L1 routers are contained in a single area, and are connected to other areas by an L1/L2 router. The L1 uses the L1/L2 router as a default gateway to reach destinations contained in other areas, much like an OSPF stub router uses the ABR as a default gateway.

L1 routers have no specific routing table entries regarding any destination outside their own area; they will use an L1/L2 router as a default gateway to reach any external networks. ISIS L1 routers in the same area must synchronize their databases with each other.

Just as we have L1 routers, we also have L2 routers. Anytime we’re routing between areas (inter-area routing), an L2 or L1/L2 router must be involved. All L2 routers will have synchronized databases as well.

Both L1 and L2 routers send out their own hellos. As with OSPF, hello packets allow ISIS routers to form adjacencies. The key difference here is that L1 routers send out L1 hellos, and L2 routers send out L2 hellos. If you have an L1 router and an L2 router on the same link, they will not form an adjacency.

An ISIS router can act as an L1 and an L2 router at the same time; these routers are L1/L2 routers. An L1/L2 router can have neighbors in separate ISIS areas. The L1/L2 router will have two separate databases, though – one for L1 routes and another for L2 routes. L1/L2 is the default setting for Cisco routers running ISIS. The L1/L2 router is the router that makes it possible for an L1 router to send data to another area.

In the next part of my ISIS tutorial, we’ll take a more detailed look at those ISIS hellos!

Cisco CCNP / BSCI Exam Tutorial: ISIS Router Types is a post from: Techno And Science News | At4k-12.org

Typical IPv4 address: 129.14.12.200

Typical IPv6 address: 1029:9183:81AE:0000:0000:0AC1:2143:019B

As you can see, IPv6 isn’t exactly just tacking two more octets onto an IPv4 address!

I haven’t met too many networkers who really like typing, particularly numbers. You’ll be happy to know there are some rules that will shorten those addresses a bit, and it’s a very good idea to be fluent with these rules for your exam.

You remember from your CCNA studies that there’s no difference between an upper-case letter and lower-case letter in hexadecimal. That’s one of three basic rules you need to know when working with IPv6 addressing. The other factors deal with all the zeroes you’ll run into in IPv6 addresses! One of these rules is the rule of zero compression.

The rule of zero compression states that if an address contains consecutive fields of zeroes, they can be expressed with two colons. It doesn’t matter if you have two fields or eight, you can simply type two colons and that will represent all of them. The key here is that you can only do this once in an IPv6 address. This is referred to as zero compression. Here’s an example:

Original format: 1234:1234:0000:0000:0000:0000:3456:3434

Using zero compression: 1234:1234::3456:3434

Again, you must remember that you can only do this once in an IPv6 address expression.

What if there are zeroes in the address that don’t quite fit this rule? The next part of our IPv6 tutorial will deal with leading zero compression, another tool you can use to shorten these long, long addresses!

Cisco CCNP / BSCI Exam Tutorial: IP Version 6 Zero Compression is a post from: Techno And Science News | At4k-12.org

Policy-based routing, generally referred to as “policy routing”, is the use of route maps to determine the path a packet will take to get to its final destination. As you progress through your CCNP studies and go on to the CCIE (or to a Cisco Quality Of Service certification), you’ll find that traffic can be “marked” by policy routing in order to give different levels of service to various classes of traffic. (This is done by marking the traffic and placing the different classes of traffic in different queues in the router, allowing the administrator to give some traffic higher priority for transmission.)

There are some basic policy routing rules you should know:

Policy routing doesn’t affect the destination of the packet, but does affect the path that is taken to get there.

Policy routing can forward traffic based on the source IP address or the destination IP address (with the use of an extended ACL).

Policy routing can be configured at the interface level, or globally.

Applying policy routing on an interface affects only packets arriving on that interface:

R2(config)#int s0

R2(config-if)#ip policy route-map CHANGE_NEXT_HOP

Applying the policy globally applies the route map to packets generated on the router, not on all packets received on all interfaces.

Whether you’re running policy routing at the interface level, on packets created locally, or both, always run the command show ip policy to make sure you’ve got the right route maps on the proper interfaces.

R2#show ip policy

Interface Route map

local CHANGE_NEXT_HOP

Serial0 CHANGE_NEXT_HOP

And here’s the big rule to remember….

