Cisco CCNP / BSCI Tutorial: Evaluating OSPF and ISIS Hellos
Whereas studying to move the BSCI examination and getting ready to earn your CCNP certification, you’ll rapidly notice that while OSPF and ISIS are each link-state protocols, there are a whole lot of differences between the two. One major distinction is the best way the 2 protocols deal with hi there packets.
Good day packets are imperative to holding OSPF and ISIS adjacencies alive. Since they are each hyperlink-state protocols, neither of them will send updates at any specified time. Hey packets are the one method by which routers working OSPF and ISIS can see that a neighboring router continues to be available.
OSPF provides us some great options relating to keeping routing table measurement down via the usage of stub and whole stub areas, however to OSPF, a hi there packet is a hello packet. ISIS routers are capable of sending two various kinds of hellos – Level 1 and Degree 2.
ISIS routers are categorised as Stage 1 (L1), Stage 2 (L2), and Stage 1-2 (L1-L2). By default, Cisco routers are L1-L2 routers; which means that every ISIS-enabled interface will ship out both L1 and L2 hellos.
If one of the interfaces is forming solely an L1 or L2 adjacency, there is not any reason to ship out hellos for the opposite adjacency type. For example, if R1 is forming an L1 adjacency with R2 via its ethernet0 interface, there isn’t any motive to allow the router to transmit L2 hellos. To hardcode a router interface to send only L1 or L2 hellos, use the isis circuit-type command.
R1(config)interface ethernet0
R1(config-if)isis circuit-sort stage-1
Notice: To configure this interface to ship only L2 hellos, the total command is “isis circuit-type stage-2-solely”, not simply “level-2”.
This configuration would stop L2 hellos from being transmitted out ethernet0. While this does save router sources and prevents unnecessary bandwidth usage, there is also no approach an L2 adjacency can be formed – so double-check your network topology earlier than utilizing this command!
To move your BSCI exam and earn your CCNP certification, you’ve got to master route summarization. If you get to the BSCI degree, truly breaking the routes down into binary strings and performing summarization is second nature to you. (If it isn’t, get some extra observe!) What makes CCNP / BSCI route summarization tougher is just protecting the completely different protocol summarization commands straight!
RIP and EIGRP both carry out route summarization on the interface level with the ip abstract-address command. Within the following example, R2 is working RIP and was sending four routes to R3, R3’s table looked like this earlier than summarization:
R3show ip route rip
172.16.0.0/24 is subnetted, 4 subnets
R 172.16.8.zero [120/1] via 172.23.23.2, 00:00:02, Ethernet0
R 172.16.9.0 [120/1] via 172.23.23.2, 00:00:02, Ethernet0
R 172.16.10.0 [120/1] through 172.23.23.2, 00:00:02, Ethernet0
R 172.16.11.zero [120/1] via 172.23.23.2, 00:00:02, Ethernet0
By summarizing the routes and using the ip abstract-tackle command, RIP advertises solely the summary path to the downstream neighbor.
R2(config)int ethernet0
R2(config-if)ip summary-tackle rip 172.16.8.0 255.255.252.0
R3clear ip route *
R3show ip route rip
172.16.0.zero/22 is subnetted, 1 subnets
R 172.16.8.0 [120/1] via 172.23.23.2, 00:01:24, Ethernet0
EIGRP works a lot the same means, besides that the EIGRP AS quantity should be named in the ip summary-handle command.
Within the following instance, R2 was advertising 4 separate routes to R3 by way of EIGRP a hundred: 100.0.0.0, 101.0.0.0, 102.0.0.zero, and 103.0.0.zero, all with an eight-bit mask. What abstract route can be used here?
The summary is 100.0.0.0 252.0.0.0. To send that route to downstream routers, configure the next on R2:
R2(config)interface ethernet0
R2(config-if)ip summary-handle eigrp 100 100.0.0.zero 252.0.0.0
R3 will then have only one route in its EIGRP table – the summary route.
R3show ip route eigrp
D 100.0.0.zero/6 [90/2297856] via 172.23.23.2, 00:02:33, Ethernet0
By mastering fundamental binary expertise and preserving in mind that RIP and EIGRP carry out route summarization at the interface level, you’re one step nearer to passing your BSCI exam and earning your CCNP certification!
In the subsequent part of this tutorial, we’ll take an in depth look at the different strategies OSPF uses for route summarization.
When you’re studying for the BSCI examination on the best way to earning your CCNP certification, you’ve got to grasp using BGP attributes. These attributes mean you can manipulate the path or paths that BGP will use to achieve a given vacation spot when a number of paths to that destination exist.
In this free BGP tutorial, we’re going to try the NEXT_HOP attribute. It’s possible you’ll be pondering “hey, how complicated can this attribute be?” It’s not very complicated in any respect, but this being Cisco, there’s received to be at the very least one unusual detail about it, proper?
The NEXT_HOP attribute is straightforward sufficient – this attribute signifies the subsequent-hop IP handle that ought to be taken to reach a destination. In the following instance, R1 is a hub router and R2 and R3 are spokes. All three routers are in BGP AS 100, with R1 having a peer relationship with both R2 and R3. There isn’t any BGP peering between R2 and R3.
R3 is promoting the community 33.3.0.0 /24 through BGP, and the value of the next-hop attribute on R1 is the IP deal with on R3 that is used within the peer relationship, 172.12.123.3.
The problem with the subsequent-hop attribute is available in when the route is marketed to BGP peers. If R3 were in a separate AS from R1 and R2, R1 would then advertise the path to R2 with the subsequent-hop attribute set to 172.12.123.3. When a BGP speaker advertises a route to iBGP friends that was originally learned from an eBGP peer, the subsequent-hop value is retained.
Right here, all three routers are in AS 100. What is going to the subsequent-hop attribute be set to when R1 advertises the path to its iBGP neighbor R2?
R2show ip bgp
There might be no subsequent-hop attribute for the route on R2, as a result of the route is not going to seem on R2. By default, a BGP speaker will not promote a route to iBGP neighbors if the route was first realized from one other iBGP neighbor.
Luckily for us, there are several methods around this rule. The commonest is the use of route reflectors, and we’ll take a look at RRs in a future free BGP tutorial.
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