24 prefix
  • C. PE5 has BGP route dampening enabled
  • D. The BGP session between PE5 and P1 is established using the loopback interface andnext-hop-self
  • E. The BGP session between PE5 and CE5 is established using the loopback interface

Answer: ACD

NEW QUESTION 16
The 224.192.16.1 multicast IP address maps to which multicast MAC address?

  • A. 01-00-5E-C0-10-01
  • B. 01-00-5E-40-10-01
  • C. 01-00-5E-00-10-01
  • D. 01-00-5E-C0-16-01

Answer: B

Explanation:
Least significant 23 bits of IP address and pre-pend 01-00-5E
224 ignore
192 less 128 becomes 64 = 40
16 = 10
1 = 01
01-00-5E-40-10-01

NEW QUESTION 17
Which of the following is a feature added in IGMPv3?

  • A. Support for source filtering
  • B. Support for Host Membership Report and a Leave Group message
  • C. Uses a new variation of the Host Membership Query called the Group-Specific Host Membership Query
  • D. Uses an election process to determine the querying router on the LAN
  • E. Uses an election process to determine the designated router on the LAN
  • F. IPv6 support

Answer: A

NEW QUESTION 18
Which two options are thecommon methods for implementing Site of Origin on Cisco IOS XE routers for loop avoidance in multihome BGP customers? (Choose two.)

  • A. Configure the route-map in command on the CE BGP neighbor.
  • B. Configure Site of Origin directly on the CE BGP neighbor command.
  • C. Configure site-map on VRF interface and redistribution of iBGP.
  • D. Configure site-map on VRF interface and network command.
  • E. Configure the route-map out command on the P router.

