ch. 1 – introduction to classless routing ccna 3 version 3.0 rick graziani cabrillo college
TRANSCRIPT
Ch. 1 – Introduction to Classless Routing
CCNA 3 version 3.0
Rick Graziani
Cabrillo College
Rick Graziani [email protected] 2
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 [email protected] (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
• 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 default-
network 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
Advanced IP Management
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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 AddressesFirst 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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Using /24 subnet...
190.52.1.2190.52.2.2190.52.3.2
Network Network Subnet Host
But internal routers think all these addresses are on different networks, called subnetworks
Internet routers still “see” this net as 190.52.0.0
Class B Network Network Host Host
Given the Class B address 190.52.0.0
Subnet Example
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Using the 3rd octet, 190.52.0.0 was divided into:190.52.1.0 190.52.2.0 190.52.3.0 190.52.4.0
190.52.5.0 190.52.6.0 190.52.7.0 190.52.8.0
190.52.9.0 190.52.10.0 190.52.11.0 190.52.12.0
190.52.13.0 190.52.14.0 190.52.15.0 190.52.16.0
190.52.17.0 190.52.18.0 190.52.19.0 and so on ...
Network Network Subnet Host
Subnet Example
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Subnet Example
Network Network Subnet Host
Network address 190.52.0.0 with /16 network mask
190 52 0 Host
190 52 1 Host
190 52 2 Host
Using Subnets: subnet mask 255.255.255.0 or /24
190 52 3 Host
190 52 Etc. Host
190 52 254 Host
190 52 255 Host
255 Subnets
28 - 1
Cannot use last subnet as it contains broadcast address
Subnets
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Subnet Example
Network Network Subnet Host
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.
190 52 0 Host
190 52 1 Host
190 52 Etc. Host
190 52 254 Host
190 52 255 Host
255 Subnets
28 - 1
Subnets
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_note09186a0080093f18.shtml
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• If you need a Review of Subnets, please review the following links on my web site:– Subnet Review (PowerPoint)– Subnets Explained (Word Doc)
Need a Subnet Review?
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Long Term Solution: IPv6 (coming)
• 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
• 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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• By 1992, members of the IETF were having serious concerns about the 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 network-prefix) 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.
CIDR (Classless Inter-Domain Routing)
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Active BGP entries
http://bgp.potaroo.net/
Report last updated at Thu, 16 Jan 2003
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• 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.
CIDR (Classless Inter-Domain Routing)
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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
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
Steps:
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CIDR (Classless Inter-Domain Routing)
• By using a prefix address to summarizes routes, administrators can 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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S ubscribers S ubscribers S ubscribers S ubscribers S ubscribers S ubscribers S ubscribers S ubscribers
IS P IS P IS P IS P IS P IS P IS P IS P
R egiona lS erviceP rovider
R egiona lS erviceP rovider
R egiona lS erviceP rovider
R egiona lS erviceP rovider
N etworkS erviceP rovider
N etworkS erviceP rovider
N A P (N etwork A ccess P o in t)
ISP/NAP Hierarchy - “The Internet: Still hierarchical after all these years.” Jeff Doyle (Tries to be anyways!)
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• 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
23 bits in common
Supernetting Example
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• 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.
Supernetting Example
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Even Better:200.199.48.32/27 11001000 11000111 00110000 0 0100000200.199.48.64/27 11001000 11000111 00110000 0 1000000200.199.48.96/27 11001000 11000111 00110000 0 1100000200.199.48.0/25 11001000 11000111 00110000 0 0000000 (As long as there are no other routes elsewhere within this range, well…)
200.199.56.0/24 11001000 11000111 0011100 0 00000000200.199.57.0/24 11001000 11000111 0011100 1 00000000200.199.56.0/23 11001000 11000111 0011100 0 00000000
CIDR and the provider
200.199.56.0/23
200.199.48.0/25
Summarization from the customer networks to their provider.
