Hey Simon There is very little documentation in FRR about this feature. You can find it here: http://docs.frrouting.org/en/latest/bgp.html#configuring-peers

When you connect to a BGP peer over an IPv6 link-local address, you have to specify the IFNAME of the interface used for the connection. To specify IPv4 session addresses, see the neighbor PEER update-source command below. This command is deprecated and may be removed in a future release. Its use should be avoided.

Please note that this feature is used for BGP unnumbered and was probably introduced by the developers working at Cumulus Networks. You can find the corresponding documentation of this feature here: https://docs.cumulusnetworks.com/cumulus-linux/Layer-3/Border-Gateway-Protoc... I hope that helps. Cheers, Manuel -- Manuel Schweizer cloudscale.ch AG Venusstrasse 29 CH-8050 Zürich Fon: +41 44 55 222 55 Fax: +41 44 55 222 56 Web: https://www.cloudscale.ch

On 9 Aug 2019, at 05:10, Simon Jones <batmanustc@gmail.com> wrote:

Hi all,

I found this is new in FRR compared to QUAGGA, what's this used for ? Why I should config interface first ? Is there some DOC about this ?

# neighbor 1.1.1.1/24 ... interface Enable BGP on interface

# neighbor 1.1.1.1/24 remote-as 5001 % Create the peer-group or interface first or specify "interface" keyword % if using an unnumbered interface neighbor

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