Answer: AB

NEW QUESTION 19
DRAG DROP
642-885 dumps exhibit

  • A. Mastered
  • B. Not Mastered

Answer: A

Explanation:
IPv6-in-IPv4 and GRE are manual and 6RDand 6to4
642-885 dumps exhibit
Download this chapter Implementing Tunnels Download the complete book
Interface and Hardware Component Configuration Guide, Cisco IOS XE Release 3S (PDF - 1 MB) Feedback
Contents Implementing Tunnels
Finding Feature Information Restrictions for Implementing Tunnels
Information About Implementing Tunnels Tunneling Versus Encapsulation
Tunnel ToS
Generic Routing Encapsulation
GRE Tunnel IP Source and Destination VRF Membership GRE IPv4 Tunnel Support for IPv6 Traffic
EoMPLS over GRE
Provider Edge to Provider Edge Generic Routing EncapsulationTunnels Provider to Provider Generic Routing Encapsulation Tunnels
Provider Edge to Provider Generic Routing Encapsulation Tunnels Features Specific to Generic Routing Encapsulation
Features Specific to Ethernet over MPLS
Features Specific to Multiprotocol Label Switching Virtual Private Network Overlay Tunnels for IPv6
IPv6 Manually Configured Tunnels Automatic 6to4 Tunnels
ISATAP Tunnels Path MTU Discovery
QoS Options for Tunnels How to Implement Tunnels Determining the Tunnel Type
Configuring an IPv4 GRE Tunnel GRE Tunnel Keepalive
What to Do Next
Configuring GRE on IPv6 Tunnels What to Do Next
Configuring GRE Tunnel IP Source and Destination VRF Membership What to Do Next
Manually Configuring IPv6 Tunnels What to Do Next
Configuring 6to4 Tunnels What to Do Next
Configuring ISATAP Tunnels
Verifying Tunnel Configuration and Operation Configuration Examples for Implementing Tunnels Example: Configuring a GRE IPv4 Tunnel Example: Configuring GRE on IPv6 Tunnels
Example: Configuring GRE Tunnel IP Source and Destination VRF Membership Example: Configuring EoMPLS over GRE
Example: Manually Configuring IPv6 Tunnels Example: Configuring 6to4 Tunnels Example: Configuring ISATAP Tunnels
Configuring QoS Options on Tunnel Interfaces Examples Policing Example
Additional References
Feature Information for Implementing Tunnels Implementing Tunnels
Last Updated: September 17, 2012
This module describes the various types of tunneling techniques. Configuration details and examples are
provided for the tunnel types that use physical or virtual interfaces. Many tunneling techniques are
implemented using technology-specific commands, and links are provided to the appropriate technology
modules.
Tunneling provides a way to encapsulate arbitrary packets inside a transport protocol.
Tunnels are
implemented as virtual interfaces to provide a simple interface for configuration purposes.
The tunnel interface
is not tied to specific "passenger" or "transport" protocols, but rather is an architecture to provide the services
necessary to implement any standard point-to-point encapsulation scheme. Note
Cisco ASR 1000 Series Aggregation Services Routers support VPN routing and forwarding (VRF)-aware
generic routing encapsulation (GRE) tunnel keepalive features. Finding Feature Information
Restrictions for Implementing Tunnels Information About Implementing Tunnels How to Implement Tunnels
Configuration Examples for Implementing Tunnels Additional References
Feature Information for Implementing Tunnels Finding Feature Information
Your software release may not support all the features documented in this module. For the latest caveats and feature information, see Bug Search Tool and the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the feature information table at the end of this module.
Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.
Restrictions for Implementing Tunnels
It is important to allow the tunnel protocol to pass through a firewall and access control list (ACL) check.
Multiple point-to-point tunnels can saturate the physical link with routing information if the bandwidth is not
configured correctly on a tunnel interface.
A tunnel looks like a single hop link, and routing protocols may prefer a tunnel over a multihop physical path.
The tunnel, despite looking like a single hop link, may traverse a slower path than a multihop link. A tunnel is as robust and fast, or as unreliable and slow, as the links that it actually traverses. Routing protocols that make their decisions based only on hop counts will often prefer a tunnel over a set of physical links. A tunnel might appear to be a one-hop, point-to-point link and have the lowest-cost path, but the tunnel may actually cost more in terms of latency when compared to an alternative physical topology. For example, in the topology shown in the figure below, packets from Host 1 will appear to travel across networks w, t, and z to get to Host 2 instead of taking the path w, x, y, and z because the tunnel hop count appears shorter. In fact, the packets going through the tunnel will still be traveling across Router A, B, and C, but they must also travel to Router D before coming back to Router C. Figure 1
