1.9 Explain the basics of routing concepts and protocols - Paiet/Tech-Journal-for-Everything GitHub Wiki
1.9 Explain the basics of routing concepts and protocols
Loopback interface
Virtual network interface on the local machine used for testing IP software
Has no actual hardware or real network connection
Allows IP software to send information up the IP stack without having to worry about failure due to broken or corrupted drivers or hardware
IPv4 Loopback address: 127.0.0.1
IPv6 Loopback address: ::1
Routing loops
A routing loop is when data is passed through routers over and over again, never actually reaching its destination
This occurs when a route dies and, due to slow route updates, other routers don't realize the route is lost.
They then send their own route updates that include the lost route, fooling other routers into thinking that the route is still alive
Usually a problem with Distance Vector routing protocols due to slow convergence times
Can be a problem with any routing protocol if configured without loop avoidance in mind
Routing tables
Router's database of known routes
Routing tables are populated through manual entry and/or learned through the use of dynamic routing protocols
Used by the router to know where to forward traffic and what's the best route to take
This is in the case of multiple good routes
Static vs dynamic routes
Static Routes
Manually entered routes
Used when data needs to be sent over a specific route
Border router to border router
Lowers extraneous network traffic due to not needing to send routing table updates
Routing tables are also not being updated by other routers, thus lowering network traffic again
No unnecessary route entries to maintain/update
Static = Efficiency + Administration
While static routes are efficient, they also require a lot of administration and management
All route changes will need to be manually updated which will be more likely to misconfigured
Dynamic Routes
Routes are learned through the use of routing protocols
RIPv2, OSPF, EIGRP, IS-IS
Routes can and do change as links are lost and created
This is done automatically by the routing protocol sending and receiving regular updates
De facto standard for large entities with multiple routes
Due to the sheer size of some networks, dynamic routing is a must as a network admin wouldn't be able to keep up with the necessary reconfigs and management
Default route
Used as the route to take when a route to the destination network is unknown
The default gateway receives the data, checks its routing table for the destination network, if not found it forwards the data to its default route (another router), and on and on until the destination network is reached
Usually this data will quickly be forwarded to an ISP router
IPv4 default route is 0.0.0.0/0
aka Zero Address or Quad-Zero Route
"Gateway of Last Resort"
IPv6 default route is ::/0
Distance Vector routing protocols
Makes routing decisions based on the "hop count" distance of the destination network and the direction of the path
A "hop" is a router that data must pass through to reach a destination network
If data has to pass through 3 routers to reach its destination, then that would be 3 hops
The route with the least amount of hops gets to pass the data
Maximum number of 15 hops allowed before network is considered unreachable
RIP v2
Dynamic routing protocol that utilizes distance vector for calculating routing decisions
This means it is only concerned with hop count and doesn't look at other metrics like link speed or network congestion
Like its predecessor RIP, it is good for smaller, static networks
RIPv2 has improved upon its predecessor in many different ways
Next Hop Addressing
Routing tables include the IP address info of all routers in a given path
This makes sure that data doesn't take a less than optimal path
Authentication
Password and authentication key option available
Variable Length Subnet Masks (VLSM)
Allows subnetting to add networks by borrowing from host portions
IPv6
Supports IPv6 addressing
RIPng
Broadcasts its routing table every 30 seconds in its entirety, with routes and costs
This creates a lot of extra traffic
Stable protocol, but is slow to converge and is prone to routing loops
To avoid routing loops, RIPv2 employs Split-Horizon and Poison Reverse
Split-Horizon: If a RouterA learns a route on interface fa0/1, RouterA will not include that route in its updates that go out of interface fa0/1
Poison Reverse: Actually sets a route to unreachable by setting the hop count to 16
This keeps this router and other routers from attempting to use that specific interface to access the poisoned route
Link state routing protocols
Makes routing decisions based on metrics such as quality, bandwidth, and availability
Each router does its own calculations about best route paths instead of relying on information learned from its neighbors
Broadcasts small updates about the availability of each of its connections, and then only when that info changes
Send a broadcast when a link comes up, goes down, changes in quality, and/or bandwidth
This makes for quick convergence
Only other communication with neighbors is through small "hello" packets
This is just a periodic update to assure the neighbors that the router is still alive and functioning
Used in large scale networks and/or networks with an ever changing topology
OSPF Open Shortest Path First
Very common link-state protocol
OSPF logically calculates the shortest path to network destinations
This is done using the Dijkstra algorithm
Supports IPv4 and IPv6 and VLSM
Able to support up to 65,535 routers
IS-IS
Intermediate System to Intermediate System
Similar to OSPF in function
Uses the same Dijkstra algorithm
Supports the use of more routers than OSPF
Actually works at Layer 2 and therefore isn't limited to Layer 3 IP addressing like OSPF
Not implemented in new networks.
