Ch. 1 – Introduction to
Classless Routing
CCNA 3 version 3.0
Rick Graziani
Cabrillo College
Note to instructors
• If you have downloaded this presentation from the Cisco Networking
Academy Community FTP Center, this may not be my latest version of
this PowerPoint.
• For the latest PowerPoints for all my CCNA, CCNP, and Wireless
classes, please go to my web site:
http://www.cabrillo.cc.ca.us/~rgraziani/
• The username is cisco and the password is perlman for all of
my materials.
• If you have any questions on any of my materials or the curriculum,
please feel free to email me at graziani@cabrillo.edu (I really don’t
mind helping.) Also, if you run across any typos or errors in my
presentations, please let me know.
• I will add “(Updated – date)” next to each presentation on my web site
that has been updated since these have been uploaded to the FTP
center.
Thanks! Rick
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Overview of Information in Module 1
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Define VLSM and briefly describe the reasons for its use
Divide a major network into subnets of different sizes using VLSM
Define route aggregation and summarization as they relate to VLSM
Configure a router using VLSM
Identify the key features of RIP v1 and RIP v2
Identify the important differences between RIP v1 and RIP v2
Configure RIP v2
Verify and troubleshoot RIP v2 operation
Configure default routes using the ip route and ip defaultnetwork commands
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Note
•
•
Much of the information in this module is in addition to the
online curriculum.
The additional information was included it add clarity and
make the topics more understandable.
– Advanced IP Management
• Subnetting
• Classless interdomain routing (CIDR)
• Variable length subnet masking (VLSM)
• Route summarization
• Network Address Translation (NAT)
– Classless Routing Protocols
• RIPv2
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Advanced IP Management
IPv4 Address Classes
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IPv4 Address Classes
• No medium size host networks
• In the early days of the Internet, IP addresses were allocated to
organizations based on request rather than actual need.
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IPv4 Address Classes
Class D Addresses
• A Class D address begins with binary 1110 in the first octet.
• First octet range 224 to 239.
• Class D address can be used to represent a group of hosts called a
host group, or multicast group.
Class E Addresses
First octet of an IP address begins with 1111
• Class E addresses are reserved for experimental purposes and should
not be used for addressing hosts or multicast groups.
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IP addressing crisis
•
•
Address Depletion
Internet Routing Table Explosion
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IPv4 Addressing
Subnet Mask
• One solution to the IP address shortage was thought to be the
subnet mask.
• Formalized in 1985 (RFC 950), the subnet mask breaks a single
class A, B or C network in to smaller pieces.
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Subnet Example
Given the Class B address 190.52.0.0
Class B
Using /24
subnet...
Network Network
Network Network
Host
Subnet
Host
Host
Internet routers still “see” this net as 190.52.0.0
190.52.1.2
190.52.2.2
190.52.3.2
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But internal routers think all
these addresses are on different
networks, called subnetworks
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Subnet Example
Network Network
Subnet
Host
Using the 3rd octet, 190.52.0.0 was divided into:
190.52.1.0
190.52.5.0
190.52.9.0
190.52.13.0
190.52.17.0
190.52.2.0
190.52.6.0
190.52.10.0
190.52.14.0
190.52.18.0
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190.52.3.0
190.52.7.0
190.52.11.0
190.52.15.0
190.52.19.0
190.52.4.0
190.52.8.0
190.52.12.0
190.52.16.0
and so on ...
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Subnet Example
Network address 190.52.0.0 with /16 network mask
Using Subnets: subnet mask 255.255.255.0 or /24
Network Network
Subnet
Host
190
190
52
52
0
1
Host
Host
190
190
190
190
52
52
52
52
2
3
Etc.
254
Host
Host
Host
Host
190
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52
255
Host
Subnets
255
Subnets
28 - 1
Cannot use last
subnet as it
contains broadcast
address
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Subnet Example
Subnet 0 (all 0’s subnet) issue: The address of the subnet,
190.52.0.0/24 is the same address as the major network,
190.52.0.0/16.
Network Network Subnet
Host
190
190
52
52
0
1
Host
Host
190
190
52
52
Etc.
254
Host
Host
Subnets
255
Subnets
28 - 1
190
52
255
Host
Last subnet (all 1’s subnet) issue: The broadcast address for
the subnet, 190.52.255.255 is the same as the broadcast
address as the major network, 190.52.255.255.
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All Zeros and All Ones Subnets
Using the All Ones and All Zeroes Subnet
• There is no command to enable or disable the use of the all-ones subnet, it is
enabled by default.
Router(config)#ip subnet-zero
• The use of the all-ones subnet has always been explicitly allowed and the use
of subnet zero is explicitly allowed since Cisco IOS version 12.0.
RFC 1878 states, "This practice (of excluding all-zeros and all-ones subnets) is
obsolete! Modern software will be able to utilize all definable networks."
Today, the use of subnet zero and the all-ones subnet is generally accepted
and most vendors support their use, though, on certain networks,
particularly the ones using legacy software, the use of subnet zero and the
all-ones subnet can lead to problems.
CCO: Subnet Zero and the All-Ones Subnet
http://www.cisco.com/en/US/tech/tk648/tk361/technologies_tech_note09186a
0080093f18.shtml
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Need a Subnet Review?
