Upload
ciscolifeguard
View
227
Download
1
Embed Size (px)
Citation preview
8/12/2019 03 01 Classless Rtg - Ppt
1/34
1
Introduction to
Classless Routing
CCNA 3/Module 1
8/12/2019 03 01 Classless Rtg - Ppt
2/34
2
Overview: Classful/Classless Routing
Classful routing - a network must use the same subnet maskfor the entire network
Network IP 192.168.187.0
Network Subnet Mask 255.255.255.0
Classless routingusing more than one subnet mask for anetwork address
subnetting a subnet
Network IP 192.168.187.0
Network Subnet Masks 255.255.255.252
255.255.255.0
8/12/2019 03 01 Classless Rtg - Ppt
3/34
3
Overview: (Classful) IPv4 Addressing Limits
IPv420 years old
IPv4even with subnetting, couldnt handle the global demand
for Internet connectivity
Class B space was on the verge of depletion.
Rapid and substantial increase in the size of the Internet's
routing tables.
As more Class C's came online, the flood of new network
information threatened Internet routers' capability to
cope.
8/12/2019 03 01 Classless Rtg - Ppt
4/34
4
Overview: (Classful) IPv4 Addressing Limits
Provides IP scheme with limitations:
Class A126 networks: 16,777,214 hosts each
Class B65,000 networks: 65,534 hosts each
Class C2 million networks: 254 hosts each
While available addresses were running out, only 3%of assigned addresses were
actually being used!
Subnet zero, broadcast addresses,
pool of unused addresses atClass A and B sites, etc.
8/12/2019 03 01 Classless Rtg - Ppt
5/34
5
Overview: Scalability & Routing Tables
Maximum theoretical routing table size is 60,000 entries.
Classful addressing would have hit this capacity by
mid-1994.
Internet growth would have ended.
8/12/2019 03 01 Classless Rtg - Ppt
6/34
6
1.1.1 What is VLSM and why is it used?
The purpose of VLSM is to alleviate the shortage of IP addresses
VLSM allows:
More than one subnet mask within the same NW
Or . . . Multiple SNMasks with ONE IP Address
Use of long maskon networks with few hosts
Use of short maskon networks with many hosts
In order to use VLSM, the routing protocol must support it.
Cisco routers with the following routing protocols support VLSM:
OSPF (Open Shortest Path First) IS-IS (Integrated Intermediate System to Intermediate System)
EIGRP (Enhanced Interior Gateway Routing Protocol)
RIP v2
Static Routing
8/12/2019 03 01 Classless Rtg - Ppt
7/347
1.1.1 What is VLSM and why is it used?
Classfulrouting protocols use one subnet mask for a single network
Ex: 192.168.187.0, must use subnet mask255.255.255.0
VLSMallows a single autonomous system to have networks withdifferent subnet masks, for example:
Use a 30-bitsubnet mask on network connections
(255.255.255.252)
Use a 24-bitsubnet mask for user networks up to 250 users
(255.255.255.0)
Use a 22-bitsubnet mask for user networks up to 1000 users
(255.255.252.0)
8/12/2019 03 01 Classless Rtg - Ppt
8/34
8/12/2019 03 01 Classless Rtg - Ppt
9/349
1.1.2 A waste of space
Network Address 192.168.187.0
Borrow 3 bits = SNM 255.255.255.224
Subnets = 0, 32, 64, 96, 128, 160, 192, 224
8/12/2019 03 01 Classless Rtg - Ppt
10/34
8/12/2019 03 01 Classless Rtg - Ppt
11/34
8/12/2019 03 01 Classless Rtg - Ppt
12/3412
1.1.3 When to use VLSM
Design addressing scheme that
allows:
Growth
Doesnt waste addresses on
point-to-point links
VLSM addressing applied instead results in:
Variable sized subnets
Take1 of the3 subnets andsubnet it againExample 192.168.187.224(last subnet)
Apply a 30 bit mask (225.225.225.252)
Creates a possible8 rangesof addresses with30 bits
Best solution forpoint-to-point linksuse 2 host addresses
instead of 30
8/12/2019 03 01 Classless Rtg - Ppt
13/34
8/12/2019 03 01 Classless Rtg - Ppt
14/34
14
1.1.4 Calculating subnets with VLSM
osters abulous ilms 2 routers 1 in Hollywood (100 hosts)
1 in Ravenna (50 hosts)
1 WAN link (2 needed)
IP/NW Address: 192.16.10.0 Class C
Use the BIGGEST first:
100
50
2
8/12/2019 03 01 Classless Rtg - Ppt
15/34
15
1.1.4 Calculating subnets with VLSM
osters abulous ilms 2 routers 1 in Hollywood (100 hosts)
1 in Ravenna (50 hosts)
1 WAN link (2 needed)
IP/NW Address: 192.16.10.0 Class C
Use the BIGGEST first:
100 /25
50 /26
2 /30
8/12/2019 03 01 Classless Rtg - Ppt
16/34
16
1.1.4 Calculating subnets with VLSM
If VLSM were used instead of classful routing:
A 24-bit maskcould be used for LAN segments for 250hosts
A 30-bit maskcould be used for WAN segments for 2hosts
172.16.32.0/20(would accommodate 4094 hosts)
Binary = 10101100.00010000.00100000.00000000
SNM = 11111111.11111111.11110000.00000000
VLSM address172.16.32.0/26(needed for 62hosts)
Binary = 10101100.00010000.00100000.00000000
SNM = 11111111.11111111.11111111.11000000
If 172.16.32.0/20used, but only 10 hostson segment, wouldprovide 4094 hostsand waste 4084addresses
By further subnetting /20 to /26, gain 64 subnets (26) eachsupporting 62 hosts
8/12/2019 03 01 Classless Rtg - Ppt
17/34
17
1.1.4 Calculating Subnets w/VLSM
Procedure to subnet a subnet /20 to /26 using VLSM:
1. Write 172.16.32.0 in binary form
Binary = 10101100.00010000.00100000.00000000
2. Draw a vertical line between the 20thand 21stbits (the originalsubnet boundary)
3. Draw a vertical line between the 26thand 27thbits extending the bits
to segment/host needs
4. Calculate the number of subnet addresses between the two vertical
lines (lowest to highest) in value
8/12/2019 03 01 Classless Rtg - Ppt
18/34
18
1.1.4 Calculating Subnets w/VLSM
Keep in mind that only unused subnets can be further
subnetted
If any address for a subnet is used cannot be further
subnetted
8/12/2019 03 01 Classless Rtg - Ppt
19/34
8/12/2019 03 01 Classless Rtg - Ppt
20/34
20
1.1.5 Route Aggregation w/VLSM
Using CIDR and VLSM prevents address wasteand promotes route
aggregationor summarization
Without summarization, Internet would collapse
Summarization reduces burdenon upstream routers
This process of summarization continues until entire networkis
advertised as a single aggregateroute
Summarization is also called supernetting
Possible if the routers of a network run a classless routing
protocolsuch as OSPF or EIGRP Consists of IP address and bit mask in routing updates
The summary routeuses prefixcommon to all addresses of
organization
8/12/2019 03 01 Classless Rtg - Ppt
21/34
21
1.1.5 Route Aggregation w/VLSM
Carefully assign addressesin a hierarchicalfashion to share same
high-order bits for summarization
A router must know subnetsattached in detail
A router does notneed to tell other routers about subnets
A router using aggregateroutes has fewerentries in routingtable
VLSM allows for summarization of routes
Works even if networks are not contiguous
VLSM increases flexibly by summarization on higher-order bits
Used to calculate the network number of the summary route
Uses only shared highest-order bits
8/12/2019 03 01 Classless Rtg - Ppt
22/34
22
1.1.6 Configuring VLSM
If VLSM is chosen, it must be configured correctly
Example: 192.168.10.0
One router has to support 60 hosts, needs 6 bits in host
portion of address to provide 62 possible address
(26
= 642 = 60)192.168.10.0/26(leaves 6 bits for hosts)
One router has to support 28 hosts, needs 5 bits in host
portion of address to provide 30 possible hosts
(25= 322 = 30) 192.168.10.64/27(leaves 5 bits for hosts)
Two routers have to support 12 hosts each, needs 4 bits in
host portion of address to provide 14 possible hosts
(24= 162 = 14) 192.168.10.96/28(leaves 4 bits for hosts)
192.168.10.112/28 (leaves 4 bits for hosts)
8/12/2019 03 01 Classless Rtg - Ppt
23/34
23
1.1.6 Configuring VLSM
Point-to-point connections are:
192.168.10.128/30(2 address required, 2 bits = 2 host addresses)
192.168.10.132/30 (2 address required, 2 bits = 2 host addresses)
192.168.10.136/30 (2 address required, 2 bits = 2 host addresses)
Choices = .136 .137 .138 .139
Configuration as follows for the 192.168.10.136/30 network (.136/30 -
network address;.139/30 - broadcast address; .137/30 and 138/30host
addresses:
(config)#interface serial 0
(config-if)#ip address 192.168.10.137 255.255.255.252
(config)#interface serial1
(config-if)#ip address 192.168.10.138 255.255.255.252
8/12/2019 03 01 Classless Rtg - Ppt
24/34
24
1.2.1 RIP History
Internet is a collection of autonomous systems (AS) Each AS is administered by a single entity
