Chap 11 - BGP (part 2) Flashcards
What is the series of 6 BGP neighbor states called?
BGP Finite State Machine
During the connection process what 3 things happen if an error causes BGP to return to the Idle State?
- ConnectRetryTimer set to 120 seconds
- New TCP connection is re-tried in 120 seconds
- Further failures to leave IDLE state causes the timer to double each time
Who manages the connection during the Connect State?
The neighbor with the higher IP address.
What 4 things are checked in the OPEN Message that is received in the OpenSent State?
- BGP versions must match
- Source IP and ASN must match what has been configured locally
- Router IDs must be unique
- Security Parameters (password and TTL) must be set appropriately
What are the 3 basic components in configuring BGP?
- BGP Session parameters
- Address Family Initialization
- Activate the Address Family on the peer
What 3 commands are used to configure BGP Session parameters?
- router bgp (ASN)
- bgp router-id (router_ID)
- neighbor (IP_address) remote-as (neighbor’s AS)
What happens if the router ID is changed after a BGP session has been established?
All BGP sessions reset and need to be re-established
What is the default address family that is already activated?
IPv4
If the router ID is dynamically configured how does that happen?
- Highest Loopback interface IP address that is up/up
- Highest Physical interface IP address in an up/up state
What do BGP network statements do?
Identify specific network prefixes to be installed into the Loc-RIB table.
In order for a new prefix to be added to the Loc-RIB table what test must it meet?
The new route must have an exact match in the Global RIB.
What 3 Path Attributes are set when a Connected Network is added to the Loc-RIB table?
- Next Hop BGP Attribute set to 0.0.0.0
- BGP Origin Attribute set to I (for IGP)
- BGP weight set to 32,768
What 4 Path Attributes are set when a Static Route or a route from a Routing Protocol is added to the Loc-RIB table?
- Next Hop BGP Attribute set to Next Hop int the RIB
- BGP Origin Attribute set to I (for IGP)
- BGP weight set to 32,768
- MED attribute set to the IGP metric
What 2 conditions have to be met before a route in the Loc-RIB table is advertised?
- Outbound route policy is applied
- Route moves to adj-RIB-out
What happens to a route in the Loc-RIB table if its found to be invalid or next hop is not in the RIB?
The route remains in the Loc-RIB table but is not processed any further.
What happens to a route in the Loc-RIB table if it isn’t denied by the outbound route policy?
The route is moved to Adj-RIB-Out table and advertised to peers
What happens if a route’s Next Hop BGP Attribute is set to 0.0.0.0?
BGP changes the Next Hop Attribute to be that of the IP address of the local interface where the advertisement will go out.
How many tables does BGP use when maintaining prefixes and path attributes?
3
What are the names of the 3 tables used by BGP?
- Adj-RIB-In
- Loc-RIB
- Adj-RIB-Out
What is in the Adj-RIB-In table?
Contains the NLRIs learned from peers in original form before any inbound route policies are processed.
What is in the Loc-RIB table?
The NLRIs in Loc-RIB have:
- been received locally or from peers
- passed the inbound router policy
- been determined to be the best path
Where does the IP Routing Table get its routes from?
The Loc-RIB table.
What is in the Adj-RIB-Out table?
Contains the NLRIs to be advertised to peers after the outbound policies have been applied.
How many paths does each entry in the Loc-RIB table contain?
At least one but could be more.
Why should BGP be thought of as a Routing Application?
Because it contains 2 parts - the BGP Session and Route Advertisement
When configuring Route Aggregation what is the key word that surpresses the summarized networks from also being advertised?
summary-only
What does the Atomic Aggregate attribute indicate?
That a loss of path information has occurred.
What are 2 Optional and Non-transitive attributes in MP-BGP?
- MP_Reach_NLRI
- MP_Unreach_NLRI
What is Multiprotocol Reachable NLRI do?
Describes IPV6 Route Information
What does Multiprotocol Unreachable NLRI do?
Withdraws the IPv6 route from service.
When looking at a BGP route what does the weight value of 32,768 mean?
That the prefix was originated locally.
How does BGP process an incoming route?
- Incoming route stored in adj-RIB-in
- Inbound routing policy applied
- BGP decision process selects best route
- Best route moved to Loc-RIB
- Validity check
- is next hop resolvable in Global RIB?
- If fail - remains in Loc-RIB but not processed further
- Install BGP best path into Global RIB
- Route then has outbound route policy applied
- Route is moved to adj-RIB-out
- Route is advertised to neighbors
How many adj-RIB-in and adj-RIB-out tables are maintained on a BGP router?
1 for each peer
What ‘show’ command displays a summary of the BGP table and neighbor peering sessions?
show bgp <afi> summary
ex. show bgp ipv4 unicast summary
What are the 6 BGP neighbor states?
- Idle
- Connect
- Active
- OpenSent
- OpenConfirm
- Established
Display the TCP session on a BGP router.
show tcp brief
Verify the BGP session
show bgp ipv4 unicast summary
Display the BGP neighbors session state.
show bgp ipv4 unicast neighbors (ip_address)
Display the contents of the Loc-RIB table.
show bgp ipv4 unicast
Display the contents of the Adj-RIB-Out table for a neighbor.
show bgp ipv4 unicast (neighbor_IP) advertised-routes
Verify the exchange of NLRIs between nodes.
show bgp ipv4 unicast summary
Display BGP routes in the Global Routing Table (RIB).
show ip route bgp
Show if the IPV6 neighbor attributes were negotiated successfully.
show bgp ipv6 unicast neighbors 2001::2 detail
Display IPV6 BGP routes.
show bgp ipv6 unicast 2001:db8::1/64
What number range is used by an AS-PATH ACL?
1 - 500
After a ‘network’ statement has been configured for a Connected network what 5 things happen?
- Global RIB searched for exact match of the prefix
- Prefix installed in Loc-RIB
- Next-hop BGP PA set to 0.0.0.0
- Origin PA set to ‘i’ for IGP
- BGP Weight PA set to 32,768
What are 3 reasons to summarize routes?
- Conserves router resources
- Accelerates best path calculation
- Provides stability by hiding route flaps
What are the 2 techniques for BGP summarization?
- Static
- Dynamic
What are the commands for configuring Static summary route for 172.21.2.0, 172.21.3.0 and 172.21.4.0?
R1(config-router)# network 172.21.0.0 mask 255.255.0.0
R1(config-router)# exit
R1(config)# ip route 172.21.0.0 255.255.0.0 null0
What is the command to configure a Dynamic summary route for 172.21.0.0/16 with suppression and preserving the path attributes?
R1(config-router)# aggregate-address 172.21.0.0 255.255.0.0 as-set summary-only