•
If you need a Review of Subnets, please review the
following links on my web site:
– Subnet Review (PowerPoint)
– Subnets Explained (Word Doc)
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Long Term Solution: IPv6 (coming)
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IPv6, or IPng (IP – the Next Generation) uses a 128-bit address
space, yielding
340,282,366,920,938,463,463,374,607,431,768,211,456
possible addresses.
IPv6 has been slow to arrive
IPv4 revitalized by new features, making IPv6 a luxury, and not
a desperately needed fix
IPv6 requires new software; IT staffs must be retrained
IPv6 will most likely coexist with IPv4 for years to come.
Some experts believe IPv4 will remain for more than 10 years.
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Short Term Solutions: IPv4 Enhancements
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CIDR (Classless Inter-Domain Routing) – RFCs 1517,
1518, 1519, 1520
VLSM (Variable Length Subnet Mask) – RFC 1009
Private Addressing - RFC 1918
NAT/PAT (Network Address Translation / Port Address
Translation) – RFC
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CIDR (Classless Inter-Domain Routing)
• By 1992, members of the IETF were having serious concerns about the
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exponential growth of the Internet and the scalability of Internet routing
tables.
The IETF was also concerned with the eventual exhaustion of 32-bit
IPv4 address space.
Projections were that this problem would reach its critical state by 1994
or 1995.
IETF’s response was the concept of Supernetting or CIDR, “cider”.
To CIDR-compliant routers, address class is meaningless.
– The network portion of the address is determined by the network
subnet mask or prefix-length (/8, /19, etc.)
– The first octet (first two bits) of the network address (or networkprefix) is NOT used to determine the network and host portion of the
network address.
CIDR helped reduced the Internet routing table explosion with
supernetting and reallocation of IPv4 address space.
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Active BGP entries
Report last updated at Thu, 16 Jan 2003
http://bgp.potaroo.net/
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CIDR (Classless Inter-Domain Routing)
• First deployed in 1994, CIDR dramatically improves IPv4’s scalability
•
and efficiency by providing the following:
– Eliminates traditional Class A, B, C addresses allowing for more
efficient allocation of IPv4 address space.
– Supporting route aggregation (summarization), also known as
supernetting, where thousands of routes could be represented by a
single route in the routing table.
• Route aggregation also helps prevent route flapping on Internet
routers using BGP. Flapping routes can be a serious concern
with Internet core routers.
CIDR allows routers to aggregate, or summarize, routing information
and thus shrink the size of their routing tables.
– Just one address and mask combination can represent the routes to
multiple networks.
– Used by IGP routers within an AS and EGP routers between AS.
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Without CIDR, a
router must
maintain
individual
routing table
entries for these
class B
networks.
With CIDR, a
router can
summarize
these routes
using a single
network
address by
using a 13-bit
prefix:
172.24.0.0 /13
Steps:
1. Count the number of left-most matching bits, /13 (255.248.0.0)
2. Add all zeros after the last matching bit:
172.24.0.0 = 10101100 00011000 00000000 00000000
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CIDR (Classless Inter-Domain Routing)
• By using a prefix address to summarizes routes, administrators can
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keep routing table entries manageable, which means the following
– More efficient routing
– A reduced number of CPU cycles when recalculating a routing
table, or when sorting through the routing table entries to find a
match
– Reduced router memory requirements
Route summarization is also known as:
– Route aggregation
– Supernetting
Supernetting is essentially the inverse of subnetting.
CIDR moves the responsibility of allocation addresses away from a
centralized authority (InterNIC).
Instead, ISPs can be assigned blocks of address space, which they
can then parcel out to customers.
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ISP/NAP Hierarchy - “The Internet: Still hierarchical after all
these years.” Jeff Doyle (Tries to be anyways!)
NAP (Network Access Point)
Network
Service
Provider
Regional
Service
Provider
ISP
Subscribers
ISP
Subscribers
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ISP
Subscribers
Network
Service
Provider
Regional
Service
Provider
Regional
Service
Provider
ISP
ISP
Subscribers
Subscribers
Regional
Service
Provider
ISP
Subscribers
ISP
Subscribers
ISP
Subscribers
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Supernetting Example
• Company XYZ needs to address 400 hosts.
• Its ISP gives them two contiguous Class C addresses:
•
•
– 207.21.54.0/24
– 207.21.55.0/24
Company XYZ can use a prefix of 207.21.54.0 /23 to supernet
these two contiguous networks. (Yielding 510 hosts)
207.21.54.0 /23
– 207.21.54.0/24
– 207.21.55.0/24
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23 bits in common
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Supernetting Example
•
With the ISP acting as the addressing authority for a CIDR block of
addresses, the ISP’s customer networks, which include XYZ, can be
advertised among Internet routers as a single supernet.
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CIDR and the Provider
Another example of route aggregation.
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CIDR and the provider
200.199.48.0/25
200.199.56.0/23
Summarization from
the customer
networks to their
provider.
