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Why EBGP export policy require next-hop self setting

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  • 1.  Why EBGP export policy require next-hop self setting

    Posted 03-26-2018 09:59

    Reading a doc from Juniper, Clos IP Fabrics with QFX5100 Switches. I saw ebgp export policy with next-hop self.  And the explanation is "we use next-hop self to change the next hop of each advertised prefix to the egress interface of the switch." As I know this is ebgp default behavior.

     

    Appreciate if someone give more detail explanation on this.

     

    One more question about bgp graceful-restart, in the same doc, "graceful-restart—Of course we want the ability to make policy changes to BGP without having to tear down existing sessions. To enable this functionality, we can enable the graceful-restart feature in Junos OS" is it true? is it bgp graceful-restart functionality?



  • 2.  RE: Why EBGP export policy require next-hop self setting

    Posted 03-26-2018 22:37

    Hi!

     

    Probably you can point to the document, it will be helpful to understand why it has been mentioned that way or if document needs correction. Your understanding is correct by default, on a e-bgp peering next-hop self is changed automatically.

     

    Graceful-restart is the capability to take out router peering and re-establishing minizing distruption to other part of the network. Helper mode for graceful-restart (to assist peer node going down) is enabled by default.

    Ideally changing BGP policy, should never cause peering to go down. However, if the policy is moved from peer level to group level or vice-versa it may cause peering to go down. This is different than graceful-restart functionality and the two should not be confused.



  • 3.  RE: Why EBGP export policy require next-hop self setting

    Posted 03-27-2018 09:02

    Morning Amit,

     

    Thanks for your reply. I still want to confirm if my knowledge is out of date or the doc need correction.

    The doc link is https://www.juniper.net/us/en/local/pdf/whitepapers/2000565-en.pdf, page 14&15

     

    Thanks again

    Jiapeng



  • 4.  RE: Why EBGP export policy require next-hop self setting
    Best Answer

    Posted 03-27-2018 10:13
    Hi Jiapeng,

    I didn’t read the whole document but If I read it correctly (from the page 14 & 15) it’s no-where mentioned that configuring “next-hop self” is must in that document.

    It just say this

    We can craft a common set of BGP policies to be used across both spines and leaves, which results in a simple copy and paste operation. Let’s walk through them.

    It seems like author just created a common set of policies (kind of template) which he could just copy/paste.

    HTH


  • 5.  RE: Why EBGP export policy require next-hop self setting

    Posted 03-27-2018 11:06

    Agree. Thanks.

     

    Page 15

    term loopback
    —The first order of business is to identify the switch’s loopback address and export it to all other
    BGP peers. We can do this by looking at the directly connected interfaces that match a 10/24 or longer bitmask.
    This quickly identifies all loopback addresses across the entire IP fabric. Because we don’t want to propagate all
    of the point-to-point addresses throughout the IP fabric, we use next-hop self to change the next hop of each
    advertised prefix to the egress interface of the switch. Now each switch in the IP fabric directly uses neighbor IP
    addresses in the forwarding table.


  • 6.  RE: Why EBGP export policy require next-hop self setting

     
    Posted 03-27-2018 19:36

    As Kingsman mentioned, there is no requirement to exclusively to do NHS for the ebgp sessions.