Hybrid routing protocols
EIGRP (Enhanced Interior Gateway Protocol)
Cisco proprietary protocol
Employs the metrics from both Link-State and Distance Vector routing
Hop count, bandwidth, availability, etc...
Supports VLSM and CIDR
Found in use with multilayer switches
Increased amount of updates to increase network stability and reduce convergence time
Path vector protocol
Path vector is similar in operation to that of Distance Vector except that it doesn't use hop count to figure out the route, it learns the entire route and chooses the best route for delivery from its routing table
Treats an entire Autonomous System/Domain (AS) as a single node
Each AS is assigned an AS number and has a border router that connects the AS to the exterior network
Routes are not calculated the same as in IGPs
BGP (Border Gateway Protocol)
The protocol of the Internet
Used to connect internet backbones
Basically the only Path Vector protocol in use
Routing decisions are often manipulated
Interior vs exterior gateway routing protocols
Interior Gateway Protocols (IGP)
Routing protocols that are used within an Autonomous System
Routes just between the routers/gateways in its own AS
e.g RIP, IGRP, IS-IS, OSPF, EIGRP
Exterior Gateway Protocols (EGP)
Routing protocols that are used to route betweeen Autonomous Systems
Routes from one AS to another
e.g. BGP
Autonomous system numbers
16 bit number that is assigned by ARIN (American Registry for Internet Numbers) after registering your AS with them
Distinguishes networks from each other on the Internet
Done by ISPs and larger organizations
Route redistribution
Routing from one routing protocol into another different protocol
Allows you to have routers with different protocols share route information, which they don't do by default
Routing protocols, by default only "talk" with devices running the same protocol as themselves
With route redistribution, we can all just get along
High availability
VRRP (Virtual Routing Redundancy Protocol)
A software router that represents a group of physical routers and acts as a single gateway for clients, adding redundancy to what would otherwise be a single point of failure
Basically takes a bunch of routers and defines them as a group that share a virtual IP address which is set as the default gateway for the clients
One router is set as the Master, the others are set as Backups
If the master goes down, then an election process is initiated and a new master is set based on highest MAC address
Since the new master uses the same virtual IP address as the old master, client access and configuration doesn't change
Virtual IP
An IP address that doesn't correlate to any actual, physical network interface
Can be used in situations like VRRP, HSRP, NAT
HSRP (Hot Standby Router Protocol)
Cisco proprietary protocol for providing a redundant default gateway using multiple routers or router interfaces attached to a virtual IP address
Similar in operation as VRRP
One router/interface is set to Active and the other(s) are set to Standby
Route aggregation
Combining multiple routes that are in the same routing path into one route, thereby reducing the number of entries in a routing table which increases network efficiency
Routing metrics
Routing metrics is/are a valuing system used for the purpose of giving value to certain attributes of a route so that routers can decide route paths based off calculations that employ the different metrics
Hop counts
How many routers does data have to "hop" through to get to its destination
Each router data has to pass through is one hop
MTU, bandwidth
Maximum Transmission Unit
How much data can be transmitted, per Protocol Data Unit (PDU)
Standard size is 1500 bytes
Jumbo frames can transmit up to 9000 bytes per PDU
Costs
Metric associated with OSPF
Reference Bandwidth / Actual Bandwidth
Reference bandwidth = 100 Mbps (100,000,000) 10^8
Latency
Delay in time for data to get from the source to the destination
Administrative distance
A numerical value administratively assigned to a static or directly connected route, or even a routing protocol, which designates route expediency
The lower the distance number, the better the route/protocol
SPB (Shortest Path Bridging)