Even Better:
200.199.48.32/27 11001000 11000111 00110000 0 0100000
200.199.48.64/27 11001000 11000111 00110000 0 1000000
200.199.48.96/27 11001000 11000111 00110000 0 1100000
200.199.48.0/25 11001000 11000111 00110000 0 0000000
(As long as there are no other routes elsewhere within this range, well…)
200.199.56.0/24
200.199.57.0/24
200.199.56.0/23
11001000 11000111 0011100 0 00000000
11001000 11000111 0011100 1 00000000
11001000 11000111 0011100 0 00000000
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CIDR and the provider
200.199.48.0/25
200.199.56.0/23
Further summarization
happens with the next
upstream provider.
200.199.48.0/25
200.199.49.0/25
200.199.56.0/23
11001000 11000111 0011 0000 00000000
11001000 11000111 0011 0001 00000000
11001000 11000111 0011 1000 00000000
200.199.48.0/20
11001000 11000111 0011 0000 00000000
20 bits in common
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CIDR Restrictions
• Dynamic routing protocols must send network address and mask
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(prefix-length) information in their routing updates.
In other words, CIDR requires classless routing protocols for dynamic
routing.
However, you can still configure summarized static routes, after all, that
is what a 0.0.0.0/0 route is.
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Summarized and Specific Routes: Longest-bit Match
(more later)
Merida
Summarized Update
Specific Route Update
172.16.0.0/16
172.16.1.0/24
172.16.5.0/24
172.16.5.0/24
Quito
Cartago
172.16.2.0/24 172.16.10.0/24
• Merida receives a summarized /16 update from Quito and a more
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specific /24 update from Cartago.
Merida will include both routes in the routing table.
Merida will forward all packets matching at least the first 24 bits of
172.16.5.0 to Cartago (172/16/5/0/24), longest-bit match.
Merida will forward all other packets matching at least the first 16 bits
to Quito (172.16.0.0/16).
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Example from online curriculum
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Another example from online curriculum
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Short Term Solutions: IPv4 Enhancements
•
•
•
•
CIDR (Classless Inter-Domain Routing) – RFCs 1517,
1518, 1519, 1520
VLSM (Variable Length Subnet Mask) – RFC 1009
Private Addressing - RFC 1918
NAT/PAT (Network Address Translation / Port Address
Translation) – RFC
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VLSM (Variable Length Subnet Mask)
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•
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Limitation of using only a single subnet mask across a
given network-prefix (network address, the number of
bits in the mask) was that an organization is locked into a
fixed-number of of fixed-sized subnets.
1987, RFC 1009 specified how a subnetted network could
use more than one subnet mask.
VLSM = Subnetting a Subnet
– “If you know how to subnet, you can do VLSM!”
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VLSM – Simple Example
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•
1st octet
2nd octet
3rd octet
4th octet
10.0.0.0/8
10
Host
Host
Host
10.0.0.0/16
10
Subnet
Host
Host
10.0.0.0/16
10
0
Host
Host
10.1.0.0/16
10.2.0.0/16
10.n.0.0/16
10.255.0.0/16
10
10
10
10
1
2
…
255
Host
Host
Host
Host
Host
Host
Host
Host
Subnetting a /8 subnet using a /16 mask gives us 256 subnets with
65,536 hosts per subnet.
Let’s take the 10.2.0.0/16 subnet and subnet it further…
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VLSM – Simple Example
Network
Subnet
Host
Host
10.2.0.0/16
10
2
Host
Host
10.2.0.0/24
10
2
Subnet
Host
10.2.0.0/24
10.2.1.0/24
10
10
2
2
0
1
Host
Host
10.2.n.0/24
10.2.255.0/24
10
10
2
2
…
255
Host
Host
•
•
Note: 10.2.0.0/16 is now a summary of all of the 10.2.0.0/24
subnets.
Summarization coming soon!
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VLSM – Simple Example
10.0.0.0/8
Subnet
10.0.0.0/16
10.1.0.0/16
“subnetted using /16”
1st host
Last host
Broadcast
10.0.0.1
10.0.255.254
10.0.255.255
10.1.0.1
10.1.255.254
10.1.255.255
10.2.0.0/16 “sub-subnetted using /24”
–Subnet
1st host
Last host
Broadcast
–10.2.0.0/24
10.2.0.1
10.2.0.254
10.2.0.255
–10.2.1.0/24
10.2.1.1
10.2.1.254
10.2.1.255
–10.2.2.0/24
10.2.2.1
10.2.2.254
10.2.2.255
– Etc.
–10.2.255.0/24 10.2.255.1 10.2.255.254 10.2.255.255
10.3.0.0/16
Etc.
10.255.0.0/16
10.3.0.1
10.3.255.254
10.0.255.255
10.255.0.1 10.255.255.254 10.255.255.255
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VLSM – Simple Example
Subnets
10.0.0.0/16
10.1.0.0/16
10.2.0.0/16
10.2.0.0/24
10.2.1.0/24
10.2.2.0/24
Etc.
10.2.255.0/24
10.3.0.0/16
Etc.
10.255.0.0/16
•
•
•
An example of VLSM, NOT of good network design.
