How to Read the BGP Table

Hello Kanu R.

Not sure if you’ve covered other routing protocols but if you didn’t, I heavily recommend it.

Every protocol maintains some sort of table or database that contains everything that protocol knows about (OSPF - LSDB, EIGRP - Topology Table).

If you take a look at Rene’s lesson
bgp-as1-as2-as3-as41
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You can see that the BGP table contains information about the networks that BGP knows about, how to reach them, and what are the path attributes for each possible path. It also displays whether the route is valid, invalid, suppressed, and so on. For example, the > symbol indicates that this path is considered the best by the BGP’s Path Selection process.

So yes, the BGP table contains information about networks that BGP knows about along with the path attributes and possible paths to reach those networks.

Now, when it comes to the routing table. The routing table is the place where the best path to reach the network is installed.
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So although BGP had two possible paths (one over 192.168.12.2 and one over 192.168.13.3) to reach 4.4.4.4/32, it considered the path over 192.168.12.2 the best (as indicated by the > symbol) and this was installed into the routing table. The routing table is then used to make forwarding decisions.

So in summary, the BGP table contains information about every network BGP knows about and about every possible path to reach them while the routing table contains the best path/route to reach the specific prefix. So the best route in the BGP table is grabbed and installed into the routing table which is then used to make forwarding decisions.

The routing table can have routes from many different sources, it doesn’t have to be just BGP.

If anything is still unclear, please let me know.

David

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