Download CCNA 3 Module 3 Single-Area OSPF

CCNP 1 v3.0 Module 8
Route Optimization
© 2003, Cisco Systems, Inc. All rights reserved.
1
Route Optimization
You can control when a router
exchanges routing updates and what
those updates contain.
1. routing update control
2. policy-based routing
3. route redistribution
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2
A route optimization example
Send and Receive
RIP Updates
RTA(config)#router rip
RTA(config-router)#network 10.0.0.0
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3
A route optimization example
Include 10.0.0.0
subnets in updates
10.1.1.0 /24
10.3.3.0 /24
10.4.4.0 /24
10.2.2.0 /24
10.3.3.0 /24
10.4.4.0 /24
10.1.1.0 /24
10.2.2.0 /24
10.4.4.0 /24
RTA(config)#router rip
RTA(config-router)#network 10.0.0.0
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4
A route optimization example
Send and Receive
RIP Updates
RTA(config)#router rip
RTA(config-router)#network 10.0.0.0
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5
Passive Interfaces
Passive Interfaces receive,
but don’t send updates
RTA(config)#router rip
RTA(config-router)#network 10.0.0.0
RTA(config-router)#passive-interface e0
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6
Passive Interfaces and DDR
• You can use the passive-interface command
on WAN interfaces to prevent routers from
sending updates to link partners.
• There may be several reasons to squelch
updates on the WAN.
– If connected by a dial-on-demand ISDN link regular
RIP updates will keep the link up constantly, and
increase the bill from the provider.
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7
Passive Interfaces and DDR
RTA(config)#router rip
RTA(config-router)#network 10.0.0.0
RTA(config-router)#passive-interface bri0
RTA(config-router)#redistribute static
RTA(config-router)#exit
RTA(config)#ip route 172.16.1.0 255.255.255.0 bri0
...
RTX(config)#ip route 0.0.0.0 0.0.0.0 Bri0
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8
Passive Interfaces
The ‘passive-interface’ command works
differently with the different IP routing
protocols that support it.
–
OSPF: the network address of the passive interface
appears as a stub network in the OSPF domain. OSPF
routing information is neither sent nor received via a
passive interface.
–
EIGRP: the router stops sending hello packets on
passive interfaces. When this happens, the EIGRP
router can’t form neighbor adjacencies on the interface
or send and receive routing updates.
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9
Route Filters
•
Configuring an interface as passive
prevents it from sending updates
entirely, but there are times when you
need to suppress only certain routes in
the update from being sent or received.
1. Use the ‘distribute-list’ command
2. Use route-maps
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10
Route Filters
By referencing an access-list, the
‘distribute-list’ creates a route filter
-- a set of rules that precisely controls
what routes a router will send or receive
in a routing update.
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11
Route Filters
Route filters may be needed to enforce a routing
policy that’s based on some external factor such
as:
– link expense
– administrative jurisdiction
– security concerns
– overhead reduction—prevents access routers from
receiving the complete (and possibly immense) core
routing table
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12
Route Filters
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13
Route Filters
When applied to inbound updates, the
syntax for configuring a route filter is as
follows:
Router(config-router)#distribute-list
access-list-number in [interface-name]
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14
Route Filters
When applied to outbound updates, the
syntax can be more complicated:
Router(config-router)#distribute-list accesslist-number out [interface-name | routingprocess | as-number]
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15
Outbound Route Filters (global)
By not specifying an interface
the distribute list is applied
to all interfaces that would
send a routing update.
RTA(config)#router rip
RTA(config-router)#network 10.0.0.0
RTA(config-router)#distribute-list 24 out
RTA(config-router)#exit
RTA(config)#access-list 24 deny 10.1.1.0 0.0.0.255
RTA(config)#access-list 24 permit any
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16
Outbound Route Filters (interface)
This time, since an interface was
specified, the distribute list only
applies to routing updates that
would exit that interface.
RTA(config)#router rip
RTA(config-router)#network 10.0.0.0
RTA(config-router)#distribute-list 24 out interface s2
RTA(config-router)#exit
RTA(config)#access-list 24 deny 10.1.1.0 0.0.0.255
RTA(config)#access-list 24 permit any
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17
Inbound Route Filters (global)
This example is from RTZ’s
perspective.
That is why the distribute list
is being applied inbound.
RTZ(config)#router rip
RTZ(config-router)#network 10.0.0.0
RTZ(config-router)#distribute-list 16 in
RTZ(config-router)#exit
RTZ(config)#access-list 16 deny 10.1.1.0 0.0.0.255
RTZ(config)#access-list 16 permit any
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18
Inbound Route Filters (interface)
This example is also from RTZ’s
perspective.
