Chapter 1) Implementing Routing in the Data Center Flashcards
Describe the role of OSPF Hello-Packets
Hello packets are sent out on each OSPF-enabled interface to discover other OSPF neighbor routers. In addition, OSPF uses hello packets for keepalive and bidirectional traffic.
What are the default OSPF Hello & Dead intervals?
Default Hello interval is 10 seconds
Default Dead interval is 4 times the hello interval (40 seconds)
What algorithm is used by routers in OSPF to built a routing table?
Dijkstra’s Shortest Path First (SPF) algorithm
What are the multicast addresses used in OSPF versions 2 & 3 for sending Hello messages to adjacent routers?
OSPF Version 2 (IPv4): 224.0.0.5
OSPF Version 3 (IPv6): FF02::05
What are addresses and subnet masks referred to as in OSPF version 3
Prefix, and Prefix Length respectively
Which version of OSPF supports BFD? (Bidirectional Forwarding Detection)
OSPF version 2 only
How often are OSPF LSAs flooded by default?
LSAs are flooded based on the link-state refresh time (every 30 minutes by default).
Define OSPF Opaque LSAs and the 3 LSA types that fall under this category
Opaque LSAs consist of a standard LSA header followed by application-specific information.
LSA type 9: Flooded to the local network.
LSA type 10: Flooded to the local area.
LSA type 11: Flooded to the local autonomous system
Define a Type 1 LSA in OSPF versions 2 & 3
Type 1 LSAs are referred to as Router LSAs in OSPF versions 2 & 3
- Sent from all OSPF-enabled routers and flooded into the local OSPF area
- Contains the costs of all links and a list of OSPF neighbors on the link
Define a Type 2 LSA in OSPF versions 2 & 3
Type 2 LSAs are referred to as Network LSAs in OSPF versions 2 & 3
- Sent only by the DR and flooded to all other routers in the local OSPF area
- Lists all routers in the multi-access network
Define a Type 3 LSA in OSPF version 2 & 3
Type 3 LSAs are referred to as Network Summary LSAs in OSPF version 2
Type 3 LSAs are referred to as Inter-Area Prefix LSAs in OSPF version 3
- LSA sent by the Area Border Router (ABR) to an external area
- Includes the link cost from the Area Border Router (ABR) to the local destination
Define a Type 4 LSA in OSPF versions 2 & 3
Type 4 LSAs are referred to as ASBR Summary LSAs in OSPF version 2
Type 4 LSAs are referred to as Inter-Area Router LSAs in OSPF version 3
- Sent by the Area Border Router (ABR) to an external area.
- This LSA advertises the link cost to the ASBR only.
Define a Type 5 LSA in OSPF versions 2 & 3
Type 5 LSAs are referred to as AS External LSAs in OSPF versions 2 & 3
- Generated by the ASBR.
- Includes the link cost to an external autonomous system.
- AS External LSAs are flooded throughout the autonomous system.
Define a Type 7 LSA in OSPF versions 2 & 3
Type 7 LSAs are referred to as NSSA External LSAs in OSPF versions 2 & 3
- Generated by the ASBR within a not-so-stubby area (NSSA)
- Includes the link cost to an external autonomous system destination.
- NSSA External LSAs are flooded only within the local NSSA.
Describe the LSA group pacing feature
Used to reduce high CPU or buffer usage. This feature groups LSAs with similar link-state refresh times and packs multiple LSAs into a single OSPF update message.
Describe the OSPF Max Age Timer
The Max Age timer represents the maximum interval that an LSA can remain in the LSDB without being updated via an OSPF UPDATE message. When the Max Age timer expires for an LSA, it is removed from the LSDB.
Describe an OSPF Area
A logical division of routers and links within an OSPF domain that creates separate subdomains.
- LSDB flooding is contained within an area
Define the term AS and the role of an ASBR
An Autonomous System (AS) is a a network controlled by a single organization or administrative entity. An Autonomous Systems Boundary Router (ASBR) is used to connects an OSPF area to a different Autonomous System (AS).
Describe the function of an OSPF Stub Area & TSA
A stub area is an area that does not allow AS External (type 5) LSAs and does not contain or connect to an ASBR (Autonomous System Boundary Router). A regular stub area receives summarized routes for areas outside of the stubby area. A TSA (Totally-Stubby-Area) will only receive a default summary route of 0.0.0.0 /24 for all areas outside of the TSA.
Describe the function of an OSPF NSSA & TNSSA
A Not-So-Stubby-Area (NSSA) is typically used to redistribute routes from other routing protocols such as RIP or BGP via the ASBR. A NSSA filters LSA types 4 & 5, whereas the Totally NSSA area filters types 3, 4, & 5.
Describe an OSPF Virtual Link
All OSPF areas must have a direct connection back to the backbone area (Area 0). However, in some topologies, a direct physical connection to the backbone may not be available. An OSPF virtual link can be used to connect a distant area to the backbone through another area.
What 2 authentication methods are supported by OSPF?
1) Simple password authentication
2) MD5 authentication digest
What routing algorithm is used by Border Gateway Protocol (BGP)?
A path-vector routing algorithm to exchange routing information between BGP speakers.
Describe BGP path selection
A single best-path is selected for a remote host or network. Each best-path carries well-known mandatory, well-known discretionary, and optional transitive attributes that are used in BGP best-path analysis.