Category - CCNA part

Routing Protocol Characteristics

Packets originating from a nonrouting device destined for another network are sent to their default gateway (Layer 3 device on segment). The router consults its routing table to deter-mine if the destination network can be reached. If not, the ICMP Destination Unreachable message is sent to the source. If so, packet is forwarded out interface associated with the des­tination network in routing table.

Routing Sources

Default Administrative Distances

Maximum Hop Counts
Routed Source
Default Distance
Connected
0
Static route
1
EIGRP (internal)
90
OSPF
110
RIPv1 and v2
120
EIGRP (external)
170

Static and Default Routes

Static routes are useful in stub networks in which we want to control the routing behavior by manually configuring destination networks into the routing table:

Router(config)#ip route 10.0.0.0 255.0.0.0 192.168.2.5

A floating static route can be configured when redundant connections exist and you want to use the redundant link if the primary fails. This is configured by adding a higher administra­tive distance at the end of a static route:

Router(config)#ip route 10.0.0.0 255.0.0.0 192.168.2.9 2

A default route is a gateway of last resort for a router when there isn’t a specific match for an IP destination network in the routing table (such as packets destined for the Internet):

Router(config)#ip route 0.0.0.00.0.0.0serial 0/0

With routing protocols, you can specify a default network, which is a network in the routingtable that routing devices consider to be the gateway of last resort. Using their routing proto­cols, they determine the best path to the default network:

Router(config)#ip default-network 192.168.1.0

Dynamic Routing Protocols

In complex networks with multiple pathways to destinations, dynamic routing protocols enable routers to advertise their networks to each other and dynamically react to topology changes.

Routing protocols determine the best path based on the lowest metric.

 Routing Metrics

Because one of the core responsibilities of routing protocols is to build routing tables to determineoptimal routing paths, we need to have some means of measuring which routes are preferred whenthere are multiple pathways to a destination. Routing protocols use some measure of metrics toidentify which routes are optimal to reach a destination network. The lowest cumulative metric toa destination is the preferred path and the one that ultimately enters the routing table. Different routing protocols use one or several of the following metrics to calculate the best path.

Routing Metrics

Metric
Description
Hop count
The number of routing devices that the packet must travel to reach a destination network
Bandwidth
The cumulative bandwidth of the links to the destination in kilobits per second
Delay
The length of time (measured in microseconds) a packet takes from source to destination
Reliability
The consistency of the links and paths toward the destination based on error rates of the interfaces
Load
The cumulative amount of congestion or saturation of the links toward the destination
MTU
The maximum frame size that is allowed to traverse the links to the destination
Cost ¬†An arbitrary number typically based on the link’s bandwidth

Interior and Exterior Gateway Routing Protocols

  1. Interior gateway routing protocols: IG routing protocols advertise networks and metrics within an autonomous system.
  2. Exterior gateway routing protocols: EG routing protocols advertise networks in between autonomous systems.

Classful and Classless Routing Updates

  1. Classful routing: The routing updates only contain the classful networks without any subnet mask. Summarization is automatically done when a router advertises a network out an interface that is not within the same major subnet. Classful routing protocols must have a FLSM design and do not operate correctly with discontiguous networks.
  2. Classless routing: The routing updates can contain subnetted networks because the subnet mask is advertised in the updates. Route summarization can be manually config­ured at any bit boundary. Classless routing protocols support VLSM designs and dis­contiguous networks.

all routing protocol

Routing Protocol Classes

  1. Distance vector: The entire routing table is periodically sent to directly connected neighbors regardless of a topology change. These routing protocols manipulate the routing table updates before sending that information to their neighbors and are slow to converge when a topology change occurs.
  2. Link state: All possible link states are stored in an independent topology table in which the best routes are calculated and put into the routing table. The topology table is ini­tially synchronized with discovered neighbors followed by frequent hello messages. These routing protocols are faster to converge than distance vector routing protocols.
  3. Hybrid: By using the best characteristics from link-state and routing protocols, these advanced routing protocols efficiently and quickly build their routing information and converge when topology changes occur.

