Redistribution into EIGRP ccie bootcamp training in gurgaon india

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This section looks at the specifics of how EIGRP performs redistribution–that is, how
EIGRP takes routes from other routing sources, such as OSPF, and advertises them into
EIGRP. Before moving into the specifics, however, note that the redistribution as discussed
in this chapter does not include any filtering or summarization. In real life, engineers
often use both route filtering and route summarization at the redistribution point on
a router. For the sake of making the underlying concepts clear, this chapter focuses on the
mechanics of redistribution, without filtering, or summarization, or any other changes to
the redistributed routes. Chapter 10 then looks at the fun options for manipulating routes
at the redistribution point.
This section begins with a couple of short discussions of reference information. The first
topic summarizes the parameters of the main configuration command, the EIGRP
redistribute command, and its parameters. Next, the baseline configuration used in the
upcoming samples is listed, including all EIGRP and OSPF configuration, but no redistribution
configuration. With those details listed for reference, the rest of this section examines
the configuration of redistribution into EIGRP.
EIGRP redistribute Command Reference
First, for reference, the following lines show the generic syntax of the redistribute command
when used as a router eigrp subcommand. Note that the syntax differs slightly depending
on the routing protocol into which routes will be redistributed. Following that,
Table 9-2 lists the options on the command with a brief description.
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Table 9-2 Commonly Used OSPF Terms
Option Description
protocol The source of routing information. Includes RIP, OSPF, EIGRP, IS-IS,
BGP, connected, and static.
process-id, asnumber
If redistributing a routing protocol that uses a process ID or ASN on the
router global config command, use this parameter to refer to that process
or ASN value.
metric A keyword after which follows the four metric components (bandwidth,
delay, reliability, link load), plus the MTU associated with the route.
match If redistributing from OSPF, this keyword lets you match internal OSPF
routes, external (by type), and NSSA external routes, essentially filtering
which routes are redistributed.
tag Assigns a unitless integer value to the routes redistributed by this command—
tags which can be later matched by other routers using a routemap.
route-map Apply the logic in the referenced route-map to filter routes, set metrics,
and set route tags.
redistribute protocol [process-id | as-number] [metric bw delay reliability load
mtu ] [match {internal | nssa-external | external 1 | external 2}] [tag tagvalue]
[route-map name]
Key
Topic
Baseline Configuration for EIGRP Redistribution Examples
The best method to see the results of redistribution is to use examples, so this section explains
the sample internetwork used in the upcoming EIGRP redistribution examples.
Figure 9-6 shows the sample internetwork. In this case, the EIGRP domain on the left uses
subnets of class B network 172.30.0.0, and the OSPF domain on the right uses subnets of
class B network 172.16.0.0. Note that all OSPF subnets reside in area 0 in this example internetwork,
although that is not a requirement.
The internetwork uses a single router (RD1) to perform redistribution, just to avoid some
interesting issues that occur when multiple routers redistribute the same routes. (Chapter
10 discusses these issues in some depth.) Example 9-1 shows the configuration on RD1,
listing the IP addresses of the four active serial interfaces shown in Figure 9-6, plus the
complete but basic EIGRP and OSPF configuration—but without any redistribution configured
yet.
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RD1
EIGRP OSPF
R2
Fa0/0
27.2/23
Fa0/1
2.2/23
S0/0/1
12.2/30
Fa0/1
7.7/23
R7
Fa0/0
27.7/23
S0/0
17.2/30
S0/0/0
12.1/30
S0/1/1
17.1/30
S0/0/1
18.1/30
S0/1/0
14.1/30
R8
Fa0/1
8.8/25
Fa0/0
48.8/25
S0/0
18.2/30
R4
Fa0/0
48.4/25
Fa0/1
4.4/25
S0/0/0
14.2/30
All addresses begin 172.30 All addresses begin 172.16
Area 0
Subnet 172.30.7.0/23 Subnet 172.16.8.0/25
Subnet 172.30.2.0/23 Subnet 172.16.4.0/25
Subnet
172.30.26.0/23
Subnet
172.16.48.0/25
Figure 9-6 Sample Internetwork Used for Redistribution Examples
interface Serial0/0/0
ip address 172.30.12.1 255.255.255.252
clock rate 1536000
!
