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Introducció

TODO

Tipus de commutadors

  • Store-and-Forward: Store-and-Forward switching will wait until the entire frame has arrived prior to forwarding it. This method stores the entire frame in memory. Once the frame is in memory, the switch checks the destination address, source address, and the CRC. If no errors are present, the frame is forwarded to the appropriate port. This process ensures that the destination network is not affected by corrupted or truncated frames.
  • Cut-Through: Cut-Through switching will begin forwarding the frame as soon as the destination address is identified. The difference between this and Store-and-Forward is that Store-and-Forward receives the whole frame before forwarding. Since frame errors cannot be detected by reading only the destination address, Cut-Through may impact network performance by forwarding corrupted or truncated frames. These bad frames can create broadcast storms wherein several devices on the network respond to the corrupted frames simultaneously.

Com funcionen?

Conceptes

NOTA: En general parlem de taula de màquines i no fem referència a taula ARP ja que cal tenir que no tot és IPv4. Per exemple IPV6 no utilitza el protocol ARP però també té un procediment per a descobrir adreces MAC utilitzant el protocol ND

  • Source MAC lookup: és el procés que realitza un commutador per buscar una adreça MAC d'origen a la taula de màquines (host table)
  • Destination MAC lookup: és el procés que realitza un commutador per buscar una adreça MAC de destinació
  • Vlan table lookup: cal tenir en compte les VLAN en aquells commutadors que les utilitzin
  • host table entry: cada màquina coneguda pel commutador té una entrada a la taula de màquines. Les entrades poder ser dinàmiques (s'ha après per algún mecanisme dinàmic com ARP o ND) o poden ser estàtiques (afegides manualment per l'administrador del commutador)
  • Rule table: alguns dispositius permeten aplicar normés per filtrar paquets en el propi commutador sense necessitant de tenir un encaminador (en certa manera fan de firewall de capa 2). Les normes es guarden a la taula de normes.
  • INGRESS port: és el port de un commutador pel qual entren els paquets per a una màquina concreta
  • EGRESS port: és el port pel que surten els paquets per a una màquina concreta.
  • cpu port: TODO

Marques

Planet

167.55€
Dispositiu Preu Observacions
RB750G 5 ports Gigabit gestionable amb routerOS 50.79 http://landashop.com/catalog/router-rb750g-gibabit-ethernet-32mb-sobremesa-p-1202.html
TP-Link Gigabit Web Smart Switch de 16 puertos 172€ + IVA http://landashop.com/catalog/smart-switch-tlsg2216web-puertos-101001000m-rj45-ports-p-989.html
TP-LINK. Gigabit Web Smart Switch de 9 puertos +1 1 GBIC 86.22 http://landashop.com/catalog/smart-switch-tlsg2109web-puertos-101001000m-rj45-ports-p-899.html
Planet 8 portsgiga sense FO. Gestionable 129€ + IVA http://www.cablematic.com/Switch-10_comma_-100-y-1000Mbps/Planet-10_quote_-Giga-Web-Switch-10_-_100_-_1000Mbps-%25288UTP%2529/?pag=10&_lang=esp
Planet 24 Ports giga sense F0, Rack 19 285.28 € + IVA http://www.cablematic.com/Switch-10_comma_-100-y-1000Mbps/Rack-19_quote_-Giga-Switch-de-10_-_100_-_1000-Mbps-de-24-UTP/?pag=4

Proveïdors

cisco

TODO

Dunc 101 posts since May 7, 2009 1. Mar 21, 2011 2:32 PM (in response to M1sh0) Re: How ASIC work on switch

Hi M1sh0,


ASIC (Application Specific Integrated Circuits) are specifically designed to support in-hardware forwarding of Layer 2 & 3 information, your currently studying Layer 2 switching so the forwarding of frames at Layer 2 using MAC addresses.


Forwarding decisions at Layer 2 are made by the CAM table (Content Addressable Memory) which represents the MAC Address to port mappings allowing the switch to make forwarding decisions.


Cisco ASIC's do more than just allow hardware forwarding of Layer 2 & 3 data they provide a whole other host of features that make the Catalyst switch line slightly better than some other vendor comparisons.


The actual hardware/software forwarding infromation isn't on the CCNA Syllabus but is on the CCNP SWITCH syallabus and contains a more detailed view of Layer 2 & 3 forwarding decisions and how CEF (Cisco Express Forwarding) works.


Might be worth a read into the following key topics:


CAM - Layer 2 Table ("sh mac-address-table")

TCAM - Layer 3 Table ("sh ip cef")

CEF - Basically reffered to as the "TCAM" but this is technology that underpins that feature.

dCEF - Distributed CEF (Catalyst 3750 / 4500 / 6500 Series).


HTH,

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