Chapter 11: BGP Flashcards
Number of unique ASNs.
4,294,967,295
Private ASN range.
16-bit range: 64,512-65,535
32-bit range: 4,200,000,000 - 4,294,967,295
Who is responsible for ensuring all public ASNs are globally unique?
IANA
Requirements for requesting a public ASN.
- Proof of a publicly allocated network range.
- Proof that internet connectivity is provided through multiple connections.
- Need for a unique routing policy from providers.
______ _______ provide BGP with granularity and control of routing policies within BGP.
Path Attributes
Types of BGP Path Attributes
Well-known mandatory
Well-known discretionary
Optional transitive
Optional non-transitive
Which path attribute must be included with every prefix advertisement?
Well-known mandatory
Which path attribute may or may not be included with a prefix advertisement?
Well-known discretionary
A routing update that consists of the network prefix, prefix length, and any BGP path attributes for the specific route.
Network Layer Reachability Information (NLRI)
T/F:
BGP does not contain a complete topology of the network.
True
T/F:
BGP is a link-state routing protocol.
False
BGP is a path vector protocol.
Attribute that includes a list of all of the ASNs that the prefix advertisement has traversed from its source.
AS_Path
What is the purpose of the Address Family Identifier?
Advertises addresses from the specified address family to a BGP neighbor.
What occurs when a BGP router receives a prefix advertisement with its AS listed in the AS_Path attribute?
The prefix advertisement is dropped because the router thinks the advertisement forms a loop.
T/F:
BGP uses Hello packets to maintain and discover neighbors.
False
BGP neighbors are defined by IP addresses.
Which port is used to communicate with other BGP routers?
TCP port 179
T/F:
BGP can only form neighbor adjacencies with directly connected AS’s.
False
BGP can can form adjacencies with directly connected AS’s or AS’s that are multiple hops away.
T/F:
A default route is not sufficient to establish a multi-hop BGP session.
True
A route between routers multiple hops away must exist in the RIB.
2 types of BGP sessions
iBGP
eBGP
iBGP administrative distance
200
eBGP administrative distance
20
2 scenarios that typically occur when BGP is needed within an AS.
- Multiple routing policies are required.
- Transit connectivity is provided between autonomous systems.
eBGP default TTL
1
iBGP default TTL
255 (allows for multi-hop sessions)
BGP Packet Types
Type 1 Open
Type 2 Update
Type 3 Notification
Type 4 Keepalive
BGP packet used to establish an adjacency.
Open
BGP packet used to advertise any feasible routes, withdraw previously advertised routers.
Update
T/F:
BGP does not rely on the TCP connection state to ensure that neighbors are still alive.
True
BGP packet used to verify neighbors are still alive.
Keepalive
Sent when an error is detected with the BGP session.
Notification
Components of the Open packet.
BGP Version Number
ASN of Originating Router
Hold Time
BGP Identifier
T/F:
Hold timer must be either zero or at least 3 seconds.
True
Default keepalive / Default hold time
60 seconds / 180 seconds
What does BGP use to maintain a table of all BGP peers and their operational status?
Finite State Machine
BGP Neighbor States
- Idle
- Connect
- OpenSent
- OpenConfirm
- Established
- Updates
BGP Path Attributes
Local_Pref
Origin
AS_Path
Next_Hop
Multi_Exit_Disc
Atomic_Aggregate
Aggregator
Which neighbor state:
- initializes all BGP resources for the peer connection.
- sets ConnectRetryCounter to zero.
- starts the ConnectRetryTimer with the initial value.
- initiates a TCP connection to the other BGP peer
- listens for a connection that may be initiated by the remote BGP peer
Idle