Each AS has its own routing technology
Routing protocol used withinAS is InteriorGateway Protocol
Routing protocol used betweenAutonomous Systems is an Exterior Gateway
Protocol
RIP v1:
is an IGP that is classful
was designed to work within moderate-sized AS
is a distance vector routing protocol by default, broadcasts entire routing table every 30 seconds
uses hop count as metric (16 max)
is capable of load balancing 6 equal-cost paths (4 default)
Does not send subnet mask information in its updates
Is not able to support VLSM or CIDR
8/12/2019 03 01 Classless Rtg - Ppt
25/34
25
1.2.1 RIP History
If the router receives information about a network, and the receiving
interface belongs to same network but is on a different subnet, the
router applies the one subnet mask configured on the receiving
interface
Class A default classful mask is 255.0.0.0
Class B default classful mask is 255.255.0.0
Class C default classful mask is 255.255.255.0
8/12/2019 03 01 Classless Rtg - Ppt
26/34
26
1.2.2 RIP v2 Features
RIP v2 is an Improved version of RIP v1 with following features:
Distance vector protocol
Uses hop count as metric
Uses hold-down timers (prevent routing loops), default 180 sec.
Uses split horizon to prevent routing loops
Uses 16 hops as infinite distance
Provides prefix routing (sends subnet mask with route update)
Supports use of classless routing (VLSM)
Multicasts updates using 224.0.0.9 address for better efficiency
Provides authentication in updates
Clear text - default
MD5 encryptiontypically used to encrypt enable secret
passwords (Message-Digest 5)
8/12/2019 03 01 Classless Rtg - Ppt
27/34
27
1.2.3 Comparing RIP v1 & v2
RIP v1 RIP v2
Easy to configure Easy to configure
Supports classful routing Supports classlessrouting
No subnet infosent with routing
updates (considered a limitation of v1)
Sends subnet maskwith routing
update
No authentication Provides for authentication
Uses hop count Uses hop count
16 hops as metric for infinite distance 16 hops as metric for infinite distance
Broadcasts routing table updates
255.255.255.255
Multicasts updates 224.0.0.9
Does not support prefix routing (all
devices in same network must use
same subnet mask)
Supports prefix routing (VLSM,
different subnet masks can be used
in same network)
8/12/2019 03 01 Classless Rtg - Ppt
28/34
28
1.2.4 Configuring RIP v2
To enable a dynamic routing protocol:
1. Select routing protocol
FOSTER(config)#router rip
FOSTER(config-router)#version 2
2. Configure routing protocol with the network IP address (identifyphysically connected network that will receive routing tables)
FOSTER(config-router)#network 10.0.0.0
FOSTER(config-router)#network 172.16.0.0
3. Assign IP/SNM to interfaces
8/12/2019 03 01 Classless Rtg - Ppt
29/34
8/12/2019 03 01 Classless Rtg - Ppt
30/34
30
1.2.5 Verifying RIP v2
RIP updates table every 30 seconds
If no update received in 180 seconds, route marked as down If no update after 240 seconds, removes from routing table entry
8/12/2019 03 01 Classless Rtg - Ppt
31/34
8/12/2019 03 01 Classless Rtg - Ppt
32/34
32
1.2.7 Default Routes
Three ways a router learns about paths:
1. Static routesmanual configuration of routes (next hop)
Uses ip route command
2. Default routesmanually defined path to take when there is no
known route to a destination
3. Dynamic routesrouters lean paths by receiving updates from
other routers
8/12/2019 03 01 Classless Rtg - Ppt
33/34
33
1.2.7 Default Routes
Default Route Command:
FOSTER(config)# ip route 172.16.1.0255.255.255.0
172.16.2.1
Default NW Tells that 8 bits of
subnetting in effectNext hop router
Default Route Command:
FOSTER(config)# ip route 172.16.1.0255.255.255.0
172.16.2.1
Default NW Tells that 8 bits of
subnetting in effectNext hop router
8/12/2019 03 01 Classless Rtg - Ppt
34/34
1.2.7 Default Routes
Used to:
1. Give packets that are not IDd in the routing table a place to go
Usually a router that connects to the Internet
2. Connect a router with a static default route
DYNAMIC PROTOCOL Default Route Command
FOSTER(config)# ip default-network 192.168.20.0
Default NW