Chapter 6 vlsm and cidr
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Chapter 6 VLSM and CIDR. TECI 185 Routing Protocols and Concepts Jack Yon Western Colorado Community College [email protected] Last Updated: 3/24/2009. Topics. Classful and Classless Addressing Classful IP Addressing Classful Routing Protocols Classless IP Addressing

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Chapter 6 VLSM and CIDR

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Chapter 6 vlsm and cidr

Chapter 6 VLSM and CIDR

TECI 185 Routing Protocols and Concepts

Jack Yon

Western Colorado Community College

[email protected]

Last Updated: 3/24/2009


Topics

Topics

  • Classful and Classless Addressing

    • Classful IP Addressing

    • Classful Routing Protocols

    • Classless IP Addressing

    • Classless Routing Protocols

  • VLSM

    • VLSM in Action

    • VLSM and IP Addresses

  • CIDR

    • Route Summarization

    • Calculating Route Summarization


Classful and classless addressing

Classful and Classless Addressing

Classful IP Addressing

Classful Routing Protocols

Classless IP Addressing

Classless Routing Protocols


Classful and classless routing protocols

Classful and Classless Routing Protocols

  • Routing protocols:

    • classful or classless.

  • This is a result of the evolution from classful to classless IPv4 addressing.

  • As networks began to use classless addressing, classless routing protocols had to be modified or developed to include the subnet mask in the routing update.


Classful ip addressing

Classful IP Addressing

  • As of January 2007, there were over 433 million hosts on the Internet.

  • IPv4 32-bit address space would now be exhausted if it were not for?

    • VLSM - 1993 (RFC 1519)

    • CIDR - 1993 (RFC 1519)

    • Network Address Translation (NAT) - 1994 (RFC 1631)

    • Private addressing- 1996 (RFC 1918)


High order bits

High-Order Bits?

  • Only these three choices - No medium sized networks .

  • How did they actually come up with these ranges?

  • How can a device such as a router quickly determine the subnet mask of the IP address?

    • By examining the first few bits of the address.


Classful routing protocol

Classful Routing Protocol

Classful Routing Protocols

  • Is the subnet mask included in the routing update?

    • No

  • How does the router determine the mask?

    • Value of the first octet (first 3 bits of the address) or Interface Mask


Classful routing protocol1

Classful Routing Protocol

R2 applies s0/0/0’s /24 subnet mask (same major network)

R1 sends a subnet address out s0/0/0 (same major network)


Classful routing protocol2

Classful Routing Protocol

R2 sends a summarized route out s0/0/1 (different major network)

R3 applies the default /16 subnet mask (different major network)


Moving toward classless addressing

Moving TowardClassless Addressing

  • By 1992, IETF had serious concerns about:

    • The exponential growth of the Internet and Internet routing tables.

    • Eventual exhaustion of 32-bit IPv4 address space.

  • 1993, IETF introduced classless interdomain routing (CIDR) (RFC 1517).

    • More efficient use of IPv4 address space

    • Prefix aggregation, which reduced the size of routing tables


Chapter 6 vlsm and cidr

CLASS A

ISPs no longer restricted to three classes. Can now allocate a large range of network addresses based on customer requirements