If a packet doesn’t match any of the specific criteria in a route map, or does match a line that has an explicit deny statement, the data is sent to the routing process and will be processed normally. If you don’t want to route packets that do not meet any route map criteria, the set command must be used to send those packets to the null0 interface. This set command should be the final set command in the route map.

There are four possibilities for an incoming packet when route maps are in use. The following example illustrates all of them.

R2(config)#access-list 29 permit host 20.1.1.1

R2(config)#access-list 30 permit host 20.2.2.2

R2(config)#access-list 31 permit host 20.3.3.3

R2(config)#access-list 32 permit host 20.4.4.4

R2(config)#route-map EXAMPLE permit 10

R2(config-route-map)#match ip address 29

R2(config-route-map)#set ip next-hop 40.1.1.1

R2(config-route-map)#route-map EXAMPLE permit 20

R2(config-route-map)#match ip address 30

Assuming the route map has been applied to the router’s ethernet0 interface, a packet sourced from 20.1.1.1 would meet the first line of the route map and have its next-hop IP address set to 40.1.1.1.

A packet sourced from 20.2.2.2 would match the next permit statement (sequence number 20). Since there is no action listed, this packet would return to the routing engine to undergo the normal routing procedure. All traffic that did not match these two addresses would also be routed normally – there would be no action taken by the route map.

Perhaps we want to specifically block traffic sourced from 20.3.3.3 or 20.4.4.4. We can use multiple match statements in one single route map, and have packets matching those two addresses sent to the bit bucket – the interface null0.

R2(config)#route-map EXAMPLE permit 30

R2(config-route-map)#match ip address 31

R2(config-route-map)#match ip address 32

R2(config-route-map)#set ?

as-path Prepend string for a BGP AS-path attribute

automatic-tag Automatically compute TAG value

comm-list set BGP community list (for deletion)

community BGP community attribute

dampening Set BGP route flap dampening parameters

default Set default information

extcommunity BGP extended community attribute

interface Output interface

ip IP specific information

level Where to import route

local-preference BGP local preference path attribute

metric Metric value for destination routing protocol

metric-type Type of metric for destination routing protocol

origin BGP origin code

tag Tag value for destination routing protocol

weight BGP weight for routing table

R2(config-route-map)#set interface null0

Any traffic matching ACLs 31 or 32 will be sent to null0, resulting in its being discarded by the router. Any traffic that didn’t match any of the route map statements will be returned to the routing engine for normal processing.

Knowing policy routing and how to apply it are essential skills for passing the BSCI exam, earning your CCNP, and becoming more valuable in today’s job market. Get some hands-on practice in a CCNA / CCNP home lab or rack rental to go along with learning the theory, and you’ll be writing and applying policy routing in no time at all.

Cisco CCNP / BSCI Exam Tutorial: Introduction To Policy Routing is a post from: Techno And Science News | At4k-12.org

R4 is advertising three networks via BGP. The downstream router R3 sees these routes and places them into its BGP table as shown below. R3 has two downstream BGP peers, R1 and R2, and is advertising itself as the next-hop IP address for all BGP routes sent to those two routers.

R4(config)#router bgp 4

R4(config-router)#network 21.0.0.0 mask 255.0.0.0

R4(config-router)#network 22.0.0.0 mask 255.0.0.0

R4(config-router)#network 23.0.0.0 mask 255.0.0.0

R3#show ip bgp

BGP table version is 4, local router ID is 3.3.3.3

Status codes: s suppressed, d damped, h history, * valid, > best, i
Internal

Origin codes: i – IGP, e – EGP, ? incomplete

Network Next Hop Metric LocPrf Weight Path

*> 21.0.0.0 10.2.2.4 0 0 4 I

*> 22.0.0.0 10.2.2.4 0 0 4 I

*> 23.0.0.0 10.2.2.4 0 0 4 I

R3(config)#router bgp 123

R3(config-router)#neighbor 172.12.123.1 next-hop-self

R3(config-router)#neighbor 172.12.123.2 next-hop-self

In turn, both R1 and R2 have these three routes in their respective BGP tables.

