TCAM allocation on 7250 IXR-6/10 and 7250 IXR-6e/10e

Each forwarding complex on a 7250 IXR and IXR-e IMM has a TCAM with 12 large banks and 4 small banks. Each of the large banks supports 2K entries each, addressable with a 160-bit key. Each of the small banks supports 256 entries each with a 160-bit key size. This TCAM bank allocation is shown in TCAM allocation on 7250 IXR and IXR-e.

Figure 1. TCAM allocation on 7250 IXR and IXR-e

ACLs can be dynamically allocated to banks 0-8. Requirements for each ACL type are as follows:

  • Ingress IPv4 ACL: entries require single-wide banks that can start at any bank number (and do not need to be contiguous)
  • Egress IPv4 ACL: entries require single-wide banks that can start at any bank number (and do not need to be contiguous)
  • Ingress IPv6 ACL: entries require double-wide (side-by-side) banks that must start at an even bank number
  • Egress IPv6 ACL: entries require double-wide (side-by-side) banks that must start at an even bank number
  • IPv4 policy-forwarding (PBF): entries require single-wide banks that can start at any bank number (and do not need to be contiguous)

Dynamic TCAM allocation works as follows:

  • When a new bank needs to be allocated, the system looks for the first available space, progressing in ascending order from bank 0. If space for a double-wide bank cannot be found, the system attempts to make space by moving the fewest number of single-wide banks.
  • When the number of entries required by a particular user drops to a level where a single-wide or double-wide bank can be freed up, the system selects the bank that can create the largest space of free banks, moving entries between banks as necessary.