That is why the distribute list
is being applied inbound.
S0
RTZ(config)#router rip
RTZ(config-router)#network 10.0.0.0
RTZ(config-router)#distribute-list 16 in interface s0
RTZ(config-router)#exit
RTZ(config)#access-list 16 deny 10.1.1.0 0.0.0.255
RTZ(config)#access-list 16 permit any
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19
Route Filters
For each routing protocol, you can have
an inbound and outbound global and
interface route filter:
RTZ(config)#router rip
RTZ(config-router)#distribute-list 1 in
RTZ(config-router)#distribute-list 2 out
RTZ(config-router)#distribute-list 3 in e0
RTZ(config-router)#distribute-list 4 out e0
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20
Route Filters
Use show ip protocols to display route
filters:
RTZ#show ip protocols
Routing Protocol is "rip"
Sending updates every 30 seconds, next due in 25 seconds
Invalid after 180 seconds, hold down 180, flushed after 240
Outgoing update filter list for all interfaces is 2
Ethernet0 filtered by 4
Incoming update filter list for all interfaces is 1
Ethernet0 filtered by 3
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21
“Passive” EIGRP interfaces
• A passive interface can’t send EIGRP
hellos, which thus prevents adjacency
relationships with link partners.
• An administrator can create a “psuedo”
passive EIGRP interface by using a route
filter that suppresses all routes from the
EIGRP routing update.
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22
“Passive” EIGRP interfaces
RTA(config)#router eigrp 364
RTA(config-router)#network 10.0.0.0
RTA(config-router)#distribute-list 5 out interface s0
RTA(config-router)#exit
RTA(config)#access-list 5 deny any
Denies all routing updates
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23
Administrative Distance
• A routing protocol’s administrative distance rates
its trustworthiness as a source of routing
information.
– Administrative distance is an integer from 0 to 255.
The lowest administrative distance has the highest
trust rating.
– An administrative distance of 255 means the routing
information source cannot be trusted at all and should
be ignored.
– An administrative distance of zero is reserved for
connected interfaces, and will always be preferred.
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24
Administrative Distance
• Specifying administrative distance values
enables the Cisco IOS software to discriminate
between sources of routing information.
• The software always picks the route whose
routing protocol has the lowest administrative
distance.
• Although we can’t easily compare apples with
oranges, we can, for example, instruct the router
to always choose oranges over apples.
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25
Administrative Distance
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26
Administrative Distance
• When using multiple IP routing protocols
on a router, the default distances almost
always suffice.
• However, some circumstances call for
changing the administrative distance
values on a router.
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27
Changing Administrative Distance
• If, for example, a router is running both
IGRP and OSPF, it may receive routes to
the same network from both protocols.
The default administrative distances favor
IGRP routes over OSPF routes:
I
10.0.0.0
[100/10576] via 192.168.0.1, Serial0
0
10.0.0.0
[110/192] via 172.17.0.1, Serial1
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28
Changing Administrative Distance
• But since IGRP doesn’t support CIDR, you may
want the router to use the OSPF route instead. In
this case, you can configure the local router to
apply a custom administrative distance to all
OSPF routes:
RTZ(config)#router ospf 1
RTZ(config-router)#distance 95
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29
Changing Administrative Distance
• With the ‘distance 95’ command, RTZ
compares the IGRP and OSPF routes and
comes up with a different result:
I
10.0.0.0
[100/10576] via 192.168.0.1, Serial0
0
10.0.0.0
[ 95/192] via 172.17.0.1, Serial1
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30
Changing Administrative Distance
• You can also apply the ‘distance’
command with optional arguments to
make changes to selected routes based
on where they originate.
• The expanded syntax of the ‘distance’
command is as follows:
Router(config-router)#distance weight [source-ip-address source-mask
(access-list-number | name)]
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31
Changing Administrative Distance
• Using the optional arguments, we can
configure a router to apply an
administrative distance of 105 to all RIP
routes received from 10.4.0.2.
RTZ(config)#router rip
RTZ(config-router)#distance 105 10.4.0.2 255.255.255.0
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32
Changing Administrative Distance
• Or, we can configure a router to apply an
administrative distance of 97 to specific
RIP routes received from 10.3.0.1.