interface Serial0/0/1
ip address 172.16.18.1 255.255.255.252
clock rate 1536000
!
interface Serial0/1/0
ip address 172.16.14.1 255.255.255.252
clock rate 1536000
!
interface Serial0/1/1
ip address 172.30.17.1 255.255.255.252
clock rate 1536000
!
router eigrp 1
network 172.30.0.0
no auto-summary
Example 9-1 Configuration on Router RD1 Before Adding Redistribution Configuration
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Configuring EIGRP Redistribution with Default Metric Components
For the internetwork of Figure 9-6, a reasonable design goal would be to redistribute
EIGRP routes into OSPF, and OSPF routes into EIGRP. This section examines the case of
redistributing the routes into EIGRP from OSPF.
First, consider the EIGRP redistribute command. For those unfamiliar with the command,
it may not be obvious of the direction of redistribution. A better command name might
have been “take-routes-from,” because the first parameter after the command tells IOS
from where to get the routes.
For example, consider the configuration in Example 9-2, which was added to RD1’s existing
configuration in Example 9-1. The configuration uses only required parameters,
namely a reference to the source from which routes should be redistributed. Because the
configuration places this command in EIGRP configuration mode, the command tells IOS
to redistribute the routes into EIGRP 1, from OSPF 2 in this case.
Example 9-2 Minimal Configuration for Redistribution from OSPF into EIGRP
RD1#configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
RD1(config)#router eigrp 1
RD1(config-router)#redistribute ospf 2
RD1(config-router)#^Z
IOS does accept the configuration; unfortunately, IOS does not actually redistribute
routes from OSPF into EIGRP in this case. EIGRP does not have a default setting for the
metric components to use when redistributing into EIGRP from OSPF. To confirm these
results, examine the output in Example 9-3, which lists show command output from RD1
when configured as shown in the previous example. Note that that RD1’s EIGRP topology
table lists only routes for class B network 172.30.0.0, which all sit inside the EIGRP domain;
none of the routes from class B network 172.16.0.0, which exist inside the OSPF domain,
have been added to RD1’s EIGRP topology table.
Example 9-3 Redistribution Did Not Work on RD1
RD1#show ip eigrp topology
IP-EIGRP Topology Table for AS(1)/ID(172.30.17.1)
Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply,
r - reply Status, s - sia Status
P 172.30.17.0/30, 1 successors, FD is 2169856
via Connected, Serial0/1/1
P 172.30.26.0/23, 2 successors, FD is 2172416
via 172.30.12.2 (2172416/28160), Serial0/0/0
!
router ospf 2
router-id 1.1.1.1
network 172.16.0.0 0.0.255.255 area 0
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via 172.30.17.2 (2172416/28160), Serial0/1/1
P 172.30.2.0/23, 1 successors, FD is 2172416
via 172.30.12.2 (2172416/28160), Serial0/0/0
via 172.30.17.2 (2174976/30720), Serial0/1/1
P 172.30.6.0/23, 1 successors, FD is 2172416
via 172.30.17.2 (2172416/28160), Serial0/1/1
via 172.30.12.2 (2174976/30720), Serial0/0/0
P 172.30.12.0/30, 1 successors, FD is 2169856
via Connected, Serial0/0/0
To complete the configuration of redistribution into EIGRP, Router RD1 needs to set the
metric values. EIGRP can set the metrics for redistributed routes in three ways, as summarized
in Table 9-3.
Key
Topic
Note: EIGRP does have a default metric when redistributing from another EIGRP
process, in which case it takes the metric from the source of the routing information. In all
other cases, the metric must be set using one of the methods in Table 9-3.
If the metrics do not matter to the design, which is likely when only a single redistribution
point exists as in Figure 9-6, either of the first two methods listed in Table 9-3 is reasonable.
The first method, using the default-metric command in EIGRP configuration mode,
sets the metric for all routes redistributed into EIGRP, unless set by one of the other methods.
