IP Routing

Routing

The process of selecting paths in a network along which to send network traffic. Performed by routers, which use routing tables and algorithms to determine the most efficient path for data packets to travel

Static Routing

Involves manually configuring routers with specific paths to reach destinations. Simple to implement, but lacks flexibility and scalability of dynamic routing since it doesn’t adjust to network changes. Difficult to maintain/manage, but you have more control of the routes the data will take

RIP

Routing Information Protocol. One of the oldest distance-vector (hop counts) routing protocols. Max of 15 hops

Versions

• RIPv1: Classful protocol, no subnet info

• RIPv2: Classless, supports subnet mask info. Multicast updates and simple authentication

Use cases:

• Suitable for small to medium-sized networks

• Limited scalability, slower convergence compared to modern protocols like OSPF and EIGRP

OSPF

Open Shortest Path First. A link-state routing protocol. Fast convergence and supports large networks

Key features:

• Hierarchical design with areas to optimize traffic

• Updates sent only when topology changes, which reduces overhead

• Supports VLSM (Variable Length Subnet Masking) and CIDR

Advantages:

• Efficient, scalable, and flexible

• Provides load balancing and fault tolerance

• Suitable for large, complex networks

Enhanced Interior Gateway Routing Protocol

Enhanced distance-vector protocol. Combines features of distance-vector and link-state protocols (basing paths combining least amount of paths and least amount of bandwidth)

Key features:

• Supports VLSM and CIDR

• Sends partial updates only when changes occur

• Uses metrics like bandwidth, delay, load, and reliability

Advantages:

• Highly efficient, scalable, and quick convergence

• Provides loop-free paths and load balancing

• Suitable for medium to large networks, especially those with Cisco devices

Metric

A value associated with routes, used by routing protocols to evaluate the cost of path traversal

Lower metric values typically indicate more desirable routes

Different routing protocols may use various factors, such as bandwidth, delay, hop count, or even custom values to calculate this metric

Border Gateway Protocol (BGP)

Essential for inter-domain routing on the internet. Uses path attributes to select the best route. Used for ISPs, powers the entire internet

Key features:

• Supports CIDR for efficient IP address allocation

• Employs policies for route selection and advertisement (policies can be set by ISP)

• Uses TCP for reliable communication between BGP peers

Advantages:

• Highly scalable and flexible

• Manages large routing tables and complex policies

• Crucial for ISPs and large enterprises with multiple connections to the internet

Route Selection

Critical process in network routing that determines the best path for data to travel from source to destination

Uses specific criteria such as administrative distance, prefix, length, and metric to choose the most efficient route

Administrative Distance

A metric used by routers to rank the trustworthiness of routes received from different routing protocols

Lower values indicate more preferred routes, helping routers decide which routes to use when multiple paths to the same destination exist from different sources. Can be manually adjusted to influence route selection

Prefix Length

Specifies the number of contiguous bits of the network mask that are set to 1

This notation of an integral part of CIDR and helps in defining network boundaries and available hosts within those networks, enhancing both routing efficiency and address allocation

VRRP/FHRP

First-Hop Redundancy Protocol, essentially a virtual router protocol that helps achieve high availability with multiple physical redundant routers

HSRP (Hot Standby Router Protocol): Cisco proprietary redundancy protocol

VRRP (Virtual Router Redundancy Protocol): Open standard redundancy

Needs a VIP (Virtual IP address)

Virtual IP (VIP)

IP address that is not tied to a specific physical network interface on a device. Used to provide redundancy and load balancing on multiple servers, allowing several servers to share the same IP address

Commonly used in network load balancers and failover configurations to ensure continuous availability and scalability of critical applications and services

Subinterface

A virtual interface created by dividing a single physical interface into multiple logical interfaces. Allows one interface to carry multiple IP addresses

Commonly used in scenarios where multiple VLANs exist on a single router or switch interface to manage traffic segregation and support various services or protocols over a single physical link

ex: interface g0/0 or g0/1 into g0/0.1 or g0/1.1

NAT

Translates one IP address to another IP address. Allows multiple devices to share the same Public IP. Can be provided by a router or firewall

Advantages:

• Conserve public IP addresses

• Eliminates address overlap events with other LANs

• Makes it easier to connect to the internet

• Eliminates address renumbering if your network changes

Disadvantages:

• Translation delays the forwarding of packets

• Cause loss of end-to-end-IP traceability

• Certain applications will not function with NAT enabled

Types of NAT

Static NAT:

• Translates one internal address to one external address

• ONLY required if an internal host needs to be accessible from the internet (for hosting a server)

Dynamic/Pooled NAT (Many-to-Many):

• Translate many different internal addresses to many different external addresses

• NOT commonly used since it can limit internet access (like pooling 10 addresses for 30 hosts… only 10 can access at a time)

Port Address Translation (Many-to-One):

• Translates may different internal addresses to one external address

• MOST commonly used to access the Internet

• Also known as overloading NAT or PNAT (overloading one IP addresses with many many addresses)

Which of the following best describes the purpose of the routing table in a router?

To provide a database of routes and associated metrics for packet forwarding