Netzwerküberwachung – Ein grundlegender Überblick

Netzwerküberwachung – Ein grundlegender Überblick

Netzwerküberwachung ist ein kritischer Teil des Netzwerkbetriebs und beinhaltet die ständige Überwachung eines Computer-Netzwerks auf langsame oder fehlgeschlagene Komponenten. Es wird in der Regel von einem Netzwerkbetriebszentrum (NOC) durchgeführt, wo Techniker fortlaufend die Statusberichte von Netzwerkgeräten wie Routern, Switches und Firewalls überprüfen.

In Echtzeit erfasste Leistungsdaten ermöglichen es den Netzwerkadministratoren, Unregelmäßigkeiten oder Ausfälle schnell zu identifizieren und zu diagnostizieren. Zu den Überwachungstools gehören Managementsoftware und Protokolle wie SNMP (Simple Network Management Protocol), um eine effiziente Problemerkennung und -behebung zu gewährleisten.

Proaktive Überwachungsstrategien beinhalten die Einrichtung von Alarmen und Benachrichtigungen, die automatisch ausgelöst werden, wenn bestimmte Schwellenwerte überschritten werden. Dies ermöglicht Netzwerkpersonal, sofortige Korrekturmaßnahmen zu ergreifen und potenzielle Ausfallzeiten zu minimieren.

Packet Type 1: Hello

• Establishes and maintains neighbor relationships.

• Determines if neighbors are reachable.

Packet Type 2: Database Description (DBD)

• Exchanges OSPF database summary information.

• Describes the contents of the link-state database.

Packet Type 3: Link State Request (LSR)

• Requests more recent link-state advertisements.

• Sent after receiving a DBD indicating newer info is available.

Packet Type 4: Link State Update (LSU)

• Responds to LSRs; contains recent LSA info.

• Used to flood LSAs to all routers in an area.

Neighbor Discovery

• Accomplished through Hello packets.

• Identifies other routers on the same network.

Exchange of Topology Information

• Initiated by DBD packets.

• Followed by LSRs and LSUs for detailed info.

Full Adjacency Formation

• Indicates a state where routers have full knowledge of each other’s databases.

• Achieved after the exchange and acknowledgment of LSAs.

Maintaining Neighbor Relationships

• Hello packets are used as keep-alives.

• Regular exchange ensures network stability.

Router LSA (Type 1)

• Advertises directly connected interfaces and neighbors.

• Originated by all routers.

Network LSA (Type 2)

• Generated by the Designated Router (DR).

• Describes all routers attached to the network.

Summary LSA (Type 3 & 4)

• Created by Area Border Routers (ABRs).

• Summarizes routes to networks outside the area but within the AS.

External LSA (Type 5)

• Used for advertising routes imported from external sources.

• Generated by Autonomous System Boundary Routers (ASBRs).

Version Number

• Identifies the OSPF version in use, typically version 2 for IPv4.

Type

• Indicates one of the 5 OSPF packet types.

Packet Length

• Specifies the length including the OSPF header.

Router ID

• Uniquely identifies the source router.

Broadcast Network Type

• Typically found on Ethernet networks.

• Utilizes Multicast for OSPF messaging.

Non-Broadcast Multiple Access (NBMA)

• Used for Frame Relay or ATM networks.

• Requires manual neighbor configuration.

Point-to-Point Network Type

• Direct connection between two routers.

• OSPF operates smoothly without any additional configuration.

Point-to-Multipoint Network Type

• Treats each connection in a multi-access network as a point-to-point link.

• Allows for more scalability.

Backbone Area (Area 0)

• Core of an OSPF network where all other areas connect.

• Essential for proper OSPF routing.

Standard Area

• An internal OSPF area connected to the backbone.

• Follows normal OSPF area rules.

Stub Area

• Cannot contain any ASBR or receive external routes.

• Reduces the size of the routing table.

Not-So-Stubby Area (NSSA)

• Extension of a stub area.

• Can import external routes and redistribute them within the area as type 7 LSAs.

OSPF (Open Shortest Path First)

OSPF is a routing protocol for Internet Protocol (IP) networks that uses a link state routing (LSR) algorithm.

Link-State Advertisement (LSA)

LSA is a basic communication means of OSPF routers, which conveys the router's local routing topology to all other local routers in the same OSPF area.

OSPF Area

A region consisting of networks and routers that all have the same area identification. Areas optimize routing within the domain.

OSPF Router Types

1. Internal Router (IR): All interfaces reside in the same area.

2. Area Border Router (ABR): Connects two or more areas.

3. Backbone Router (BR): Resides in the backbone area (area 0).

4. Autonomous System Boundary Router (ASBR): Connects OSPF to other routing protocols.

Establishing Neighbor Relationships

Routers exchange Hello packets to elect Designated Router (DR) and Backup Designated Router (BDR) and to form adjacencies.

OSPF States

1. Down

2. Init

3. Two-Way

4. Exstart

5. Exchange

6. Loading

7. Full

Database Synchronization

Routers exchange database description packets, synchronizing their LSDB, which contains the state of the network.

Route Calculation

OSPF uses the Dijkstra algorithm to compute the shortest path tree for each running OSPF process.

Types of OSPF Packets

1. Hello packets — Establish and maintain adjacency.

2. Database Description (DBD) — Describe the contents of the router's LSDB.

3. Link State Request (LSR) — Request pieces of the LSDB from other routers.

4. Link State Update (LSU) — Response to LSRs, carrying LSAs.

5. Link State Acknowledgment (LSAck) — Acknowledge receipt of LSUs.

Hello Packets

Used to discover OSPF routers and establish neighbor relationships. It carries key parameters that must match between neighbors.

Database Description Packets

Exchanges LSDB contents between neighbors during the initial adjacency formation.

Link State Update (LSU)

Used to flood LSAs to all neighbors, allowing all routers within an OSPF area to have synchronized copies of the LSDB.

OSPF LSA Types

1. Type 1: Router LSA

2. Type 2: Network LSA

3. Type 3: Summary LSA

4. Type 4: Summary ASBR LSA

5. Type 5: Autonomous system external LSA

6. Type 7: NSSA external LSA

7. Type 8-11: Used for various OSPF extensions

Type 1: Router LSA

Generated by all routers, describing their interfaces and states.

Type 2: Network LSA

Generated by the DR, listing all routers on that segment.

Type 3, 4: Summary LSAs

Type 3 are generated by ABR and describe routes to networks in other areas. Type 4 describe routes to ASBRs.

Standard Area

A normal OSPF area that carries a routing table with all OSPF network types and routes.

Backbone Area (Area 0)

The core area of an OSPF network. All other areas must connect to it. ABRs sit between the backbone and other areas.

Stub Area

Does not accept routes from external sources (non-OSPF networks), except default routes.

NSSA (Not So Stubby Area)

Allows the distribution of external routes within the area but does not flood them to the entire OSPF network.

Timers

Carefully configure OSPF timers like Hello and Dead intervals to optimize convergence time without causing unnecessary traffic.

Load Balancing

OSPF can balance traffic on paths with equal cost. Maximize this by properly designing and subnetting the network.

Route Summarization

On ABRs and ASBRs, summarize routes to reduce the routing table size and improve efficiency.

MPLS with OSPF

Integrate OSPF with MPLS to support larger and more complex network architectures and enhance the scalability.