10.1.0.0/16
10.2.0.0/24
10.2.1.0/24
10.7.0.0/16
10.3.0.0/16
10.2.6.0/24
10.4.0.0/16
10.2.3.0/24
10.2.8.0/24
10.5.0.0/16 10.8.0.0/16
10.2.5.0/24
10.6.0.0/16
10.2.4.0/24
Your network can now have 255 /16 subnets with 65,534 hosts each AND
256 /24 subnets with 254 hosts each.
All you need to make it work is a classless routing protocol that passes
the subnet mask with the network address in the routing updates.
Classless routing protocols: RIPv2, EIGRP, OSPF, IS-IS, BGPv4 (coming)
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Another VLSM Example using /30 subnets
207.21.24.0/24 network subnetted into eight /27 (255.255.255.224)
subnets
207.21.24.192/27 subnet, subnetted into eight /30
(255.255.255.252) subnets
•
•
This network has seven /27 subnets with 30 hosts each
AND eight /30 subnets with 2 hosts each.
/30 subnets are very useful for serial networks.
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207.21.24.192/27
0
1
2
3
4
5
6
7
207.21.24.192/30
207.21.24.196/30
207.21.24.200/30
207.21.24.204/30
207.21.24.208/30
207.21.24.212/30
207.21.24.216/30
207.21.24.220/30
Rick Graziani graziani@cabrillo.edu
207.21.24. 11000000
/30
207.21.24. 110 00000
207.21.24. 110 00100
207.21.24. 110 01000
207.21.24. 110 01100
207.21.24. 110 10000
207.21.24. 110 10100
207.21.24. 110 11000
207.21.24. 110 11100
Hosts Bcast
01 10 11
01 10 11
01 10 11
01 10 11
01 10 11
01 10 11
01 10 11
01 10 11
2 Hosts
.193 & .194
.197 & .198
.201 & .202
.205 & .206
.209 & .210
.213 & .214
.217 & .218
.221 & .222
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207.21.24.192/30
207.21.24.204/30
207.21.24.216/30
207.21.24.96/27
207.21.24.128/27
207.21.24.64/27
207.21.24.196/30
207.21.24.160/27
•
•
207.21.24.208/30
207.21.24.200/30
207.21.24.224/27
207.21.24.32/27
207.21.24.212/30
207.21.24.0/27
This network has seven /27 subnets with 30 hosts each AND seven
/30 subnets with 2 hosts each (one left over).
/30 subnets with 2 hosts per subnet do not waste host addresses on
serial networks .
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VLSM and the Routing Table
Displays one subnet mask for all child routes.
Classful mask is assumed for the parent route.
Routing Table without VLSM
RouterX#show ip route
207.21.24.0/27 is subnetted,
C
207.21.24.192 is directly
C
207.21.24.196 is directly
C
207.21.24.200 is directly
C
207.21.24.204 is directly
4 subnets
connected,
connected,
connected,
connected,
Serial0
Serial1
Serial2
FastEthernet0
Each child routes displays its own subnet mask.
Classful mask is included for the parent route.
Routing Table with VLSM
RouterX#show ip route
207.21.24.0/24 is variably subnetted, 4 subnets, 2 masks
C
207.21.24.192 /30 is directly connected, Serial0
C
207.21.24.196 /30 is directly connected, Serial1
C
207.21.24.200 /30 is directly connected, Serial2
C
207.21.24.96 /27 is directly connected, FastEthernet0
• Parent Route shows classful mask instead of subnet mask of the child
routes.
• Each Child Routes includes its subnet mask.
Rick Graziani graziani@cabrillo.edu
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Final Notes on VLSM
• Whenever possible it is best to group contiguous routes together so
•
•
they can be summarized (aggregated) by upstream routers. (coming
soon!)
– Even if not all of the contiguous routes are together, routing tables
use the longest-bit match which allows the router to choose the
more specific route over a summarized route.
– Coming soon!
You can keep on sub-subnetting as many times and as “deep” as you
want to go.
You can have various sizes of subnets with VLSM.
Rick Graziani graziani@cabrillo.edu
44
Route flapping
•
•
•
•
•
•
Route flapping occurs when a router interface alternates rapidly between the
up and down states.
Route flapping can cripple a router with excessive updates and recalculations.
However, the summarization configuration prevents the RTC route flapping
from affecting any other routers.
The loss of one network does not invalidate the route to the supernet.
While RTC may be kept busy dealing with its own route flap, RTZ, and all
upstream routers, are unaware of any downstream problem.
Summarization effectively insulates the other routers from the problem of route
flapping.
Rick Graziani graziani@cabrillo.edu
45
Short Term Solutions: IPv4 Enhancements
•
•
•
•
CIDR (Classless Inter-Domain Routing) – RFCs 1517,
1518, 1519, 1520
VLSM (Variable Length Subnet Mask) – RFC 1009
Private Addressing - RFC 1918
NAT/PAT (Network Address Translation / Port Address
Translation) – RFC
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Private IP addresses (RFC 1918)
If addressing any of the following, these private addresses can be used instead of globally
unique addresses:
• A non-public intranet
• A test lab
• A home network
Global addresses must be obtained from a provider or a registry at some expense.
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Discontiguous subnets
• “Mixing private addresses with globally unique addresses can create
•
•
discontiguous subnets.” – Not the main cause however…
Discontiguous subnets, are subnets from the same major network that
are separated by a completely different major network or subnet.