CLASS B

11111111.00000000.00000000.00000000 /8 (255.0.0.0)16,777,216 host addresses

11111111.10000000.00000000.00000000 /9 (255.128.0.0)8,388,608 host addresses

11111111.11000000.00000000.00000000 /10 (255.192.0.0)4,194,304 host addresses

11111111.11100000.00000000.00000000 /11 (255.224.0.0)2,097,152 host addresses

11111111.11110000.00000000.00000000 /12 (255.240.0.0)1,048,576 host addresses

11111111.11111000.00000000.00000000 /13 (255.248.0.0)524,288 host addresses

11111111.11111100.00000000.00000000 /14 (255.252.0.0)262,144 host addresses

11111111.11111110.00000000.00000000 /15 (255.254.0.0)131,072 host addresses

11111111.11111111.00000000.00000000 /16 (255.255.0.0)65,536 host addresses

11111111.11111111.10000000.00000000 /17 (255.255.128.0)32,768 host addresses

11111111.11111111.11000000.00000000 /18 (255.255.192.0)16,384 host addresses

11111111.11111111.11100000.00000000 /19 (255.255.224.0)8,192 host addresses

11111111.11111111.11110000.00000000 /20 (255.255.240.0)4,096 host addresses

11111111.11111111.11111000.00000000 /21 (255.255.248.0)2,048 host addresses

11111111.11111111.11111100.00000000 /22 (255.255.252.0)1,024 host addresses

11111111.11111111.11111110.00000000 /23 (255.255.254.0)512 host addresses

11111111.11111111.11111111.00000000 /24 (255.255.255.0)256 host addresses

11111111.11111111.11111111.10000000 /25 (255.255.255.128)128 host addresses

11111111.11111111.11111111.11000000 /26 (255.255.255.192)64 host addresses

11111111.11111111.11111111.11100000 /27 (255.255.255.224)32 host addresses

11111111.11111111.11111111.11110000 /28 (255.255.255.240)16 host addresses

11111111.11111111.11111111.11111000 /29 (255.255.255.248)8 host addresses

11111111.11111111.11111111.11111100 /30 (255.255.255.252)4 host addresses

11111111.11111111.11111111.11111110 /31 (255.255.255.254)2 host addresses

11111111.11111111.11111111.11111111 /32 (255.255.255.255)“Host Route”

CLASS C


Cidr and route summarization

CIDR and Route Summarization

  • CIDR = Route summarization

  • A supernet summarizes multiple network addresses with a mask less than the classful mask.


Cidr and route summarization1

CIDR and Route Summarization

  • 192.168.0.0/23, 192.168.2.0/23, 192.168.4.0/22, and 192.168.8.0/21 are all subnets of 192.168.0.0/20


Cidr and route summarization2

CIDR and Route Summarization

  • Propagating VLSM and supernet routes requires a classless routing protocol, because the subnet mask can no longer be determined by the value of the first octet.


Classless routing protocol

Classless Routing Protocol

  • Classless routing protocols include the subnet mask with the network address in their routing updates.


Classless routing protocol1

Classless Routing Protocol

  • 172.16.0.0/16, 172.17.0.0/16, 172.18.0.0/16, and 172.19.0.0/16 summarized as 172.16.0.0/14.

  • What is this called? (Subnet mask is less than the classful default mask.)

    • Supernet

    • /14 (255.252.0.0) subnet mask is included in the routing update.

/14


Chapter 6 vlsm and cidr

VLSM

VLSM in Action

VLSM and IP Addresses


Chapter 6 vlsm and cidr

VLSM

  • The network 10.0.0.0/8 has been subnetted using the subnet mask of /16, which gives the potential of 256 subnets:

    10.0.0.0/16

    10.1.0.0/16

    10.2.0.0/16

    .

    .

    .

    10.255.0.0/16


Chapter 6 vlsm and cidr

VLSM

  • Any of these /16 subnets can be subnetted further.

  • For example the 10.1.0.0/16 subnet is subnetted again using the /24 mask.


Chapter 6 vlsm and cidr

  • 10.1.0.0/16 subnet is subnetted again using the /24 mask

  • 10.2.0.0/16 subnet is also subnetted again with a /24 mask.

  • 10.3.0.0/16 subnet is subnetted again with the /28 mask.

  • 10.4.0.0/16 subnet is subnetted again with the /20 mask.


Chapter 6 vlsm and cidr

A

10.1.4.10/24

  • Individual host addresses are assigned from the addresses of “sub-subnets.”

  • What would be a valid Host IP address for Host A?


Vlsm a different way to look at it

VLSM: A different way to look at it

  • Subnet 10.0.0.0/8 into /16 subnets.

  • Subnet 10.1.0.0/16 into /24 subnets.


Vlsm a different way to look at it1

VLSM: A different way to look at it

  • Subnet 10.2.0.0/16 into /24 subnets.

    • Subnets ranging from 10.2.0.0/24 to 10.2.255.0/24


Vlsm a different way to look at it2

VLSM: A different way to look at it

  • Subnet 10.3.0.0/16 is further subnetted with a /28 mask

    • 14 host addresses per subnet.

    • Subnets ranging from 10.3.0.0/28 to 10.3.255.240/28.


Vlsm a different way to look at it3

VLSM: A different way to look at it

  • Subnet 10.4.0.0/16 subnetted with a /20 mask

    • 4094 host addresses per subnet

    • subnets ranging from 10.4.0.0/20 to 10.4.240.0/20


Chapter 6 vlsm and cidr

VLSM

These subnets could be subnetted further!

All other /16 subnets are still available for use as /16 networks or to be subnetted.


Chapter 6 vlsm and cidr

Hosts are assigned an IP address and mask from a specific subnet.

VLSM

What are the valid host IP Addresses?

10.2.1.55/24

10.2.5.55/24

All other /16 subnets are still available for use as /16 networks or to be subnetted.

10.255.0.5/16

10.4.0.55/20


Chapter 6 vlsm and cidr

Host can only be a member of the subnet. Host can NOT be a member of the network that was subnetted.

VLSM

Are these valid host IP Addresses?

YES!

10.2.1.55/24

10.2.0.55/16

NO!

All other /16 subnets are still available for use as /16 networks or to be subnetted.