R2#show ip bgp

BGP table version is 4, local router ID is 2.2.2.2

Status codes: s suppressed, d damped, h history, * valid, > best, i
Internal

Origin codes: i – IGP, e – EGP, ? incomplete

Network Next Hop Metric LocPrf Weight Path

*>i21.0.0.0 172.12.123.3 0 100 0 4 I

*>i22.0.0.0 172.12.123.3 0 100 0 4 I

*>i23.0.0.0 172.12.123.3 0 100 0 4 I

R1#show ip bgp

BGP table version is 4, local router ID is 19.1.1.1

Status codes: s suppressed, d damped, h history, * valid, > best, i
Internal

Origin codes: i – IGP, e – EGP, ? incomplete

Network Next Hop Metric LocPrf Weight Path

*>i21.0.0.0 172.12.123.3 0 100 0 4 I

*>i22.0.0.0 172.12.123.3 0 100 0 4 I

*>i23.0.0.0 172.12.123.3 0 100 0 4 I

If we wanted R3 to receive all three of these routes from R4 but not advertise all of them to R2 and R1, we’ve got a couple of options on how to block these routes. Cisco’s recommendation is the use of prefix-lists, and once you get used to the syntax (which you should do before taking and passing the BSCI), you’ll see they are actually easier to use than access-lists.

In this case, we’re going to configure R3 to send only the route to 21.0.0.0 to R1 and 23.0.0.0 to R2. However, we do want these two routers to get any future routes that R4 advertises into BGP.

Since R1 and R2 will learn about these routes from an iBGP neighbor, they will not advertise the routes to each other.

On R3, we’ll write a prefix-list that denies 22.0.0.0/8 and 23.0.0.0/8, but permits all other routes. After applying the prefix list as shown, R1 sees only the 21.0.0.0 /8 route.

R3(config)#ip prefix-list FILTER_R1 deny 22.0.0.0/8

R3(config)#ip prefix-list FILTER_R1 deny 23.0.0.0/8

R3(config)#ip prefix-list FILTER_R1 permit 0.0.0.0/0 le 32

R3(config)#router bgp 123

R3(config-router)#neighbor 172.12.123.1 prefix-list FILTER_R1 out

R3#clear ip bgp * soft

R1#show ip bgp

BGP table version is 6, local router ID is 19.1.1.1

Status codes: s suppressed, d damped, h history, * valid, > best, i
Internal

Origin codes: i – IGP, e – EGP, ? incomplete

Network Next Hop Metric LocPrf Weight Path

*>i21.0.0.0 172.12.123.3 0 100 0 4 I

The paths to 22.0.0.0/8 and 23.0.0.0/8 have been successfully filtered.

We’ll do the same for R2, except the route not being expressly blocked is 23.0.0.0/8. The line “ip prefix-list permit 0.0.0.0/0 le 32″ is the prefix list equivalent of a “permit any” statement in an ACL.

R3(config)#ip prefix-list FILTER_R2 deny 21.0.0.0/8

R3(config)#ip prefix-list FILTER_R2 deny 22.0.0.0/8

R3(config)#ip prefix-list FILTER_R2 permit 0.0.0.0/0 le 32

R3(config)#router bgp 123

R3(config-router)#neighbor 172.12.123.2 prefix-list FILTER_R2 out

R3#clear ip bgp * soft

R2#show ip bgp

BGP table version is 6, local router ID is 2.2.2.2

Status codes: s suppressed, d damped, h history, * valid, > best, i
Internal

Origin codes: i – IGP, e – EGP, ? incomplete

Network Next Hop Metric LocPrf Weight Path

*>i23.0.0.0 172.12.123.3 0 100 0 4 I

The paths to 21.0.0.0/8 and 22.0.0.0/8 have been successfully filtered.

To see the prefix lists configured on a route as well as the order of the statements in each list, run show ip prefix-list.

R3#show ip prefix-list

ip prefix-list FILTER_R1: 3 entries

seq 5 deny 22.0.0.0/8

seq 10 deny 23.0.0.0/8

seq 15 permit 0.0.0.0/0 le 32

ip prefix-list FILTER_R2: 3 entries

seq 5 deny 21.0.0.0/8

seq 10 deny 22.0.0.0/8

seq 15 permit 0.0.0.0/0 le 32

Get some hands-on practice with prefix lists and you’ll quickly master them. Prefix lists are an important part of working with BGP in the exam room and production networks, so it’s vital that you are comfortable working with them.

