Basics of BGP Flashcards
Which RFC defines BGP?
RFC 4271
Why was BGP originally created?
to allow seperate organizations to connect to each other and share routes with each other over the internet or via private networks
Who assigns public BGP AS Numbers?
Internet Assigned Numbers Authority (IANA)
What are the ranges of BGP AS numbers?
1 to 64,511
What is the resereved range for the private BGP AS numbers?
64,512 to 65,534
What are the 3 basic characteristics of BGP?
- open standard
- path vector
- exterior gateway protocol
Does BGP have topology visibility?
no, it uses IGP as transport in order to advertise reachability information about the destination
What protocol and port does BGP use?
TCP 179
Why BGP is not a routing protocol per-se? (3)
-
BGP is an application, as it operates on L7
- is a reachability protocol
-
doesn’t provide it’s own transport protocol
- normally has to rely on IGP like OSPF or EIGRP in order to establish BGP sessions in 99% of the cases
-
generally cannot route the network alone
- if a route is advertised to a router and it does not have an underlying IGP to find the outgoing interface, the prefix cannot be used
How many autonomous systems can be configured on any given router?
1
When are BGP routes are considered most desirable?
when they traverse the least possible number of autonomous systems
How is a network commonly refered to in BGP?
a prefix
Why is traffic engineering easier to do compared to other protocols, such as OSPF?
in case of BGP, policies can be applied for individual prefixes; unlike the case of OSPF, where cost is a function of the links and not the route itself (if the cost is changed, it affects all destinations as well)
What is an Autonomus System?
set of routers under a single technical administration
Describe Stub AS
connected to only one other AS