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CIDR and the provider200.199.48.0/25
200.199.56.0/23
200.199.48.0/25 11001000 11000111 0011 0000 00000000
200.199.49.0/25 11001000 11000111 0011 0001 00000000
200.199.56.0/23 11001000 11000111 0011 1000 00000000
200.199.48.0/20 11001000 11000111 0011 0000 00000000
20 bits in common
Further summarization happens with the next upstream provider.
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• Dynamic routing protocols must send network address and mask (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.
CIDR Restrictions
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172.16.2.0/24
• Merida receives a summarized /16 update from Quito and a more 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).
Summarized and Specific Routes: Longest-bit Match (more later)
172.16.10.0/24
172.16.1.0/24 172.16.5.0/24
172.16.0.0/16 172.16.5.0/24Summarized Update Specific Route Update
Merida
Quito Cartago
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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)
• 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
• 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…
10.0.0.0/8
10.0.0.0/16
10 Host Host Host
10 Subnet Host Host
1st octet 2nd octet 3rd octet 4th octet
10.0.0.0/16 10 0 Host Host
10.1.0.0/16 10 1 Host Host
10.2.0.0/16 10 2 Host Host
10.n.0.0/16 10 … Host Host
10.255.0.0/16 10 255 Host Host
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VLSM – Simple Example
• Note: 10.2.0.0/16 is now a summary of all of the 10.2.0.0/24 subnets.
• Summarization coming soon!
10.2.0.0/16 10 2 Host Host
Network Subnet HostHost
10.2.0.0/24 10 2 Subnet Host
10.2.0.0/24 10 2 0 Host
10.2.1.0/24 10 2 1 Host
10.2.n.0/24 10 2 … Host
10.2.255.0/24 10 2 255 Host
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VLSM – Simple Example
10.0.0.0/8 “subnetted using /16”
Subnet 1st host Last host Broadcast10.0.0.0/16 10.0.0.1 10.0.255.254 10.0.255.25510.1.0.0/16 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 10.3.0.1 10.3.255.254 10.0.255.255 Etc.10.255.0.0/16 10.255.0.1 10.255.255.254 10.255.255.255
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VLSM – Simple Example
• 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)
Subnets10.0.0.0/16 10.1.0.0/1610.2.0.0/16
10.2.0.0/24 10.2.1.0/2410.2.2.0/24 Etc.10.2.255.0/24
10.3.0.0/16 Etc.10.255.0.0/16
10.1.0.0/16
An example of VLSM, NOT of good network design.
10.3.0.0/16
10.4.0.0/16 10.5.0.0/16
10.6.0.0/16
10.7.0.0/1610.2.0.0/24
10.2.3.0/24 10.2.4.0/2410.2.5.0/24
10.2.8.0/2410.8.0.0/16
10.2.6.0/24
10.2.1.0/24
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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
• 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.
207.21.24.192/27 subnet, subnetted into eight /30 (255.255.255.252) subnets
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207.21.24.192/27 207.21.24. 11000000
/30 Hosts Bcast 2 Hosts
0 207.21.24.192/30 207.21.24. 110 00000 01 10 11 .193 & .194
1 207.21.24.196/30 207.21.24. 110 00100 01 10 11 .197 & .198
2 207.21.24.200/30 207.21.24. 110 01000 01 10 11 .201 & .202
3 207.21.24.204/30 207.21.24. 110 01100 01 10 11 .205 & .206
4 207.21.24.208/30 207.21.24. 110 10000 01 10 11 .209 & .210
5 207.21.24.212/30 207.21.24. 110 10100 01 10 11 .213 & .214
6 207.21.24.216/30 207.21.24. 110 11000 01 10 11 .217 & .218
7 207.21.24.220/30 207.21.24. 110 11100 01 10 11 .221 & .222
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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
207.21.24.32/27
207.21.24.64/27207.21.24.96/27 207.21.24.128/27
207.21.24.160/27 207.21.24.224/27 207.21.24.0/27
207.21.24.216/30
• 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
Routing Table without VLSMRouterX#show ip route 207.21.24.0/27 is subnetted, 4 subnetsC 207.21.24.192 is directly connected, Serial0 C 207.21.24.196 is directly connected, Serial1C 207.21.24.200 is directly connected, Serial2C 207.21.24.204 is directly connected, FastEthernet0
Routing Table with VLSMRouterX#show ip route 207.21.24.0/24 is variably subnetted, 4 subnets, 2 masksC 207.21.24.192 /30 is directly connected, Serial0 C 207.21.24.196 /30 is directly connected, Serial1C 207.21.24.200 /30 is directly connected, Serial2C 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.
