BGP-Implement BGP Communities

[JMarquez99]

Hi
Can someone please help me answer the following questions in my lab activity about BGP-Implement BGP Communities.

The pdf file of the whole lab activity is attached at the bottom most.

1. Name the three common well known communities.

1. When setting a community inside a route map using the set community command, what is the function of the optional “additive” keyword?

Would really appreciate to have your feedback.

TIA

[Giuseppe Larosa]

Hello @JMarquez99 ,

1)

The three BGP well known communities are Internet, No-Export, No-Advertise. The no-advertise community tells that this prefix should not be advertised to any BGP peer either iBGP or eBGP. The No-Export says that the prefix can be advertised only to iBGP peers , BGP peers in the same AS number.

2) Actually multiple BGP communities can be attached to a BGP prefix the use of the keyword additive allows to add a value to the existing set of BGP communties attached to the BGP prefix and it is considered best practice

A standard BGP community is an unsigned 32 bit integer that provide a way to give a "color" to a prefix or group of prefixes.

What is most important is that BGP communities provide an abstraction layer that allows the service providers to write routing policies based on BGP communities instead of the actual IP prefixes.

If  a customer adds or changes its own prefixes it is enough to use the agreed BGP communities to signal to the upstream ISP how to treat the new / changed prefixes.

Hope to help

Giuseppe

[JMarquez99]

Thank you so much

Best Regards, 

Aaron