CIS 185 CCNP ROUTE Ch. 4 Manipulating Routing Updates Rick Graziani Cabrillo College...

CIS 185 CCNP ROUTECh. 4 Manipulating Routing Updates

Rick Graziani

Cabrillo College

[email protected]

Last Updated: Fall 2011

2

Materials

Book: Implementing Cisco IP Routing

(ROUTE) Foundation Learning Guide: Foundation learning for the ROUTE 642-902 Exam

By Diane Teare Book

ISBN-10: 1-58705-882-0 ISBN-13: 978-1-58705-882-0

eBook ISBN-10: 0-13-255033-4 ISBN-13: 978-0-13-255033-8

Network Performance Issues

Common network performance issues include the following: Excessive routing updates:

Decrease network performance CPU utilization spikes The size of the routing update The frequency of the updates

The presence of any route maps or filters: Incorrectly configured route maps or filters can cause too much or the

wrong data to be sent. The number of routing protocols running in the same AS:

Processing the updates. Routes may also be redistributed between protocols, which can add to

the number of updates that a specific protocol must process.3

Controlling routing updates involves a variety of solutions, including the: Design changes:

Limiting the number of routing protocols used Choice of routing protocol Network design (areas, stub networks, etc.)

Using passive interfaces Route filtering using:

Access lists Route maps Distribute lists Prefix lists 4

Route Redistribution

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Routing protocols were not designed to interoperate with one another using different: Metrics Reactions to topology changes Timers Processes

Routers using different routing protocols can exchange routing information. Route redistribution is the capability of boundary routers connecting

different routing domains to exchange and advertise routing information between those routing domains. 6

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One-way route redistribution - one protocol receives the routes from another)

Two-way route redistribution - both protocols receive routes from each other.

Boundary routers:Boundary routers: Routers that perform redistribution Borders two or more ASs or routing domains. Note: The term boundary routerboundary router is also sometimes used to

describe a router running a classful routing protocol (like RIP) that has interfaces in more than one classful network.

Redistribution is always performed outbound The router doing redistribution does not change its routing table.

Router A (boundary router) participates in both: OSPF EIGRP

Two-way redistribution does not affect the routing table on Router A However:

Router C will learn about redistributed EIGRP networks (via OSPF) Router B will learn about redistributed OSPF networks (via EIGRP)

Only networks in Router A’s routing table can be redistributed.8

Why configure redistribution? Company mergers and different IGPs are used Company has different divisions with the network under separate

control for business or political reasons Company has connections between business partners To allow multivendor interoperability (OSPF on non-Cisco, EIGRP

on Cisco, for instance)


Incompatible routing information Each routing protocol uses different metrics.

EIGRP uses slowest BW and cumulative Delay OSPF use cumulative BW

Metrics cannot be translated exactly into a different protocol Path selection may not be optimal.

Potential Routing loops – Depending on how redistribution is used, routers can send routing information received from one AS back into the AS. (Route Feedback)

Inconsistent convergence times: Different routing protocols converge at different rates.

These potential trouble spots can be avoided with careful planning and implementation.

Configuring Redistribution

My best path to 192.100.10.0 is this way.

My best path to 192.100.10.0 is this way.

192.168.10.0

EIGRP

OSPFRouting Loop!

R3

R2

R1

R2 and R3 are running both OSPF and EIGRP

Selecting the Best Route in a Redistribution Environment Cisco routers use the

following two parameters to select the best path:

Administrative distance: Trustworthiness of the

routing source Modifying the

administrative distance to influence the route-selection process is discussed later

When using route redistribution, you might occasionally need to modify a protocol’s administrative distance so that it is preferred and to prevent routing loops. (later)

Routing metric: Best path

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Concepts of Redistribution

Multiple Routing Processes

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 eigrp 53 network 172.16.0.0 network 172.17.0.0!router eigrp 141 network 10.0.0.0 network 192.168.3.0

Not usually recommended

Not usually recommended

Cisco routers support up to 30 dynamic routing processes on a single router.

Most routing protocols allow an administrator to configure multiple processes of the same routing algorithm

RIP and BGP are notable exceptions.

Route redistribution - The process of exchanging routing information between routing protocols. EIGRP routing domain learns about networks in OSPF routing

domain. OSPF routing domain learns about networks in EIGRP routing

domain. Done by a boundary router which participates in both routing protocols.


Redistribution Concepts and Processes

The redistribution command (“take routes from”) Configured on the boundary router. Participates in both routing protocols. Independent of any one protocol Various complexities depending on the routing protocols and

the options.

Router(config-router)# redistribute from-protocol [process-id]

Note: Other parameters may be required and will be discussed.

I run both EIGRP and OSPF.

Redistributing from OSPF into EIGRP

Our Topology

Boundary router R2-E-O is running: EIGRP for 172.30.0.0 subnets and 172.31.0.0 network OSPF for 172.16.0.0 subnets and 172.17.0.0 network 192.168.1.0 or 10.0.0.0 not currently included in either routing

protocol (more on this later)

EIGRP 1 OSPF 1

Redistribution into EIGRP

The syntax differs slightly depending on the routing protocol into which routes will be redistributed.

redistribute protocol [process-id | as-number] [metric bw delay reliability load mtu ] [match {internal | nssa-external | external 1 | external 2}] [tag tag-value] [route-map name]

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protocol - The source of routing information. Includes RIP, OSPF, EIGRP, IS-IS, BGP, connected, and static.

process-id, as-number - 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 route, which can be later matched by other routers using a route-map.