RTZ(config)#router rip
RTZ(config-router)#distance 97 10.3.0.1 255.255.255.0 2
RTZ(config-router)#exit
RTZ(config)#access-list 2 permit 192.168.3.0 0.0.0.255
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33
Changing Administrative Distance
The result from both previous examples:
RTZ#show ip route
R
192.168.5.0/24 [105/1] via 10.4.0.2, 00:00:02, Serial1
10.0.0.0/16 is subnetted, 5 subnets
R
10.2.0.0 [120/1] via 10.3.0.1, 00:00:02, Serial0
C
10.3.0.0 is directly connected, Serial0
R
10.1.0.0 [120/2] via 10.3.0.1, 00:00:02, Serial0
C
10.4.0.0 is directly connected, Serial1
R
192.168.1.0/24 [120/3] via 10.3.0.1, 00:00:02, Serial0
R
192.168.2.0/24 [120/2] via 10.3.0.1, 00:00:02, Serial0
R
192.168.3.0/24 [97/1] via 10.3.0.1, 00:00:02, Serial0
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34
Policy Routing
• You can use the ‘ip route’ command to
dictate which path a router will select to a
given destination.
• However, through policy routing, you can
manually program a router to choose a
route based not only on destination, but
on source as well.
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35
Policy Routing
• Human factors such as monetary expense,
organizational jurisdiction, or security
issues can lead administrators to
establish policies, or rules that routed
traffic should follow.
• Left to their default behavior, routing
protocols may arrive at path decisions that
conflict with these policies.
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36
Policy Routing
• Administrators use policy routing to override
dynamic routing and take precise control of how
their routers handle certain traffic.
• Although policy routing can be used to control
traffic within an AS, it is typically used to control
routing between autonomous systems (ASs).
• Policy routing is used extensively with exterior
gateway protocols (EGPs), such as BGP.
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37
Policy Routing – Route Maps
The ‘route-map’ command is used to
configure policy routing, which is often a
complicated task.
A route map is defined using the following
syntax:
Router(config)# route-map map-tag [permit | deny]
[sequence-number]
Router(config-map-route)#
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38
Policy Routing – Route Maps
You can use the optional sequencenumber to indicate the position a new
route map is to have in the list of route
maps already configured with the same
name.
If you do not specify a sequence number,
the first route map condition will be
automatically numbered as 10.
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39
Policy Routing
Once you have entered the route-map command,
you can enter ‘set’ and ‘match’ commands in
the route-map configuration mode.
– Each route-map command has a list of match and set
commands associated with it.
– The match commands specify the match criteria—the
conditions that should be tested to determine whether
or not to take action.
– The set commands specify the set actions—the
actions to perform if the match criteria are met.
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40
Policy Routing Example
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41
Policy Routing Example
Assume for this example that the policy
we want to enforce is this:
Internet-bound traffic from 192.168.1.0 /24
is to be routed to ISP1, and Internet-bound
traffic from 172.16.1.0 /24 is to be routed
to ISP2.
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42
Policy Routing Example
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43
Policy Routing Example
RTA(config)#access-list 1 permit 192.168.1.0 0.0.0.255
RTA(config)#access-list 2 permit 172.16.1.0 0.0.0.255
RTA(config)#route-map ISP1 permit 10
RTA(config-route-map)#match ip address 1
RTA(config-route-map)#set interface s0
RTA(config)#route-map ISP2 permit 10
RTA(config-route-map)#match ip address 2
RTA(config-route-map)#set interface s1
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44
Policy Routing Example
• We have actually configured two policies with
these commands:
– The ISP1 route map will match access-list 1, and route
traffic out S0 toward ISP1.
– The ISP2 route map will match access-list 2, and route
that traffic out S1 toward ISP2.
• The final step is to apply each route map to the
appropriate interface on RTA using the ‘ip
policy route-map’ command.
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45
Policy Routing Example
RTA(config)#interface e0
RTA(config-if)#ip policy route-map ISP1
RTA(config-if)#interface e1
RTA(config-if)#ip policy route-map ISP2
With the route maps applied to the
appropriate LAN interfaces, we have
successfully implemented policy routing.
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46
Policy Routing Example
Assume for this example that our policy
allows for traffic from from 192.168.1.0 /24
to be routed to ISP2, if the link to ISP1 is
down.
And, Internet-bound traffic from 172.16.1.0
/24 can be routed via ISP1, if the link to
ISP2 is down.
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47
Policy Routing Example
RTA(config)#access-list 1 permit 192.168.1.0
0.0.0.255
RTA(config)#access-list 2 permit 172.16.1.0
0.0.0.255
RTA(config)#route-map ISP1 permit 10
RTA(config-route-map)#match ip address 1
RTA(config-route-map)#set interface s0 s1
RTA(config)#route-map ISP2 permit 10
RTA(config-route-map)#match ip address 2
RTA(config-route-map)#set interface s1 s0
© 2003, Cisco Systems, Inc. All rights reserved.
