Routing and Switching – Page 4 – Network Interview QnA

If the successor path is lost & there is no feasible successor path is available, router sends out query messages on all EIGRP enable interfaces & tries to find out an alternative path to the network. It is active state for that route.Now Router is waiting for reply from its neighbors. If reply is missing [...]

What are communities? How are they enabled? What are three predefined communities

A community is a group of prefixes that share some common property and can be configured with the BGP community attribute. The BGP Community attribute is an optional transitive attribute of variable length. The attribute consists of a set of four octet values that specify a community. The community attribute values are encoded with an [...]

What is the purpose of Synchronisation?

BGP synchronization was an old routing loop prevention mechanism that worked in the following way: A BGP border router would not propagate a BGP advertisement to an eBGP peer until the router does see the same IP prefix learned in IGP ( OSPF, ISIS or other internal protocol). This would ensure that there are no [...]

What are route reflectors? Why these used?

A route reflector is BGP router that is allowed to break the iBGP loop avoidance rule. Route reflectors can advertise updates received from an iBGP peer to another iBGP peer under specific conditions. By breaking the rules, route reflectors are used to eliminate the full mesh requirement and allow for building iBGP networks that scale [...]

When are hello packets sent? On what different types of media?

EIGRP sends hello packets every 5 seconds on high bandwidth links and every 60 seconds on low bandwidth multipoint links. -5-second hello: broadcast media, such as Ethernet, Token Ring, and FDDI point-to-point serial links, such as PPP or HDLC leased circuits, Frame Relay point-to-point subinterfaces, and ATM point-to-point subinterface high bandwidth (greater than T1) multipoint [...]

What are two values used by default to calculate the EIGRP metric

-Bandwidth -Delay

What does the ‘bandwidth’ interface command do to EIGRP

You can set the bandwidth value of an interface using the BANDWIDTH command.

If you have the two routers in the same area, can you use the distribute-list out command to filter resources between them

No to filter the routes use the command distribute-list in command not the distribute-list out. To filter networks received in updates, use the distribute-list in command in address family or router configuration mode. To change or cancel the filter, use the no form of this command. distribute-list [access-list-number | name] | [route-map map-tag] in [interface-type [...]

What is the difference between type 1 & type 2 external routes which is preferred

External routes fall under two categories, external type 1 and external type 2. The difference between the two is in the way the cost (metric) of the route is being calculated. The cost of a type 2 route is always the external cost, irrespective of the interior cost to reach that route. A type 1 [...]

What is difference between DR,BDR,ABR & an ASBR

The DR serves as a common point for all adjacencies on a multiaccess segment The BDR also maintains adjacencies with all routers in case the DR fails Area Border Router (ABR) Connects two or more areas AS Boundary Router (ASBR) Connects to additional routing domains; typically located in the backbone

What protocol does OSPF uses to send link updates

OSPF relies on several types of Link State Advertisements (LSAs) to communicate link state information between neighbors.

What are different types of stub areas in OSPF

OSPF relies on several types of Link State Advertisements (LSAs) to communicate link state information between neighbors. A brief review of the most applicable LSA types: Type 1 – Represents a router Type 2 – Represents the pseudonode (designated router) for a multiaccess link Type 3 – A network link summary (internal route) Type 4 – Represents an ASBR Type 5 – [...]

How are routing neighbours discovered in BGP

A BGP-speaking router does not discover another BGP-speaking device automatically. A network administrator usually manually configures the relationships between BGP-speaking routers. A BGP neighbor device is a BGP-speaking router that has an active TCP connection to another BGP-speaking device. This relationship between BGP devices is often referred to as a peer instead of neighbor because [...]

What is the concept of NLRI

BGP was designed to carry only unicast IPv4 routing information. BGP configuration used the Network Layer Reachability Information (NLRI) format CLI in Cisco IOS software. The NLRI format offers only limited support for multicast routing information and does not support multiple network layer protocols.

What are BGP path attribute

-Prefer the path with the highest WEIGHT. Note: WEIGHT is a Cisco-specific parameter. It is local to the router on which it is configured. -Prefer the path with the highest LOCAL_PREF. Note: A path without LOCAL_PREF is considered to have had the value set with the bgp default local-preferencecommand, or to have a value of [...]

Can you explain the concept of BGP confederations

A fully meshed iBGP network becomes complex as the number of iBGP peers grows. You can reduce the iBGP mesh by dividing the autonomous system into multiple subautonomous systems and grouping them into a single confederation. A confederation is a group of iBGP peers that use the same autonomous system number to communicate to external [...]

Can you explain autonomous system in BGP

There are two main types of AS: Stub AS: This is an AS that is connected to only one other AS. It is comparable to a cul-de-sac (dead-end street) in our road analogy; usually, only vehicles coming from or going to houses on the street will be found on that street. Multihomed AS: This is [...]