Tunnel Precautions: Hop Counts
A tunnel may have a recursive routing problem if routing is not configured accurately. The best path to a tunnel destination is via the tunnel itself; therefore recursive routing causes the tunnel interface to flap. To avoid recursive routing problems, keep the control-plane routing separate from the tunnel routing by using the following methods:
Use a different autonomous system number or tag. Use a different routing protocol.
Ensure that static routes are used to override the first hop (watch for routing loops). The following error is displayed when there is recursive routing to a tunnel destination:
%TUN-RECURDOWN Interface Tunnel 0 temporarily disabled due to recursive routing Information About Implementing Tunnels Tunneling Versus Encapsulation
Tunnel ToS
Generic Routing Encapsulation EoMPLS over GRE
Overlay Tunnels for IPv6
IPv6 Manually Configured Tunnels Automatic 6to4 Tunnels
ISATAP Tunnels Path MTU Discovery
QoS Options for Tunnels
Tunneling Versus Encapsulation
To understand how tunnels work, you must be able to distinguish between concepts of encapsulation and tunneling. Encapsulation is the process of adding headers to data at each layer of a particular protocol stack.
The Open Systems Interconnection (OSI) reference model describes the functions of a network. To send a data packet from one host (for example, a PC) to another on a network, encapsulation is used to add a header in front of the data packet at each layer of the protocol stack in descending order. The header must contain a data field that indicates the type of data encapsulated at the layer immediately above the current layer. As the packet ascends the protocol stack on the receiving side of the network, each encapsulation header is removed in reverse order.
Tunneling encapsulates data packets from one protocol within a different protocol and transports the packets on a foreign network. Unlike encapsulation, tunneling allows a lower-layer protocol and a same-layer protocol to be carried through the tunnel. A tunnel interface is a virtual (or logical) interface. Tunneling consists of three main components: Passenger protocol--The protocol that you are encapsulating. For example, IPv4 and IPv6 protocols. Carrier protocol--The protocol that encapsulates. For example, generic routing encapsulation (GRE) and Multiprotocol Label Switching (MPLS).
Transport protocol--The protocol that carries the encapsulated protocol. The main transport protocol is IP.
The figure below illustrates IP tunneling terminology and concepts: Figure 2
IP Tunneling Terminology and Concepts Tunnel ToS
Tunnel type of service (ToS) allows you to tunnel network traffic and group all packets in the same ToS byte value. The ToS byte values and Time-to-Live (TTL) hop-count value can be set in the encapsulating IP header of tunnel packets for an IP tunnel interface on a router. Tunnel ToS feature is supported for Cisco Express Forwarding (formerly known as CEF), fast switching, and process switching.
The ToS and TTL byte values are defined in RFC 791. RFC 2474, and RFC 2780 obsolete the use of the ToS byte as defined in RFC 791. RFC 791 specifies that bits 6 and 7 of the ToS byte (the first two least significant bits) are reserved for future use and should be set to
1. For Cisco IOS XE Release 2.1, the Tunnel ToS feature does not conform to this standard and allows you touse the whole ToS byte value, including bits 6 and 7, and to decide to which RFC standard the ToS byte of your packets should conform.
Generic Routing Encapsulation
GRE is defined in RFC 2784. GRE is a carrier protocol that can be used with many different underlying transport protocols and can carry many passenger protocols. RFC
2784 also covers the use of GRE with IPv4 as the transport protocol and the passenger protocol. Cisco software supports GRE as the carrier protocol with many combinations of passenger and transport protocols.
GRE tunnels are described in the following sections: GRE Tunnel IP Source and Destination VRF Membership GRE IPv4 Tunnel Support for IPv6 Traffic
GRE Tunnel IP Source and Destination VRF Membership
The GRE Tunnel IP Source and Destination VRF Membership feature allows you to configure the source and destination of a tunnel to belong to any VPN routing and forwarding (VRFs) tables. A VRF table stores routing data for each VPN. The VRF table defines the VPN membership of a customer site that is attached to the network access server (NAS). Each VRF table comprises an IP routing table, a derived Cisco Express Forwarding table, and guidelines and routing protocol parameters that control the information that is included in the routing table.