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 tag-value] [route-map name]


Current configurations

R1-E

router eigrp 1

network 172.30.0.0

network 172.31.0.0

auto-summary

R2-E-O

router eigrp 1

network 172.30.0.0

auto-summary

router ospf 1

network 172.16.0.0 0.0.0.3 area 0

R3-O

router ospf 1

network 172.16.0.0 0.0.255.255 area 0

R4-O

router ospf 1

network 172.16.0.0 0.0.255.255 area 0

network 172.17.0.0 0.0.255.255 area 0


R1-E# show ip route

C 172.31.0.0/16 is directly connected, Loopback31

172.30.0.0/16 is variably subnetted, 6 subnets, 3 masks

C 172.30.2.0/24 is directly connected, FastEthernet0/1


C 172.30.0.0/30 is directly connected, Serial0/0

D 172.30.0.0/16 is a summary, 00:02:41, Null0



R1-E#

What do you expect to see?

Directly Connected and any EIGRP networks – NO OSPF networks

What networks do I know about and how did I learn about them?


R2-E-O# show ip route

O 172.17.0.0/16 [110/846] via 172.16.0.1, 00:02:32, Serial0/1


O 172.16.0.4/30 [110/845] via 172.16.0.1, 00:02:32, Serial0/1


O 172.16.1.0/24 [110/782] via 172.16.0.1, 00:02:32, Serial0/1

O 172.16.2.0/24 [110/846] via 172.16.0.1, 00:02:32, Serial0/1

D 172.31.0.0/16 [90/20640000] via 172.30.0.1, 00:03:46, Serial0/0


D 172.30.2.0/24 [90/20514560] via 172.30.0.1, 01:22:36, Serial0/0

D 172.30.3.0/24 [90/20640000] via 172.30.0.1, 01:22:36, Serial0/0


D 172.30.1.0/24 [90/20514560] via 172.30.0.1, 01:22:36, Serial0/0

D 172.30.4.0/24 [90/20640000] via 172.30.0.1, 01:22:36, Serial0/0

10.0.0.0/24 is subnetted, 1 subnets

C 10.0.0.0 is directly connected, FastEthernet0/1


R2-E-O#

What do you expect to see?EIGRP and OSPF networks What networks

do I know about and how did I learn about them?


R3-O# show ip route

O 172.17.0.0/16 [110/65] via 172.16.0.6, 00:09:06, Serial0/2





O 172.16.2.0/24 [110/65] via 172.16.0.6, 00:09:06, Serial0/2

R3-O#


Only OSPF networks – NO EIGRP networks



R4-O# show ip route




O 172.16.0.0/30 [110/128] via 172.16.0.5, 00:09:52, Serial0/0

O 172.16.1.0/24 [110/65] via 172.16.0.5, 00:09:52, Serial0/0


R4-0#


Only OSPF networks – NO EIGRP networks



No change for R1-E! No OSPF networks Let’s see what happened (or didn’t happen)…

R2-E-O(config)# router eigrp 1

R2-E-O(config-router)# redistribute ospf 1

R1-E# show ip route









R1-E#

I will redistribute my OSPF learned networks (and OSPF network command networks) into EIGRP, telling my EIGRP neighbors about these networks

Hey! I don’t see any of the networks in the OSPF domain! What happened?

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O 172.17.0.0/16 [110/846] via 172.16.0.1, 00:02:32, Serial0/1


O 172.16.0.4/30 [110/845] via 172.16.0.1, 00:02:32, Serial0/1


O 172.16.1.0/24 [110/782] via 172.16.0.1, 00:02:32, Serial0/1

O 172.16.2.0/24 [110/846] via 172.16.0.1, 00:02:32, Serial0/1

D 172.31.0.0/16 [90/20640000] via 172.30.0.1, 00:03:46, Serial0/0


D 172.30.2.0/24 [90/20514560] via 172.30.0.1, 01:22:36, Serial0/0

D 172.30.3.0/24 [90/20640000] via 172.30.0.1, 01:22:36, Serial0/0


D 172.30.1.0/24 [90/20514560] via 172.30.0.1, 01:22:36, Serial0/0

D 172.30.4.0/24 [90/20640000] via 172.30.0.1, 01:22:36, Serial0/0




R2-E-O#

Should R2’s routing table change? No

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R2-E-O# show ip eigrp top

IP-EIGRP Topology Table for AS(1)/ID(192.168.1.1)

P 172.30.2.0/24, 1 successors, FD is 20514560

via 172.30.0.1 (20514560/28160), Serial0/0


via 172.30.0.1 (20640000/128256), Serial0/0


via Connected, Serial0/0


via 172.30.0.1 (20640000/128256), Serial0/0


via 172.30.0.1 (20514560/28160), Serial0/0


via 172.30.0.1 (20640000/128256), Serial0/0

For now notice that there are no “OSPF networks” in R2’s topology table.

