Cisco (300-410-ENARSI) Exam Questions And Answers page 22

External BGP (eBGP) peers do update the AS_Path attribute before sending updates to another eBGP peer. This helps to maintain the path back to the source of the update.
eBGP peers use TCP to communicate, and they do so on port 179 by default.
Internal BGP (BGP) peers are routers that reside in the same AS. iBGP peers do not update the AS_Path attribute before sending updates to an iBGP peer. That is only done when an update is sent from an eBGP peer to another eBGP peer.
Objective:
Layer 3 Technologies
Sub-Objective:
Explain BGP attributes and best-path selection
Home > About Cisco > Publications and Merchandise > The Internet Protocol Journal > Back issues > Volume 9,Number 1, March 2006 > Autonomous System Numbers > Exploring Autonomous System Numbers

Network Prefix Translation (NPTv6) is a stateless method of translating the prefix of a received IPv6 address to another prefix without changing the host portion of the IPv6 address. Some of its characteristics are:
• It supports both transports that perform checksums on the IP header and those that do not.
• It provides a 1 to 1 relationship between the inside and outside prefixes.
• It translates only the prefix, and not the entire address.
Objective:
Infrastructure Services
Sub-Objective:
Describe IPv6 NAT
Cisco > Publications and Merchandise > The Internet Protocol Journal > Issues > Volume 14, Number 2, June 2011 > IPv6 Site Multihoming
Howfunky...a place with useless technical content!>IPv6 to IPv6 Network Prefix Translation or NPTv6

The only loopback interface used in the communication is the loopback 0 interface of rtrA. The configuration on the rtrA router indicates that BGP is enabled on rtrA in the autonomous system number (ASN) 450. The neighbor 131.78.45.2 remote-as 450 command establishes a connection with the rtrB interface having the 131.78.45.2 address. The Gi0/1 interface of rtrB has the address 131.78.45.2, which is directly connected to the Gi0/0 interface (132.78.45.1) of rtrA. The next line, neighbor 131.78.45.2 update-source loopback 0, specifies that the 131.78.45.2 interface (Gi0/1) of rtrB communicates with the loopback 0 interface on rtrA.
In the configuration of rtrB, the neighbor 10.144.1.1 remote-as 450 command establishes a neighboring relationship with the interface having the address10.144.1.1. The loopback 0 interface of rtrA has the address 10.144.1.1. The loopback 1 interface on rtrB is assigned an IP address but not used in establishing BGP connections between rtrA and rtrB
Loopback 1 interface of rtrB only would only be used in the communication between rtrA and rtrB if you configured rtrA and rtrB as follows:
rtrA(config)#router bgp 450
rtrA(config-router)# neighbor 131.78.1.1 remote-as 450
rtrB(config)#router bgp 450
rtrB(config-router)# neighbor 131.78.45.1 remote-as 450
rtrB(config-router)# neighbor 131.78.45.1 update-source loopback 1

Both loopback 0 and loopback 1 interfaces are NOT used for communication between rtrA and rtrB. Only the loopback 0 interface of rtrA is used. Both of the loopback interfaces would be used in the communication between rtrA and rtrB only if you changed the configuration of rtrA and rtrB, as given below:
rtrA(config)# router bgp 450
rtrA(config-router)# neighbor 131.78.1.1 remote-as 450
rtrA(config-router)# neighbor 131.78.1.1 update-source loopback 0
rtrB(config)#router bgp 450
rtrB(config-router)# neighbor 10.144.1.1 remote-as 450
rtrB(config-router)# neighbor 10.144.1.1 update-source loopback 1

Because the loopback 0 interface of rtrA is used in communication, is incorrect to state that neither loopback 0 nor loopback 1 interface is used. To ensure that neither of the loopback interfaces are be used for communication, you would configure rtrA and rtrB as follows:
rtrA(config)# router bgp 450
rtrA(config-router)# neighbor 131.78.45.2 remote-as 450
rtrB(config)# router bgp 450
rtrB(config-router)# neighbor 131.78.45.1 remote-as 450