Prior to Cisco IOS XE Release 2.2, GRE IP tunnels required the IP tunnel destination to be in the global routing table. The implementation of this feature allows you to configure a tunnel source and destination to belong to any VRF. As with existing GRE tunnels, the tunnel becomes disabled if no route to the tunnel destination is defined.
GRE IPv4 Tunnel Support for IPv6 Traffic
IPv6 traffic can be carried over IPv4 GRE tunnels by using the standard GRE tunneling technique to provide the services necessary to implement a standard point-to-point encapsulation scheme. GRE tunnels are links between two points, with a separate tunnel for each point. GRE tunnels are not tied to a specific passenger or transport protocol, but in case of IPv6 traffic, IPv6 is the passenger protocol, GRE is the carrier protocol, and IPv4 is the transport protocol.
The primary use of GRE tunnels is to provide a stable connection and secure communication between two edge devices or between an edge device and an end system. The edge device and the end system must have a dual-stack implementation.
GRE has a protocol field that identifies the passenger protocol. GRE tunnels allow intermediate system to intermediate system (IS-IS) or IPv6 to be specified as the passenger protocol, therebyallowing both IS-IS and IPv6 traffic to run over the same tunnel. If GRE does not have a protocol field, it becomes impossible to distinguish whether the tunnel is carrying IS-IS or IPv6 packets.
EoMPLS over GRE
Ethernet over MPLS (EoMPLS) is a tunneling mechanism that allows you to tunnel Layer 2 traffic through a Layer 3 MPLS network. EoMPLS is also known as Layer 2 tunneling.
EoMPLS effectively facilitates Layer 2 extension over long distances. EoMPLS over GRE helps you to create the GRE tunnel as hardware-based switched, and encapsulates EoMPLS frames within the GRE tunnel. The GRE connection is established between the two core routers, and then the MPLS label switched path (LSP) is tunneled over.
GRE encapsulation is used to define a packet that has header information added to it prior to being forwarded.
De-encapsulation is the process of removing the additional header information when the packet reaches the destination tunnel endpoint.
When a packet is forwarded through a GRE tunnel, two new headers are added to the front of the packet and hence the context of the new payload changes. After encapsulation, what was originally the data payload and separate IP header are now known as the GRE payload. A GRE header is added to the packet to provide information on the protocol type and the recalculated checksum. A new IP header is also added to the front of the GRE header. This IP header contains the destination IP address of the tunnel. The GRE header is added to packets such as IP, Layer 2 VPN, and Layer 3 VPN before the header enters into the tunnel. All routers along the path that receives the encapsulated packet use the new IP header to determine how the packet can reach the tunnel endpoint.
In IP forwarding, on reaching the tunnel destination endpoint, the new IP header and the GRE header are removed from the packet and the original IP header is used to forward the packet to the final destination.
The EoMPLS over GRE feature removes the new IP header and GRE header from the packet at the tunnel destination, and the MPLS label is used to forward the packet to the appropriate Layer 2 attachment circuit or Layer 3 VRF.
The scenarios in the following sections describe the L2VPN and L3VPN over GRE deployment on provider edge (PE) or provider (P) routers:
Provider Edge to Provider Edge Generic Routing EncapsulationTunnels Provider to Provider Generic Routing Encapsulation Tunnels
Provider Edge to Provider Generic Routing Encapsulation Tunnels Features Specific to Generic Routing Encapsulation
Features Specific to Ethernet over MPLS
Features Specific to Multiprotocol Label Switching Virtual Private Network Provider Edge to Provider Edge Generic Routing EncapsulationTunnels
In the Provider Edge to Provider Edge (PE) GRE tunnels scenario, a customer does not transition any part of the core to MPLS but prefers to offer EoMPLS and basic MPLS VPN services. Therefore, GRE tunneling of MPLS traffic is done between PEs.
Provider to Provider Generic Routing Encapsulation Tunnels
In the Provider to Provider (P) GRE tunnels scenario, Multiprotocol Label Switching (MPLS) is enabled between Provider Edge (PE ) and P routers but the network core can either have non-MPLS aware routers or IP encryption boxes. In this scenario, GRE tunneling of the MPLS labeled packets is done between P routers.