Question: If a classful routing protocol like RIPv1 or IGRP is being used, what
do the routing updates look like between Site A router and Site B router?
Rick Graziani graziani@cabrillo.edu
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Discontiguous subnets
•
•
•
•
Classful routing protocols, notably RIPv1 and IGRP, can’t support
discontiguous subnets, because the subnet mask is not included in routing
updates.
RIPv1 and IGRP automatically summarize on classful boundaries.
Site A and Site B are all sending each other the classful address of
207.21.24.0/24.
A classless routing protocol (RIPv2, EIGRP, OSPF) would be needed:
– to not summarize the classful network address and
– to include the subnet mask in the routing updates.
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Discontiguous subnets
•
•
RIPv2 and EIGRP automatically summarize on classful boundaries.
When using RIPv2 and EIGRP, to disable automatic summarization (on both
routers):
Router(config-router)#no auto-summary
•
•
SiteB now receives 207.21.24.0/27
SiteB now receives 207.21.24.32/27
Rick Graziani graziani@cabrillo.edu
50
Short Term Solutions: IPv4 Enhancements
•
•
•
•
CIDR (Classless Inter-Domain Routing) – RFCs 1517,
1518, 1519, 1520
VLSM (Variable Length Subnet Mask) – RFC 1009
Private Addressing - RFC 1918
NAT/PAT (Network Address Translation / Port Address
Translation) – RFC
Rick Graziani graziani@cabrillo.edu
51
Network Address Translation (NAT)
NAT: Network Address Translatation
• NAT, as defined by RFC 1631, is the process of swapping one address
for another in the IP packet header.
• In practice, NAT is used to allow hosts that are privately addressed to
access the Internet.
Rick Graziani graziani@cabrillo.edu
52
Network Address Translation (NAT)
•
•
TCP Source Port 1026
2.2.2.2 TCP Source Port 1923
TCP Source Port 1026
2.2.2.2 TCP Source Port 1924
NAT translations can occur dynamically or statically.
The most powerful feature of NAT routers is their capability to use port
address translation (PAT), which allows multiple inside addresses to map to
the same global address.
• This is sometimes called a many-to-one NAT.
• With PAT, or address overloading, literally hundreds of privately addressed
nodes can access the Internet using only one global address.
• The NAT router keeps track of the different conversations by mapping TCP and
UDP port numbers.
Rick Graziani graziani@cabrillo.edu
53
Classless Routing Protocols
RIPv2
Classless routing protocols
• The true defining characteristic of classless routing protocols is the
•
capability to carry subnet masks in their route advertisements.
“One benefit of having a mask associated with each route is that the
all-zeros and all-ones subnets are now available for use.”
– Cisco allows the all-zeros and all-ones subnets to be used with
classful routing protocols.
Rick Graziani graziani@cabrillo.edu
55
Classless Routing Protocols
“The true characteristic of a classless routing protocol is the ability to
carry subnet masks in their route advertisements.” Jeff Doyle, Routing
TCP/IP
Benefits:
• All-zeros and all-ones subnets
– - Although some vendors, like Cisco, can also handle this with
classful routing protocols.
• VLSM
– Can have discontiguous subnets
– Better IP addressing allocation
• CIDR
– More control over route summarization
Rick Graziani graziani@cabrillo.edu
Classless Routing Protocols
Classless Routing Protocols:
• RIPv2
• EIGRP
• OSPF
• IS-IS
• BGPv4
Note: Remember classful/classless routing protocols is different than
classful/classless routing behavior. Classlful/classless routing protocols
(RIPv1, RIPv2, IGRP, EIGRP, OSPF, etc.) has to do with how routes get into
the routing table; how the routing table gets built. Classful/classless routing
behavior (no ip classless or ip classless) has to do with the lookup process of
routes in the routing table (after the routing table has been built). It is possible
to have a classful routing protocol and classless routing behavior or visa
versa. It is also possible to have both a classful routing protocol and classful
routing behavior; or both a classless routing protocol and classless routing
behavior.
Rick Graziani graziani@cabrillo.edu
Few RIP facts
•
RIP still working on routers and hosts
today.
•
IP RIP derived from RIP by Xerox for its
XNS protocol stack.
•
Initially implemented in Berkeley UNIX
routed program.
•
RIPv1 – Charles Hedrick, RFC 1058,
1988
• RIPv2 – Gary Malkin, RFC 1723, 1994
• RIPng for IPv6 – Gary Malkin, RFC 2080,
1997 (proposed standard), extension to
RIPv2 message format.
Rick Graziani graziani@cabrillo.edu
The Grim Router
RIP version 1
•
•
•
•
Classful Routing Protocol, sent over UDP port 520
Does not include the subnet mask in the routing updates.
Automatic summarization done at major network boundaries.
Updates sent as broadcasts unless the neighbor command is uses
which sends them as unicasts.
