- The Control Plane Network layer is a component in networking that manages the communication and coordination between network devices. It is responsible for handling tasks such as routing, signaling, and configuration.
- In essence, the control plane determines how data should be forwarded through the network by making decisions based on the network's state and topology.
Distance Vector Algorithm: Each router maintains a table with distances to destinations, updating based on information exchanged with neighbors (e.g., RIP protocol).
Link State Algorithm: Routers share comprehensive information about network link states to build a shortest path based on the complete network topology for efficient path calculations (e.g., OSPF protocol).
| Feature | Distance Vector Routing | Link State Routing |
|---|---|---|
| Information Exchange | Exchange routing tables | Exchange Link State Database |
| Update Triggers | Periodic updates or triggered | Event-driven updates |
| Hop Count | Based on hop count | Based on shortest path |
| Path Selection | May not always find shortest | Always finds shortest path |
| Convergence Time | Slower convergence | Faster convergence |
| Memory Usage | Lower memory usage | Higher memory usage |
| Bandwidth Usage | Higher bandwidth usage | Lower bandwidth usage |
| Routing Table Size | Larger routing tables | Smaller routing tables |
| Example Protocols | RIP, EIGRP | OSPF, IS-IS |
| Loop Prevention | Split Horizon, Poison Reverse | SPF Algorithm |
| Scalability | Limited scalability | Highly scalable |
| Fault Tolerance | Less fault-tolerant | More fault-tolerant |
| Example Implementations | Traditional networks | Internet scale networks |
An autonomous system is identified by its globally unique autonomous system number (ASN). AS numbers, like IP addresses, are assigned by
ICANNregional registries.
- Definition: Routers organized into Autonomous Systems (ASs), each under the same administrative control.
- AS Identification: Globally unique Autonomous System Numbers (ASNs) assigned by ICANN.
- Routing Algorithm: Intra-Autonomous System Routing Protocol.
OSPF is a link state protocol that uses flooding of link state information and a Dijkstra’s least cost path algorithm. With OSPF, each router constructs a complete topological map (that is, a graph) of the entire autonomous system. Each router then locally runs Dijkstra’s shortest path algorithm to determine a shortest path tree to all subnets
- Link State Protocol:
- Utilizes flooding of link state information.
- uses Dijkstra’s least cost path algorithm.
- Complete Topological Map:
- Each router constructs a full topological map of the entire AS.
- Locally runs Dijkstra’s algorithm to determine shortest path trees.
- Link Costs:
- Configured by the network administrator.
- Allows flexibility (e.g., minimum hop routing or weights based on link capacity).
-
Security:
- Authentication to ensure only trusted routers participate.
- Supports
simpleandMD5authentication, the latter providing higher security. - Guards against replay attacks using sequence numbers.
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Multiple Same Cost Paths:
- OSPF permits the use of multiple paths when several have the same cost.
-
Integrated Unicast and Multicast Routing:
- MOSPF (Multicast OSPF) extends OSPF to support multicast routing.
-
Hierarchy Support:
- OSPF AS can be configured hierarchically into areas.
- Area Border Routers facilitate routing between areas, with a designated backbone area.
BGP (Border Gateway Protocol) is a fundamental inter autonomous system routing protocol in the Internet. It acts as the glue that binds thousands of ISPs together, facilitating communication across multiple ASs.
- Destination Representation: Routes packets to
CIDRized prefixes, each representing a subnet or a collection of subnets. - Advertising Reachability Information: Allows subnets to advertise their existence across ASs.
- BGP Connections:
- Advertising reachability information through BGP messages.
- External BGP (eBGP) connections: Between gateway routers in different ASs.
- Internal BGP (iBGP) connections: Within routers of the same AS.
When a router advertises a prefix across a BGP connection, it includes with the prefix several BGP attributes. In BGP jargon, a prefix along with its attributes is called a route. Two of the more important attributes are
AS-PATHandNEXT-HOP.
The AS-PATH attribute contains the list of ASs through which the advertisement has passed. To generate the AS-PATH value, when a prefix is passed to an AS, the AS adds its ASN to the existing list in the AS-PATH. The NEXT-HOP is the IP address of the router interface that begins the AS-PATH.
- BGP Attributes:
AS-PATH: List of ASs through which the advertisement has passed.NEXT-HOP: IP address of the router interface starting the AS-PATH.
- Choosing the Best Route: Routers choose among various paths based on cost and policy.
Three components: NEXT-HOP; AS-PATH; destination prefix.
3d; AS3; X --> 2a; AS2 AS3; X
Hot Potato Routing is a fundamental algorithm in BGP (Border Gateway Protocol) used for selecting the best route to a destination prefix. This algorithm prioritizes getting packets out of an Autonomous System (AS) quickly with minimal cost.
Goal: Quickly move packets out of the AS with the least possible cost.Analogy: Similar to passing a burning "hot potato" to another person (AS) as quickly as possible.Selfish Algorithm: Focuses on reducing costs within its AS, ignoring other end to end costs outside the AS.