Alternatively, the second method, which uses additional parameters on the
redistribute command, sets the metric for all routes redistributed because of that one
redistribute command. Finally, if the redistribute command also refers to a route map, the
route map can use the set metric command to set the metric components for routes
matched by the route map clause, overriding the metric settings in the default-metric
command or with the metric keyword on the redistribute command.
Example 9-4 shows the addition of the default-metric 1000 33 255 1 1500 command to
RD1’s configuration. This command sets the bandwidth to 1000 (Kbps), the delay to 33
(tens-of-microseconds, or 330 microseconds), reliability to 255 (a value between 1–255,
Table 9-3 Methods of Setting EIGRP Metrics When Redistributing into EIGRP
Function Command
Setting the default for all redistribute commands
The default-metric bw delay reliability load
mtu EIGRP subcommand
Setting the component metrics applied to all
routes redistributed by a single redistribute
command
The metric bw delay reliability load mtu parameters
on the redistribute command
Setting different component metrics to different
routes from a single route source
Use the route-map parameter on the
redistribute command, matching routes and
setting metric components.
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255 is best), load to 1 (a value between 1–255, 1 is best), and MTU of 1500. Note that
even though EIGRP ignores the last three parameters by default when calculating integer
metrics, you still must configure these settings for the commands to be accepted.
Example 9-4 Redistributed Routes in RD1
RD1#configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
RD1(config)#router eigrp 1
RD1(config-router)#default-metric 1000 33 255 1 1500
RD1(config-router)#^Z
Because this example uses a single redistribute command for the EIGRP 1 process, you
could have used the redistribute ospf 2 metric 1000 33 255 1 1500 command and ignored
the default-metric command to achieve the same goal.
Verifying EIGRP Redistribution
As shown earlier in Figure 9-5, redistribution takes routes from the routing table and
places the correct information for those subnets into the redistributing router’s topology
table. The redistributing router then advertises the routes from its topology table as it
would for other routes. To verify that redistribution works, Example 9-5 shows the proof
that RD1 indeed created entries in its EIGRP topology table for the five subnets in the
OSPF domain.
Example 9-5 Verifying RD1 Added EIGRP Topology Data for Five OSPF Subnets
RD1#show ip eigrp topology
IP-EIGRP Topology Table for AS(1)/ID(172.30.17.1)
Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply,
r - reply Status, s - sia Status
! Note – all lines for class B network 172.30.0.0 have been omitted for brevity
P 172.16.48.0/25, 1 successors, FD is 2568448
via Redistributed (2568448/0)
P 172.16.18.0/30, 1 successors, FD is 2568448
via Redistributed (2568448/0)
P 172.16.14.0/30, 1 successors, FD is 2568448
via Redistributed (2568448/0)
P 172.16.8.0/25, 1 successors, FD is 2568448
via Redistributed (2568448/0)
P 172.16.4.0/25, 1 successors, FD is 2568448
via Redistributed (2568448/0)
RD1#show ip eigrp topology 172.16.48.0/25
IP-EIGRP (AS 1): Topology entry for 172.16.48.0/25
State is Passive, Query origin flag is 1, 1 Successor(s), FD is 2568448
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Routing Descriptor Blocks:
172.16.18.2, from Redistributed, Send flag is 0x0
Composite metric is (2568448/0), Route is External
Vector metric:
Minimum bandwidth is 1000 Kbit
Total delay is 330 microseconds
Reliability is 255/255
Load is 1/255
Minimum MTU is 1500
Hop count is 0
External data:
Originating router is 172.30.17.1 (this system)
AS number of route is 2
External protocol is OSPF, external metric is 65
Administrator tag is 0 (0x00000000)
The show command output lists several interesting facts, including
■ On Router RD1, which performed the redistribution, the EIGRP topology table lists
the outgoing interface as “via redistributed.”
■ All the redistributed routes have the same feasible distance (FD) calculation
(2568448), because all use the same component metrics per the configured defaultmetric
command.
■ RD1’s two connected subnets in the OSPF 2 domain–subnets 172.16.14.0/30 and
172.16.18.0/30–were also redistributed, even though these routes are connected
routes in RD1’s routing table.
■ The output of the show ip eigrp topology 172.16.48.0/25 command confirms the
component metrics match the values configured on the default-metric command.