They are still in the routing table because R2 also runs OSPF, but this is an EIGRP command.


When redistributing into EIGRP from another routing protocol you must convert the other routing protocol’s metric (OSPF’s cost, bandwidth) into EIGRP’s metric (BW, DLY, Reliability and Load).

This metric, referred to as the seed or default metric, is defined during redistribution configuration.

Three methods: Metric parameter with redistribute command

Sets the default for all redistribute commands Default-metric command

Sets the default for all redistribute commands Route-map

Sets different metrics for routes learned from a single source

redistribute protocol [process-id | as-number] [metric bw delay reliability load mtu ]

default-metric bw delay reliability load mtu

BW/DLY BW


router eigrp 1

network 172.20.0.0

redistribute ospf 1

redistribute eigrp 2

default-metric 10000 100 255 1 1500

redistribute rip metric 50000 500 255 1 1500

EIGRP 1 EIGRP 2

OSPF 1

RIP

default-metricdefault-metric command is used where the metric parameter is not being applied in the redistribute command.

metricmetric parameter takes precedence over the default-metricdefault-metric command Note: The metric will give all redistributed networks the same starting

metric. This is known as the seed metric

50000 500 255 1

10000 100 255 1


Note: MTU is NOT one of the EIGRP metrics (never has been, never will

be) MTU is included because it is tracked through the path to find the

smallest MTU.



R2-E-O(config-router)# default-metric 1000 33 255 1 1500


R2-E-O(config-router)# redistribute ospf 1 metric 1000 33 255 1 1500

ORBW DLY RLY Load MTU

BW DLY RLY Load MTU

1000 33 255 1

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New Entries


IP-EIGRP Topology Table for AS(1)/ID(192.168.1.1)


via Redistributed (2568448/0)









All the redistributed routes have the same feasible distance (FD) calculation (2568448), because all use the same component metrics per the configured default-metric command

EIGRP topology table lists the outgoing interface as "via redistributed"

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R2-E-O# show ip eigrp top 172.16.0.0/30

IP-EIGRP (AS 1): Topology entry for 172.16.0.0/30

State is Passive, Query origin flag is 1, 1 Successor(s), FD is 2568448

Routing Descriptor Blocks:

0.0.0.0, 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 192.168.1.1 (this system)

AS number of route is 1

External protocol is OSPF, external metric is 0

Administrator tag is 0 (0x00000000)

From default-metric command

"(this system)", meaning that the router on which the command was issued (R2 in this case) redistributed the route.


R1-E# show ip route

D EX 172.17.0.0/16 [170/3080448] via 172.30.0.2, 00:01:50, Serial0/0


D EX 172.16.0.4/30 [170/3080448] via 172.30.0.2, 00:01:50, Serial0/0

D EX 172.16.0.0/30 [170/3080448] via 172.30.0.2, 00:01:50, Serial0/0

D EX 172.16.1.0/24 [170/3080448] via 172.30.0.2, 00:01:50, Serial0/0

D EX 172.16.2.0/24 [170/3080448] via 172.30.0.2, 00:01:50, Serial0/0









EX: External Route (redistributed) 170: Administrative distance (90 for EIGRP internal

routes) R1-E has the same metric (3080448) for all external

EIGRP networks (from the OSPF domain)

Great! Now I see all the networks in the OSPF domain but as EIGRP routes.

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R2 redistributed into EIGRP the routes learned via OSPF and its own directly connected network 172.16.0.0/30. But not 192.168.1.0/24 and 10.0.0.0/8 This is because 172.16.0.0/30 is an OSPF enabled interface (network

statement) Redistribute command, redistributes 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 Otherwise must be redistributed another way (connected or static) – coming





Two ways to redistribute 10.0.0.0/24 network. Redistribute Connected Add OSPF network command

Also propagates 10.0.0.0/24 throughout OSPF domain

R2-E-O(config)# router ospf 1

R2-E-O(config-router)# network 10.0.0.0 0.0.0.255 area 0




No change to routing table

What about the 10.0.0.0/24 network? How can I redistribute it into EIGRP?


10.0.0.0 is now redistributed into the EIGRP domain with the rest of the OSPF networks.

R1-E# show ip route

D EX 10.0.0.0 [170/3080448] via 172.30.0.2, 00:01:33, Serial0/0

R4-0# show ip route

O 10.0.0.0 [110/129] via 172.16.0.5, 00:04:02, Serial0/0

The 10.0.0.0 network is now included as one of my EIGRP routes.


192.168.1.0/24 is redistributed into EIGRP as a connected network. metric option is not required for this command (default 0, but beyond the scope of this

pres.) 192.168.1.0/24 is redistributed into the EIGRP domain using the default metric but

it is NOT propagated throughout OSPF domain


R2-E-O(config-router)# redistribute connected metric 1000 33 255 1 1500

R1-E# show ip route


D EX 10.0.0.0 [170/3080448] via 172.30.0.2, 00:01:57, Serial0/0

D EX 192.168.1.0/24 [170/3080448] via 172.30.0.2, 00:01:57, Serial0/0

R1-E#

What about the 192.168.1.0 network? How can I redistribute it into EIGRP?