Provider Edge to Provider Generic Routing Encapsulation Tunnels in a Provider Edge to Provider GRE tunnels scenario, a network has MPLS-aware P to P nodes. GRE tunneling is done between a PE to P non-MPLS network segment. Features Specific to Generic Routing Encapsulation You should understand the following configurations and information for a deployment scenario:
Tunnel endpoints can be loopbacks or physical interfaces.
Configurable tunnel keepalive timer parameters per endpoint and a syslog message must be generated when the keepalive timer expires.
Bidirectional forwarding detection (BFD) is supported for tunnel failures and for the Interior Gateway Protocol (IGP) that use tunnels.
IGP load sharing across a GRE tunnel is supported. IGP redundancy across a GRE tunnel is supported. Fragmentation across a GRE tunnel is supported. Ability to pass jumbo frames is supported.
All IGP control plane traffic is supported.
IP ToS preservation across tunnels is supported.
A tunnel should be independent of the endpoint physical interface type; for example, ATM, Gigabit, Packet over SONET (POS), and TenGigabit.
Up to 100 GRE tunnels are supported. Features Specific to Ethernet over MPLS
Any Transport over MPLS (AToM) sequencing. IGP load sharing and redundancy.
Port mode Ethernet over MPLS (EoMPLS). Pseudowire redundancy.
Support for up to to 200 EoMPLS virtual circuits (VCs).
Tunnel selection and the ability to map a specific pseudowire to a GRE tunnel. VLAN mode EoMPLS.
Features Specific to Multiprotocol Label Switching Virtual Private Network Support for the PE role with IPv4 VRF.
Support for all PE to customer edge (CE) protocols.
Load sharing through multiple tunnels and also equal cost IGP paths with a single tunnel. Support for redundancy through unequal cost IGP paths with a single tunnel.
Support for the IP precedence value being copied onto the expression (EXP) bits field of the Multiprotocol Label Switching (MPLS) label and then onto the precedence bits on the outer IPv4 ToS field of the generic routing encapsulation (GRE) packet.
See the section, "Example: Configuring EoMPLS over GRE" for a sample configuration sequence of EoMPLS over GRE. For more details on EoMPLS over GRE, see the Deploying and Configuring MPLS Virtual Private Networks
In IP Tunnel Environments document. Overlay Tunnels for IPv6
The figure below illustrates how overlay tunneling encapsulates IPv6 packets in IPv4 packets for delivery across an IPv4 infrastructure (a core network or the Internet). By using overlay tunnels, you can communicate with isolated IPv6 networks without upgrading the IPv4 infrastructure between them. Overlay tunnels can be configured between border routers or between a border router and a host; however, both tunnel endpoints must support, IPv4 and IPv6 protocol stacks. IPv6 supports the following types of overlay tunneling mechanisms:
6to4 GRE
Intra-Site Automatic Tunnel Addressing Protocol (ISATAP) IPv4-compatible
Manual Figure 3
Overlay Tunnels Note
If the basic IPv4 packet header does not have optional fields, overlay tunnels can reduce the maximum transmission unit (MTU) of an interface by 20 octets. A network that uses overlay tunnels is difficult to troubleshoot. Therefore, overlay tunnels that connect isolated IPv6 networks should not be considered as the final IPv6 network architecture. The use of overlay tunnels is considered as a transition technique for a network that supports either both IPv4 and IPv6 protocol stacks or just the IPv6 protocol stack.
Consult the table below to determine which type of tunnel you want to configure to carry IPv6 packets over an IPv4 network.
Table 1
Suggested Usage of Tunnel Types to Carry IPv6 Packets over an IPv4 Network Tunneling Type
Suggested Usage Usage Notes 6to4
Point-to-multipoint tunnels that can be used to connect isolated IPv6 sites. Sites use addresses that begin with the 2002::/16 prefix.
GRE/IPv4
Simple point-to-point tunnels that can be used within a site or between sites.
Tunnels can carry IPv6, Connectionless Network ServiceCLNS, and many other types of packets.
ISATAP
Point-to-multipoint tunnels that can be used to connect systems within a site. Sites can use any IPv6 unicast addresses.
Manual
Simple point-to-point tunnels that can be used within a site or between sites. Tunnels can carry IPv6 packets only.
Individual tunnel types are discussed in detail in the following concepts, and we recommend that you review and understand the information on the specific tunnel type that you want to implement. Consult the table below for a summary of the tunnel configuration parameters that you may find useful.
Table 2
