chapter 2.1 - Static and Dynamic routing, Routing Techs., and NAT

How do routers route traffic?

Forward traffic between IP subnets

1. Identify destination of IP address (its in the packet)

2. Examine tables for best route

   1. If on LOCAL connected subnet - sends directly

   2. If on REMOTE subnet - forward to next- hop router/gateway

3. Repeat with the new router if necessary

If router does not find next hop on routing table then it discards that traffic

What is static routing? Advantages? Disadvantages?

Manually configured define routes

Advantages: Easy to configure for small networks, no overhead, more secure since it has no protocols to analyze

Disadvantages: Difficult to configure for larger networks, no automatic method to prevent routing loops, no automatic rerouting if an outage

What is dynamic routing? Advantages? Disadvantages?

Routers send their routing tables to other routers so its constantly updated

Advantages: no manual route calculation or managment, new routes populate automatically, scalable

Disadvantages: Some router overhead that requires additional monitoring, requires initial configuration

What are dynamic routing protocols?

Listen for subnet information from other routers

Provide subnet information to other routers

Determine the best path based on this information

Update the available routes

How long can dynamic routing take to recover after a change in the network?

seconds to minutes - depends on the routing protocols

What is Enhanced Interior Gateway Routing Protocol (EIGRP)?

Commonly used in Cisco-routed networks

Easy to enable and use

Updates quickly, loop free, and efficient bandwidth use

What is Open Shortest Path First (OSPF)?

Common interior gateway protocol, used in completely admin controlled systems (autonomous systems)

Link-state protocol - routing is based on connectivity between routers, low cost wins and identical costs are load balanced

Cost is based on throughput, reliability, round-trip time

What are route entries made of?

ex.

R 10.10.30.0/24 [120/1] via 10.10.50.2, 00:00:14, Serial10/3/1

Route code

Subnet ID w/Prefix Length

[Administrative Distance

/Metric]

Next Hop,

Route Timestamp,

Outgoing interface

What are prefix lengths?

For subnet IDs the more specific route “wins” as the route the router uses

Routes are more specific as the prefix increases

What are Administrative Distances?

Used by router to determine which routing protocol has priority by calculating how far away the route is

If multiple routes are available, it chooses the route with the least distance

What is the administrative distance for:

1. Local

2. Static route

3. EIGRP

4. OSPF

5. RIPv1 and RIPv2

6. DHCP default route

7. Unknown

1. 0

2. 1

3. 90

4. 110

5. 120

6. 254

7. 255

What is First Hop Redundancy Protocol (FHRP)?

Device use virtual IP (VIP) as default gateway to create multiple since they come with a single default gateway

If router disappears, other one changes to active and takes its place

One gateway can really be many different routers

What are subinterfaces?

Mutiple virtual interface on 1 physical interface

ex. VLAN in a trunk

What is Network Address Translation?

A way to use more IPv4 addresses

IPV4 have private IP addresses that cant communicate with internet so the NAT converts the private to public and back

Built into the routers

What is the IP address range for Single class A?

10.0.0.0 - 10.255.255.255

What is the IP address range for 16 contiguous class B?

172.16.0.0 - 172.31.255.255

What is the IP address range for 256 contiguous class C?

192.168.0.0 - 192.168.255.255