-
Learn Routes:
- Router 1b learns about two possible BGP routes to prefix x.
-
Cost Calculation:
- Utilizes intra AS routing information to find the least cost intra AS path to NEXT-HOP routers (2a and 3d).
- Defines cost as the number of links traversed.
-
Route Selection:
- Selects the route with the smallest of these least cost paths.
- Example: Cost to router 2a is 2, cost to router 3d is 3, so router 2a is selected.
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Forwarding Table Update:
- Consults the forwarding table (configured by intra AS algorithm) to find the interface (I) on the least cost path to router 2a.
- Adds (x, I) to its forwarding table.
-
Adding Outside AS Prefix
- When adding an outside AS prefix to the forwarding table, both inter AS (BGP) and intra AS (e.g., OSPF) routing protocols are utilized.
BGP is also utilized for implementing the IP anycast service. IP anycast is used in applications like DNS to replicate content across dispersed geographical locations, ensuring users access the nearest server. IP Anycast in BGP facilitates efficient content distribution by leveraging BGP's route selection capabilities.
-
IP-Anycast Configuration:
- CDN assigns the same IP address to all servers.
- Standard BGP is used to advertise this IP address from each server.
-
BGP Route Selection Algorithm:
- BGP routers treat multiple route advertisements for the same IP address as different paths to the same physical location.
- Local BGP route selection algorithm is applied to choose the "best" route (e.g., closest in AS hop counts).
-
Routing Table Configuration:
- Each router configures its routing table to route packets to the chosen location based on the BGP route selection.
-
Content Distribution:
- CDN distributes content, and when a client requests the common IP address, routers forward the request to the "closest" server as per BGP route selection.
The Internet Control Message Protocol (ICMP) facilitates communication of network layer information among hosts and routers. Primarily used for error reporting.
- ICMP Message Structure
- ICMP messages consist of a
typeand acodefield. - They contain the header and the initial 8 bytes of the IP datagram causing the ICMP message in error identification.
- ICMP messages consist of a
-
Ping Program (Echo Request and Echo Reply):
- Type 8 (Echo Request) and type 0 (Echo Reply) messages.
- Ping client sends an Echo Request, and the destination host responds with an Echo Reply.
-
Source Quench Message:
- Used for congestion control, but used in practice.
- Allows a congested router to send a source quench ICMP message to instruct a host to reduce its transmission rate.
-
Traceroute Program:
- Implemented using ICMP messages (type 11 code 0).
- Determines routers between source and destination by sending UDP datagrams with incrementing TTL values.
- Round trip time, router names, and IP addresses are obtained from ICMP warning messages.
Network management includes the deployment, integration, and coordination of the hardware, software, and human elements to monitor, test, poll, configure, analyze, evaluate, and control the network and element resources to meet the realtime, operational performance, and Quality of Service requirements at a reasonable cost.
- centralized network that controls collection, processing, analysis, dispatching of network management information and commands.
- Initiates actions to configure, monitor, and control managed devices.
- Network equipment, like hosts, routers, switches, including software residing on a managed network.
- Holds configuration parameters, operational data, and device statistics.
- Configuration data: Explicitly configured device information by the network manager.
- Operational data: Information acquired by the device during operation (e.g., OSPF neighbors).
- Device statistics: Status indicators and counts updated during operation.
- Software in the managed device that communicates with the managing server, taking local actions as directed.
- Facilitates communication between managing server and managed devices.
- Allows querying device status and taking actions via agents.
- Informs managing server of exceptional events (e.g., component failures).
- MIB objects represent operational state and configuration data of managed devices.
| SNMPv3 PDU Type | Description | Sender-Receiver |
|---|---|---|
| GetRequest | Get value of one or more MIB object instances | Manager-to-Agent |
| GetNextRequest | Get value of next MIB object instance in list or table | Manager-to-Agent |
| GetBulkRequest | Get values in a large block of data, e.g., values in a large table | Manager-to-Agent |
| InformRequest | Inform remote managing entity of MIB values remote to its access | Manager-to-Manager |
| SetRequest | Set value of one or more MIB object instances | Manager-to-Agent |
| Response | Generated in response to GetRequest, GetNextRequest, GetBulkRequest, SetRequest, or InformRequest PDUs | Agent-to-Manager or Manager-to-Manager |
| SNMPv2-Trap | Inform manager of an exceptional event | Agent-to-Manager |
NETCONF specifies in a structured XML document, and activates a configuration at the managed device. NETCONF uses a remote procedure call (RPC), where protocol messages are also encoded in XML and exchanged between the managing server and a managed device over a secure, connection oriented session such as the TLS protocol.
YANG is the data modeling language used to precisely specify the structure, syntax, and semantics of network management data used by NETCONF. All YANG definitions are contained in modules, and an XML document describing a device and its capabilities can be generated from a YANG module.
- A more abstract, network wide approach to network management.
- Emphasizes configuration management and atomic operations over multiple devices.
- YANG (data modeling language) models configuration and operational data.
- NETCONF protocol communicates YANG compatible actions and data.