Objective:
Layer 3 Technologies
Sub-Objective:
Configure and verify eBGP (IPv4 and IPv6 address families)
Cisco > Home > Support > Technology Support > IP > IP Routing > Design > Design Technotes > BGP Case Studies > eBGP Multihop
Cisco > Cisco IOS IP Routing: Protocol-Independent Command Reference > neighbor update-source
Cisco > Cisco IOS IP Routing: Protocol-Independent Command Reference > neighbor remote-as

When an IPv6 packet is tunneled across a portion of the network that does not support IPv6, the IPv6 packet is encapsulated in an IPv4 packet using an IPv4 protocol type of 41. When it reaches the other end of the tunnel, the IPv4 portion is stripped off and the packet is routed the rest of the way by using the remaining IPv6 header.
This method does not include a 20-byte IPv6 header with no options and an IPv4 payload. On the contrary, it includes a 20-byte IPv4 header with no options and an IPv6 payload.
The maximum transmission unit is not increased by 20 octets with this method. Rather, it is decreased by 20 bytes due to the extra overhead.
The IPv6 packet does not have its header removed and replaced with an IPv4 header. It encapsulates the entire IPv6 packet within an IPv4 header.
Objective:
Network Principles
Sub-Objective:
Recognize proposed changes to the network
Cisco > Home > Support > Technology Support > IP > IP Version 6 > Configure > Configuration Examples and Technotes > Tunneling IPv6 through an IPv4 Network

When implementing an automatic 6to4 tunnel, each IPv6 site receives a 48-bit prefix. The hexadecimal equivalent of the IPv4 address of the edge router is appended to 0x2002 and followed with the prefix to identify each end of the tunnel.
Each end of the tunnel must be a dual stack router, which is one that can route both IPv4 and IPv6 traffic. For example, if the edge router's IPv4 address were 192.168.99.1, the hexadecimal equivalent of the address (c0a8:6301) would be inserted between 0X2002 and the /48 prefix, resulting in a packet with the IPv6 address 2002:c0a8:6301::/48 to arrive at the tunnel endpoint address.
A Network Address Translation - Port Translation (NAT-PT) router performs translation from IPv4 to IPv6. It is not used in a 6to4 tunnel.
Each site does not have a /16 prefix with a 6to4 tunnel. Rather, each site has a /48 prefix.
The IPv6 address of each IPv6 host is not part of the site prefix. These addresses are retained within the IPv6 portion of the header, and will be read after the frame reaches the end of the tunnel for eventual IPv6 routing on the far end.
Objective:
Network Principles
Sub-Objective:
Recognize proposed changes to the network
Cisco > Products > Collateral > Whitepaper > Enterprise IPv6 Transition Strategy > IPv6 Deployment Solution Options

Network Prefix Translation (NPTv6) is a stateless method of translating the prefix of a received IPv6 address to another prefix without changing the host portion of the IPv6 address. Its mappings are 1 to 1, and it translates only the prefix of the address.
NAT64 translates from IPv6 to IPv4 and vice versa. It does not translate from IPv6 to IPv6.
NAT44 translates from IPv4 to IPv4. It does not translate from IPv6 to IPv6.
There is IPv4 version of Network Prefix Translation, called NPTv4. IT does not translate from IPv6 to IPv6.
Objective:
Infrastructure Services
Sub-Objective:
Describe IPv6 NAT
RFC 6296 > IPv6-to-IPv6 Network Prefix Translation
Cisco > Publications and Merchandise > The Internet Protocol Journal > Issues > Volume 14, Number 2, June 2011 > IPv6 Site Multihoming

