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Deploying Clos design network using leaf Cisco Nexus 9396PX and when trying to configure arp-suppression using tcam carving getting this error

Free up tcam slice from VACL (default vacl tcam is 512)

# hardware access-list tcam region vacl 0

Giving it to arp-ether but throwing error.

# hardware access-list tcam region arp-ether 256 double-wide
ERROR: Aggregate TCAM region configuration exceeded the available Ingress TCAM slices. Please re-configure.

If i remove double-wide then its not throwing error, now question is do i need double-wide and what is the use of double-wide tcam for arp-ether?

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  • double-wide doubles the allocation to be 512 (256 x 2) instead of 256. Clearly you only have < 512 available in the TCAM.
    – ditrapanij
    Oct 23 '20 at 0:54
  • VACL has 512 which i free up and make it zero 0 and now i want to use that 512 for double-wide arp-ether. why double-wide throwing error but not single wide
    – Satish
    Oct 23 '20 at 3:33
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First of all, when I configure non double-wide arp-ether region the following warning pops up which is quite self-explanatory with the conclusion being -- we have to use double-wide for VxLAN.

WARNING: Configuring the arp-ether region without "double-wide" is deprecated and can result in silent non-vxlan packet drops. Use the "double-wide" keyword when carving TCAM space for the arp-ether region.

Reading this document from Cisco (https://www.cisco.com/c/en/us/support/docs/switches/nexus-9000-series-switches/119032-nexus9k-tcam-00.html) which you probably already saw I draw the following conclusions:

vacl that you try to use to free up 512 entries is actually a single "slice" and "double-wide" needs two slices of 256 or 512, so you have to reconsider the way to allocate the regions...

This error occurs when you try to configure a valid amount of TCAM space with regards to the 4k limit, but your allocation consumes more slices than are available. The only solution for this error is to revisit your intended TCAM carving design in order to free up slices. This error is more common when you try to configure a new double-width feature, as they require at least two slices of 256 or 512.

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  • what will go wrong if i use hardware access-list tcam region arp-ether 256 without double-wide? am i going to loose some feature or just matter of space?
    – Satish
    Mar 1 at 14:24
  • @Satish as per warning I've added: "Configuring the arp-ether region without "double-wide" is deprecated and can result in silent non-vxlan packet drops" -- I can not add anything on top of that, but considering it's coming from the Cisco switch itself I would not go with such config Mar 1 at 14:55

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