0
1
2
3 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| command (1)
| version (1)
|
must be zero (2)
|
+---------------+---------------+-------------------------------+
| address family identifier (2) |
must be zero (2)
|
+-------------------------------+-------------------------------+
|
IP address (4)
|
+---------------------------------------------------------------+
|
must be zero (4)
|
+---------------------------------------------------------------+
|
must be zero (4)
|
+---------------------------------------------------------------+
|
metric (4)
|
+---------------------------------------------------------------+
Rick Graziani graziani@cabrillo.edu
RIP version 2
•
•
•
•
Classless Routing Protocol, sent over UDP port 520
Includes the subnet mask in the routing updates.
Automatic summarization at major network boundaries can be disabled.
Updates sent as multicasts unless the neighbor command is uses which
sends them as unicasts.
0
1
2
3 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| command (1)
| version (1)
|
must be zero (2)
|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address Family Identifier (2) |
Route Tag (2)
|
+-------------------------------+-------------------------------+
|
IP Address (4)
|
+---------------------------------------------------------------+
|
Subnet Mask (4)
|
+---------------------------------------------------------------+
|
Next Hop (4)
|
+---------------------------------------------------------------+
|
Metric (4)
|
+---------------------------------------------------------------+
Rick Graziani graziani@cabrillo.edu
RIP v2 operation
•
•
Rick Graziani graziani@cabrillo.edu
All of the operational procedures, timers,
and stability functions of RIP v1 remain the
same in RIP v2, with the exception of the
broadcast updates.
RIP v2 updates use reserved Class D
address 224.0.0.9.
61
Issues addressed by RIP v2
The following four features are the most significant new features added to RIP v2:
• Authentication of the transmitting RIP v2 node to other RIP v2 nodes
• Subnet Masks – RIP v2 allocates a 4-octet field to associate a subnet mask to
a destination IP address.
• Next Hop IP addresses – A better next-hop address, that the advertising
router, if one exists.
– It indicates a next-hop address, on the same subnet, that is metrically
closer to the destination than the advertising router.
– If this router’s interface is closest, then it is set to 0.0.0.0
– See Doyle, Routing TCP/IP for an example
• Multicasting RIP v2 messages – Multicasting is a technique for
simultaneously advertising routing information to multiple RIP or RIP v2
devices.
Rick Graziani graziani@cabrillo.edu
62
RIP v2 message format
• All the extensions to the original protocol are carried in the unused
•
fields.
The Address Family Identifier (AFI) field is set to two for IP. The only
exception is a request for a full routing table of a router or host, in
which case it will be set to zero.
Rick Graziani graziani@cabrillo.edu
63
RIP v2 message format
•
•
•
The Route Tag field provides a way to differentiate between internal and
external routes. (RIP itself does not use this field.)
– External routes are those that have been redistributed into the RIP v2.
The Next Hop field contains the IP address of the next hop listed in the IP
Address field.
Metric indicates how many internetwork hops, between 1 and 15 for a valid
route, or 16 for an unreachable route.
Rick Graziani graziani@cabrillo.edu
64
Compatibility with RIP v1
RFC 1723 defines a compatibility with four settings, which allows versions
1 and 2 to interoperate:
1. RIP v1, in which only RIP v1 messages are transmitted
2. RIP v1 Compatibility, which causes RIP v2 to broadcast its messages
instead of multicast them so that RIP v1 may receive them
3. RIP v2, in which RIP v2 messages are multicast to destination
address 224.0.0.9
4. None, in which no updates are sent
•
RFC 1723 recommends that routers be configurable on a perinterface basis. (coming soon)
Rick Graziani graziani@cabrillo.edu
65
Authentication
Authentication is
supported by
modifying what
would normally be
the first route entry
of the RIP message
• A security concern with any routing protocol is the possibility of a router
•
•
•
accepting invalid routing updates.
The Authentication Type for simple password authentication is two,
0x0002,
The remaining 16 octets carry an alphanumeric password of up to 16
characters.
Configuration is coming!
Rick Graziani graziani@cabrillo.edu
66
Authentication
• RFC 1723 describes only simple password authentication
• Cisco IOS provides the option of using MD5 authentication instead of
•
•
simple password authentication.
Cisco uses the first and last route entry spaces for MD5 authentication
purposes.
MD5 computes a 128-bit hash value from a plain text message of
arbitrary length and a password.
Rick Graziani graziani@cabrillo.edu
67
Authentication
Rick Graziani graziani@cabrillo.edu
68
MD5 Authentication (FYI)
http://www.cisco.com/en/US/tech/tk713/tk507/technologies_tech_note09186a00800b4131.shtml
1
2
3
4
5
6
Rick Graziani graziani@cabrillo.edu
69
Same limitations of RIPv2 as with RIPv1
•
Slow convergence and the need of holddown timers to
reduce the possibility of routing loops.
Note: See CCNA 2 for review if needed.
Rick Graziani graziani@cabrillo.edu
70
Same limitations of RIPv2 as with RIPv1
•
•
•
RIP v2 continues to rely on counting to infinity as a means
of resolving certain error conditions within the network.
Dependent upon holddown timers.
Triggered updates are also helpful.
Note: See CCNA 2 for review if needed.
Rick Graziani graziani@cabrillo.edu
71
Same limitations of RIPv2 as with RIPv1
• Perhaps the single greatest limitation that RIP v2 inherited from RIP is
that its interpretation of infinity remained at 16.