Where we left off…

R2: Currently

router eigrp 1

network 172.30.0.0

auto-summary

redistribute ospf 1

default-metric 1000 33 255 1 1500

redistribute connected 1000 33 255 1 1500

!

router ospf 1

network 10.0.0.0 0.0.0.255 area 0

network 172.16.0.0 0.0.0.3 area 0

Redistributing from EIGRP into OSPF

Redistribution into OSPF

Several similarities and differences to redistributing into EIGRP. In this case we must convert the EIGRP metric to the Cisco OSPF

metric of Bandwidth.

BW/DLY BW

redistribute protocol [process-id | as-number] [metric {metric-value | transparent}] [metric-type type-value] [match {internal | external 1 | external 2 | nssa-external}] [tag tag-value] [route-map map-tag] [subnets]

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Metric - Defines the cost metric assigned to the route in the Type 5 (or Type 7 if NSSA) LSA. metric transparent when taking from another OSPF process, pass through the metric with the route.

metric-type {1 | 2} - Defines the external metric type of 1 (E1 routes) or 2 (E2 routes).

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 route, which can be later matched by other routers using a route-map.

route-map - Apply the logic in the referenced route-map to filter routes, set metrics, and set route tags.

Subnets - Redistribute subnets of classful networks. Without this parameter, only routes for classful networks are redistributed. (This behavior is particular to the OSPF redistribute command.)



Defaults when redistributing into OSPF: When redistributing networks from all other sources the default

metric is 20. External metric type 2 (metric does not change throughout OSPF

routing domain) Only redistributes routes of classful (Class A, B, and C) networks,

and not for subnets

BW/DLY BW=20 BW=20



Where we left off…

R2: Currently

router eigrp 1

network 172.30.0.0

auto-summary

redistribute ospf 1

default-metric 1000 33 255 1 1500

redistribute connected 1000 33 255 1 1500

!

router ospf 1

network 10.0.0.0 0.0.0.255 area 0

network 172.16.0.0 0.0.0.3 area 0



O 172.17.0.0/16 [110/846] via 172.16.0.1, 00:02:32, Serial0/1


O 172.16.0.4/30 [110/845] via 172.16.0.1, 00:02:32, Serial0/1


O 172.16.1.0/24 [110/782] via 172.16.0.1, 00:02:32, Serial0/1

O 172.16.2.0/24 [110/846] via 172.16.0.1, 00:02:32, Serial0/1

D 172.31.0.0/16 [90/20640000] via 172.30.0.1, 00:03:46, Serial0/0


D 172.30.2.0/24 [90/20514560] via 172.30.0.1, 01:22:36, Serial0/0

D 172.30.3.0/24 [90/20640000] via 172.30.0.1, 01:22:36, Serial0/0


D 172.30.1.0/24 [90/20514560] via 172.30.0.1, 01:22:36, Serial0/0

D 172.30.4.0/24 [90/20640000] via 172.30.0.1, 01:22:36, Serial0/0




R2-E-O#

What do you expect to see?EIGRP and OSPF networks What networks

do I know about and how did I learn about them?

45


No External Type 5 LSAs No EIGRP networks being redistributed into OSPF

R2-E-O# show ip ospf data

OSPF Router with ID (192.168.1.1) (Process ID 1)

Router Link States (Area 0)

Link ID ADV Router Age Seq# Checksum Link count

172.16.1.1 172.16.1.1 85 0x80000005 0x006220 5

172.30.0.6 172.30.0.6 2000 0x80000006 0x006BB4 4

192.168.1.1 192.168.1.1 1117 0x80000003 0x009742 3

R2-E-O#


By default, only classful networks will be redistributed from EIGRP into OSPF. Subnets will not be redistributed Supernets will also be redistributed (such as 173.0.0.0/8)


R2-E-O(config-router)# redistribute eigrp 1

% Only classful networks will be redistributed

R2-E-O(config-router)#


<Router Link States omitted>

Type-5 AS External Link States

Link ID ADV Router Age Seq# Checksum Tag

172.31.0.0 192.168.1.1 9 0x80000001 0x0094D4 0

R2-E-O#

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O 172.17.0.0/16 [110/846] via 172.16.0.1, 00:03:56, Serial0/1


