Ch. 1 – Introduction to
Classless Routing
CCNA 3 version 3.0
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
Note
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Much of the information in this module is in addition to the
online curriculum.
The additional information was included to 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
IPv4 Address Classes
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.
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.
IP addressing crisis
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Address Depletion
Internet Routing Table Explosion
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.
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
But internal routers think all
these addresses are on different
networks, called subnetworks
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
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 ...
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
52
255
Host
Subnets
255
Subnets
28 - 1
Cannot use last
subnet as it
contains broadcast
address
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.
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
Need a Subnet Review?
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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)
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.
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)
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.
Active BGP entries
Report last updated at Thu, 16 Jan 2003
http://bgp.potaroo.net/
CIDR (Classless Inter-Domain Routing)
• First deployed in 1994, CIDR dramatically improves IPv4’s scalability
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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.
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
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.
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
ISP
Subscribers
Network
Service
Provider
Regional
Service
Provider
Regional
Service
Provider
ISP
ISP
Subscribers
Subscribers
Regional
Service
Provider
ISP
Subscribers
ISP
Subscribers
ISP
Subscribers
Supernetting Example
• Company XYZ needs to address 400 hosts.
• Its ISP gives them two contiguous Class C addresses:
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– 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.
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.
Example from online curriculum
Number of Networks Aggregated = 2^(network bits borrowed)
Are we over summarizing here?
Summarized and Specific Routes: Longest-bit Match
(more later)
ISP
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
Sub1
Sub2
172.16.2.0/24 172.16.10.0/24
• ISP receives a summarized /16 update from Sub1 and a more specific
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/24 update from Sub2.
ISP will include both routes in the routing table.
ISP will forward all packets matching at least the first 24 bits of
172.16.5.0 to Sub2 (172/16/5/0/24), longest-bit match.
ISP will forward all other packets matching at least the first 16 bits to
Sub1 (172.16.0.0/16).
Another example from online curriculum
Route flapping
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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.
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
VLSM (Variable Length Subnet Mask)
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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!”
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
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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
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
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
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
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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 .
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.
Final Notes on VLSM
• Whenever possible it is best to group contiguous routes together so
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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.
Discontiguous subnets
• “Mixing private addresses with globally unique addresses can create
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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?
Discontiguous subnets
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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.
Discontiguous subnets
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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
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SiteB now receives 207.21.24.0/27
SiteB now receives 207.21.24.32/27
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
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.
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
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.
Network Address Translation (NAT)
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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.
Classless Routing Protocols
RIPv2
Classless routing protocols
• The true defining characteristic of classless routing protocols is the
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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.
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
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.
RIP version 1
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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 used
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)
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+---------------+---------------+-------------------------------+
| address family identifier (2) |
must be zero (2)
|
+-------------------------------+-------------------------------+
|
IP address (4)
|
+---------------------------------------------------------------+
|
must be zero (4)
|
+---------------------------------------------------------------+
|
must be zero (4)
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+---------------------------------------------------------------+
|
metric (4)
|
+---------------------------------------------------------------+
RIP version 2
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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 (224.0.0.9) unless the neighbor command is
used 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)
|
+---------------------------------------------------------------+
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, than 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
• Multicasting RIP v2 messages – Multicasting is a technique for
simultaneously advertising routing information to multiple RIP or RIP v2
devices.
RIP v2 message format
• All the extensions to the original protocol are carried in the unused
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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.
Authentication
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RFC 1723 describes only simple password authentication
Cisco IOS provides the option of using MD5 authentication
instead of simple password authentication.
Same limitations of RIPv2 as with RIPv1
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Slow convergence and the need of holddown timers to
reduce the possibility of routing loops.
Note: See CCNA 2 for review if needed.
Same limitations of RIPv2 as with RIPv1
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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.
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.
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
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
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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.
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
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.
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
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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.
Show commands
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
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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
Show commands
Debug commands
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
192.168.4.20/30
172.30.200.32/28
Lo2
.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
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
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
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
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>
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
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