Second
interface will
be used if
first is
unavailable
48
Route Redistribution
• Cisco routers support up to 30 dynamic routing
processes.
– A router can run RIP, OSPF, IGRP, IS-IS, EIGRP, IPX RIP,
RTMP (AppleTalk), and other protocols
simultaneously.
– Most of these routing protocols allow an administrator
to configure multiple processes of the same routing
algorithm; RIP is a notable exception.
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49
Multiple Routing Protocols
RTA#show running-config
router ospf 24
network 10.2.0.0 0.0.255.255 area 0
!
router ospf 46
network 192.168.2.0 0.0.0.255 area 2
!
router igrp 53
network 172.16.0.0
network 172.17.0.0
!
router igrp 141
network 10.0.0.0
network 192.168.3.0
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50
Route Redistribution
• To support multiple routing protocols
within the same internetwork efficiently,
routing information must be shared
among the different routing protocols.
For example, routes learned from a RIP
process may need to be imported into an IGRP
process.
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51
Route Redistribution
• The process of exchanging routing
information between routing protocols is
called route redistribution.
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52
Route Redistribution
• Route redistribution can be one-way (that
is, one protocol receives the routes from
another) or two-way (that is, both
protocols receive routes from each other).
• Routers that perform redistribution are
called boundary routers because they
border two or more ASs or routing
domains.
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53
Route Redistribution
•
Why configure redistribution?
1. You want to run IGRP/EIGRP in one or more areas in
a mixed vendor environment
2. You want to support legacy UNIX systems that
support RIP only, but use a more scalable protocol
elsewhere.
3. You need a temporary fix during a prolonged upgrade
from older protocols and hardware to newer, more
scalable solutions.
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54
Route Redistribution
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55
Route Redistribution
• Because each routing process places
substantial demands on the router’s
memory and CPU resources, only
boundary routers should run more than
one routing process for the same routed
protocol, and only when absolutely
necessary.
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56
Configuring Redistribution
• In the following example:
RTB will inject routes learned from the RIP
domain into the EIGRP domain.
RIP routers will not learn about routes from the
EIGRP domain. (one-way route distribution)
RIP routers can use a default route to handle
any traffic bound for non-local destinations.
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57
Configuring Redistribution
RTB(config)#router rip
RTB(config-router)#network 172.16.0.0
RTB(config-router)#router eigrp 24
RTB(config-router)#network 172.24.0.0
RTB(config-router)#redistribute rip metric 10000 1 255
1 1500
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58
Configuring Redistribution
The metric argument sets up the values used
by EIGRP to translate the metric from RIP’s hop
count, to EIGRP’s composite metric.
When used with IGRP/EIGRP, the metric
keyword sets the bandwidth value (in kbps), the
delay (in tens of microseconds), the reliability
(out of 255), the load (out of 255), and finally, the
maximum transmission unit (MTU).
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59
Configuring Redistribution
• These five values constitute the seed
metric in our example.
• The seed metric is the initial metric value
of an imported route.
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60
Configuring Redistribution
• Once imported into the EIGRP AS, a RIP route
will begin its life as an EIGRP route with a
composite metric derived from these values—
regardless of its former RIP metric.
– So, using the configuration the previous example, RIP
routes with metrics of 2, 6, and 14 will all be
redistributed with the same EIGRP metric value.
– However, as the imported route is propagated to other
EIGRP routers, its metric values will increment
according the rules of EIGRP.
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61
Configuring Redistribution
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62
Configuring Redistribution
RTA’s Routing Table (after redistribution)
C
172.24.0.0/16 is directly connected, Serial0
C
172.25.0.0/16 is directly connected, Serial1
C
172.26.0.0/16 is directly connected, Serial2
C
172.27.0.0/16 is directly connected, Serial3
D
172.28.0.0/16 [90/2681856] via 172.20.0.2, 00:00:02, Serial1
D
172.29.0.0/16 [90/2681856] via 172.21.0.2, 00:00:02, Serial3
D EX 172.17.0.0/16 [170/2195456] via 172.24.0.1, 00:00:02, Serial0
D EX 172.18.0.0/16 [170/2195456] via 172.24.0.1, 00:00:02, Serial0
D EX 172.19.0.0/16 [170/2195456] via 172.24.0.1, 00:00:02, Serial0
D EX 172.20.0.0/16 [170/2195456] via 172.24.0.1, 00:00:02, Serial0
D EX 172.21.0.0/16 [170/2195456] via 172.24.0.1, 00:00:02, Serial0
© 2003, Cisco Systems, Inc. All rights reserved.
