Method of generating TCAM entry and method and apparatus for searching for TCAM entry
View Patent ↗Provided is a method of generating and searching for a single ternary content addressable memory (TCAM) entry for range search and exact-match search. First, it is determined whether an entry to be added is a range search entry or an exact-match search entry. When the entry is the range search entry, a bit at a predetermined position in the upper m bits corresponding to a range represented by the entry is set to “1” and the remaining bits including lower n bits is set to a “don't care” bit x, based on a range table for representing position information of one of the upper m bits which is set to “1” in ranges. When the entry is the exact-match search entry, the upper m bits is set to “don't care” bit x and the lower n bits is set to the entry value. By generating and searching for a single TCAM entry for a range search and an exact-match search, a space for storing the TCAM entry can be optimized and efficiency thereof can be improved.
1. A method of generating an entry in TCAM (ternary content addressable memory) having upper m bits for range search and lower n bits for exact match search, comprising:
(a) determining whether the entry to be added is a range search entry or an exact-match search entry;
(b) when the entry is the range search entry, setting a bit at a predetermined position in the upper m bits corresponding to a range represented by the entry to “1” and setting the remaining bits including lower n bits to a “don't care” bit x, based on a range table for representing position information of one of the upper m bits which is set to “1” in ranges; and
(c) when the entry is the exact-match search entry, setting the upper m bits to “don't care” bit x and setting the lower n bits to the entry.
2. The method of claim 1 , further comprising (d) adding a newly set TCAM entry to a TCAM table.
3. The method of claim 1 , wherein the (a) comprises determining that the entry is the exact-match search entry if a start position value and an end position value included in the entry are equal to each other and determining that the entry is the range search entry if the start position value and the end position value are different from each other.
4. The method of claim 1 , wherein the range table includes position information of a specific bit of the m bits which is set to “1” in the ranges, when m ranges which can overlap each other are represented by m bits.
5. The method of claim 1 , further comprising (e) when the entry is the range search entry, setting a predetermined bit of the entries in a range conversion table corresponding to a range represented by the entry to “1”, in the range conversion table composed of 2 n m-bit entries which can simultaneously specify an n-bit exact match value and m ranges.
6. A method of searching for a TCAM entry comprising:
(a) searching a range conversion table composed of 2 n m-bit entries which can simultaneously specify an n-bit exact match value and m ranges for an entry using an n-bit lookup value as an index;
(b) setting upper m bits of a lookup key to the entry searched from the range conversion table;
(c) setting lower n bits of the lookup key to the n-bit lookup value; and
(d) searching for the TCAM entry using the lookup key.
7. The method of claim 6 , wherein, in the range conversion table, a bit at a predetermined position in entries corresponding to the range is set to “1” when a range search entry is added, and a bit of entries corresponding to a range to be deleted is set to “0” when a range entry is deleted.