Rick Graziani graziani@cabrillo.edu
72
Basic RIPv2 configuration
Other:
For RIP and IGRP, the passive interface command stops the router from
sending updates to a particular neighbor, but the router continues to
listen and use routing updates from that neighbor. (More later.)
Router(config-router)# passive-interface interface
Default behavior of version 1 restored:
Router(config-router)# no version
Rick Graziani graziani@cabrillo.edu
73
Compatibility with RIP v1
NewYork
interface fastethernet0/0
ip address 192.168.50.129 255.255.255.192
ip rip send version 1
ip rip receive version 1
RIPv2
interface fastethernet0/1
ip address 172.25.150.193 255.255.255.240
ip rip send version 1 2
•
•
•
Interface FastEthernet0/0 is
configured to send and receive
RIP v1 updates.
FastEthernet0/1 is configured
to send both version 1 and 2
updates.
FastEthernet0/2 has no special
configuration and therefore
sends and receives version 2
by default.
Rick Graziani graziani@cabrillo.edu
interface fastethernet0/2
ip address 172.25.150.225 225.255.255.240
router rip
version 2
network 172.25.0.0
network 192.168.50.0
74
Discontiguous subnets and classless
routing
router rip
version 2
no auto-summary
• RIP v1 always uses automatic summarization.
• The default behavior of RIP v2 is to summarize at network
boundaries the same as RIP v1.
Rick Graziani graziani@cabrillo.edu
75
Configuring authentication (EXTRA)
Router(config)#key chain Romeo
Router(config-keychain)#key 1
Router(config-keychain-key)#key-string Juliet
The password must be the same on both routers (Juliet), but the name of the
key (Romeo) can be different.
Router(config)#interface fastethernet 0/0
Router(config-if)#ip rip authentication key-chain Romeo
Router(config-if)#ip rip authentication mode md5
•
If the command ip rip authentication mode md5 is not added, the interface will
use the default clear text authentication. Although clear text authentication may be
necessary to communicate with some RIP v2 implementations, for security concerns use
the more secure MD5 authentication whenever possible.
Rick Graziani graziani@cabrillo.edu
76
Show commands
Rick Graziani graziani@cabrillo.edu
77
show ip rip database
Router# show ip rip database
172.19.0.0/16 auto-summary
172.19.64.0/24 directly connected, Ethernet0
172.19.65.0/24
[1] via 172.19.70.36, 00:00:17, Serial1
[2] via 172.19.67.38, 00:00:25, Serial0
172.19.67.0/24 directly connected, Serial0
172.19.67.38/32 directly connected, Serial0
172.19.70.0/24 directly connected, Serial1
172.19.86.0/24[1] via 172.19.67.38, 00:00:25, Serial0
[1] via 172.19.70.36, 00:00:17, Serial1
• The show ip rip database command to check summary address
•
•
entries in the RIP database.
These entries will appear in the database if there are only relevant
child or specific routes being summarized.
When the last child route for a summary address becomes invalid, the
summary address is also removed from the routing table.
Router#show ip rip database
Rick Graziani graziani@cabrillo.edu
78
Show commands
Rick Graziani graziani@cabrillo.edu
79
Debug commands
Rick Graziani graziani@cabrillo.edu
80
RIPv2 Example
Scenario:
•
•
•
•
Internet
Discontiguous subnets
VLSM
static route to
207.0.0.0/8
10.0.0.0/8
CIDR
.1
.1 e0
ISP
Supernet to 207.0.0.0/8
With the default
auto-summary on
ISP, it will load
balance for all
packets destined for
172.30.0.0/16
.25
s0
s1
.21
192.168.4.24/30
Lo2
s0
Lo0
.1 SantaCruz1
.1 e0
172.30.1.0/24
Rick Graziani graziani@cabrillo.edu
192.168.4.20/30
172.30.200.32/28
.26
172.30.2.0/24
207.0.0.0/16
207.1.0.0/16
207.2.0.0/16
207.3.0.0/16
etc.
s0
.22
Lo1
`
172.30.200.16/28
SantaCruz2 Lo0
.1 e0
.1
172.30.100.0/24
172.30.110.0/24
SantaCruz1
router rip
network 172.30.0.0
network 192.168.4.0
version 2
no auto-summary
RIPv2 Example
Internet
static route to
207.0.0.0/8
10.0.0.0/8
.1
SantaCruz2
router rip
network 172.30.0.0
network 192.168.4.0
version 2
no auto-summary
207.0.0.0/16
207.1.0.0/16
207.2.0.0/16
207.3.0.0/16
etc.