Can you explain different OSPF packet types

Hello-Used to discover and maintain neighbours. Database Description-Used to form adjacencies. The router summarises all its linkstate advertisements and passes this information, via database description packets to the router it is forming an adjacency with Link State Request After the database description packets have been exchanged with a neighbour, the router may detect link state advertisements it requires to update [...]

Can you explain the different router types in OSPF

Internal Router – all interfaces in single area Backbone Router – at least 1 interface in area 0 Area Border Router – has interfaces in multiple areas Autonomous System Border Router – act as gateways between OSPF and other routing protocols

Can you explain different areas in the OSPF

OSPF allows the grouping of networks into a set, called an area. The topology of an area is hidden from the rest of the Autonomous System. This technique minimizes the routing traffic required for the protocol. When multiple areas are used, each area has its own copy of the topological database.

What are different tables in OSPF

OSPF Tables: In link state routing protocol there are different tables for storing different types of information regarding router and its networks. There are three tables in OSPF same like in EIGRP. 1. OSPF Neighbor table 2. OSPF Topology table 3. OSPF Routing table

Can you explain the concept of successor & feasible successor

The term successor can be defined as “one thing that succeeds another.” In IP routing, this simply refers to the next-hop of the best route. A feasible successor, therefore, is not our current best route, but one which could be used in the event our successor route disappears.

What is the concept of sucessor in EIGRP

Successor is the neighbouring router with the best cost path too a destination network, will be marked as the successor for that network and will be used as the next hop to forward traffic to it.

How does EIGRP protocol update route information to it’s neighbours

A router discovers a neighbor when it receives its first hello packet on a directly connected network. The router requests DUAL to send a full route update to the new neighbor. In response, the neighbor sends its full route update. Thus, a new neighbor relationship is established in the following steps: When a router A [...]

What are different types of packets in EIGRP

There are 5 types of packets in EIGRP -Hello -Update -Query -Reply -ACK (Acknowledgement) Hello packets are used for neighbor discovery. As soon as you send hello packets and receive them your EIGRP routers will try to form the neighbor adjacency. Update packets have routing information and are sent reliable to whatever router that requires [...]

What does neighbour terminology mean in EIGRP

Neighbour, a neighbour is a router that can be reached through a network segment that is running the same EIGRP AS and is directly sharing routing information with the local router.

Which processes does TCP, but not UDP, use?

A. Windowing B. Acknowledgements C. Source Port D. Destination Port Answer: A & B UDP (User Datagram Protocol) does not use sequence or acknowledgement fields in transmission. UDP is a connectionless and unreliable protocol, since there is no delivery checking mechanism in the UDP data format.

What is the function of DDR on Cisco routers?

A. DDR is dial–on-demand routing. It provides a continuous LAN only connection. B. DDR is dial-on-demand routing. It provides routing for high volume traffic. C. DDR is dial–on-demand routing. It provides a continuous WAN connection. D. DDR is dial-on-demand routing. It provides routing for low volume and periodic traffic. Answer D

Access lists are numbered. Which of the following ranges could be used for an IP access list?

A. 600 – 699 B. 100 – 199 C. 1 – 99 D. 800 – 899 E. 1000 – 1099 Answer:wer: B & C

In order to limit the quantity of numbers that a system administrator has to enter, Cisco can use which abbreviation to indicate 0.0.0.0

A. host B. any C. all D. include Answer:: A

What do the following statements in an extended access list accomplish?

What do the following statements in an extended access list accomplish? access-list 101 deny TCP 172.16.4.0 0.0.0.255 172.16.3.0 0.0.0.255 eq 21 access-list 101 deny TCP 172.16.4.0 0.0.0.255 172.16.3.0 0.0.0.255 eq 20 access-list 101 permit TCP 172.16.4.0 0.0.0.255 0.0.0.0 255.255.255.255 A. This will block ftp traffic. B. This will block http traffic. C. This will permit [...]

Access lists are numbered. Which of the following ranges could be used for an IP access list?

Access lists are numbered. Which of the following ranges could be used for an IP access list? A. 600 – 699 B. 100 – 199 C. 1 – 99 D. 800 – 899 E. 1000 – 1099 –> B & C

Cisco routers use wildcard masking to identify how to check or ignore corresponding IP address bits. What does setting a wildcard mask bit to 0 cause the router to do?

Cisco routers use wildcard masking to identify how to check or ignore corresponding IP address bits. What does setting a wildcard mask bit to 0 cause the router to do? A. It tells the router to check the corresponding bit value. B. It tells the router to ignore the corresponding bit value. C. It tells [...]