SKFREE
Software - Linux bridge
Robert - 04.05.2007 - 10:04
Post subject: Linux bridge
Pred par dnami som musel riesit trochu netradicny problem - potreboval som medzi sebou prepojit dva vzdialene switche, ale prepojovaci kabel bol nakrimpovany napriamo (nie prekrizeny) a ani jeden zo switchov nemal autosense, takze mi to neslo. Preto som to narychlo vyriesil tak, ze som tam vradil Linuxbox a obe eth. rozhrania dal do bridge. Siet je 10mbit/s a pri FTP som mal priepustnost cca 900kbyte/s. Vcera som jednu stranu prekrimpoval a na FTP vidim cez 1mbyte/s.
Chcem sa spytat, aku mate skusenost s bridge pod Linux. Mam dojem, ze ta implementacia nie je uplne 100%. Cosi take som cital aj na Internete. Udajne routovanie je podstatne efektivnejsie implementovane, ale FTP cez router som neskusal.
keo - 04.05.2007 - 14:05
Post subject:
Nebolo by jednoduchsie odcvaknut koncovku a urobit tam krizenu ? Pripadne, ak je to kratke a neda sa to odcvaknut, kupit za 40 SK RJ45 spojku a patch kabel krizeny /alebo krizenu spojku a rovny kabel/ a nadpojit to kusok ?
qido - 04.05.2007 - 14:32
Post subject:
keo wrote: ›Nebolo by jednoduchsie odcvaknut koncovku a urobit tam krizenu ? Pripadne, ak je to kratke a neda sa to odcvaknut, kupit za 40 SK RJ45 spojku a patch kabel krizeny /alebo krizenu spojku a rovny kabel/ a nadpojit to kusok ?
no tu asi ide o princip implementacie bridge rezimu v linuxe...
Robert - 04.05.2007 - 14:44
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Asi som sa zle vyjadril Ked som jednu stranu prekrimpoval na krizenu a Linux box vypustil, priepustnost znatelne narastla.
cobain - 04.05.2007 - 16:09
Post subject:
Robert jednoznacne som to pochopil hned z prveho prispevku a pretozze som lama tak som na to nepisal, ale mam podobne poznatky ako ty ze bridge neni vhodne riesenie. Mi to pripomina ako mi to raz jeden manik vysvetlil. SWITCH manik v nom rozhadzuje pakety lopatkou, ROUTER manik ukazuje kam paket ma ist. predpokladam ze bridge je nieco ako prekladacia stanica, co znamena ze manik je moz namahany 
no musim si to este overit a ujasnit
bakula - 04.05.2007 - 19:02
Post subject:
* Bridging will be slower the more hosts you have in your "learn" table.
* Bridging more than two interfaces will easily lead to inefficiencies. consider bridges as hubs that can sometimes optimize by forwarding the packet out only one (or more) interfaces). Packet duplication is not cheap!
* Bridging puts the interfaces in promiscous mode which will lead to more to do for the input path.
* Bridging uses 802.1d algorithm (afaik) and so it sacrifices packet processing efficiency to gain correctness (which is a very good thing!)
* Bridging has an extra firewall to traverse when it's an ip packet (which is not necessarily a large penalty but processor instruction is a processor instruction.
* route lookups require at most somewhere around 32 lookup steps, whereas bridging will have many many more lookup steps. it would have to compare source address to as many hosts learned on the incoming interface and then compare destination address to all hosts learned on all other interfaces. 48 bit compares are not very "natural" for 32 bit architectures Smile
* routers only forwards packets destined for router mac address (no manycast or poorly bridged packets wasting forwarding capacity).