.1 e0
ISP
.25
s0
s1
.21
192.168.4.24/30
192.168.4.20/30
172.30.200.32/28
ISP
router rip
redistribute static
network 10.0.0.0
network 192.168.4.0
version 2
no auto-summary
Lo2
.26
172.30.2.0/24
ip route 207.0.0.0 255.0.0.0 null0
Rick Graziani graziani@cabrillo.edu
s0
Lo0
.1 SantaCruz1
.1 e0
172.30.1.0/24
s0
.22
Lo1
`
172.30.200.16/28
SantaCruz2 Lo0
.1 e0
.1
172.30.100.0/24
172.30.110.0/24
SantaCruz2#show ip route
C
C
R
R
C
C
R
C
R
R
Examining a Routing Table
172.30.0.0/16 is variably subnetted, 6 subnets, 2 masks
172.30.200.32/28 is directly connected, Loopback2
172.30.200.16/28 is directly connected, Loopback1
172.30.2.0/24 [120/2] via 192.168.4.21, 00:00:21, Serial0
172.30.1.0/24 [120/2] via 192.168.4.21, 00:00:21, Serial0
172.30.100.0/24 is directly connected, Ethernet0
172.30.110.0/24 is directly connected, Loopback0
192.168.4.0/30 is subnetted, 2 subnets
192.168.4.24 [120/1] via 192.168.4.21, 00:00:21, Serial0
192.168.4.20 is directly connected, Serial0
Internet
10.0.0.0/8 [120/1] via 192.168.4.21, 00:00:21, Serial0
static route to
207.0.0.0/8 [120/1] via 192.168.4.21, 00:00:21, 10.0.0.0/8
Serial0
207.0.0.0/8
.1
207.0.0.0/16
207.1.0.0/16
207.2.0.0/16
207.3.0.0/16
etc.
.1 e0
ISP
.25
Supernet, classless routing protcols
will route supernets (CIDR)
s0
s1
.21
192.168.4.24/30
192.168.4.20/30
172.30.200.32/28
Lo2
.26
172.30.2.0/24
s0
Lo0
.1 SantaCruz1
.1 e0
172.30.1.0/24
Rick Graziani graziani@cabrillo.edu
s0
.22
Lo1
`
172.30.200.16/28
SantaCruz2 Lo0
.1 e0
.1
172.30.100.0/24
172.30.110.0/24
RIPv2: Sending and Receiving Updates
ISP(config)# line console 0
ISP(config-line)# logging synchronous
ISP#debug ip rip
RIP protocol debugging is on
ISP#01:23:34: RIP: received v2 update from 192.168.4.22 on Serial1
01:23:34:
172.30.100.0/24 -> 0.0.0.0 in 1 hops
01:23:34:
172.30.110.0/24 -> 0.0.0.0 in 1 hops
Includes mask
ISP#
01:23:38: RIP: received v2 update from 192.168.4.26 on Serial0
01:23:38:
172.30.2.0/24 -> 0.0.0.0 in 1 hops
01:23:38:
172.30.1.0/24 -> 0.0.0.0 in 1 hops
multicast
ISP#
01:24:31: RIP: sending v2 update to 224.0.0.9 via Ethernet0 (10.0.0.1)
01:24:31:
172.30.2.0/24 -> 0.0.0.0, metric 2, tag 0
01:24:31:
172.30.1.0/24 -> 0.0.0.0, metric 2, tag 0
01:24:31:
172.30.100.0/24 -> 0.0.0.0, metric 2, tag 0
01:24:31:
172.30.110.0/24 -> 0.0.0.0, metric 2, tag 0
01:24:31:
192.168.4.24/30 -> 0.0.0.0, metric 1, tag 0
01:24:31:
192.168.4.20/30 -> 0.0.0.0, metric 1, tag 0
<text omitted>
Rick Graziani graziani@cabrillo.edu
Adding a default Routes to RIPv2
ISP
207.0.0.0/16
207.1.0.0/16
207.2.0.0/16
207.3.0.0/16
etc.
Internet
router rip
redistribute static
static route to
207.0.0.0/8
10.0.0.0/8
network 10.0.0.0
.1
.1 e0
ISP
network 192.168.4.0
.25
s0
s1
.21
version 2
no auto-summary
192.168.4.24/30
192.168.4.20/30
default-information originate
172.30.200.32/28
Lo2
ip route 207.0.0.0 255.0.0.0 null0
ip route 0.0.0.0 0.0.0.0 10.0.0.2
etherenet0
.26
172.30.2.0/24
s0
Lo0
.1 SantaCruz1
.1 e0
172.30.1.0/24
Rick Graziani graziani@cabrillo.edu
s0
.22
Lo1
`
172.30.200.16/28
SantaCruz2 Lo0
.1 e0
.1
172.30.100.0/24
172.30.110.0/24
Other RIPv2 Commands (EXTRA)
Router(config-router)# neighbor ip-address
Defines a neighboring router with which to exchange unicast routing
information. (RIPv1 or RIPv2)
Router(config-if)# ip rip send|receive version 1 | 2 | 1 2
Configures an interface to send/receive RIP Version 1 and/or Version 2 packets
Router(config-if)# ip summary-address rip ip_address
ip_network_mask
Specifies the IP address and network mask that identify the routes to be
summarized.
Authentication and other nice configuration commands and examples:
http://www.cisco.com/en/US/products/sw/iosswrel/ps1831/products_configurati
on_guide_chapter09186a00800d97f7.html
Rick Graziani graziani@cabrillo.edu
RIPv2 Summary
Rick Graziani graziani@cabrillo.edu
87
Ch. 1 – Introduction to
Classless Routing
CCNA 3 version 3.0
Rick Graziani
Cabrillo College