Vlsm 1

VLSM 1

255.255.255.240 or /28


Vlsm 2

VLSM 2

/30 – Gives 4 addresses

- 2 usable host addresses


Vlsm 2 possible 30 options

VLSM 2 – Possible /30 options

Conflicts

Existing /27 Networks

1286432168421

.64 0 1 0 0 0 0 0 0

.96 0 1 1 0 0 0 0 0

.128 1 0 0 0 0 0 0 0

---------------------------------------

.113 0 1 1 1 0 0 0 1

.145 1 0 0 1 0 0 0 1

.193 1 1 00 0 0 0 1

Conflict

Conflict

/30 Choices

Answer


Vlsm 2 our new vslm subnet

VLSM 2 – Our new VSLM Subnet

Existing /27 Networks

1286432168421

.64 0 1 0 0 0 0 0 0

.96 0 1 1 0 0 0 0 0

.128 1 0 0 0 0 0 0 0

----------------------------------------------

.192 1 1 00 0 0 0 0 (Net)

.193 1 1 00 0 0 0 1 (1st hst)

.194 1 1 00 0 0 1 0 (2nd hst)

.195 1 1 00 0 0 1 1 (Bcast)

.192 Network


Vlsm 2 other vlsm subnets

VLSM 2 – Other VLSM Subnets

Existing /27 Networks

.192 Network

1286432168421

.64 0 1 0 0 0 0 0 0

.96 0 1 1 0 0 0 0 0

.128 1 0 0 0 0 0 0 0

---------------------------------------

.192 1 1 00 0 0 0 0

.196 1 1 00 0 1 0 0

.200 1 1 00 1 0 0 0

.204 1 1 00 1 1 0 0

.208 1 1 01 0 0 0 0

.212 1 1 01 0 1 0 0

.216 1 1 01 1 0 0 0

.220 1 1 01 1 1 0 0

Other /30 Networks


Chapter 6 vlsm and cidr

CIDR

Route Summarization

Calculating Route Summarization


Chapter 6 vlsm and cidr

CIDR

CIDR Report: www.cidr-report.org

  • CIDR allows routing protocols to summarize multiple networks, a block of addresses, as a single route.

  • An example is 172.16.1.0/24.


Route summarization

Route Summarization

  • Route summarization (route aggregation) - Process of advertising a contiguous set of addresses as a single address with a less-specific, shorter subnet mask.

  • Remember that CIDR is a form of route summarization and is synonymous with the term…?

    • Supernetting.


Route summarization1

Route Summarization

  • CIDR ignores the limitation of classful boundaries and allows summarization with masks that are less than that of the default classful mask.

  • What type of routing protocols can propagate (distribute) supernets?

    • Classless routing protocols

  • Why?

    • Classless routing protocols include both the network address and the mask in the routing update.

  • Why can’t a classful routing protocol propagate supernets?

    • Classful routing protocols cannot include supernets in their routing updates because they cannot apply a mask less than the default classful mask.


Route summarization2

Route Summarization

  • For example, RIPv1 will summarize 172.30.0.0/24 subnets (172,30.1.0/24, 172.30.2.0/24 and 172.30.3.0/24) as 172.30.0.0.

  • R3 applies the /8 mask (classful routing protocol)


Route summarization3

Route Summarization

  • Why is this static route a supernet?

    • The /13 mask is less than the default Class B /16.


More specific match

More specific match?

Different example from book.

172.16.0.0/16

172.16.10.0/24

S0/0/0

S0/0/1

  • Could a router have both a specific route entry and a summary route entry covering the same network.

    • Yes

  • What if a packet with the destination IP address 172.16.10.10 entered this router? Where would it be forwarded and why?

    • The packet has a more specific (longer) match with 172.16.10.0/24, so S0/0/1 would be used to forward this packet.

    • A minimum of 24 bits match between the IP address and the route.

  • What is a packets with the destination IP address 172.16.20.10 entered this router? Where would it be forwarded and why?

    • The packet only has a match with the less specific172.16.10.0/24, so S0/0/1 would be used to forward this packet

    • A minimum of 16 bits match between the IP address and the route.


Calculating route summarization

Calculating Route Summarization

  • Calculating route summaries and supernets is identical to the process that you already learned in Chapter 2.


Topics1

Topics

  • Classful and Classless Addressing

    • Classful IP Addressing

    • Classful Routing Protocols

    • Classless IP Addressing

    • Classless Routing Protocols

  • VLSM

    • VLSM in Action

    • VLSM and IP Addresses

  • CIDR

    • Route Summarization

    • Calculating Route Summarization


Chapter 6 vlsm and cidr1

Chapter 6 VLSM and CIDR

TECI 185 Routing Protocols and Concepts

Jack Yon

Western Colorado Community College

[email protected]

Last Updated: 3/24/2008


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