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Filter excessively prepended BGP paths

A few months ago, a small ISP was able to disrupt numerous BGP sessions in the Internet core by prepending over 250 copies of its AS number to the outbound BGP updates. While you should use the bgp maxas-limit command to limit the absolute length of AS-path in the inbound updates, you might also want to drop all excessively prepended BGP paths.

The Filter excessively prepended BGP paths article in the CT3 wiki describes the AS-path access list you can use to drop any BGP prefix that has more than X consecutive copies of the same AS number.

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