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  • 1.  Aggregate VS Generate routes

    Posted 11-11-2023 18:24

    Hi, 

    I'm currenty studding for junos exam and doing some routing lab using Juniper VLAB.  For this lab I'm using topology named "Intra-AS BGP-CT".  I erased all router configuration and paste the confirgurate attached to this post. I also include a diagram in PDF format as reference.

    When I use aggregated route function to generate a summary route for 172.16.0.0/16 on router PE2 the summary route is not advertised to CE2, I supect this is due of the link to CE2 is part of 172.16.0.0./16 network.

    When I replace "aggregated" feature with "generate"  without any other modification the summary is successfully advertised to CE2.  Anybody can explain ? and what would be the benefit of using one over the other feature aggregate VS generated.

    Thank you 



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    Xine
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    Attachment(s)

    txt
    ce1.txt   2 KB 1 version
    txt
    PE2.txt   3 KB 1 version
    pdf
    Intra-AS BGP-CT.pdf   75 KB 1 version
    txt
    ce2.txt   2 KB 1 version
    txt
    PE1.txt   3 KB 1 version
    txt
    P.txt   2 KB 1 version


  • 2.  RE: Aggregate VS Generate routes

    Posted 11-12-2023 05:48

    Chris Paker explains it really well Aggregate vs Generated Route



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    THOMAS SCOTT
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  • 3.  RE: Aggregate VS Generate routes

    Posted 11-12-2023 05:48

    ack. Chris Parker*



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    THOMAS SCOTT
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  • 4.  RE: Aggregate VS Generate routes

    Posted 11-12-2023 05:48

    Hi Xine,

    Aggregate routes will only become active when at least one of the contributing routes are active in the routing-table.

    Whereas Generate Routes  create a summarized route of prefixes that are then advertised into an IGP.

    When you have the aggregate configuration configured, can you run the command:

    # show route protocol aggregate


    If this shows as 'reject' then it means that it will reject the traffic as a non-matching prefix arrives on the interface. 

    Unfortunately I can't see the files you applied as I'm on my phone, but I hope this helps and gives you a bit more information on the issue.

    HTH,



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    Ethan Jackson
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  • 5.  RE: Aggregate VS Generate routes

    Posted 11-13-2023 10:18

    as an example, if you are generating a default route (0/0), you would see the contributing route like this...

    show route 0/0 exact detail | find contrib

    if you don't see a contributing listed there, try this....

    show route 0/0 exact hidden

    if the intended generated route is hidden, it's probably because the contributing dependency route is missing, and the route will be listed as "reject" as someone else has already mentioned

    an interesting point about generated vs aggregate routes, is that they are both of protocol type "aggregate" with default route preference of 130.  A few notes I have when I was learning about them is the following...

    show route a.b.c.d exact detail

    Aggregate Route

    Aggregate Preference: 130  <<<------ Aggregate and Generated routes look the same

     Next hop type: Reject   <<<------ Aggregate defaults as Reject and can be configured as Discard

     

    Generated Route

    Next hop type: Router, Next hop index: 546   <<<------ Generated Route will show as type: Router

    Next hop: a.b.c.x via ge-0/0/1.0, selected  <<<------ Generated has valid next-hop proving this to be a Generated Route



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    - Aaron
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