Survey and taxonomy of ip address lookup

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Veeramani , Manas Kumar , Sk. Noor Mahammad.

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K Asst. References Publications referenced by this paper. Biersack , Walid Dabbous. Using multiple hash functions to improve IP lookups Andrei Z. Broder , Michael Mitzenmacher. Multi-dimensional prefix matching using line search Marcel Waldvogel.

Th first lvl of th multibit tri hs 2 24 nos n is implmnt s tbl with th sm numbr of ntris. An ntry in th first lvl ontins ithr th forwring informtion or pointr to th orrsponing subtri t th son lvl. Entris in th first tbl n 2 byts to stor pointr; hn, mmory bnk of 32 Mbyts is us to stor 2 24 ntris. Atully, th pointrs us 5 bits bus th first bit of n ntry inits if th informtion stor is th forwring informtion or pointr to son-lvl subtri.

Bh telecom address

Th numbr of subtris t th son lvl pns on th numbr of prfixs longr thn 24 bits. In th worst s h of ths prfixs will n iffrnt subtri t th son lvl. Sin th stri for th son lvl is 8 bits, subtri t th son lvl hs lvs. Th son-lvl subtris r stor in son mmory bnk. Th siz of this son mmory bnk pns on th xpt worst s prfix lngth istribution.

In th MEst tbl [5] w xmin on August 6, , only 96 prfixs wr longr thn 24 bits. For xmpl, for mmory bnk of 2 2 ntris of byt h i.. Th first 24 bits of th stintion rss r us to inx into th first mmory bnk th first lvl of th multibit tri. If th first bit of th ntry is, th ntry ontins th forwring informtion; othrwis, th forwring informtion must b look up in th son mmory bnk th son lvl of th multibit tri. In tht s, w ontnt th lst 8 bits of th stintion rss with th pointr just foun in th first tbl. Th rsult is us s n inx to look up th forwring informtion in th son mmory bnk. Th vntg of this simpl shm is tht th lookup rquirs mximum of two mmory sss.

Morovr, sin it is hrwr pproh, th mmory sss n b piplin or prllliz. As rsult th lookup oprtion tks prtilly on mmory ss tim.

Nvrthlss, sin th first stri is 24 bits n lf pushing is us, upts my tk long tim in som ss. Strting t th root, thy rpl th lrgst full binry subtri with orrsponing on-lvl multibit subtri. This pross is rpt rursivly with th hilrn of th multibit subtri obtin. Aitionlly, on-hil pths r omprss. Sin w rpl t h stp binry subtri of svrl lvls with multibit tri of on lvl, th pross n b viw s omprssion of th lvls of th originl binry tri.

Lvl-omprss LC is th nm givn by Nilsson to ths multibit tris.

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Nvrthlss, ltting th strutur of th binry tri stritly trmin th hoi of stris os not llow ontrol of th hight of th rsulting multibit tri. On wy to furthr ru th hight of th multibit tri is to lt th strutur of th tri only gui, not trmin, th hoi of stris. In othr wors, w will rpl nrly full binry subtris with multibit subtri i.. Inst, thr r nough nos t th thir lvl 5 of th 8 possibl nos for multibit subtri of stri 3. A two-lvl fully xpn multibit tri.

Morovr, intrnl nos r not llow to stor prfixs. Inst, h lf hs linr list with prfixs, in s th pth to th lf shoul hv on or svrl prfixs lss spifi prfixs. As rsult, srh in n LC tri pros s follows. Th LC tri is trvrs s is th bsi multibit tri. Nvrthlss, sin pth omprssion is us, n xpliit omprison must b prform whn rriving t lf. In s of mismth, srh of th list of prfixs must b prform lss spifi prfixs, i.. Sin th LC tri is implmnt using singl rry of onsutiv mmory lotions n list of prfixs must b mintin t lvs, inrmntl upts r vry iffiult. Multibit Tris n Optimiztion Thniqus On sy wy to boun worst-s srh tims is to fin fix stris tht yil wll-fin hight for th multibit tri.

Th problm is tht, in gnrl, mmory onsumption will b lrg, s sn rlir. On th othr hn, w n minimiz th mmory onsumption by ltting th prfix istribution stritly trmin th hoi of stris. Unfortuntly, th hight of th rsulting multibit tri nnot b ontroll n pns xlusivly on th spifi prfix istribution. W sw in th lst stion tht Nilsson uss th fill ftor s prmtr to ontrol th influn of th prfix istribution on stri hoi, n so influns somwht th hight of th rsulting multibit tri. Sin prfix istribution still guis stri hoi, mmory onsumption is still ontroll.