O 172.16.0.4/30 [110/845] via 172.16.0.1, 00:03:56, Serial0/1


O 172.16.1.0/24 [110/782] via 172.16.0.1, 00:03:56, Serial0/1

O 172.16.2.0/24 [110/846] via 172.16.0.1, 00:03:56, Serial0/1

D 172.31.0.0/16 [90/20640000] via 172.30.0.1, 00:18:29, Serial0/0


D 172.30.2.0/24 [90/20514560] via 172.30.0.1, 01:37:19, Serial0/0

D 172.30.3.0/24 [90/20640000] via 172.30.0.1, 01:37:19, Serial0/0


D 172.30.1.0/24 [90/20514560] via 172.30.0.1, 01:37:19, Serial0/0

D 172.30.4.0/24 [90/20640000] via 172.30.0.1, 01:37:19, Serial0/0




Remember, routes are onlyRedistributed if they are in theRouting table


Only the class B network 172.31.0.0/16 is redistributed into OSPF

R3-O# show ip route

O 172.17.0.0/16 [110/65] via 172.16.0.6, 00:01:16, Serial0/2





O 172.16.2.0/24 [110/65] via 172.16.0.6, 00:01:16, Serial0/2

O E2 172.31.0.0/16 [110/20] via 172.16.0.2, 00:01:16, Serial0/1


O 10.0.0.0 [110/65] via 172.16.0.2, 00:01:17, Serial0/1

R3-O#

I only see the class B 172.31.0.0/16 network in the EIGRP domain.

49


External Type 5 LSA

R3-O# show ip ospf data

<Router Link States omitted>



172.31.0.0 192.168.1.1 88 0x80000001 0x0094D4 0

R3-O#


Subnets – Subnets are now included in the redistribution.


R2-E-O(config-router)# redistribute eigrp 1 subnets

No warning message “Only classful networks will be redistributed”

I will add the subnets option.

51


R2 now includes Type 5 LSAs for subnets




172.30.0.0 192.168.1.1 79 0x80000001 0x008EDE 0

172.30.1.0 192.168.1.1 79 0x80000001 0x0095D3 0

172.30.2.0 192.168.1.1 79 0x80000001 0x008ADD 0

172.30.3.0 192.168.1.1 79 0x80000001 0x007FE7 0

172.30.4.0 192.168.1.1 79 0x80000001 0x0074F1 0

172.31.0.0 192.168.1.1 220 0x80000001 0x0094D4 0

R2-E-O#

Redistribution into OSPF – E2

R3-O#show ip route

O 172.17.0.0/16 [110/65] via 172.16.0.6, 00:13:41, Serial0/2





O 172.16.2.0/24 [110/65] via 172.16.0.6, 00:13:41, Serial0/2

O E2 172.31.0.0/16 [110/20] via 172.16.0.2, 00:13:41, Serial0/1


O E2 172.30.2.0/24 [110/20] via 172.16.0.2, 00:00:12, Serial0/1

O E2 172.30.3.0/24 [110/20] via 172.16.0.2, 00:00:12, Serial0/1

O E2 172.30.0.0/30 [110/20] via 172.16.0.2, 00:00:12, Serial0/1

O E2 172.30.1.0/24 [110/20] via 172.16.0.2, 00:00:14, Serial0/1

O E2 172.30.4.0/24 [110/20] via 172.16.0.2, 00:00:14, Serial0/1


O 10.0.0.0 [110/65] via 172.16.0.2, 00:00:14, Serial0/1

External OSPF routes are E2 with a default cost of 20.

metric-type E2 - The cost of a type 2 route is always the external cost, irrespective of the interior cost to reach that route.

BW=20

Now I see all networks and subnets from the EIGRP domain.


R4-0# show ip route




O 172.16.0.0/30 [110/128] via 172.16.0.5, 00:04:02, Serial0/0

O 172.16.1.0/24 [110/65] via 172.16.0.5, 00:04:02, Serial0/0


O E2 172.31.0.0/16 [110/20] via 172.16.0.5, 00:04:02, Serial0/0


O E2 172.30.2.0/24 [110/20] via 172.16.0.5, 00:01:46, Serial0/0

O E2 172.30.3.0/24 [110/20] via 172.16.0.5, 00:01:46, Serial0/0

O E2 172.30.0.0/30 [110/20] via 172.16.0.5, 00:01:46, Serial0/0

O E2 172.30.1.0/24 [110/20] via 172.16.0.5, 00:01:46, Serial0/0

O E2 172.30.4.0/24 [110/20] via 172.16.0.5, 00:01:46, Serial0/0


O 10.0.0.0 [110/129] via 172.16.0.5, 00:04:04, Serial0/0


metric-type 2 - The cost of a type 2 route is always the external cost, irrespective of the interior cost to reach that route.

BW=20 BW=20

54


R4 now includes Type 5 LSAs for subnets

R4-0# show ip ospf data



172.30.0.0 192.168.1.1 113 0x80000001 0x008EDE 0

172.30.1.0 192.168.1.1 113 0x80000001 0x0095D3 0

172.30.2.0 192.168.1.1 113 0x80000001 0x008ADD 0

172.30.3.0 192.168.1.1 113 0x80000001 0x007FE7 0

172.30.4.0 192.168.1.1 113 0x80000001 0x0074F1 0

172.31.0.0 192.168.1.1 254 0x80000001 0x0094D4 0

R4-0#


Let’s redistribute the 192.168.1.0/24 network into OSPF as a connected network. This is okay because 192.168.1.0/24 is a Class C network. If it was a subnet then…

R2-E-O(config)#router ospf 1

R2-E-O(config-router)#redistribute connected ?

