Chapter 7

Process Switching

Process switching was the earliest Cisco route processing implementation. Process switching required the router to process each received frame individually

Unicast addressing

-Link-local addresses are addresses that are valid on only the current subnet: Hosts and routers running IPv6 create link-local addresses for interfaces on the subnet. Protocols generating packets that remain within the subnet use link-local addressing. -Global addresses are unique addresses similar to public addresses in IPv4. An organization is assigned a global unique address by an ISP. Each entity within the organization uses the unique prefix. -Unique local unicast addressing is similar to private addresses in IPv4. Organizations use unique local addressing to communicate within a site or between a limited number of sites.

Ping

-Ping operates at the Network layer. A successful ping test verifies Network layer connectivity between devices as well as the -TCP/IP configuration of all devices in the path. -Ping works as follows: --Ping sends an ICMP echo request packet to a remote host to start the test. --The source address of the echo request packet is the IP address of the interface from which the packet is sent. --An echo reply response from the target device verifies that the host can communicate with the destination. -Ping reports success or failure, together with round-trip statistics. -An advantage of the ping command is it allows you to test communication near the source of the problem. -The ping command uses hostnames as well as IP addresses.

DHCP

-Static address assignment, which can be configured in one of the following ways: --Static full assignment assigns the entire 128-bit IPv6 address and configuration information to the host. --Static partial assignment assigns the prefix. The remaining address is the modified EUI-64 format derived from the MAC address. -An updated version of DHCP (DHCPv6) that has two modes: --Stateful DHCPv6, which follows the same process in IPv6 as in IPv4: a DHCP server exists on the network and hosts contact the DHCP server to lease an IP address and obtain other settings. However, in IPv6: ---A stateful DHCP server does not supply default router information. ---Hosts send packets requesting local routers to provide information using Neighbor Discovery Protocol (NDP). --Stateless DHCPv6, which supplies the client with the IP address of the DNS server. Stateless DHCPv6 is most useful when used in conjunction with stateless autoconfiguration. -Stateless address autoconfiguration (SLAAC) automatically generates the interface ID and: --Uses NDP to learn: ---The subnet prefix ---The prefix length ---The default gateway --Builds the host's IPv6 address on the host without network messages. --Learns DNS server addressing using stateless DHCPv6 from a DHCPv6 server.

Extended ping

-The source IP address of the echo request packet can be changed to any address on the router. -The extend ping command works only at the privileged EXEC command line. -When you enter ping at the command line and press enter, you are prompted to enter a command field, such as: --The supported protocol. The default is IP. --The protocol address or hostname of the target. --The number of echo request packets that are sent to the target. --The timeout interval.

Traceroute

-Traceroute sends successive ICMP messages to an unreachable port address at a remote host. -The successive ICMP messages have increasing time-to-live (TTL) values. By default, traceroute sends three ping tests for each TTL value. -Traceroute records the source of each ICMP time exceeded message, providing a trace of the path the packet took to reach the destination. -A time exceeded error indicates that a server along the route has seen the packet and discarded it. -A destination unreachable error indicates that the destination node has received the message and discarded it because it was undeliverable.

Extended traceroute

-You can use the extended traceroute command to see the path the packets take to get to the destination from a specified source. -The traceroute command can be used to check routing along the path to the destination.

Floating

A floating static route is a static route whose administrative distance has been manually configured to be greater than the administrative distance of dynamic routes, making it less desirable than the dynamic route it supports. This configuration: -Does not use the floating static route by default while a dynamic route is active. -Enables a floating static route to automatically act as a backup for a dynamic route if it should fail.

Cisco Express Forwarding (CEF)

CEF is an advanced routing mechanism designed to optimize packet processing in very large networks. CEF increases packet switching speed, reduces the overhead and delays introduced by other routing techniques, and increases overall router performance. CEF incorporates the optimizations provided by fast switching.

IPv6 Configuration

Configure IPv6 routing as follows: -Enable IPv6 using the global command ipv6 unicast-routing. -Enable IPv6 on each interface using the ipv6 address address/length subcommand.

(config-if)#ip summary-address [routing_protocol] a.b.c.d m.m.m.m

Configures a summary address on the specified interface: -Use this command on outbound interfaces of the appropriate routers. -The neighboring device will only have a summary route in its routing table. -If the neighboring devices receive a query packet for a network that matches the summary route, it will send a network a.b.c.d/m unreachablemessage in response and will not extend the query packets any further. -This command will add a summary route to the routing table, with the route's next-hop interface set to null0.

Router(config-subif)#encapsulation dot1q [vlan id] native

Configures the VLAN that is sending and receiving untagged traffic on the trunk port when the interface is in 802.1Q trunking mode. This should match the native VLAN on the connected switch for a router-on-a-stick configuration.

Router#show ip route [hostname or address]

Displays details about the specific route.

Router#show ip route

Displays the routing table.

Router(config-subif)#ip helper-address

Enables the DHCP relay agent feature for a router-on-a-stick configuration.

