2014 Latest Cisco 350-001 Dump Free Download(141-150)!
Router 1 is configured for BGP as dual-homed on the Cisco network. Which three BGP attributes
are carried in every BGP update on this router (both IBGP and EBGP)? (Choose three.)
There are basically two major types of attribute:
Well known attributes are must be recognized by each compliant of BGP implementations. Well known attributes are propagated to other neighbors also. Further divided into:
1. Mandatory: It is BGP well known attributes. Mandatory attributes are must be present in all update message passed between BGP peers. It is present in route description. Must be supported and propagated.
2. Discretionary: It is BGP well known attributes. Discretionary attributes may be present on update message.
Must be supported; propagation optional.
Optional attributes are recognized by some implementation of BGP & expected that not recognized by everyone. Optional attributes are propagated to their neighbors based on the meanings.
Further divided into:
1. Transitive: Optional transitive attributes don’t have to be supported, but must be passed onto peers. Marked as partial if unsupported by neighbor
2. Non Transitive: Optional non-transitive attributes don’t have to be supported, and can be ignored.
Deleted if unsupported by neighbor
1. Weight (Attribute Type Mandatory):
Weight is a Cisco-defined attribute that is local to a router. The weight attribute is not advertised to neighboring routers. If the router learns about more than one route to the same destination, the route with the highest weight is preferred.
2. Local preference (Attribute Type Discretionary):
The local preference attribute is used to prefer an exit point from the local autonomous system. Unlike the weight attribute, the local preference attribute is propagated throughout the local AS. If there are multiple exit points from the AS, the local preference attribute is used to select the exit point for a specific route.
3. AS path (Attribute Type Mandatory):
When a route advertisement passes through an autonomous system, the AS number is added to an ordered list of AS numbers that the route advertisement has traversed.
The origin attribute indicates how BGP learned about a particular route. The origin attribute can have one of three possible values:
a. IGP The route is interior to the originating AS. This value is set when the network router configuration command is used to inject the route into BGP. b. EGP -The route is learned via the Exterior Gateway Protocol (EGP).
The origin of the route is unknown or is learned some other way. An origin of Incomplete occurs when a route is redistributed into BGP.
5. Multi-exit discriminator (Attribute Type – Non Transitive):
The multi-exit discriminator (MED) or metric attribute is used as a suggestion to an external AS regarding the preferred route into the AS that is advertising the metric.
6. Next-hop (Attribute Type Mandatory):
The EBGP next-hop attribute is the IP address that is used to reach the advertising router. For EBGP peers, the next-hop address is the IP address of the connection between the peers.
7. Community (Attribute Type – Transitive):
The community attribute provides a way of grouping destinations, called communities, to which routing decisions (such as acceptance, preference, and redistribution) can be applied. Route maps are used to set the community attribute. The predefined community attributes are as follows:
a. No-export: Do not advertise this route to EBGP peers. b. No-advertise: Do not advertise this route to any peer. c. Internet: Advertise this route to the Internet community; all routers in the network belong to it.
8. Atomic Aggregate (Attribute Type – Discretionary):
Notes that route summarization has been performed.
9. Aggregator (Attribute Type – Transitive):
Identifies the router and AS where summarization was performed.
10. Originator ID (Attribute Type – Non Transitive): Identifies a route reflector.
11. Cluster List (Attribute Type – Non Transitive):
Records the route reflector clusters the route has traversed.
In your Cisco EIGRP network, you notice that the neighbor relationship between two of your
routers was recently restarted. Which two of these choices could have made this occur? (Choose
A. An update packet with init flag set from a known, already established neighbor relationship was
received by one of the routers.
B. The ARP cache was cleared.
C. The counters were cleared.
D. The IP EIGRP neighbor relationship was cleared manually.
The following are the most common causes of problems with EIGRP neighbor relationships:
Uncommon subnet, primary, and secondary address mismatch Mismatched masks
K value mismatches
Mismatched AS numbers
Stuck in active
Layer 2 problem
Access list denying multicast packets
Manual change (summary router, metric change, route filter) According till Ivan Pepelnjak’s book “EIGRP Network Design Solutions” the Init flag is set in the initial update packet when to neighbors discover each other and start their initial topology table exchange. There are two basic purposes for the Init flag. First, it’s a part of the three way handshake that eigrp uses when building an adjacency.
5. Router B comes up on a wire.
6. Router A receives Router B’s hello, and places it in “pending” state. This is a not completely formed adjacency; as long as B is in this state, A won’t send any routing information to it.
7. Router A sends an empty unicast update with the Init bit set.
8. Router B receives this update with the Init bit set, and places Router A in the “pending” state.
9. Router B now transmits an empty update with the Init bit set, unicast, to A. This empty update also contains the acknowledgement for Router A’s Init update (that this ack is piggybacked is an integral part of the three way handshake process).
10.Router A, on receiving this Init update, places Router B in the “neighbor” state, and sends an acknowledgement for the Init update from Router B.
11.Router B receives this ack, and places A in “neighbor” state. The two routers can now exchange routing information, knowing they have full two way connectivity between them. The second use of the Init bit is more esoteric. Suppose you have Routers A and B, running along fine, for many hours. Router A reloads, but comes back up before Router B’s hold timer has expired. When Router B sees A’s hellos, it will assume that A just missed a couple, and everything is fine. But everything isn’t fine-A just lost all of its routing information! How can A signal this state, and as B to resynchronize? A can send an empty update, with the Init bit set. This causes Router B to place A in the “pending” state, and wipe out all the information it’s learned from A (unless, of course, graceful restart is configured/etc.).
Your Cisco network currently runs OSPF and you have a need to policy-route some specific traffic, regardless of what the routing table shows. Which one of these options would enable you to
policy-route the traffic?