Translation from IPv6 Internet addresses to an IPv4 network is not supported by the stateless version of NAT64. There are two versions of NAT 64: stateful and stateless. Stateful NAT64 creates or modifies bindings or session state while performing translation, while stateless NAT64 does not create or modify bindings or session state while performing translation/
Translation from IPv4 Internet to an IPv6 network is supported by both NAT64 methods, although the stateful version requires static 6 to 4 mappings.
Translation from an IPv6 network to an IPv4 network is supported by both methods, stateful and stateless.
Translation from an IPv4 network to an IPv6 network is supported by both methods, although the stateful version requires static 6-to-4 mappings.
Objective:
Infrastructure Services
Sub-Objective:
Describe IPv6 NAT
Home > Products & services > Cisco IOS and NX-OS software > Cisco IOS Technologies > Enterprise IPv6 solution > Data sheets and literature > NAT64 Technology: Connecting IPv6 and IPv4 Networks

The show ip bgp neighbors command will show you detailed information about all of the router's neighbors or peers. A sample of the show ip bgp neighbors output is shown below. The sample utilizes the ip address parameter, which is optional, but can used to limit the output to display information about only one neighbor:

In the above example, router15 has sent out a BGP open packet to the peer at 10.5.1.6 and is listening for a connection request from the peer. This can be determined by the line that says BGP state = Active. It can also be determined that router has established a TCP connection two times, as evidenced by the line Connections established 2.
The show ip bgp command displays the contents of the BGP routing table. It will not display detailed information about a router's BGP connections to neighboring routers.
The show ip bgp summary command displays a summary of the status of BGP connections. It will not display detailed information about a router's BGP connections to neighboring routers.
There is no show ip bgp connections command.
Objective:
Layer 3 Technologies
Sub-Objective:
Describe, configure, and verify BGP peer relationships and authentication
Cisco IOS Master Command List, Release 12.4 > a through b > BGP Commands: show ip through T > show ip bgp neighbors

The correct command is show ip bgp.
The BGP table lists all the paths that the BGP router has learned. Each destination network listed might have multiple possible paths listed. Given that the criteria are met for each destination network, BGP will choose a path to put in the IP routing table.
The BGP table is in many ways analogous to EIGRP's topology table in that it lists many known paths, not just the best path. Below is an example partial output of the show ip bgp command:

The following facts can be determined from this output:
• All of the routes were redistributed into BGP from an IGP. In the status column (located to the left of the Network column and to right of the column where some lines have a > symbol) is a column that is either blank or has an i symbol. In this case, all of the columns are blank. If the status column is blank, then BGP learned the route from an external peer. If it has an i symbol, an iBGP neighbor advertised this path to the router. It was learned from an Interior Gateway Protocol (IGP) and was advertised as a result of executing a network statement on the neighbor under the router bgp context as shown below adding the 30.0.0.0 network under BGP 100.
R4(config)#router bgp 100
R4(config-router)#network 30.0.0.0

• Four routes will be installed in the routing table. These routes have both an * symbol and a > symbol.
• l in the status column. The * symbol indicates that the next hop is valid and the > symbol indicates that this is the best route.
The output is slightly different if you specify the network that you are interested in, as shown below in the show ip bgp 214.5.98.0 command output:

This output focuses solely on the route to the network 214.5.98.0 and provides the following pieces of information:
The neighbor that sent this route is at 192.168.1.1
The AS of the network where 214.5.98.0 is located is 5760
The IGP metric to reach the neighbor that sent this route is 886, as shown by the text 192.168.1.1 (metric 886)
The complete metric to 214.5.98.0 is 1652, as shown in the last line by Origin IGP, metric 1652
The commands show ip bgp table and show ip bgp topology are not valid Cisco commands.
The show ip bgp summary command displays the status of BGP connections.
Objective:
Layer 3 Technologies
Sub-Objective:
Explain BGP attributes and best-path selection
Cisco IOS Master Command List, Release 12.4 > l through q > Cisco IOS IP Routing: BGP Command Reference > show ip bgp