CCNA 2 Chapter 4 - Routers
- Routers are Computers
- It has a CPU, OS (Routers use Cisco IOS), Memory & Storage (RAM/ROM/NVRAM/FLASH/HD)
Important Table - Router Components (of Memory)
Routers use specialized ports and network interface cards to interconnect to other networks.
- Routers connect multiple networks.
- Routers have multiple interfaces, each on a different IP network.
> Routers Choose Best Paths
- Routers use static routes and dynamic routing protocols to learn about remote networks and build their routing tables.
- Routers use routing tables to determine the best path to send packets.
- Routers encapsulates the packet and forwards it to the interface indicated in the routing table.
> Packet Forwarding Methods
- Process Switching
- An older packet forwarding mechanism still available for Cisco router.
- Fast Switching
- A common packet forwarding mechanism which uses a fast-switching cache to store next-hop information.
- Cisco Express Forwarding (CEF)
- The most recent, fastest, and preferred Cisco IOS packet-forwarding mechanism. Table entries are not packet-triggered like fast switching but change-triggered.
> Default Gateways
- To enable network access devices must be configured with the following IP address information:
- IP Address
- Identifies unique host on local network.
- Subnet Mask
- Identifies the host’s network subnet.
- Default Gateway
- TLDR “How to get out of the network”.
> Enable IP on a Host
- Statically Assigned IP Address
- Manually assigned IP.
- Used to identify specific network resources such as servers/printers.
- Can be used in small networks with little amount of hosts.
- Dynamically Assigned IP Address
- Automatically obtained IP address.
- From DHCP Server.
- Most hosts acquire their IP address information through DHCP.
> Device LEDs
- Lights on the back of the router provide information if needed.
> Console Access
- Console Access requires…
- A computer with proper software (see third item: terminal emu).
- Console Cable (RJ-45 to DB9 Console Cable).
- Terminal Emulation Software: TeraTerm/ PuTTY/ HyperTerminal.
> Enabling IP on a Switch
- Infrastructure devices require IP addresses.
- Management IP addresses is assigned on a virtual interface.
> Configure Basic Router Settings
- Name the Device
- Distinguish the router’s name from other routers.
- Secure Management Access
- Secure privileged exec, user exec, telnet access, and encrypted passwords.
> Configure IPv4 Router Interface
- To Configure:
- Configured with an IP & Subnet Address.
- Must use ‘no shutdown’.
- Serial Cable using ‘DCE’ must have a clock rate.
- Provide a description.
> Configure IPv6 Router Interface
- To Configure:
- Use IPv6 address (link local / eui-64).
- Activate using ‘no sh’.
- IPv6 supports more than one address.
- Configure a specified global unicast address (addr/length).
- Configure a global IPv6 Address with an Interface ID in the low order 64 bits.
- Configure a link-local address.
> Configure a Loopback Address
- A loopback interface is a logical interface that is internal to the router.
- It is not assigned to a physical port, it is considered a software interface.
- A loopback interface is used for testing.
- It is important in the OSPF routing process.
> Verify Interface Settings
- Show commands are used to verify operation and configuration of interface:
- show ip int brief
- show ip route
- show running-config
- show interface …
- show ip interfaces
- You can filter show commands.
- Use the ‘terminal length <number>’ command to specify the number of lines to be displayed.
- To filter out specific output of commands, use the “|” pipe character.
- Can use parameters to filter:
- section, include, exclude, and begin
> Best Path
- Best path is selected by a routing protocol based on the value or metric it uses to determine the distance of a network.
- A metric is the value used to measure the distance to a given network.
- Best path to a network is the path with the lowest network.
- Dynamic routing protocols use their own rules and metrics to build and update tables:
- Routing Information Protocol (RIP) - Hop Count
- Open Shortest Path First (OSPF) - Cost-based on cumulative bandwidth from source to destination.
- Enhanced Interior Gateway Routing Protocol (EIGRP) - Bandwidth, delay, load, reliability.
> Load Balancing
- When a router has two or more paths to a destination with equal cost metrics, then the router forwards the packets using both paths equally:
- Equal cost load balancing can improve network performance.
- Equal cost load balancing can be configured to use both dynamic routing protocol and static routes.
> Administrative Distance
- If multiple paths to a destination are configured on a router, the path installed in the routing table is the one with the lowest Administrative Distance (AD).
- A static route with an AD of 1 is more reliable than an EIGRP discovered route with an AD of 90.
- A directly connected route with an AD of 0 is more reliable than a static route with an AD of 1.
> Routing Table Sources
- show ip route
- Display the contents of the routing table.
- local route interfaces
- Added to the routing table when an interface is configured.
- directly connected interfaces
- Added to the routing table when an int is configured and active.
- static routes
- Added when a route is manually configured and the exit interface is active.
- dynamic routing protocol
- Added when EIGRP or OSPF are implemented networks are identified.
> Static Routes
- Static routes and default static routes can be implemented after directly connected interfaces are added to the routing table.
> Dynamic Routing
- Where the routers “do the work for us”.
- Dynamic routing is used by routers to share information about the reachability and status of remote networks. It performs network discovery and maintains routing tables.