Redistribution

Redistribution is the method of configuring routing protocols to advertise networks from other routing protocols:

  1. One-way redistribution: Networks from an edge protocol are injected into a more robust core routing protocol, but not the other way around. This method is the safest way to perform redistribution.
  2. Two-way redistribution: Networks from each routing protocol are injected into the other. This is the least preferred method because it is possible that suboptimal routing or routing loops might occur because of the network design or the difference in con­vergence times when a topology change occurs.

Distance Vector Routing Loop Mitigation

Distance vector routing protocols contain several measures to prevent routing loops:

Maximum hop counts: To ensure that routing metrics do not increment until infinity in a routing loop, distance vector routing protocols have a maximum hop count.

Protocol
Distance Vector/Link State/Hybrid
Maximum Hop Count
RI Pv1
Distance vector
15
RI Pv2
Distance vector
15
EIG RP
Hybrid
224
OSPF
Link state
Infinite

Split horizon:

Subnets learned from neighbor routers should not be sent back out the same interface from which the original update came.

Route poisoning with poison reverse:

When a route to a subnet fails, the subnet is advertised with an infinite metric. Routers receiving the poisoned route override the split horizon rule and send a poison reverse back to the source.

Hold-down timers:

The amount of time a router ignores any information about an alternative route with a higher metric to a poisoned subnet.

Flash updates/triggered updates:

When a route fails, the router immediately shoots out an update as opposed to waiting for a normal update interval.

Virtual LANs (VLANs)

VLANs logically divide a switch into multiple broadcast domains at Layer 2.

Each VLAN can represent a logical grouping of users by function or department. As users in these VLANs move, we simply need to change the VLAN assigned to their switch port. VLANs also enhance security because users in one VLAN cannot communicate to users in another VLAN without the use of a Layer 3 device providing inter-VLAN routing.

VLAN Configuration

VLANs can be statically assigned to switch access ports or dynamically assigned by using a VMPS. By default, all interfaces are assigned to the management VLAN, VLAN 1.

To configure a VLAN:

  1. Create the VLAN in global configuration:

Switch(config)#vlan2 Switch(config-vlan)#

  1. The VLAN must be named:

Switch(config-vlan)#vlan2 name ExamPrep

  1. The desired ports must be added to the new VLAN:

Switch(config)#interfaceFastEthernet 0/1 Switch(config-if)#switchportaccess vlan 2

Vlan configuration

Voice VLANs

Voice VLANs are used to separate VoIP traffic from data on an access port for QoS, managea­bility, and traffic confinement.

Switch(config-if)#switchportvoice vlan 30

Trunks

VLANS can span multiple switches using trunks. Trunks multiplex traffic from all VLANs over a single connection. The VLAN identifier is tagged over the trunk using one of the following tagging methods:

  1. ISL: A Cisco-proprietary trunk that encapsulates the original Ethernet frame with a 26-byte header and a 4-byte CRC.
  2. IEEE 802.1q: Standards-based VLAN tagging that inserts a 4-byte tag in the original Ethernet frame. Traffic originating from the native VLAN (VLAN 1 by default) is not tagged over the trunk. If native VLAN configuration does not match on both sides, this could cause VLAN leakage.

Trunk Configuration

Switch(config)#interfaceFastEthernet 0/24

Switch(config-if)#switchporttrunk encapsulation [isl|dot1q] Switch(config-if)#switchportmode trunk

Trunks can be secured by allowing only specific VLANs to traverse to switches that specificallyrequire access to those VLANs. The command to specify the VLANs to be included in the ‚Äúallowed list of VLANs‚ÄĚ is switchport trunk allowed vlan {add | remove | except} vlan_list.