Displays one subnet mask for all child routes. Classful mask is assumed for the parent route.
Each child routes displays its own subnet mask. Classful mask is included for the parent route.
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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.
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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.
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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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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?
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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
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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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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.
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Network Address Translation (NAT)
• 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.
2.2.2.2 TCP Source Port 1923
2.2.2.2 TCP Source Port 1924
TCP Source Port 1026
TCP Source Port 1026
Classless Routing ProtocolsRIPv2
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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.
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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
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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.
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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.
The Grim Router
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RIP version 1
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) |
+---------------------------------------------------------------+
• 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.
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RIP version 2
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) |
+---------------------------------------------------------------+
• 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.
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RIP v2 operation
• 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.
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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.
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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.
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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.
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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 per-interface basis. (coming soon)
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Authentication
• 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!
Authentication is supported by modifying what would normally be the first route entry of the RIP message
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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.
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Authentication
Rick Graziani [email protected] 69
MD5 Authentication (FYI) http://www.cisco.com/en/US/tech/tk713/tk507/technologies_tech_note09186a00800b4131.shtml
1 2
3 4
5 6
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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.
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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.
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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.
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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
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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
interface fastethernet0/1
ip address 172.25.150.193 255.255.255.240
ip rip send version 1 2
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
• 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.
RIPv2
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Discontiguous subnets and classless routing
• RIP v1 always uses automatic summarization.
• The default behavior of RIP v2 is to summarize at network boundaries the same as RIP v1.
router ripversion 2no auto-summary
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Configuring authentication (EXTRA)
Router(config)#key chain RomeoRouter(config-keychain)#key 1Router(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 0/0Router(config-if)#ip rip authentication key-chain RomeoRouter(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.
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Show commands
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show ip rip database
Router# show ip rip database172.19.0.0/16 auto-summary172.19.64.0/24 directly connected, Ethernet0172.19.65.0/24[1] via 172.19.70.36, 00:00:17, Serial1[2] via 172.19.67.38, 00:00:25, Serial0172.19.67.0/24 directly connected, Serial0172.19.67.38/32 directly connected, Serial0172.19.70.0/24 directly connected, Serial1172.19.86.0/24[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
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Show commands
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Debug commands
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RIPv2 Example
Scenario:
• Discontiguous subnets
• VLSM
• CIDR
• Supernet to 207.0.0.0/8
e0
ISP
SantaCruz2SantaCruz1
192.168.4.20/30
172.30.1.0/24
Internet
s0
s0 s0
s1
172.30.100.0/24
e0
192.168.4.24/30
.21
.22
.25
.26
10.0.0.0/8
e0.1
.1.1
Lo0Lo0
172.30.110.0/24172.30.2.0/24 .1
.1
.1
static route to207.0.0.0/8
207.0.0.0/16207.1.0.0/16207.2.0.0/16207.3.0.0/16
etc.