Cisco CCNP / BSCI Exam Tutorial: Filtering BGP Updates With Prefix Lists is a post from: Techno And Science News | At4k-12.org

We’ll use the following four loopback addresses in this example:

Loopback 16, 16.16.16.16 /32

Loopback 17, 17.17.17.17 /32

Loopback 18, 18.18.18.18 /32

Loopback 19. 19.19.19.19 /32

On R1, we’ll place these four addresses into EIGRP AS 100.

R1(config-if)#router eigrp 100

R1(config-router)#network 16.16.16.16 0.0.0.0

R1(config-router)#network 17.17.17.17 0.0.0.0

R1(config-router)#network 18.18.18.18 0.0.0.0

R1(config-router)#network 19.19.19.19 0.0.0.0

R3 is an EIGRP neighbor of R1, and that router’s EIGRP routing table now looks like this:

R3#show ip route eigrp

17.0.0.0/32 is subnetted, 1 subnets

D 17.17.17.17 [90/2297856] via 172.12.123.1, 00:00:29, Serial0

16.0.0.0/32 is subnetted, 1 subnets

D 16.16.16.16 [90/2297856] via 172.12.123.1, 00:00:36, Serial0

19.0.0.0/32 is subnetted, 1 subnets

D 19.19.19.19 [90/2297856] via 172.12.123.1, 00:00:08, Serial0

18.0.0.0/32 is subnetted, 1 subnets

D 18.18.18.18 [90/2297856] via 172.12.123.1, 00:00:22, Serial0

To perform manual route summarization, write out the network addresses in binary and then determine the point at which the addresses no longer have a bit in common. For these four addresses, it will be enough to write out the first octet in binary:

16 00010000

17 00010001

18 00010010

19 00010011

Working from left to right, the common bits are the first six bits – 000100xx. In decimal, this value is 16. The summary mask must be determined as well, and that value is derived from putting a “1″ in the mask for each common bit. With the first six bits all set to one – 11111100 – the resulting mask is 252.0.0.0. The full summary address is 16.0.0.0 252.0.0.0.

In EIGRP, the summary address is actually configured on an interface, not under the routing process.

R1(config)#interface serial0

R1(config-if)#ip summary-address eigrp 100 16.0.0.0 252.0.0.0

02:39:50: %DUAL-5-NBRCHANGE: IP-EIGRP 100: Neighbor
172.12.123.3 (Serial0) is down: summary configured

02:39:50: %DUAL-5-NBRCHANGE: IP-EIGRP 100: Neighbor
172.12.123.2 (Serial0) is down: summary configured

02:40:16: %DUAL-5-NBRCHANGE: IP-EIGRP 100: Neighbor
172.12.123.2 (Serial0) is up : new adjacency

02:40:17: %DUAL-5-NBRCHANGE: IP-EIGRP 100: Neighbor
172.12.123.3 (Serial0) is up: new adjacency

There’s an immediate side effect here that most books leave out. Your EIGRP adjacencies are going to come down after you configure this summary, but they should come back up quickly. The key word there is “should”. If you configure EIGRP summary addresses on a production network, you may want to do this during non-peak hours. The timestamps on the above commands indicate that the adjacencies were down for about 27 seconds over the NBMA network. That’s about 30 minutes in end-user time.

Check R3′s EIGRP routing table.

R3#show ip route eigrp

D 16.0.0.0/6 [90/2297856] via 172.12.123.1, 00:01:46, Serial0

The four summarized routes are no longer in the routing table, and they have been replaced by the summary route shown at the bottom of the routing table. Notice the mask is /5, which is prefix notation for 248.0.0.0.

Knowing how and why to summarize routes is a valuable skill, regardless of the protocol in use. But before you take the BSCI exam on your way to the CCNP, make sure you know how to perform summarization with all of the core protocols!

Cisco CCNP / BSCI Exam Tutorial: EIGRP Route Summarization is a post from: Techno And Science News | At4k-12.org

In the following example, a BGP peering is being created between R1 and R3.
R1(config-router)#neighbor 172.12.123.3 remote-as 200

BGP speakers do not have to be in the same AS to become peers. To verify that the remote BGP speaker has become a peer, run show ip bgp neighbor.

