Posts Tagged ‘bsci’
To be successful on the BSCI exam and in earning your CCNP, you’ve got to master route redistribution. This isn’t as easy as it sounds, because configuring route redistribution is only half the battle. Whether it’s on an exam or in a real-world production network, you’ve got to identify possible points of trouble before you configure route redistribution – and you need to be able to control redistribution as well. You may have an OSPF domain with 100 routes, but only need to redistribute 10 of them into a neighboring RIPv2 domain. You’ve got to know how to do that, and one method is the use of a distribute-list.
A distribute-list is an access-list that is used to determine what routes can and cannot be redistributed. Distribute-lists let you specify what routes will be filtered from the process. You can use standard or extended ACLs, and you can filter routes that are coming into a routing process or being injected into another process.
In the following example, R1 is redistributing RIP routes into OSPF, but only wants to advertise network 150.1.1.0 /24 to other OSPF routers. An ACL will be written to match that particular network, and then the distribute-list will be written under the routing process. I’m going to show you the IOS Help output for the distribute-list command, and please note that routing updates can be controlled at the interface level or protocol level.
R1(config)#access-list 24 permit 150.1.1.0 0.0.0.255
R1(config)#router ospf 1
R1(config-router)#redistribute rip subnets
R1(config-router)#distribute-list 24 ?
in Filter incoming routing updates
out Filter outgoing routing updates
R1(config-router)#distribute-list 11 out ?
Async Async interface
BRI ISDN Basic Rate Interface
BVI Bridge-Group Virtual Interface
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To pass the BSCI exam and become a CCNP, you have to be aware of the proper use of passive interfaces. You learned about passive interfaces in your CCNA studies, but here we’ll review the basic concept and clear up one misconception regarding passive interfaces and OSPF.
Configuring an interface as passive will still allow the interface to receive routing updates, but the interface will no longer transmit them. While the command itself would make you think this command will be applied at the interface level, that is not the case. Below, we’ll configure ethernet0 as a RIP passive interface.
R1(config)#router rip
R1(config-router)#passive-interface ethernet0
Ethernet0 will no longer send RIP routing updates, but will accept them.
The passive interface concept is clear enough with RIP, IGRP, and EIGRP – all protocols that send routing update packets. But OSPF doesn’t send routing update packets – OSPF sends link state advertisements. It’s the inability of the passive interface command to stop LSAs that lead many to think that passive interfaces cannot be used with OSPF. Read the rest of this entry »
Your BSCI exam and CCNP certification success depend on mastering BGP, and a big part of that is knowing how and when to use the many BGP attributes. And for those of you with an eye on the CCIE, believe me – you’ve got to know BGP attributes like the back of your hand. One such BGP attribute is the Multi-Exit Discriminator, or MED.
The MED attribute is sent from a router or routers in one AS to another AS to indicate what path the remote AS should use to send data to the local AS.
That sounds a little confusing on paper, so let’s walk through an example. R1 is in AS 1, and R2, R3, and R4 are in AS 234. R4 is advertising a loopback into BGP, and R1 has two possible next-hops to get to that loopback – R2 (172.12.123.2) and R3 (172.12.123.3). Let’s see which of the two paths R1 is using.
R1#show ip bgp 4.4.4.4
BGP routing table entry for 4.4.4.4/32, version 8
Paths: (2 available, best #2, table Default-IP-Routing-Table)
Flag: 0×208
Advertised to non peer-group peers:
172.12.123.3
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To pass the BSCI exam and earn your CCNP, you’ve got to keep a lot of details in mind. It’s easy to overlook the “simpler” protocols and services such as static routing and distance vector protocols. With this in mind, here’s a quick review of some details you should know for success in the exam room and real-world networks!
When packets need to be routed, the routing table is parsed for the longest prefix match if multiple paths exist with the same prefix length, the route with the lowest AD is preferred. If there are still multiple valid paths, equal-cost load-sharing goes into effect.
The ip route command is used to create static routes the command ip route 0.0.0.0 0.0.0.0 < next-hop-IP or local exit interface> creates a default static route.
A static route with a next-hop IP address has an AD of one, while a static route with a local exit interface has an AD of zero.
A floating static route is a static route with an AD higher than that of the dynamic routing protocols running on the router, ensuring that the static route can only be used if the routing protocol goes down.
On-Demand Routing (ODR) is only appropriate in a hub-and-spoke network. The spokes effectively become stub routers. ODR uses Cisco Discovery Protocol (CDP) to send route information.
To propagate a default route with IP routing, use the ip default-network command. To do so with IP routing disabled, use ip default-gateway. You can also redistribute a static route into most protocols, but not IGRP. IGRP does not understand a static route to 0.0.0.0.
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