VLAN Trunking Protocol

Cisco created VTP to minimize the amount of VLAN administration in switches by enabling a VTP server to multicast VTP advertisements to other switches in the same VTP domain. Switches receiving these advertisements synchronize their VLAN database with the VLAN information advertised from the server, assuming that the revision number is higher.

 

 VTP Modes

Mode                       Function

Server                               Default VTP mode that enables you to create, modify, and delete VLANS. These VLANs are advertised to                                                       other switches and saved in the VLAN database.

Client                               Cannot create, modify, or delete VLANs. Forwards advertisements received from the server, but does not                                                    save the VLAN configuration in the VLAN database.

Transparent                    Creates, modifies, and deletes VLANs only on the local switch. Does not participate in VTP but forwards VTP                                                advertisements received from servers. Also saves the VLAN configuration in the VLAN database.

VTP Configuration

Changing the VTP domain name from NULL to ExamPrep:

Switch(config)#vtpdomain ExamPrep

Setting the device VLAN database password to examcram:

Switch(config)#vtppassword examcram

Setting the device to VTP TRANSPARENT mode:

Switch(config)#vtptransparent

InterVLAN Routing

InterVLAN routing requires a Layer 3 device such as router or a Layer 3 switch:

. Router-on-a-stick: The connection between router and switch must be at least Fast

Ethernet speeds and must be a trunk. The router interface consists of subinterfaces to assign an IP gateway for each VLAN. The VLAN is associated with a subinterface using the encapsulation command:

Router(config)#interfaceFastEthernet 0/1 .2

Router(config-subif)#ipaddress 192.168.2.1 255.255.255.0 Router(config-subif)#encapsulationdot1q 2

Router(config)#interfaceFastEthernet 0/1 .3

Router(config-subif)#ipaddress 192.168.3.1 255.255.255.0 Router(config-subif)#encapsulationdot1q 3

. Switched virtual interfaces: VLAN interfaces configured in a Layer 3 switch that enables inter-VLAN routing using ASIC technology:

Router(config)#interfaceVlan 2

Router(config-if)#ipaddress 192.168.2.1 255.255.255.0 Router(config)#interfaceVlan 3

Router(config-if)#ip address 192.168.3.1 255.255.255.0

 

Port Security

Here’s the configuration that limits the number of MAC addresses that can be dynamically learned on a switch port:

Switch(config-if)#switchportmode access

Switch(config-if)#switchportport-security

Switch(config-if)#switchportport-security maximum 1

Switch(config-if)#switchportport-security violation {protect | restrict| shutdown}

If a violation occurs, the default response of a Catalyst switch is to shut down the port. To havethe port increase a violation counter and alert an administrator using SNMP, use therestrictkeyword. The protectkeyword allows only traffic from the secure port and drops packets from other MAC addresses until the number of MAC addresses drops below the maximum.

To secure an interface by statically assigning the permitted MAC address(es) attached to the port, use the switchport port-security mac-address MAC_address command on the interface. Alternatively, you can have the switch learn these addresses up to the maximum byusing sticky-learned addresses with the commandswitchport port-security mac-address sticky.

CCNA Labs Scenario

Scenario Labs For CCNA

  1. Setting up a Serial Interface 
  2. CDP
  3. IP Addressing
  4. Static Routes
  5. Default Routes
  6. RIP Routes
  7. IGRP Routes
  8. Using Loopback Interfaces
  9. RIP v2 Routes
  10. CHAP and RIP
  11. Standard Access-Lists with RIP
  12. Extended Access-Lists with RIP
  13. EIGRP Routes
  14. OSPF Routes
  15. Static NAT
  16. Many to One NAT
  17. NAT Pool
  18. Telnet
  19. 2950 IP Addresses
  20. 2950 Trunk
  21. 2950 Trunk (Dynamic)
  22. 2950 VLANs
  23. 2950 Deleting VLANs
  24. 2950 VTP
  25. 2950 VTP w/ client
  26. 2950 Telnet

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