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about ACL

Dear Sirs,

How much does ACL consume DRAM?

Best regards,


Re: about ACL

Hi hiroshi,

In New range of multilayer switches, all the matching process that ACLs provide is implemented in hardware.

Inbound and outbound access lists are compiled into TCAM entries so that decisions of whether to forward a packet can be determined as a single table lookup.

Here is as excerpt from the BCMSN book

TCAM entries are composed of Value, Mask, and Result (VMR) combinations. Fields from frame or packet headers are fed into the TCAM, where they are matched against the value and mask pairs to yield a result.

Values are always 134-bit quantities, consisting of source and destination addresses and other relevant protocol informationall patterns to be matched. The information concatenated to form the value depends on the type of access list, as shown in Table 3-2. Values in the TCAM come directly from any address, port, or other protocol information given in an ACE.

Masks are also 134-bit quantities, in exactly the same format, or bit order, as the values. Masks select only the value bits of interest; a mask bit is set to exactly match a value bit, or is not set for value bits that do not matter. The masks used in the TCAM stem from address or bit masks in ACEs.

Results are numerical values that represent what action to take after the TCAM lookup occurs. Whereas traditional access lists offer only a permit or deny result, TCAM lookups offer a number of possible results or actions. For example, the result can be a permit or deny decision, an index value to a QoS policer, a pointer to a next-hop routing table, and so on.

I could not find the exact number of bytes each ACL will consume



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