metric Metric for redistributed routes

metric-type OSPF/IS-IS exterior metric type for redistributed routes

route-map Route map reference

subnets Consider subnets for redistribution into OSPF

tag Set tag for routes redistributed into OSPF

<cr>


R2-E-O(config-router)#redistribute connected

% Only classful networks will be redistributed

R2-E-O(config-router)#redistribute connected subnets


R4-0# show ip route

<other output omitted>

E2 192.168.1.0/24 [110/20] via 172.16.0.5, 00:03:08, Serial0/0

R4-0# show ip ospf data



<omitted>

192.168.1.0 192.168.1.1 193 0x80000001 0x0012B8 0

R4-0#

Summaryso far…

So far…

R2 summary:

router eigrp 1

network 172.30.0.0

auto-summary

redistribute ospf 1

default-metric 1000 33 255 1 1500

redistribute connected metric 1000 33 255 1 1500

!

router ospf 1

network 10.0.0.0 0.0.0.255 area 0

network 172.16.0.0 0.0.0.3 area 0

redistribute eigrp 1 subnets

redistribute connected

1000 33 255 1 BW=20 BW=20

OSPF learned networks are distributed into the EIGRP domain

Use the metrics for BW DLY RLY Load

Distribute any directly connected networks and use these metrics for BW DLY RLY Load

EIGRP learned networks are distributed into the OSPF domain, default metric of 20

Distribute any directly connected networks and use default metric of 20

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R3-O#show ip route

O 172.17.0.0/16 [110/65] via 172.16.0.6, 00:13:41, Serial0/2





O 172.16.2.0/24 [110/65] via 172.16.0.6, 00:13:41, Serial0/2

O E2 172.31.0.0/16 [110/20] via 172.16.0.2, 00:13:41, Serial0/1


O E2 172.30.2.0 [110/20] via 172.16.0.2, 00:11:25, Serial0/1

O E2 172.30.3.0 [110/20] via 172.16.0.2, 00:11:25, Serial0/1

O E2 172.30.1.0 [110/20] via 172.16.0.2, 00:11:25, Serial0/1

O E2 172.30.4.0 [110/20] via 172.16.0.2, 00:11:25, Serial0/1


O 10.0.0.0 [110/65] via 172.16.0.2, 00:13:43, Serial0/1

O E2 192.168.1.0/24 [110/20] via 172.16.0.2, 00:07:30, Serial0/1



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R4-0#show ip route




O 172.16.0.0/30 [110/128] via 172.16.0.5, 00:14:05, Serial0/0

O 172.16.1.0/24 [110/65] via 172.16.0.5, 00:14:05, Serial0/0


O E2 172.31.0.0/16 [110/20] via 172.16.0.5, 00:14:05, Serial0/0


O E2 172.30.2.0 [110/20] via 172.16.0.5, 00:11:49, Serial0/0

O E2 172.30.3.0 [110/20] via 172.16.0.5, 00:11:49, Serial0/0

O E2 172.30.1.0 [110/20] via 172.16.0.5, 00:11:49, Serial0/0

O E2 172.30.4.0 [110/20] via 172.16.0.5, 00:11:49, Serial0/0


O 10.0.0.0 [110/129] via 172.16.0.5, 00:14:07, Serial0/0

O E2 192.168.1.0/24 [110/20] via 172.16.0.5, 00:07:54, Serial0/0

External OSPF routes are E2 with a default cost of 20

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Redistribution into OSPF modifying the metric

192.168.1.0/24 still has a cost of 20. Why? It was redistributed with the redistribute connected command without the

metric 100 parameter. <redistribute connected metric 100>


R2-E-O(config-router)#redistribute eigrp 1 subnets metric 100

R2-E-O(config-router)#redistribute connected

R4-0#show ip route <external route>

O E2 172.31.0.0/16 [110/100] via 172.16.0.5, 00:00:04, Serial0/0


O E2 172.30.2.0 [110/100] via 172.16.0.5, 00:00:05, Serial0/0

O E2 172.30.3.0 [110/100] via 172.16.0.5, 00:00:05, Serial0/0

O E2 172.30.1.0 [110/100] via 172.16.0.5, 00:00:05, Serial0/0

O E2 172.30.4.0 [110/100] via 172.16.0.5, 00:00:05, Serial0/0

O E2 192.168.1.0/24 [110/20] via 172.16.0.5, 00:12:36, Serial0/0

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metric-type {1 | 2} - Defines the external metric type of 1 (E1 routes) or 2 (E2 routes).

metric-type 1 - A type 1 cost is the addition of the external cost and the internal cost used to reach that route.



R2-E-O(config-router)# redistribute eigrp 1 subnets metric-type 1

R2-E-O# show run

router ospf 1

log-adjacency-changes

redistribute connected

redistribute eigrp 1 metric 100 metric-type 1 subnets

network 10.0.0.0 0.0.0.255 area 0

network 172.16.0.0 0.0.0.3 area 0

Notice that the previous metric 100 parameter is still included!

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E1 routes, seed metric of 100 plus internal cost. 192.168.1.0/24 still has a cost of 20.