R1#show ip bgp neighbor

BGP neighbor is 172.12.123.3, remote AS 200, external link

BGP version 4, remote router ID 0.0.0.0

BGP state = Active

Last read 00:01:39, hold time is 180, keepalive interval is 60 seconds

Received 0 messages, 0 notifications, 0 in queue

Sent 0 messages, 0 notifications, 0 in queue

Route refresh request: received 0, sent 0

Default minimum time between advertisement runs is 30 seconds

The output here can be a little misleading the first time you read it. The first highlighted line shows 172.12.123.3 is a BGP neighbor, is located in AS 200, and is an external link, indicating that the neighbor is in another AS entirely. The second highlighted line shows the BGP state as Active. This sounds great, but it actually means that a BGP peer connection does not yet exist with the prospective neighbor. Before we continue with this example, lets look at the different BGP states:

Idle is the initial state of a BGP connection. The BGP speaker is waiting for a start event, generally either the establishment of a TCP connection or the re-establishment of a previous connection. Once the connection is established, BGP moves to the next state.

Connect is the next state. If the TCP connection completes, BGP will move to the OpenSent stage if the connection does not complete, BGP goes to Active.

Active indicates that the BGP speaker is continuing to create a peer relationship with the remote router. If this is successful, the BGP state goes to OpenSent. Youll occasionally see a BGP connection flap between Active and Connect. This indicates an issue with the physical cable itself, or with the configuration.

OpenSent indicates that the BGP speaker has received an Open message from the peer. BGP will determine whether the peer is in the same AS (iBGP) or a different AS (eBGP) in this state.

In OpenConfirm state, the BGP speaker is waiting for a keepalive message. If one is received, the state moves to Established, and the neighbor relationship is complete. It is in the Established state that update packets are actually exchanged.

So even though the show ip bgp neighbor output indicated that this is an Active neighbor relationship, thats not as good as it sounds. Of course, the reason the peer relationship hasnt been established is that we havent configured R3 yet!

R3(config)#router bgp 200

R3(config-router)#neighbor 172.12.123.1 remote-as 100

Verify the peer establishment with show ip bgp neighbor:

R3#show ip bgp neighbor

BGP neighbor is 172.12.123.1, remote AS 100, external link

BGP version 4, remote router ID 172.12.123.1

BGP state = Established, up for 00:01:18

Last read 00:00:17, hold time is 180, keepalive interval is 60 seconds

Neighbor capabilities:

Route refresh: advertised and received(old & new)

Address family IPv4 Unicast: advertised and received

Received 5 messages, 0 notifications, 0 in queue

Sent 5 messages, 0 notifications, 0 in queue

Route refresh request: received 0, sent 0

Default minimum time between advertisement runs is 30 seconds

Local host: 172.12.123.3, Local port: 179 (BGP uses TCP Port 179)

Foreign host: 172.12.123.1, Foreign port: 11007

The peer relationship between R1 and R3 has been established!

Cisco CCNP / BSCI Exam Tutorial: BGP Adjacency States is a post from: Techno And Science News | At4k-12.org

In IPv4, a unicast address is simply an address used to represent a single host, where multicast addresses represent a group of hosts and broadcasts represent all hosts.

In IPv6, it’s not quite that simple. There are actually different types of unicast addresses, each with its own separate function. This allows IPv6 to get data where it’s supposed to go quicker than IPv4 while conserving router resources.

IPv6 offers two kinds of local addresses, link-local and site-local. Site-local addresses allow devices in the same organization, or site, to exchange data. Site-local addresses are IPv6′s equivalent to IPv4′s private address classes, since hosts using them are able to communicate with each other throughout the organization, but these addresses cannot be used to reach Internet hosts.

Site-local and link-local addresses are actually derived from a host’s MAC address. Therefore, if HostA has HostB’s IPv6 address, HostA can determine HostB’s MAC address from that, making ARP unnecessary.

Link-local addresses have a smaller scope than site-local. Link-local addresses are just that, local to a physical link. These particular addresses are not used at all in forwarding data. One use for these addresses is Neighbor Discovery, which is IPv6′s answer to ARP.

You can identify these and other IPv6 addresses by their initial bits:

001 – Global address

(first 96 bits set to zero) – IPv4-compatible address

1111 1111 Multicast

1111 1110 11 – Site local

1111 1110 10 – Link Local

As a future CCNP, you’re more than familiar with the reserved IPv4 address classes. You also know that they’re not exactly contiguous. The developers of IPv6 took a structured approach to IPv6 reserved addresses – any address that begins with “0000 0000″ is an IPv6 reserved address. One of these is the IPv6 loopback address, and this will give you some practice with your zero compression!

