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48 Cards in this Set

  • Front
  • Back
What is the term IDRP?
Interdomain routing protocol, also known as EGP
What version of BGP is used today?
BGP-4
Who are responsible for the allocation of Autonomous system numbers?
The IANA (Internet Assigned Numbers Authority)
What organizations is responsible for the administration and registration of IP address space and Autonomous system numbers?
RIRs (Regional Internet registries)
How many RIRs are there and what are their names?
There are 5 RIRs:

* AfriNIC (Africa)
* APNIC (Asia)
* ARIN (America)
* LACNIC (Latin America)
* RIPE NCC (Europe)
What is the range of Autonomous system numbers and how many bits?
The range is 1 - 65,535. 16-bit number
What is the range of private Autonomous system numbers?
64512 - 65535
How does BGP-4 prevent the internet routing table from becoming too large?
BGP-4 supports VLSM
How does BGP choose the best path?
BGP is a policy-based routing protocol, so it looks at multiple attributes to decide the best path
What are the requirements to connect an enterprise to an ISP?
* Public IP address space
* Enterprise-to-ISP connection link type and bandwidth
* Routing protocol (static or dynamic)
* Connection redundancy
When would Layer 2 connectivity be needed between two or more locations? (L2 MPLS VPN)
* 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
What is it called when a customer is connected to a single ISP with no link redundancy?
Single homed. If the ISP network fails, connectivity to the Internet is interrupted
What is it called when a customer is connected to a single ISP with two links towards the same ISP?
Dual homed.
What is it called when a customer is connected to multiple ISPs?
Multihomed. The customer is resistant to a single ISP failure
What is it called when a customer has two links connected to multiple ISPs?
Dual multihomed
How is single-homed internet access typcially deployed?
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.
What would be the use of running BGP in a single homed connection type?
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.
What are the two options for dual homing a connection?
Option 1: One CPE router with two links to the ISP
Option 2: Two CPE routers, each with one link to the ISP
What two types of scenarios can be achieved with a dual homing connection?
* Primary and backup link functionality
or
* Load sharing between the links
What sort of routing is used in dual homed connections?
It can be either static or dynamic (typically BGP)
What is the benefit of a multihomed connection?
* 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
What sort of routing is used in multihomed connections?
The routing must be capable of reacting dynamically to changes. Therefore BGP is typically used
What are 2 typical reasons for using multihoming?
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)
What are three common ways to perform multihoming with BGP?
* 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
What are the limitations of only receiving a default route from the service providers?
* 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
How does BGP guarantee loop-free paths?
A router running BGP does not accept a routing update that already includes its AS nr in the path list
When should BGP not be used?
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
What type of protocol is BGP?
A path vector routing protocol
What does BGP use as transport?
TCP /179
How big is the dynamic window that TCP uses before it stops and waits for an ACK?
65,576 bytes
(512kb)
What are the 3 requirements for eBGP neighborship?
- Different autonomous system
- Define neighbors
- Reachability
Requirements for iBGP neighborship?
- Same AS
- Define neighbors
- Reachability
Does routers running iBGP have to be directly connected?
No, not as long as they can establish a TCP connection
What is the BGP synchronization rule?
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
What happens when synchronization is enabled?
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
What is the benefit of having synchronization disabled?
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
When should synchronization be enabled?
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)
How often does BGP send keepalives?
Every 60 sec
What are the BGP message types?
Open
Keepalive
Update
Notification
What does the Open message contain?
Version, Senders AS nr, Hold time, BGP RID, optional parameters
What does the BGP update message contain?
Information on one path only, containing:
Withdrawn routes
Path attributes
NLRI
When is Notification messages sent?
When a router detects an error.
What happens after a BGP notification message is sent out?
The BGP connection is closed immediately after sending the message
What are the BGP Neighbor states?
Idle, Connect, Active, Open sent, Open confirm, Established
What different types of BGP attributes are there?
Well known mandatory, well known discretionary, Optional transitive, optional nontransitive
Which attribute type can be marked as partial?
Optional transitive
What does a BGP path attribute consist of?
Attribute type
Attribute length
Attribute value
What command erases a private AS number from BGP routes exchanged with a neighbor?
(config-router)#neighbor 192.168.1.5 remove-private-as

(Where 192.168.1.5 is the neighbor receiving the private ASN)