BGP full-routes vs partial-routes vs default-route

Image from https://www.cidr-report.org/

The IPv4 full BGP table size is at around 725000 prefix now. This may cause problems for companies who do not have the resources to update or upgrade their edge routers. But, except for Internet transit providers, who does really need to get the full IPv4 BGP table today? And what are the alternatives? Let’s see that in details with some use-cases.

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BGP load sharing and unequal cost load sharing

On Cisco routers, by default the BGP protocol will not do load-sharing – and even less unequal cost load-sharing – across multiple links, for traffic to the same eBGP destination with different AS-path. Let’s see how we can change this. We can configure the command: “maximum-paths n”, but it only works if the weight, local-pref. and AS-path attributes are the same across the different uplinks. So how can we do load sharing if we are multihomed to different ASes? In that case, we must use the BGP command: “bgp bestpath as-path multipath-relax”. VIRL lab…

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