IP v6 Loopback: 0000:0000:0000:0000:0000:0000:0000:0001

Using Leading Zero Compression Only: 0:0:0:0:0:0:0:1

Combining Leading Zero and Zero Compression: ::1

Zero compression looks pretty good now, doesn’t it? You just have to get used to it and keep the rules in mind. You can use all the leading zero compression you want, but zero compression (“double-colon”) can only be used once in a single address.

IPv6 is here to stay, not only on your BSCI and CCNP exams, but in the real world as well. Learning it now will not only aid you in passing your Cisco exams, but in supporting IPv6 in the future.

Cisco CCNP / BSCI Exam Tutorial: A Guide To Ipv6 Addressing is a post from: Techno And Science News | At4k-12.org

The virtual link command includes the area number of the transit area, and if authentication is being used on Area 0, the virtual link command must include the authentication statement. Since the virtual link is a logical extension of Area 0, it stands to reason that it has to be configured with the authentication type and password configured on Area 0.

OSPF requires no seed metric when routes are being redistributed into an OSPF domain. The default cost for such routes is 20, but you do need to use the “subnets” option if you want to redistribute subnets into OSPF.

There are two kinds of external OSPF routes. The default, E2, reflects the cost of the path from the ASBR to the external destination. The other option, E1, has a cost reflecting the entire path from the local router to the external destination.

When configuring stub areas, each router in the area must agree that the area is stub. For a total stub area, only the ABR needs to be configured with the “no-summary” option, but all routers in the area still must agree that the area is stub.

Routers in a stub area will have a default route to use to reach external destinations; routers in total stub areas will have a default route to use in order to reach both external and inter-area networks.

The BSCI exam and CCNP certification require a great deal of dedication and hard work. Keep studying and paying attention to the details, and you will get there!

Cisco CCNP / BSCI Certification Exam: Five OSPF Details You Must Know is a post from: Techno And Science News | At4k-12.org

We are using a three-router network. R5 is running RIP, R1 is serving as a hub between R5 and R3 and is running RIP and OSPF, and R3 is running OSPF.

To begin this lab, we’ll add three loopbacks to R3 and advertise them to R1 via OSPF.

R3(config)#int loopback33

R3(config-if)#ip address 33.3.3.3 255.255.255.255

R3(config-if)#int loopback34

R3(config-if)#ip address 34.3.3.3 255.255.255.255

R3(config-if)#int loopback35

R3(config-if)#ip address 35.3.3.3 255.255.255.255

R3(config-if)#router ospf 1

R3(config-router)#network 33.3.3.3 0.0.0.0 area 1

R3(config-router)#network 34.3.3.3 0.0.0.0 area 1

R3(config-router)#network 35.3.3.3 0.0.0.0 area 1

R1 sees all three of these routes in its routing table.

R1#show ip route ospf

34.0.0.0/32 is subnetted, 1 subnets

O IA 34.3.3.3 [110/65] via 172.12.123.3, 00:00:55, Serial0

35.0.0.0/32 is subnetted, 1 subnets

O IA 35.3.3.3 [110/65] via 172.12.123.3, 00:00:45, Serial0

33.0.0.0/32 is subnetted, 1 subnets

O IA 33.3.3.3 [110/65] via 172.12.123.3, 00:00:55, Serial0

We’ll now redistribute these routes into RIP on R1. Remember the “subnets” option we talked about in the first part of this tutorial? There is no such option when redistributing OSPF routes into RIP, as IOS Help shows us.

R1(config)#router rip

R1(config-router)#redistribute ospf 1 ?

match Redistribution of OSPF routes

metric Metric for redistributed routes

route-map Route map reference

vrf VPN Routing/Forwarding Instance

R1(config-router)#redistribute ospf 1

The routes have been redistributed into RIP with the redistribute ospf 1 command. (The “1″ is the OSPF process number.) Let’s look at R5 and see the results.

R5#show ip route rip

R5#

The routes aren’t there, but we didn’t get a warning from the router that we needed to do anything else. What is the problem?