Overlay Tunnel Configuration Parameters by Tunneling Type Overlay Tunneling Type
Overlay Tunnel Configuration Parameter Tunnel Mode
Tunnel Source Tunnel Destination
Interface Prefix/Address 6to4
ipv6ip 6to4
An IPv4 address or a reference to an interface on which IPv4 is configured.
Not required. These are all point-to-multipoint tunneling types. The IPv4 destination address is calculated, on a per-packet basis, from the IPv6 destination.
An IPv6 address. The prefix must embed the tunnel source IPv4 address.
GRE/IPv4
gre ip
An IPv4 address. An IPv6 address. ISATAP
ipv6ip isatap
Not required. These are all point-to-multipoint tunneling types. The IPv4 destination address is calculated on a per-packet basis from the IPv6 destination.
An IPv6 prefix in modified eui-64 format. The IPv6 address is generated from the prefix and the tunnel source IPv4 address.
Manual ipv6ip
An IPv4 address. An IPv6 address.
IPv6 Manually Configured Tunnels
A manually configured tunnel is equivalent to a permanent link between two IPv6 domains over an IPv4 backbone. The primary use of a manually configured tunnel is to stabilize connections that require secure communication between two edge routers, or between an end system and an edge router. The manual configuration tunnel also stabilizes connection between remote IPv6 networks.
An IPv6 address is manually configured on a tunnel interface. Manually configured IPv4 addresses are assigned to the tunnel source and destination. The host or router at each end of a configured tunnel must support both the IPv4 and IPv6 protocol stacks. Manually configured tunnels can be configured between border routers or between a border router and a host. Cisco Express Forwarding switching can be used for manually configured IPv6 tunnels. Switching can be disabled if process switching is required.
Automatic 6to4 Tunnels
An automatic 6to4 tunnel allows isolated IPv6 domains to be connected over an IPv4 network to remote IPv6 networks. The key difference between automatic 6to4 tunnels and manuallyconfigured tunnels is that the tunnel is not point-to-point; it is point-to-multipoint. In automatic 6to4 tunnels, routers are not configured in pairs because they treat the IPv4 infrastructure as a virtual nonbroadcast multiaccess (NBMA) links. The IPv4 address embedded in the IPv6 address is used to find the other end of the automatic tunnel.
An automatic 6to4 tunnel may be configured on a border router in an isolated IPv6 network, which creates a tunnel on a per-packet basis on a border router in another IPv6 network over an IPv4 infrastructure. The tunnel destination is determined by the IPv4 address of the border router extracted from the IPv6 address that starts with the prefix 2002::/16, where the format is 2002:border-router-IPv4-address ::/48.The embedded IPv4 addresses are 16 bits and can be used to number networks within the site. The border router at each end of a 6to4 tunnel must support both IPv4 and IPv6 protocol stacks. 6to4 tunnels are configured between border routers or between a border router and a host.
The simplest deployment scenario for 6to4 tunnels is to interconnect multiple IPv6 sites, each of which has at least one connection to a shared IPv4 network. This IPv4 network could either be the Internet or a corporate backbone. The key requirement is that each site have a globally unique IPv4 address; the Cisco software uses this address to construct a globally unique 6to4/48 IPv6 prefix. A tunnel with appropriate entries in a Domain Name System (DNS) that maps hostnames and IP addresses for both IPv4 and IPv6 domains, allows the applications to choose the required address IPv6 traffic can be carried over IPv4 GRE tunnels by using the standard GRE tunneling technique to provide the services necessary to implement a standard point-to-point encapsulation scheme. GRE tunnels are links between two points, with a separate tunnel for each point. GRE tunnels are not tied to a specific passenger or transport protocol, but in case of IPv6 traffic, IPv6 is the passenger protocol, GRE is the carrier protocol, and IPv4 is the transport protocol.
The primary use of GRE tunnels is to provide a stable connection and secure communication between two edge devices or between an edge device and an end system. The edge device and the end system must have a dual-stack implementation. GRE has a protocol field that identifies the passenger protocol. GRE tunnels allow intermediate system to intermediate system (IS-IS) or IPv6 to be specified as the passenger protocol, thereby allowing both IS-IS and IPv6 traffic to run over the same tunnel. If GRE does not have a protocol field, it becomes impossible to distinguish whether the tunnel is carrying IS-IS or IPv6 packets.

