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  • 1.  ISIS :purpose of Extended TLV ( type 135)

    Posted 03-16-2024 21:19

    Hi everyone,

    In ISIS protocol, IP PREFIXES  are advertised inside Internal TLV , I noticed that same IP PREFIX that is announced inside Internal TLV, also  gets  announced inside " Extended TLV".

    In the example below, we see MX4 announces 172.172.172.0/24, 10.10.10.0/24, 4.4.4.4/32 inside Internal TLV and also inside Extended TLV.

    What is the purpose of announcing IP PREFIX  in Extended TLV when it is already advertised inside Internal TLV?



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    Be kind!!
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  • 2.  RE: ISIS :purpose of Extended TLV ( type 135)

    Posted 03-18-2024 04:20

    Hi,

    If I am not wrong, this happens when you enable wide metrics.



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    FARID AKHUNDOV
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    Original Message


  • 3.  RE: ISIS :purpose of Extended TLV ( type 135)

    Posted 03-18-2024 23:22
    Edited by LEEBAHI 03-18-2024 23:23

    Thanks Farid!!

    Wide metric is on by default on Juniper so extended TLV is also added, when enable wide metric only,is enabled ,  then  internal TLV are suppressed., extended TLV are only present.

    But I was curious what would be the rational behind to have wide metric also enabled along site with narrow metric ( which is default on JUNOS).



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    Be kind!!
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    Original Message


  • 4.  RE: ISIS :purpose of Extended TLV ( type 135)

    Posted 03-19-2024 06:42

    As far as I remember, by default both narrow and wide-metrics are enabled on both L1 and L2 for backward compatibility with routers, who do not support wide metrics.

    If both sides support wide metrics, it makes sense to keep wide metrics only by set level X wide-metrics-only  and disable generation of narrow metrics.



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    FARID AKHUNDOV
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    Original Message


  • 5.  RE: ISIS :purpose of Extended TLV ( type 135)

    Posted 03-20-2024 07:27

    Absolutely, such default behaviour is completely obsolete: decided probably 25 years ago, for compatibility with equipments that no longer exist.

    Plenty of default behaviours in JunOS (in Cisco IOS too, actually) are actually obsolete and you start your configurations by changing them :D



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    Olivier Benghozi
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    Original Message