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48 Cards in this Set
- Front
- Back
What is the term IDRP?
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Interdomain routing protocol, also known as EGP
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What version of BGP is used today?
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BGP-4
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Who are responsible for the allocation of Autonomous system numbers?
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The IANA (Internet Assigned Numbers Authority)
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What organizations is responsible for the administration and registration of IP address space and Autonomous system numbers?
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RIRs (Regional Internet registries)
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How many RIRs are there and what are their names?
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There are 5 RIRs:
* AfriNIC (Africa) * APNIC (Asia) * ARIN (America) * LACNIC (Latin America) * RIPE NCC (Europe) |
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What is the range of Autonomous system numbers and how many bits?
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The range is 1 - 65,535. 16-bit number
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What is the range of private Autonomous system numbers?
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64512 - 65535
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How does BGP-4 prevent the internet routing table from becoming too large?
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BGP-4 supports VLSM
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How does BGP choose the best path?
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BGP is a policy-based routing protocol, so it looks at multiple attributes to decide the best path
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What are the requirements to connect an enterprise to an ISP?
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* Public IP address space
* Enterprise-to-ISP connection link type and bandwidth * Routing protocol (static or dynamic) * Connection redundancy |
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When would Layer 2 connectivity be needed between two or more locations? (L2 MPLS VPN)
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* The locations include data centers with geographically distributed clusters that require Layer 2 connectivity to function properly
* The enterprise is in a process of migrating to a Layer 3 solution but still require Layer 2 connectivity * The enterprise connects to another partner that requires Layer 2 connectivity |
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What is it called when a customer is connected to a single ISP with no link redundancy?
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Single homed. If the ISP network fails, connectivity to the Internet is interrupted
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What is it called when a customer is connected to a single ISP with two links towards the same ISP?
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Dual homed.
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What is it called when a customer is connected to multiple ISPs?
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Multihomed. The customer is resistant to a single ISP failure
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What is it called when a customer has two links connected to multiple ISPs?
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Dual multihomed
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How is single-homed internet access typcially deployed?
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BGP is not required so static routes is typically used with a static default route from to customer to the ISP and static routes in the ISP pointing toward the customer networks.
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What would be the use of running BGP in a single homed connection type?
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The only use would be for the customer to dynamically announce its public networks to the ISP. The ISP announced only a default route to the customer.
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What are the two options for dual homing a connection?
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Option 1: One CPE router with two links to the ISP
Option 2: Two CPE routers, each with one link to the ISP |
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What two types of scenarios can be achieved with a dual homing connection?
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* Primary and backup link functionality
or * Load sharing between the links |
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What sort of routing is used in dual homed connections?
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It can be either static or dynamic (typically BGP)
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What is the benefit of a multihomed connection?
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* Resistance to failure beyond a directly connected link to a single ISP
* Load sharing for different destination networks between ISPs, based on the network proximity * Scalability of the solution, beyond two ISPs * Acheiving an ISP-independent solution |
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What sort of routing is used in multihomed connections?
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The routing must be capable of reacting dynamically to changes. Therefore BGP is typically used
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What are 2 typical reasons for using multihoming?
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1. To increase the reachability of the connection to the internet
2. To increase the performance of the connection (better paths can be used to certain destinations) |
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What are three common ways to perform multihoming with BGP?
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* Each ISP passes only a default route which is passed to the internal routers
* Each ISP passes a default route plus specific provider-owned routes * Each ISP passes all routes |
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What are the limitations of only receiving a default route from the service providers?
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* path manipulation annot be performed because only a single route is received from each ISP
* Bandwidth manipulation is extremely difficult * Diverting some of the traffic from one exit point to another is challenging because all destinations are using the same default route for path selection |
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How does BGP guarantee loop-free paths?
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A router running BGP does not accept a routing update that already includes its AS nr in the path list
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When should BGP not be used?
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When the company has..
- A single connection to the internet or another AS - Lack of router performance on the edge routers - Limited understanding of route filtering and BGP-path selection process |
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What type of protocol is BGP?
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A path vector routing protocol
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What does BGP use as transport?
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TCP /179
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How big is the dynamic window that TCP uses before it stops and waits for an ACK?
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65,576 bytes
(512kb) |
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What are the 3 requirements for eBGP neighborship?
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- Different autonomous system
- Define neighbors - Reachability |
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Requirements for iBGP neighborship?
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- Same AS
- Define neighbors - Reachability |
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Does routers running iBGP have to be directly connected?
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No, not as long as they can establish a TCP connection
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What is the BGP synchronization rule?
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It states that a BGP router should not use or advertise to an external neighbor a router learned by iBGP unless that route is local or is learned from the IGP
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What happens when synchronization is enabled?
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A router learning a route via iBGP waits until the IGP has propagated the route within the autonomous system and then adverises it to external peers
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What is the benefit of having synchronization disabled?
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Allows the router to carry fewer routes in IGP and allows BGP to converge more quicky because it can advertise the routes as soon as it learns them
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When should synchronization be enabled?
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If there are routers in the BGP transit path in the AS that are not running BGP (and therefore the routers do not have full mesh iBGP with the AS)
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How often does BGP send keepalives?
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Every 60 sec
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What are the BGP message types?
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Open
Keepalive Update Notification |
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What does the Open message contain?
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Version, Senders AS nr, Hold time, BGP RID, optional parameters
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What does the BGP update message contain?
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Information on one path only, containing:
Withdrawn routes Path attributes NLRI |
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When is Notification messages sent?
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When a router detects an error.
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What happens after a BGP notification message is sent out?
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The BGP connection is closed immediately after sending the message
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What are the BGP Neighbor states?
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Idle, Connect, Active, Open sent, Open confirm, Established
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What different types of BGP attributes are there?
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Well known mandatory, well known discretionary, Optional transitive, optional nontransitive
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Which attribute type can be marked as partial?
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Optional transitive
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What does a BGP path attribute consist of?
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Attribute type
Attribute length Attribute value |
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What command erases a private AS number from BGP routes exchanged with a neighbor?
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(config-router)#neighbor 192.168.1.5 remove-private-as
(Where 192.168.1.5 is the neighbor receiving the private ASN) |