NEW QUESTION 20
You noticed a recent change to the BGP configuration on a PE router, the bgp scan time has been changed from the default value to 30s. Which three effects will this change have? (Choose three.)

  • A. The BGP table will be examined and verified more frequently
  • B. The BGP keepalive messages will be sent to the BGP peers at a faster rate
  • C. The BGP table will be modified more quickly in the event that a next-hop address becomes unreachable
  • D. The CPU load of the router will increase
  • E. The minimum time interval between sending EBGP and IBGP routing updates will decrease
  • F. The BGP convergence time will increase

Answer: ACD

NEW QUESTION 21
On Cisco IOS-XR, which BGP configuration group allows you to define address-family independent commands and address-family dependent commands for each address family?

  • A. neighbor-group
  • B. session-group
  • C. af-group
  • D. peer-group

Answer: A

Explanation:
•Commands relating to a peer group found in Cisco IOS Release 12.2 have been removed from Cisco IOS XR software. Instead, the af-group, session-group, and neighbor-group configuration commands are added to support the neighbor in Cisco IOS XR software:
–The af-group command is used to group address family-specific neighbor commands within an IPv4 or IPv6 address family. Neighbors that have the same address family configuration are able to use the address family group name for their address family- specific configuration. A neighbor inherits the configuration from an address family group by way of the use command. If a neighbor is configured to use an address family group, the neighbor will (by default) inherit the entire configuration from the address family group. However, a neighbor will not inherit all ofthe configuration from the address family group if items are explicitly configured for the neighbor.
–The session-group command allows you to create a session group from which neighbors can inherit address family-independent configuration. A neighbor inherits the configuration from a session group by way of the use command. If a neighbor is configured to use a session group, the neighbor (by default) inherits the session group's entire configuration. A neighbor does not inherit all the configuration from a session group if a configuration is done directly on that neighbor.
–The neighbor-group command helps you apply the same configuration to one or more neighbors. Neighbor groups can include session groups and address family groups. This additional flexibility can create a complete configuration for a neighbor. Once a neighbor group is configured, each neighbor can inherit the configuration through the use command. If a neighbor is configured to use a neighbor group, the neighbor (by default) inherits the neighbor group's entire BGP configuration.
–However, a neighbor will not inherit all of the configuration from the neighbor group if items are explicitly configured for the neighbor. In addition, some part of the neighbor group's configuration could be hidden if a session group or address family group was also being used

NEW QUESTION 22
In secure multicast, which protocol is used to distribute secure keys to a multicast group?

  • A. ISAKMP
  • B. RSA
  • C. IPsec
  • D. GDOI
  • E. SKIP

Answer: D

NEW QUESTION 23
A service providerrequests more details about the recent Inter-AS MPLS VPN Option B configuration that was recently deployed. Consider this configuration:
router bgp 3717
address-family vpnv4 unicast retain route-target all
commit
!
Which option describes why this particular command is needed?

  • A. The ASBRcan have many working customer VRFs, so this configuration ensures the coexistence of all the route-target extended communities that belong to the all ASBR- terminated customer VRFs.
  • B. When implementing the Inter-AS Option B MPLS VPN solution, all the route targets that are transmitted over the Inter-AS links need an ASBR local database to forward thecustomer traffic correctly.
  • C. The Inter-AS Option B design implements VPNv4 communication over the Inter-AS link, hence the requirement for a route-target association for each customer VPN connected across two or more ASs.
  • D. In the Inter-AS Option B design, no local VRF is maintained on the ASBR routers,so the default behavior of the operating system is to deny any route-target extended community that is encoded in the incoming iBGP update
  • E. This configuration permits VPNv4 communication by accepting the iBGP updates even if no route targets are configured locally.

Answer: D

NEW QUESTION 24
What must occur before an (S,G) entry can be populated in the multicast routing table?

  • A. The (*,G) entry must have timed out
  • B. The (*,G) entry OIL must be null
  • C. The router must be directly connected to the multicast source
  • D. The parent (*,G) entry must be created first

Answer: D

NEW QUESTION 25
DRAG DROP
642-885 dumps exhibit

  • A. Mastered
  • B. Not Mastered

Answer: A

Explanation:
The amount of time for the penalty to decrease to one-half of its current value - 60 Suppress a route when its penalty exceeds this value - 2400
If a flapping route penalty decreases and falls below this value , the route is unsuppressed
- 600
The maximum time a route can be suppressed – 240
642-885 dumps exhibit
SO bgp dampening 60 600 2400 240 is:
60 half life
600 reuse
2400 suppress
240 max-suppress-time

NEW QUESTION 26
......

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