` 172.30.200.16/28
172.30.200.32/28
Lo1
Lo2
With the default auto-summary on ISP, it will load balance for all packets destined for 172.30.0.0/16
Rick Graziani [email protected]
SantaCruz1
router rip
network 172.30.0.0
network 192.168.4.0
version 2
no auto-summary
SantaCruz2
router rip
network 172.30.0.0
network 192.168.4.0
version 2
no auto-summary
ISP
router rip
redistribute static
network 10.0.0.0
network 192.168.4.0
version 2
no auto-summary
ip route 207.0.0.0 255.0.0.0 null0
e0
ISP
SantaCruz2SantaCruz1
192.168.4.20/30
172.30.1.0/24
Internet
s0
s0 s0
s1
172.30.100.0/24
e0
192.168.4.24/30
.21
.22
.25
.26
10.0.0.0/8
e0.1
.1.1
Lo0Lo0
172.30.110.0/24172.30.2.0/24 .1
.1
.1
static route to207.0.0.0/8
207.0.0.0/16207.1.0.0/16207.2.0.0/16207.3.0.0/16
etc.
` 172.30.200.16/28
172.30.200.32/28
Lo1
Lo2
RIPv2 Example
Rick Graziani [email protected]
e0
ISP
SantaCruz2SantaCruz1
192.168.4.20/30
172.30.1.0/24
Internet
s0
s0 s0
s1
172.30.100.0/24
e0
192.168.4.24/30
.21
.22
.25
.26
10.0.0.0/8
e0.1
.1.1
Lo0Lo0
172.30.110.0/24172.30.2.0/24 .1
.1
.1
static route to207.0.0.0/8
207.0.0.0/16207.1.0.0/16207.2.0.0/16207.3.0.0/16
etc.
` 172.30.200.16/28
172.30.200.32/28
Lo1
Lo2
SantaCruz2#show ip route
172.30.0.0/16 is variably subnetted, 6 subnets, 2 masks
C 172.30.200.32/28 is directly connected, Loopback2
C 172.30.200.16/28 is directly connected, Loopback1
R 172.30.2.0/24 [120/2] via 192.168.4.21, 00:00:21, Serial0
R 172.30.1.0/24 [120/2] via 192.168.4.21, 00:00:21, Serial0
C 172.30.100.0/24 is directly connected, Ethernet0
C 172.30.110.0/24 is directly connected, Loopback0
192.168.4.0/30 is subnetted, 2 subnets
R 192.168.4.24 [120/1] via 192.168.4.21, 00:00:21, Serial0
C 192.168.4.20 is directly connected, Serial0
R 10.0.0.0/8 [120/1] via 192.168.4.21, 00:00:21, Serial0
R 207.0.0.0/8 [120/1] via 192.168.4.21, 00:00:21, Serial0
Examining a Routing Table
Supernet, classless routing protcols will route supernets (CIDR)
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RIPv2: Sending and Receiving Updates
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
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
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>
ISP(config)# line console 0
ISP(config-line)# logging synchronous
multicast
Includes mask
Rick Graziani [email protected]
Adding a default Routes to RIPv2
e0
ISP
SantaCruz2SantaCruz1
192.168.4.20/30
172.30.1.0/24
Internet
s0
s0 s0
s1
172.30.100.0/24
e0
192.168.4.24/30
.21
.22
.25
.26
10.0.0.0/8
e0.1
.1.1
Lo0Lo0
172.30.110.0/24172.30.2.0/24 .1
.1
.1
static route to207.0.0.0/8
207.0.0.0/16207.1.0.0/16207.2.0.0/16207.3.0.0/16
etc.
` 172.30.200.16/28
172.30.200.32/28
Lo1
Lo2
ISP
router rip
redistribute static
network 10.0.0.0
network 192.168.4.0
version 2
no auto-summary
default-information originate
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
Rick Graziani [email protected]
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_configuration_guide_chapter09186a00800d97f7.html
Rick Graziani [email protected] 87
RIPv2 Summary
Ch. 1 – Introduction to Classless Routing
CCNA 3 version 3.0
Rick Graziani
Cabrillo College