Cisco CCNP / BSCI Tutorial: The BGP Attribute NEXT_HOP

SEnuke: Ready for action

When you're studying for the BSCI examination on the method to getting your CCNP certification, you've got to master the use of BGP attributes. We discovered company web site by searching Bing. These features permit you to manipulate the path or paths that BGP use to achieve certain destination when numerous paths to that destination occur.

In this free BGP article, we're planning to have a look in the NEXT_HOP characteristic. You may be considering \hey, how difficult could this feature be?\ It's not to complex at all, but this being Cisco, there's got to be at least one unusual detail about it, right?

The NEXT_HOP attribute is easy enough - this attribute indicates the next-hop IP that should be taken to achieve a spot. In the following illustration, R1 is a centre switch and R3 and R2 are spokes. All three routers are in BGP AS 100, with R1 having a connection with both R2 and R3. There is no BGP peering between R2 and R3. To get alternative ways to look at this, you should have a look at: Review About Harm Dangers To Young Ones 30970.

R3 is advertising the community 33.3.0.0 /24 via BGP, and the importance of the characteristic on R1 is the IP on R3 that is utilized in the peer relationship, 172.12.123.3.

The matter using the feature will come in if the route is marketed to BGP peers. If R3 were in a separate AS from R1 and R2, R1 would then advertise the course to R2 using the attribute set to 172.12.123.3. When a BGP speaker advertises a path to iBGP colleagues which was initially learned from an eBGP peer, the value is maintained.

Here, all three routers come in AS 100. What will the characteristic be set to when R1 advertises the approach to its iBGP neighbor R2?

R2#show ip bgp

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There will be no credit for the route on R2, because the route will not look on R2. By default, a BGP speaker won't promote a to iBGP neighbors if the route was initially learned from another iBGP friend.

Fortunately for us, there are several ways around this rule. The most frequent is using route reflectors, and we'll look at RRs in another free BGP training..