■ The bottom of the output of the show ip eigrp topology 172.16.48.0/25 command
lists information about the external source of the route, including the routing source
(OSPF) and that source’s metric for the route (65). It also lists the phrase “(this system),”
meaning that the router on which the command was issued (RD1 in this case)
redistributed the route.
The third item in the list–the fact that RD1 redistributed some connected routes–bears
further consideration. The redistribute ospf 2 command tells EIGRP to redistribute routes
learned by the OSPF 2 process. However, it also tells the router to redistribute connected
routes for interfaces on which process OSPF 2 has been enabled. Back in Example 9-1, the
configuration on RD1 lists a network 172.16.0.0 0.0.255.255 area 0 command, enabling
OSPF 2 on RD1’s S0/0/1 and S0/1/0 interfaces. As such, the redistribution process also redistributed
those routes.
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Stated more generally, when the redistribute command refers to another IGP as the routing
source, it tells the router to redistribute the following:
■ All routes in the routing table learned by that routing protocol
■ All connected routes of interfaces on which that routing protocol is enabled
Although Example 9-5 shows the evidence that Router RD1 added the topology data to its
EIGRP topology database, it did not show any routes. Example 9-6 shows the IP routing
tables on both RD1 and Router R2, a router internal to the EIGRP domain. R2’s routes forward
the packets toward the redistributing router, which in turn has routes from the OSPF
domain with which to forward the packet to the destination subnet.
Example 9-6 Verification of IP Routes on RD1 and R2
! First, on RD1
RD1#show ip route 172.16.0.0
Routing entry for 172.16.0.0/16, 5 known subnets
Attached (2 connections)
Variably subnetted with 2 masks
Redistributing via eigrp 1
O 172.16.48.0/25 [110/65] via 172.16.18.2, 00:36:25, Serial0/0/1
[110/65] via 172.16.14.2, 00:36:25, Serial0/1/0
C 172.16.18.0/30 is directly connected, Serial0/0/1
C 172.16.14.0/30 is directly connected, Serial0/1/0
O 172.16.8.0/25 [110/65] via 172.16.18.2, 00:36:25, Serial0/0/1
O 172.16.4.0/25 [110/65] via 172.16.14.2, 00:36:25, Serial0/1/0
! Next, on Router R2
R2#show ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route
Gateway of last resort is not set
172.16.0.0/16 is variably subnetted, 5 subnets, 2 masks
D EX 172.16.48.0/25 [170/3080448] via 172.30.12.1, 00:25:15, Serial0/0/1
D EX 172.16.18.0/30 [170/3080448] via 172.30.12.1, 00:25:15, Serial0/0/1
D EX 172.16.14.0/30 [170/3080448] via 172.30.12.1, 00:25:15, Serial0/0/1
D EX 172.16.8.0/25 [170/3080448] via 172.30.12.1, 00:25:15, Serial0/0/1
D EX 172.16.4.0/25 [170/3080448] via 172.30.12.1, 00:25:15, Serial0/0/1
172.30.0.0/16 is variably subnetted, 5 subnets, 2 masks
D 172.30.17.0/30 [90/2172416] via 172.30.27.7, 00:25:15, FastEthernet0/0
Key
Topic
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C 172.30.26.0/23 is directly connected, FastEthernet0/0
C 172.30.2.0/23 is directly connected, FastEthernet0/1
D 172.30.6.0/23 [90/30720] via 172.30.27.7, 00:25:15, FastEthernet0/0
C 172.30.12.0/30 is directly connected, Serial0/0/1
Beginning with the output for R2, in the second half of the example, R2 knows routes for
all five subnets in class B network 172.16.0.0, listing all as external EIGRP routes. The
routes all use R2’s link connected to RD1. Also, note that the administrative distance (AD)
is set to 170, rather than the usual 90 for EIGRP routes. EIGRP defaults to use AD 90 for
internal routes and AD 170 for external routes. Chapter 10 shows cases in which this default
helps prevent routing loops when multiple redistribution points exist.
RD1 has routes for all routes in the OSPF domain as well, but as either connected or
OSPF-learned routes.