63
Configuring Redistribution
RTB’s Routing Table
C
172.16.0.0/16 is directly connected, Serial0
C
172.24.0.0/16 is directly connected, Serial1
R
172.17.0.0/16 [120/1] via 172.16.0.2, 00:00:02, Serial0
R
172.18.0.0/16 [120/1] via 172.16.0.2, 00:00:02, Serial0
R
172.19.0.0/16 [120/1] via 172.16.0.2, 00:00:02, Serial0
R
172.20.0.0/16 [120/2] via 172.16.0.2, 00:00:02, Serial0
R
172.21.0.0/16 [120/2] via 172.16.0.2, 00:00:02, Serial0
D
172.25.0.0/16 [90/2681856] via 172.24.0.2, 00:00:02, Serial1
D
172.26.0.0/16 [90/2681856] via 172.24.0.2, 00:00:02, Serial1
D
172.37.0.0/16 [90/2681856] via 172.24.0.2, 00:00:02, Serial1
D
172.28.0.0/16 [90/3193856] via 172.24.0.2, 00:00:02, Serial1
D
172.29.0.0/16 [90/3193856] via 172.24.0.2, 00:00:02, Serial1
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64
Configuring Redistribution
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65
Configuring Redistribution
RTC’s Routing Table (after redistribution)
C
172.16.0.0/16 is directly connected, Serial0
C
172.17.0.0/16 is directly connected, Serial1
C
172.18.0.0/16 is directly connected, Serial2
C
172.19.0.0/16 is directly connected, Serial3
R
172.20.0.0/16 [120/1] via 172.17.0.2, 00:00:02, Serial1
R
172.21.0.0/16 [120/1] via 172.19.0.2, 00:00:02, Serial3
Since the table is not complete, we may need to add a
default route:
RTC(config)#ip route 0.0.0.0 0.0.0.0 172.16.0.1
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66
Configuring Redistribution
Two-way redistribution
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67
Configuring Redistribution
RTB(config-router)#router eigrp 24
RTB(config-router)#network 172.24.0.0
RTB(config-router)#redistribute rip metric 10000 1 255 1 1500
RTB(config-router)#router rip
RTB(config-router)#network 172.16.0.0
RTB(config-router)#redistribute eigrp 24 metric 2
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68
Configuring Redistribution
• Notice that the syntax of the metric keyword
varies depending on the routing protocol it is
used with.
• For RIP, OSPF, and the metric option is
followed by a single number that represents the
metric value (hop count, cost, etc.).
• For IGRP and EIGRP, the metric option is
followed by five values that represent
bandwidth, delay, reliability, load and MTU.
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69
OSPF WARNING
• Whenever there is a major net that is subnetted,
you need to use the keyword ‘subnets’ to
redistribute protocols into OSPF.
• Without this keyword, OSPF only redistributes
major nets that aren’t subnetted.
• For example, to inject EIGRP routes, including
subnets, into an OSPF area, use the command:
redistribute eigrp 24 metric 100 subnets
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70
A complex example
RTB(config-router)#router eigrp 24
RTB(config-router)#network 172.24.0.0
RTB(config-router)#redistribute rip
RTB(config-router)#redistribute connected
RTB(config-router)#redistribute static
RTB(config-router)#default-metric 10000 100 255 1 1500
RTB(config-router)#router rip
RTB(config-router)#network 172.16.0.0
RTB(config-router)#redistribute eigrp 24
RTB(config-router)#redistribute connected
RTB(config-router)#redistribute static
RTB(config-router)#default-metric 2
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Default-metric
• We can simplify our redistribution configuration
by using the ‘default-metric’ command
instead of including the same seed metric with
each redistribute statement.
• Whenever the redistribute command is used
and the metric is not specified, the router will use
the default metric value as the seed metric.
© 2003, Cisco Systems, Inc. All rights reserved.
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Redistribution Example
• Phase 1: configuring a RIP network
• Phase 2: adding OSPF to the core of a RIP
network
• Phase 3: adding OSPF areas
© 2003, Cisco Systems, Inc. All rights reserved.
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Phase 1: Configuring a RIP Network
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Phase 2: Adding OSPF to the Core of a RIP
Network
© 2003, Cisco Systems, Inc. All rights reserved.
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Phase 3: Adding OSPF Areas
© 2003, Cisco Systems, Inc. All rights reserved.
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Summary
• Key IOS Route Optimization Features
Routing update control
Policy-based routing
Route redistribution
© 2003, Cisco Systems, Inc. All rights reserved.
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