Cisco 3550-24 - Catalyst SMI Switch Manual de usuario descargar pdf (Pagina 3)

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of the packet. Control plane and dataplane accesscontrol

lists (ACLs) are supported on all ports to ensure proper

policing and marking on a per packet basis.

After the packet goes through classiﬁcation, policing, and

marking, it is then assigned to the appropriate queue

before exiting the switch. The Catalyst 3550 supports

four egress queues per port, which allows the network

administrator to be more discriminating and speciﬁc in

assigning priorities for the various applications on the

LAN. At egress, the switch performs scheduling and

congestion control. Scheduling is an algorithm/process

that determines the order in which the queues are

processed. The switches support Weighted Round Robin

(WRR) scheduling and strict priority queuing. The WRR

queuing algorithm ensures that the lower priority packets

are not entirely starved for bandwidth and are serviced

without compromising the priority settings administered

by the network manager. Strict priority queuing ensures

that the highest priority packets will always get serviced

ﬁrst, ahead of all other trafﬁc, and allows the other three

queues to be serviced using WRR scheduling. In

conjunction with scheduling, the Catalyst 3550 Gigabit

Ethernet ports support congestion control via Weighted

Random Early Detection (WRED). WRED avoids

congestion by setting thresholds at which packets are

dropped before congestion occurs.

These features allow networkadministrators to prioritize

mission-critical and/or bandwidth-intensivetraffic, such as

ERP (Oracle, SAP, and so on.), voice (IP telephony traffic)

and CAD/CAM over less time-sensitive applications such

as FTP or e-mail (SMTP). For example, it would be highly

undesirable to have a large file download destined to one

port on a wiring closet switch and have quality

implications such as increased latency in voice traffic,

destined to another port on this switch. This condition is

avoided by ensuring that voice traffic is properly classified

and prioritized throughout the network. Other

applications, such as web browsing, can be treated as low

priority and handled on a best-efforts basis.

The Cisco Catalyst 3550 is capable of performing rate

limiting via its support of the Cisco Committed

Information Rate (CIR) functionality. Through CIR,

bandwidth can be guaranteed in increments as low as

8 Kbps. Bandwidth can be allocated based on several

criteria including MAC sourceaddress, MAC destination

address, IP source address, IP destination address, and

TCP/UDP port number. Bandwidth allocation is essential

in network environments requiring service-level

agreements or when it is necessary for the network

manager to control the bandwidth given to certain users.

Each Catalyst 3550 10/100 port supports 8 aggregate or

individualingresspolicersand8aggregateegresspolicers.

Each Catalyst 3550 Gigabit Ethernet port supports 128

aggregate or individual policers and 8 aggregate egress

policers. This gives the network administrator very

granular control of the LAN bandwidth.

Network Scalability through

High-Performance IP Routing

With hardware-based IP routing and the Enhanced

Multilayer Software Image, the Catalyst 3550 switches

deliver high performance dynamic IP routing. The Cisco

Express Forwarding (CEF)-based routing architecture

allows for increased scalability and performance. This

architectureallowsforveryhigh-speedlookupswhilealso

ensuring thestability and scalability necessaryto meet the

needs of future requirements. In addition to dynamic IP

unicast routing, the Catalyst 3550 Series is perfectly

equipped for networks requiring multicast support.

Multicast routing protocol (PIM) and Internet Group

Management Protocol (IGMP) snooping in hardware

make the Catalyst 3550 Series switches ideal for intensive

multicast environments.

These switches offer several advantages to improve

network performance when used as a stackable wiring

closet switch or as a top-of-the-stack wiring closet

aggregator switch. For example, implementing routed

uplinks from the top of the stack will improve network

availability by enabling faster failover protection and

simplifying the Spanning-Tree Protocol algorithm by

terminating all Spanning-Tree Protocol instances at the

aggregator switch. If one of the uplinks fails, quicker

failover to the redundant uplink can be achieved via a

scalablerouting protocolsuch asOpen ShortestPathFirst

(OSPF) or Enhanced Interior Gateway Routing Protocol

(EIGRP) rather than relying on standard Spanning-Tree

Protocol convergence. Redirection of a packet after a link

failure via a routing protocol results in faster network

convergence than a solution that uses Layer 2 Spanning

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