It was redistributed with the redistribute connected command without the metric-type 1 parameter, E2 is the default. <redistribute connected metric 100 metric-type 1>

R3-O#show ip route

O E1 172.31.0.0/16 [110/164] via 172.16.0.2, 00:00:23, Serial0/1


O E1 172.30.2.0 [110/164] via 172.16.0.2, 00:00:24, Serial0/1

O E1 172.30.3.0 [110/164] via 172.16.0.2, 00:00:24, Serial0/1

O E1 172.30.1.0 [110/164] via 172.16.0.2, 00:00:24, Serial0/1

O E1 172.30.4.0 [110/164] via 172.16.0.2, 00:00:24, Serial0/1


O 10.0.0.0 [110/65] via 172.16.0.2, 00:21:45, Serial0/1

O E2 192.168.1.0/24 [110/20] via 172.16.0.2, 00:15:32, Serial0/1

More Redistribution Examples

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Same Protocol Stack

You can only redistribute routes from routing protocols that support the same protocol stack. IPv4 to IPv4 IPv6 to IPv6

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RIPv2 and OSPF Example

Routing tables prior to redistribution

65

The passive-interface command is configured for interface serial 0/0/2 to prevent RIPv2 from sending route advertisements out that interface.

OSPF is configured on interface serial 0/0/2.

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X

The goal of redistribution in this network is for all routers to recognize all routes within the company.

RIPv2 is redistributed into the OSPF process, and the metric is set using the redistribute command (help prevent routing loops - later). A metric value of 300 is selected because it is a worse metric than any

belonging to a native OSPF route. Routes from OSPF process 1 are redistributed into the RIPv2 process with

a metric of 5. A value of 5 is chosen because it is higher than any metric in the RIP

network. 67

There is complete reachability; however, Routers A and C now have many more routes to keep track of than before.

They also will be affected by any topology changes in the other routing domain. 68

R 10.0.0.8/30 O E2 10.0.0.0/30

For RIPv2 on Router A, the summarization command is configured on the interface connecting to Router B, interface S0/0/0. Interface S0/0/0 advertises the summary address instead of the

individual subnets. 10.0.0.0 255.252.0.0 summarizes the four subnets on Router A

(including the 10.0.0.0/30 subnet).69

For OSPF, summarization must be configured on an area border router (ABR) or an ASBR.

Router C summarization command is configured under the OSPF process on Router C.

10.8.0.0 255.252.0.0 summarizes the four subnets on Router C. 70

Redistribution Techniques and Issues

71

Seed Metric

router ospf 1

network 172.20.0.0

redistribute rip

default-metric 501

or

redistribute rip metric 501

OSPF1 RIP

When redistributing information, the seed metric should be set to a value When redistributing information, the seed metric should be set to a value larger than the largest metric within the receiving autonomous system (aka larger than the largest metric within the receiving autonomous system (aka the largest native metric).the largest native metric).

This will help prevent suboptimal routing and routing loops.This will help prevent suboptimal routing and routing loops.

501

501

Largest metricis 500

The default seed metric value for routes that are redistributed into each IP routing protocol.

A metric of infinity tells the router that the route is unreachable and, therefore, should not be advertised. When redistributing routes into RIP, IGRP, and EIGRP, you must specify

a seed metric, or the redistributed routes will not be advertised. For OSPF, the redistributed routes have a default type 2 (E2) metric of 20,

(except for redistributed BGP routes, which have a default type 2 metric of 1)

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One-Point Redistribution

One-point redistribution has only one router redistributing between two routing protocols.

A one-way redistribution issue that could occur… 74

R3 receives routing update information for the external route 10.0.0.0. directly from: R1 via EIGRP (AD = 170) R2 via OSPF (AD = 110)

Because the AD of OSPF (110) is lower than AD of external EIGRP routes (170), R3 selects the OSPF route. Suboptimal routing

Instead of sending packets directly from router R3 to router R1, router R3 prefers the path via router R2, resulting in suboptimal routing.

Solution: R2 should redistribute EIGRP route into OSPF with an AD of 115. We will see how to do this later.

75

R2 and R3 are both running OSPF and EIGRP

Only R2 is redistributing between OSPF en EIGRP

R1 has an External Route 10.0.0.0 that it is redistributing into its AS.

R1 is propagating this route to both R2 and R3.

10.0.0.0 via R1 has AD 170 (EX EIGRP)10.0.0.0 via R2 has AD 110 (OSPF)So, I will choose (include in my routing table) the path via R2 (OSPF)

Multipoint redistribution

Multipoint redistribution has two separate routers running both routing protocols.

Two possibilities exist: Multipoint one-way redistribution Multipoint two-way redistribution

Likely to introduce potential routing loops

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Therefore, R2 and R3 receive routing update information for the external route 10.0.0.0: via EIGRP from router R1 and via OSPF (R2 from R3, and R3 from R2).

The AD of OSPF (110) is lower than AD of external EIGRP (170): So R2 selects the OSPF route instead of sending packets directly to R1 R2 prefers the path via router R3

Routing Loop! 77

A one-way multipoint redistribution issue.

R1 (EIGRP) is announcing routes, including the external route, to R2 and R3.

R2 and R3 are both running two routing protocols (EIGRP and OSPF) and redistributing EIGRP into OSPF.



