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helpfulqua587

helpfulqua587   , 31

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Cisco CCNP / BSCI Tutorial: The BGP Attribute NEXT_HOP

When you're studying for the BSCI assessment on the solution to making your CCNP certification, you've surely got to master the usage of BGP attributes. These features enable you to manipulate the path or paths that BGP use to attain certain destination when numerous paths to that destination occur.

In this free BGP guide, we're planning to take a look at-the NEXT_HOP characteristic. Maybe you are thinking "hey, how complicated could this attribute be?" It's not to difficult at all, but this being Cisco, there is got to be at least one unusual aspect about it, right?

The NEXT_HOP attribute is straightforward enough - this attribute indicates the next-hop IP that should be taken to attain a spot. In the following instance, R1 is a center hub and R2 and R3 are spokes. All three routers come in BGP AS 100, with R1 having a relationship with both R3 and R2. There's no BGP peering between R2 and R3.

R3 is advertising the community 33.3.0.0 /24 via BGP, and the value of the next-hop characteristic on R1 is the IP on R3 that is used in the peer relationship, 172.12.123.3.

The problem using the attribute comes in once the route is advertised to BGP peers. If R3 were in another AS from R1 and R2, R1 could then advertise the course to R2 with the attribute set to 172.12.123.3. Linklicious is a salient database for further concerning the meaning behind this viewpoint. The value is kept, when a BGP speaker advertises an approach to iBGP peers that was actually learned from an eBGP fellow. Be taught additional info on backlinksindexer.com by going to our original article directory.

Here, all three routers come in AS 100. What'll the next-hop attribute be set to when R1 advertises the approach to its iBGP friend R2?

R2#show internet protocol address bgp

< no output >

There will be no attribute for the route on R2, as the route won't look on R2. Automagically, a BGP speaker will not promote a to iBGP neighbors if the route was first learned from another iBGP neighbor.

Fortuitously for all of us, there are lots of ways around this principle. This dazzling linklicious.me use with has various fine lessons for the inner workings of it. The most common is the utilization of route reflectors, and we'll look at RRs in another free BGP article..