A. source IP address and the protocol (such as SSL, HTTPS, SSH)
B. the packet Time to Live and the source IP address
C. type of service header and DSCP value
D. destination IP address
Policy-based routing (PBR) provides a mechanism for expressing and implementing forwarding/routing of data packets based on the policies defined by the network administrators. It provides a more flexible mechanism for routing packets through routers, complementing the existing mechanism provided by routing protocols. Routers forward packets to the destination addresses based on information from static routes or dynamic routing protocols such as Routing Information Protocol (RIP), Open Shortest Path First (OSPF), or Enhanced Interior Gateway Routing Protocol (Enhanced IGRP). Instead of routing by the destination address, policybased routing allows network administrators to determine and implement routing policies to allow or deny paths based on the following:
Identity of a particular end system
Size of packets
You use OSPF as your network routing protocol. You use the command show ip route and you
see several routes described as O, O IA, O E1, and O E2. What routes are in your area?
A. O IA
B. O E1
C. O E2
Depending on the point where a network is sourced, there are various types of routes that could be present in an OSPF domain. When there are multiple routes to a particular network in a OSPF domain, the type of the route influences the route that is selected and installed by the router in the routing table. In OSPF, routes that are learned by a router from OSPF sources within the same area are known as intra-area routes. Routes that originate from an OSPF router in a different area are considered as inter-area routes. Certain networks could belong to a domain outside OSPF, which could then be redistributed into the OSPF by an Autonomous System Boundary Router (ASBR). Such routes are considered external routes. They can be further divided into external type-1 or external type-2 routes, depending on how they are advertised while being redistributing on the ASBR. The difference between these two types is the way in which the metric for the route is calculated.
OSPF-running routers use these criteria to select the best route to be installed in the routing table:
1. Intra-area routes.
2. Inter-area routes.
3. External Type-1 routes.
4. External Type-2 routes.
a. If there are multiple routes to a network with the same route type, the OSPF metric calculated as cost based on the bandwidth is used for selecting the best route. The route with the lowest value for cost is chosen as the best route.
b. If there are multiple routes to a network with the same route type and cost, it chooses all the routes to be installed in the routing table, and the router does equal cost load balancing across multiple paths.
What are the mandatory, well-known BGP attributes?
A. origin, AS-path, next-hop
B. AS-path, origin, MED
C. AS-path, origin, weight
D. AS-path, weight, MED
BGP Path Attributes
Mandatory Well-Known Attributes
Origin: Specifies the router’s origin
Unknown — Route was redistributed
AS-Path: Sequence of AS numbers through which the route is accessible Next-Hop: IP address of the next-hop router
Discretionary Well-Known Attributes
Used for consistent routing policy with an AS
Atomic Aggregate: Informs the neighbor AS that the originating router aggregated routes Nontransitive Attributes
Multiexit Discriminator: Used to discriminate between multiple entry points into an AS Transitive Attributes
Aggregator: IP address and AS of the router that performed aggregation Community: Used for route tagging
Network A has a spanning-tree problem in which the traffic is selecting a longer path. How is the path cost calculated?
A. number of hops
B. priority of the bridge
C. interface bandwidth
D. interface delay
E. None of the above
STP Path Cost Automatically Changes When a Port Speed/Duplex Is Changed STP calculates the path cost based on the media speed (bandwidth) of the links between switches and the port cost of each port forwarding frame. Spanning tree selects the root port based on the path cost. The port with the lowest path cost to the root bridge becomes the root port. The root port is always in the forwarding state.
If the speed/duplex of the port is changed, spanning tree recalculates the path cost automatically. A change in the path cost can change the spanning tree topology.
You deployed new fibers in your network to replace copper spans that were too long. While
reconnecting the network, you experienced network problems because you reconnected wrong
fibers to wrong ports. What could you do to prevent this type of problem in the future, particularly when connecting and reconnecting fiber pairs?
A. Only use fiber in pairs.
B. Configure root guard on your switches.
C. Do not use fiber but use copper.
D. Configure UDLD to prevent one-way link conditions.
UDLD is a Layer 2 protocol that enables devices connected through fiber-optic or twisted-pair Ethernet cables to monitor the physical configuration of the cables and detect when a unidirectional link exists. All connected devices must support UDLD for the protocol to successfully identify and disable unidirectional links. When UDLD detects a unidirectional link, it administratively shuts down the affected port and alerts you. Unidirectional links can cause a variety of problems, including spanning-tree topology loops.
While deploying a new switch, you accidently connect ports 3/12 and 3/18 together, creating a
loop. STP detected it and placed port 3/18 in blocking mode. Why did STP not place port 3/12 in
blocking mode instead?
A. Port 3/12 was already up and forwarding before the loop was created.
B. Port priority is based on lowest priority and lowest port number.
C. You connected the wire on port 3/18 last.
D. None of the above, it is purely random.
Spanning-tree select the port, by first calculating the cost (which depends on the bandwidth) then the port priority which is based on the lowest priority (in case configured) and the lowest port number.
What keywords do you need to the access-list to provide to the logging message like source
address and source mac address?
The log-input keyword exists in Cisco IOS Software Release 11.2 and later, and in certain Cisco IOS Software
Release 11.1 based software created specifically for the service provider market. Older software does not support this keyword. Use of this keyword includes the input interface and source MAC address where applicable.
The OSPF RFC 3623 Graceful Restart feature allows you to configure IETF NSF in ultivendor
networks. When using OSPF Graceful Restart, which mechanism is used tocontinue forwarding
packets during a switchover?
A. Reverse Path Forwarding
B. Hardware-based forwarding
C. UDP forwarding
D. Layer 2 Forwarding
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