To prevent routing loops in multipoint redistribution scenario the following recommendations should be considered: Tag routes in redistribution points and filter based on these tags when

redistributing (later) Modify the Administrative Distance of redistributed routes (later) Use default routes to avoid having to do two-way redistribution

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The best path between R1 and R4 is via R3 But during redistribution from routing protocol B to routing protocol A, the

metric is lost Domain A doesn’t know about metrics in Domain B

R1 will send packets toward router R4 via router R2 (its best path outside its domain) Resulting in suboptimal routing.

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A multi-way multipoint redistribution issue

Modifying Administrative Distance

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AD

The administrative distance affects only the choice of path for identical IP routes. In other words, routes that have identical prefix and mask.

Routes with a distance of 255 are not installed in the routing table.

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This command can be used for all protocols. There are additional options for each routing protocol.

82

Router(config-router)# distance administrative-distance [address wildcard-mask [ip-standard- list] [ip-extended-list]]

distance eigrp 80 130 Sets the administrative distance for internal EIGRP routes to 80 and for

external EIGRP routes to 130. distance 90 192.168.7.0 0.0.0.255

Sets the administrative distance to 90 for all routes learned from routers on the Class C network 192.168.7.0

distance 120 172.16.1.3 0.0.0.0 Sets the administrative distance to 120 for all routes from the router with

the address 172.16.1.3.

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distance ospf external 100 inter-area 100 intra-area 100 Sets the administrative distance for external, inter-area, and intra-area

OSPF routes to 100 (default values are 110). distance 90 10.0.0.0 0.0.0.255, distance 110 10.11.0.0

0.0.0.255, and distance 130 10.11.12.0 0.0.0.255 Sets the administrative distance to 90, 110, and 130 respectively, for all

routes learned from routers with specific addresses Routes from a router with address 10.10.0.1 will have an AD of 90 Routes from a router with address 10.11.12.1 will have an AD of 130.

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85

Example

R1 and R2

AD = 120

AD = 110 OSPF (AD 110) is by

default considered more believable than RIPv2 (120)

If R1 learns about network 10.3.3.0: via R2 (OSPF) Via R3 (RIPv2)

The OSPF route is used because OSPF has a lower administrative distance than RIPv2, even though the path via OSPF might be the longer (worse) path.

10.3.3.0/24

Preferred

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Example

R1 and R2

Metric = 10,000 Metric = 10,000

Metric = 5

AD = 120

AD = 110 Note: RIPv2 routes redistributed into OSPF have an OSPF seed metric of 10,000 (higher than any other OSPF route).

This does not prevent our previous problem

Makes these routes less preferred than native OSPF routes

Protects against route feedback.

Prevents R1 from choosing R2 for OSPF routes it learns from internal OSPF routers.

The redistribute command also sets the metric type to 1 (external type 1) so that the route metrics continue to accrue.

The routers also redistribute subnet information.

10.3.3.0/24

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Example

R1 and R2

Metric = 10,000 Metric = 10,000

Metric = 5

AD = 120

AD = 110 The OSPF routes

redistributed into RIPv2 have a RIP seed metric of five hops to also protect against route feedback.

10.3.3.0/24

R2, receives information about the RIPv2 domain routes (also called the native RIPv2 routes) from both OSPF and RIPv2.

R2 prefers the OSPF routes because OSPF has a lower administrative distance

Therefore, none of the RIPv2 routes appears in R2’s routing table. All routes are via OSPF or directly connected.

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My best path to all RIP networks is via R1 because OSPF (110) is better than RIP (120).

Solution: Modifying the AD

You can change the administrative distance of the redistributed RIPv2 routes to ensure that the boundary routers select the native RIPv2 routes.

The distance command on R1 and R2 changes the administrative distance of the OSPF routes to the networks that match access list 64 to 125 (from 110).

Access list 64 is used to match all the native RIPv2 routes. 89

90

Metric = 10,000AD = 125

Metric = 10,000AD = 125

Metric = 5

AD = 120

AD = 110

R1 and R2 are assign an AD of 125 to routes listed in access list 64 (routes learned from OSPF).

R1 and R2 prefer the native RIPv2 routes (AD 120) over the redistributed OSPF routes (AD 125) in their routing tables.

R1 will put the 10.200.200.34 network in its routing table as a RIP route (AD 120) instead of the OSPF (AD 125) route it learned via R2.

Preferred

However, some routing information is lost with this configuration. For example, depending on the actual bandwidths, the OSPF path

might have been better for the 10.3.1.0 network; it might have made sense not to include 10.3.1.0 in the access list for R2.

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My best path to all RIP networks is via R4 because RIP (120) is better than redistributed RIP (125).

Verifying Redistribution

The best way to verify redistribution operation is as follows: Know your network topology, particularly where redundant routes exist. Study the routing tables on a variety of routers in the internetwork using

the show ip route Perform a trace using the traceroute on some of the routes that go

across the autonomous systems to verify that the shortest path is being used for routing.

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CIS 185 CCNP ROUTE Ch. 4 Manipulating Routing Updates Rick Graziani Cabrillo College...

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