The problem is that RIP requires a seed metric to be specified when redistributing routes into that protocol. A seed metric is a “starter metric” that gives the RIP process a metric it can work with. The OSPF metric of cost is incomprehensible to RIP, since RIP’s sole metric is hop count. We’ve got to give RIP a metric it understands when redistributing routes into that protocol, so let’s go back to R1 and do so.

R1(config)#router rip

R1(config-router)#no redistribute ospf 1

R1(config-router)#redistribute ospf 1 metric 2

R5 now sees the routes. Note that the metric contained in the brackets is the seed metric.

R5#show ip route rip

34.0.0.0/32 is subnetted, 1 subnets

R 34.3.3.3 [120/2] via 100.1.1.1, 00:00:24, Ethernet0

35.0.0.0/32 is subnetted, 1 subnets

R 35.3.3.3 [120/2] via 100.1.1.1, 00:00:24, Ethernet0

33.0.0.0/32 is subnetted, 1 subnets

R 33.3.3.3 [120/2] via 100.1.1.1, 00:00:24, Ethernet0

If you read the previous tutorial, you may have noticed that we did not specify a seed metric for OSPF. OSPF does not require a seed metric to be set during redistribution. You also noticed that the router did tell us that there might be a problem when we left the “subnets” option out of RIP>OSPF redistribution, but the router didn’t tell us anything about a seed metric when we performed OSPF>RIP redistribution. This is a detail you must know by heart in order to make your route redistribution successful!

Cisco CCNP / BSCI Certification: Route Redistribution And The Seed Metric is a post from: Techno And Science News | At4k-12.org

In this free CCNP / BSCI tutorial series, we’ll take a look at three common errors in route redistribution configurations, and how to fix them. We’ll use three routers, R1, R3, and R5. R1 and R5 are in a RIPv2 domain and R1 and R3 are in an OSPF domain. R1 will be performing two-way route redistribution.

R5 is advertising its loopback, 5.5.5.5/24, into the RIPv2 domain. R1 sees this route in its RIP routing table:

R1#show ip route rip

5.0.0.0/24 is subnetted, 1 subnets

R 5.5.5.0 [120/1] via 100.1.1.5, 00:00:01, Ethernet0

For R3 to see this route, route redistribution must be configured on R1. We’ll use the redistribute rip command to do so.

R1(config)#router ospf 1

R1(config-router)#redistribute rip

% Only classful networks will be redistributed

The router immediately gives us a message that “only classful networks will be redistributed”. What does this mean? Let’s go to R3 and see if that router is receiving this route.

R3#show ip route ospf

< no output >

When we get no result from a show command, that means there’s nothing to show. The only routes that will be successfully redistributed with the current configuration on R1 are classful networks, and 5.5.5.0/24 is a subnet.

To further illustrate the point, a classful network has been added to R5. This network is 16.0.0.0 /8, and is now being advertised by RIP. R1 sees this network as classful…

R1#show ip route rip

R 16.0.0.0/8 [120/1] via 100.1.1.5, 00:00:00, Ethernet0

5.0.0.0/24 is subnetted, 1 subnets

R 5.5.5.0 [120/1] via 100.1.1.5, 00:00:00, Ethernet0

… and R3 is receiving the route through redistribution.

R3#show ip route ospf

O E2 16.0.0.0/8 [110/20] via 172.12.123.1, 00:00:08, Serial0.31

To redistribute both classful and classless networks, the option “subnets” must be added to the redistribute command on R1.

R1(config)#router ospf 1

R1(config-router)#no redistribute rip

R1(config-router)#redistribute rip subnets

R3 will now see both the classful and classless networks being redistributed into OSPF. (100.1.1.0 is the network connecting R1 and R5.)

R3#show ip route ospf

O E2 16.0.0.0/8 [110/20] via 172.12.123.1, 00:00:20, Serial0.31

100.0.0.0/24 is subnetted, 1 subnets

O E2 100.1.1.0 [110/20] via 172.12.123.1, 00:00:20, Serial0.31

5.0.0.0/24 is subnetted, 1 subnets

O E2 5.5.5.0 [110/20] via 172.12.123.1, 00:00:20, Serial0.31

This is one of the most common errors made during route redistribution, but now you know what to look out for! In the next part of this free CCNP / BSCI tutorial, we’ll take a look at another such error.

Cisco CCNP / BSCI Certification: Troubleshooting Route Redistribution, Part I is a post from: Techno And Science News | At4k-12.org