Router(config)#interface fa0/1 Router(config-if)#no shutdown Router(config-if)#interface fa0/1.1 Router(config-subif)#

Enables the interface. Creates a subinterface and enters the subinterface configuration mode for a router-on-a-stick configuration.

Router(config)#ip classless

Enables the router to match routes based on the number of bits in the mask and not the default subnet mask.

Network

Following the route type is the network address and subnet mask. This identifies the specific subnet address for the route.

Last update

For routes learned through a routing protocol, the time value (such as 00:00:08) indicates the elapsed time since the last update about the route was received. Most protocols periodically send information about known routes. The update time helps you to know the age of the route information

Router(config)#ip route 0.0.0.0 0.0.0.0 [next_hop|interface]

Identifies a default route to the specified destination network or through an interface.

Router(config)#ip route [destination] [next_hop]

Identifies a next hop router to receive packets sent to the specified destination network.

Router(config)#ip route [destination] [interface]

Identifies the interface used to forward packets to the specified destination network.

Router(config-subif)#encapsulation dot1q [vlan id] Router(config-subif)#encapsulation isl [vlan id]

Sets the trunking encapsulation method for the VLAN on the subinterface for a router-on-a-stick configuration.

Router(config-subif)#ip address [a.b.c.d] [a.b.c.d]

Specifies an IP address and subnet mask on the subinterface for a router-on-a-stick configuration.

Next hop router

The address indicated by via identifies the router address where packets will be sent when sending to the destination network. The next hop router address is a router on the same subnet as a directly connected interface. However, this does not mean that the next hop router is connected directly to the destination network, but rather that it is the next stop in the path to the destination.

Route type

The first characters of a routing table entry identifies the source or type of the route: -C is for directly connected networks. -S is for static routes. -R is for routes learned through RIP. -Additional codes indicate routes learned through other routing protocols. A route marked with * indicates a route that is a candidate for the default route. The router uses this route to determine whether the route can be used to set the gateway of last resort information. If it meets several conditions, the information in the route marked with * is used for the gateway of last resort information.

Gateway of last resort

The gateway of last resort identifies a route to use if the packet does not match any other route. In this example, the route of 0.0.0.0 with a mask of 0.0.0.0 matches every packet. If the destination IP address does not match any other route, the next hop address of 192.168.2.1 is used for this packet.

Out interface

The interface designation at the end of the route identifies the local router interface used to reach the next hop router and therefore to reach the destination network.

Default route

The most common type of static route is a default route. A default route is a route that is considered to match all destination IP addresses. With a default route, when a packet's destination IP address does not match any other routes, the router uses the default route to forward the packet. You should be familiar with the following default route details: -Default routes work best when only one path exists to a part of the network. -One default route in the routing table could replace hundreds of static route entries in the routing table. -When the default route is not set, the router discards packets that do not match a route in the routing table.

Administrative distance and cost

The numbers in brackets following non-connected routes identify the following two items: -The first number is the administrative distance. The administrative distance is a description of the trustworthiness or preferability of a route learned from a specific source. Each source type (such as each routing protocol) is given a different administrative distance value. A lower number indicates a more preferred route. For example, a static route (AD = 1) is preferred over a route learned through RIP (AD = 120). -The second number is the cost to reach the route. The meaning of the route cost number is different depending on the source of the route, but generally it identifies how far away the destination is, either in distance or time. -The cost is also referred to as the metric. The cost is only comparable when talking about routes learned from the same routing protocol. For example: --For two RIP routes, a cost of 1 indicates a lower cost (shorter) route than a route with a cost of 2. --For a route learned through EIGRP, a cost of 312560 might identify a route that is faster than a route learned through RIP with a cost of 2.

(config-router)#no auto-summary

Turns off automatic route summarization: -By default, subnets are summarized based on classful boundaries when advertising routes on networks with a different class boundary. -You must disable automatic summarization if you have a network address (such as 10.0.0.0) subnetted into smaller subnets and separated by a network with a different classful network address (such as 12.0.0.0). -Summarizing routes at classful major network boundaries creates smaller routing tables, causing the routing update process to consume less bandwidth.

Automatic

With automatic summarization, the router identifies adjacent networks and calculates the summarized route: -Auto-summarization is supported on classless and classful routing protocols. -Auto-summarization uses the default class boundary to summarize routes. -RIP (version 1 and version 2) and EIGRP support auto-summarization; OSPF does not. -For RIPv2 and EIGRP, you can disable automatic summarization.

Manual

With manual summarization, an administrator identifies the summarized route to advertise. The route you specify includes the summarized subnet address with the subnet mask that includes all summarized subnets.

Fast Switching

processes packets in the same manner as process switching; however, it incorporates several mechanisms designed to optimize the process. The key idea behind fast switching is that packets addressed to the same destination can be processed in an identical manner. Instead of processing each packet individually, fast switching caches frequently used routing information