Network Systems - Routing Overview

Network Systems - Routing

• Routers connect multiple networks.
• They forward packets between networks.
• Routers connect dissimilar networks (LANs and WANs).
• They interpret Layer 3 and often Layer 4 addressing.
• They determine the best path for data.
• They can re-route traffic if a path fails.

Router Functions

• Routers may filter broadcast transmissions.
• They can prevent specific types of traffic.
• Routers support simultaneous local and remote connectivity.
• They provide high network fault tolerance using redundant components (e.g., power supplies).
• They monitor network traffic and report statistics.
• They diagnose connectivity problems.

Router Categories

• Core routers are within the same autonomous system (AS).
• They handle data between networks within the same AS.
• Edge routers connect an AS to an outside network.
• Exterior routers are external to an organization's AS.

Routing Tables

• Routing tables are databases that hold information about host locations and the best routes.
• Routers rely on routing tables to locate destinations.
• Routing tables include IP addresses and network masks.
• Network masks identify networks.

Static vs. Dynamic Routing

• Static routing involves administrators configuring a routing table with specific paths.
• Dynamic routing automatically calculates the best paths and maintains the routing table.
• Routers can detect problems with routes (failed or congested) and re-route messages.

The Route Command

• The route command (Linux/UNIX) or netstat -r (macOS) displays a host's routing table.
• Windows systems use the route print command to view the routing table.

Routing Metrics

• Routing metrics are properties routers use to determine the best paths to destinations.
• Hop count is the number of routers between source and destination.
• Theoretical bandwidth and actual throughput are factors.
• Delay (latency) on potential paths.
• Load (traffic/processing burden).
• MTU (maximum transmission unit).
• Routing cost (value assigned to a route).
• Reliability of the path.
• Network topology.

Determining Best Routing Paths

• Routing protocols allow routers to communicate and determine the best path.
• Protocols are rated based on criteria, including administrative distance (AD) and convergence time.
• Administrative distance is a number indicating the protocol's reliability.
• Convergence time is the time it takes for a router to find the best path following a topology change.
• Overhead is the burden placed on the network to support the protocol.

Common Routing Protocols

• Routing protocols, like RIP, RIPv2, OSPF, IS-IS, and BGP, are categorized as IGPs (interior gateway protocols) or EGPs (exterior gateway protocols).
• IGPs are used within an autonomous system (e.g., OSPF, IS-IS, EIGRP, RIP).
• EGPs are used between autonomous systems (e.g., BGP).

IGP and EGP

• Interior gateway protocols (IGPs) are used by core and edge routers.
• Exterior gateway protocol (EGPs) are used by edge and exterior routers to manage data outside autonomous systems.
• Distance-vector routing protocols calculate paths based on distance from the destination.
• Link-state protocols let routers map the networks to determine the best path.
• The BGP routing protocol is the only EGP protocol still in use.

BGP (Border Gateway Protocol)

• BGP is a path-vector routing protocol used to communicate between autonomous systems.
• It can span multiple autonomous systems.
• It determines the best path based on various factors.
• Policy-based routing can be used to implement specific policies.

OSPF (Open Shortest Path First)

• OSPF is an IGP, a link-state protocol that supports large networks without hop limit restrictions.
• OSPF uses a more complex algorithm to determine best paths.
• OSPF creates and maintains a database of other routers and their links.
• It has low overhead and fast convergence.

IS-IS (Intermediate System to Intermediate System)

• IS-IS is an IGP and link-state routing protocol.
• It uses a best-path algorithm similar to OSPF.
• IS-IS is designed for use on core routers only.
• IS-IS is not tied to IPv4, allowing easy adaptation to IPv6.

EIGRP (Enhanced Interior Gateway Routing Protocol)

• EIGRP is a hybrid protocol combining distance-vector and link-state features.
• It offers fast convergence and low overhead.
• It's easier to configure and less CPU intensive than OSPF.
• EIGRP supports multiple protocols and limits unnecessary routing traffic.

Supernetting

• Network summarization; grouping contiguous subnets into a single network.
• Used to reduce the size of routing tables.
• Consolidate continuous routes into a single route for route advertisements.

Supernetting Examples

• A 193.2.1.0/24 is seen as a whole network externally.
• 193.2.1.0/25, 193.2.1.128/25, 193.2.1.0/26, and 193.2.1.64/26 are subnets that are grouped into a supernet.

Supernetting Comparison to Subnetting

• Supernetting is the opposite of subnetting.
• Supernetting involves combining contiguous subnets.
• Supernetting uses masks to form a supernet.
• Routers only need one address for the supernet, reducing Internet router load.

"Giving Away" Bits for Supernetting

• Supernetting involves giving away network bits from the left of the default mask boundary.
• Subnetting involves borrowing host bits from the right of the default mask boundary.

Supernet - Smaller Routing Table

• A routing table example shows how supernetting reduces the number of routes.

Benefits of Supernetting

• Minimizes latency in complex networks.
• Reduces routing overhead.
• Improves network stability.
• Reduces processor workloads, memory requirements, and bandwidth demand.

Example and Solution

• A medium-size organization requiring 1000 addresses, and the required subnet mask.
• Converting 1000 addresses to class C addresses and a single subnetted address.

Example Continued

• Demonstrates the calculation of supernetting. This involves allocating class C addresses to the organization, and calculating the network ID.

Verifying Network ID with Mask

• A tabular example showing how network address is verified with the supernet mask.

Common Command-Line Utilities

• arp, dig, ipconfig, ifconfig, netstat, nmap, nslookup, pathping, ping. route, tcpdump.

Explore the essential functions and categories of routers in network systems. This quiz covers how routers connect different networks, manage traffic, and maintain connectivity. Test your knowledge of routing tables and the critical roles routers play in data communication.