Fine tuning route advertisements


Megaport provides two BGP route servers to make connecting to all peers on our network simple and fast. With just one BGP session you can pick up routes from almost all of the connected networks.

Using the route servers however can hamper traffic engineering as all routes are advertised to all peers equally. To help work around this limitation we’ve defined numerous BGP communities and features to allow networks to control how their routes are advertised to each peer.

Our route servers do not insert their own autonomous system number into the BGP path. This makes the path shorter, and more accurately reflects the traffic flow through the network.

BGP multi-exit discriminator metrics on the Megaport IX are passed transparently between peers. Combined with a direct AS path, this allows MED to be used for traffic engineering.

BGP communities – using the BGP communities below, peers can prevent their prefixes from being advertised to specific neighbours.

| Community | Action |
| 64990:ASN | Do not advertise to ASN |
| 64991:ASN | Prepend once to ASN |
| 64992:ASN | Prepend twice to ASN |

| Extended Community | Action |
| RT 64990:ASN | Do not advertise to ASN |
| RT 64991:ASN | Prepend once to ASN |
| RT 64992:ASN | Prepend twice to ASN |
| RT 64999:0 | Do not advertise this prefix unless explicitly permitted |
| RT 64999:ASN | Permit this prefix to be advertised to ASN |

These can be adapted for peers with 4-byte AS numbers. Let us know if you want to know how!

Filed under: Blog News & Updates

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