Nvrthlss, th us of th fill ftor is simply rsonbl huristi n, mor importnt, os not llow gurnt on worst-s hight. Srinivsn t l. Th uthors giv mtho to fin th optiml stris for th two typs of multibit tris: fix stri n vribl stri. Anothr wy to minimiz lookup tim is to tk into ount, on on hn, th hirrhil strutur of th mmory in systm n, on th othr, th probbility istribution of th usg of prfixs whih is trffi-pnnt. Chung t l. Thy suppos systm hving thr typs of hirrhil mmoris with iffrnt ss tims n sizs.

Using optimiztion thniqus mks sns if th ntris of th forwring tbl o not hng t ll or hng vry littl, but this is rrly th s for bkbon routrs. Insrting n lting prfixs grs th improvmnt u to optimiztion, n rbuiling th strutur my b nssry. Thus, if w us multibit tris with lrg stris, w will hv grt numbr of ontiguous nos with th sm BMP. W n us this ft n omprss th runnt informtion, whih will llow sving mmory n mk th srh oprtion fstr bus of th smll hight of th tri.

W will illustrt thir mtho with smll xmpl whr w o mximl xpnsion supposing 5-bit rsss n us twolvl multibit tri. Th first lvl uss stri of 2 bits, th son lvl stri of 3 bits, s shown in Fig. Th i is to omprss h of th subtris t th son lvl. Eh olumn orrspons to on of th son-lvl subtris. Th gol is to omprss th rpt ourrns of th BMPs. Nvrthlss, th omprssion is on in suh wy tht t h stp th numbr of omprss symbols is th sm for h olumn. With this strtgy th omprssion is not optiml for ll olumns, but sin th omprssion is m in synhroniz wy for ll th olumns, ssing ny of th omprss subtris n b m with on ommon itionl tbl of pointrs, s shown in Fig.

To fin th BMP of givn rss w trvrs th first lvl of th multibit tri s usul; tht is, th first 2 bits of th rss r us to hoos th orrt subtri t th son lvl. Thn th lst 3 bits of th rss r us to fin th pointr in th itionl tbl. With this pointr w n rily fin th BMP in th omprss subtri. For xmpl, srhing for th rss will gui us to th thir subtri olumn in th omprss strutur; n using th Aitionl tbl Figur 7. A full xpnsion prlll omprssion shm. Binry srh on prfix lngths. In th tul shm propos by Crsnzi, prfixs r xpn to 32 bits. A multibit tri of two lvls is lso us, but th stri of th first n son lvls is 6 bits.

It is worth noting tht vn though omprssion is on, th rsulting strutur is not smll nough to fit in th h mmory. Nvrthlss, bus of th wy to ss th informtion, srh lwys tks only thr mmory sss. Th rport mmory siz for typil bkbon forwring tbl is. Anothr shm tht ombins multibit tris with th omprssion i hs bn ubb th Lul lgorithm [2]. In this shm, multibit tri with fix stri lngths is us. Th stris r 6,8,8, for th first, son, n thir lvl rsptivly, whih givs tri of hight 3. In orr to o ffiint omprssion, th Lul shm must us st of isjoint prfixs; hn, th Lul shm first trnsforms th st of prfixs into isjoint-prfix st.

Thn th prfixs r xpn in orr to mt th stri onstrints of th multibit tri. Aitionlly, in orr to sv mmory, prfixs r not llow t intrnl nos of th multibit tri ; thus, lf pushing is us. Agin, th i is to omprss th prfix informtion in th subtris by supprssing rpt ourrns of onsutiv BMPs. Nvrthlss, ontrry to th lst shm, h subtri is omprss inpnnt of th othrs. On subtri is omprss, lvr oing mhnism llows th ss to th BMPs. Du to lk of sp w o not giv th tils of th oing mhnism. Whil th tri hight in th Lul shm is 3, tully mor thn thr mmory rfrns r n bus of th oing rquir to ss th omprss t strutur. Srhing t h lvl of th multibit tri ns, in gnrl, four mmory rfrns.