Intended to replace Spanning Tree Protocol for simplifying the creation and configuration of networks while also supporting multipath routing
1.9 Explain the basics of routing concepts and protocols
Path vector protocol
Path vector is similar in operation to that of Distance Vector except that it doesn't use hop count to figure out the route, it learns the entire route and chooses the best route for delivery from its routing table
Treats an entire Autonomous System/Domain (AS) as a single node
Each AS is assigned an AS number and has a border router that connects the AS to the exterior network
Routes are not calculated the same as in IGPs
BGP (Border Gateway Protocol)
The protocol of the Internet
Used to connect internet backbones
Basically the only Path Vector protocol in use
Routing decisions are often manipulated
Interior vs exterior gateway routing protocols
Interior Gateway Protocols (IGP)
Routing protocols that are used within an Autonomous System
Routes just between the routers/gateways in its own AS
e.g RIP, IGRP, IS-IS, OSPF, EIGRP
Exterior Gateway Protocols (EGP)
Routing protocols that are used to route between Autonomous Systems
Routes from one AS to another
e.g. BGP
Autonomous system numbers
16 bit number that is assigned by ARIN (American Registry for Internet Numbers) after registering your AS with them
Distinguishes networks from each other on the Internet
Done by ISPs and larger organizations
Route redistribution
Routing from one routing protocol into another different protocol
Allows you to have routers with different protocols share route information, which they don't do by default
Routing protocols, by default only "talk" with devices running the same protocol as themselves
With route redistribution, we can all just get along
High availability
VRRP (Virtual Routing Redundancy Protocol)
A software router that represents a group of physical routers and acts as a single gateway for clients, adding redundancy to what would otherwise be a single point of failure
Basically takes a bunch of routers and defines them as a group that share a virtual IP address which is set as the default gateway for the clients
One router is set as the Master, the others are set as Backups
If the master goes down, then an election process is initiated and a new master is set based on highest MAC address
Since the new master uses the same virtual IP address as the old master, client access and configuration doesn't change
Virtual IP
An IP address that doesn't correlate to any actual, physical network interface
Can be used in situations like VRRP, HSRP, NAT
HSRP (Hot Standby Router Protocol)
Cisco proprietary protocol for providing a redundant default gateway using multiple routers or router interfaces attached to a virtual IP address
Similar in operation as VRRP
One router/interface is set to Active and the other(s) are set to Standby
Route aggregation
Combining multiple routes that are in the same routing path into one route, thereby reducing the number of entries in a routing table which increases network efficiency
Routing metrics
Routing metrics is/are a valuing system used for the purpose of giving value to certain attributes of a route so that routers can decide route paths based off calculations that employ the different metrics
Hop counts
How many routers does data have to "hop" through to get to its destination
Each router data has to pass through is one hop
MTU, bandwidth
Maximum Transmission Unit
How much data can be transmitted, per Protocol Data Unit (PDU)
Standard size is 1500 bytes
Jumbo frames can transmit up to 9000 bytes per PDU
Costs
Metric associated with OSPF
Reference Bandwidth / Actual Bandwidth
Reference bandwidth = 100 Mbps (100,000,000) 10^8
Latency
Delay in time for data to get from the source to the destination
Administrative distance
A numerical value administratively assigned to a static or directly connected route, or even a routing protocol, which designates route expediency
The lower the distance number, the better the route/protocol
SPB (Shortest Path Bridging)
Intended to replace Spanning Tree Protocol for simplifying the creation and configuration of networks while also supporting multipath routing