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Cisco LAN Switch Configuration
A collection of chapter notes from the CLSC course book. Use this in conjunction with other material to prepare yourself for the
CLSC 604-404 test.
- Eric
Chapter 1 - Introduction:
- No pertinent information in this chapter to note.
Chapter 2 - Introduction to Switching Concepts:
Shared Networks, Advantages/Disadvantages:
传统FDDI网络
- PROS:
- Faster shared medium network
- Dual ring safeguards against downtime
- CONS:
- High latency (due to FDDI -> Ethernet/Ethernet -> FDDI Translation)
- No full duplex
- Expensive
- 一般的以太网都会有冲突，大量的冲突令带宽减少，drop掉的数据包会又要重传也要占用带宽，
更多的用户将会抱怨
- 广播消耗的带宽
- ARP
- 分配路由更新信息
- 寻找网络服务器 GNS
- 在分享的带宽上传给所有的机器
- 安全问题:
- 网络不安全
- 网络数据可能被捕获
LAN Segmentation:
- Why Segment LANs?
- 支持相同网段内沟通
- 每个用户都增加了带宽
- LAN 可用以下分段
- 桥 (OSI Level 2)
- 每段内的用户更少
- 存储，转发帧
- Protocol-independent, 既插既用
- 渐渐被交换机代替
- 路由器 (OSI Level 3)
- Manageability:
- 网管能更好的控制路径选择，路由行为更可视化
- Functionality:
- 路由器可以使用流控制，错误和数据拥挤控制，fragmentation和重组服务
和数据包生存时间控制
- Multiple active paths:
- Network topologies can offer more than one path between stations. Operating at the network layer, routers can examine protocol, destination service access point (DSAP),
source service access point (SSAP), and path metric
information before making forwarding or filtering decisions.
- Switches
- Enables multiple high-speed data exchanges
- Low latency and high frame-forwarding rates
- Increases available bandwidth of a network
- Works with existing 802.3 compliant network interface cards and cabling.
- Port configuration switching:
- Allows a port to be assigned to a physical network segment
under software control. This is a very simplistic form
of switching.
- Frame switching:
- Primarily used to increase available bandwidth on the
network. Frame switching allows multiple transmissions
to occur in parallel. This is the type of switching
performed by all Catalyst switches.
- Cell switching (ATM):
- Similar to frame switching. In ATM, small cells of
fixed length are switched on the network. This is
the type of switching performed by all Cisco LightStream switches.
Switching Methods:
------------------
- Cut-through:
- In the cut-through mode, the switch checks the destination
address (DA) as soon as the header is received and immediately
begins forwarding the frame.
- Catalyst 1900, 2820, and 3000 series.
- Store-and-forward:
- The complete frame is received by the switch before forwarding
takes place. The destination and source addresses are read,
the cyclic redundancy check (CRC) is performed, relevant
filters are applied, and the frame is forwarded. (If the
CRC is bad, the frame is discarded.) Latency through the
switch varies with frame length. This is the mode used by
Catalyst 5000 switches.
- Catalyst 1900, 2820, 3000, and 5000 series.
====================
Router and Switch Implementation:
- Switching and routing are complementary
- Switching enhances throughput
- Routers provide network security
- Routers enable dissimilar LANs
LAN Switching:
- Multiple media support
- Ethernet, FastEthernet, ATM, FDDI, and Token Ring.
- Dedicated bandwidth
- Full duplex
- Backplane bandwidth
- Virtual LANs
Benefits of Switching:
- Number of collisions reduced
- Simultaneous, multiple communications
- High-speed uplinks
- Improved network responses
- Increased user productivity
Full-Duplex Ethernet:
---------------------
- Significant performance improvement over shared, half-duplex ethernet.
- Uses point-to-point connections--no hubs
- Collision free (as long as it is a point-to-point connection)
- Full-duplex port connections can use:
- 10BaseT (100 Meters is max distance)
- 10BaseFL (Fiber, 2 kilometers is max distance)
- 100BaseTX
- 100BaseFX
- ATM
- Half-Duplex uses CSMA/CD:
- Collision Sense Multiple Access / Carrier Detect.
- Detects collisions in an ethernet environment.
- Narrow one way bridge, only TX or RX can submit at any one time.
- 50-60% reliability
- Full-Duplex Ethernet Design:
- Transmit (TX) circuit connects directly to receive (RX) circuit.
- No collisions (in point-to-point situations)
- Significant performance improvement
- Eliminates contention on Ethernet point-to-point link
- Uses a single port for each full-duplex connection
- 100% reliability
Token Ring Switching:
---------------------
- Based on IEEE 802.5
- Consists of ring stations and transmission media
- Uses a deterministic media access method
- Passes a special bit pattern token (3 bytes) from station to station
- Segmentation by using Source-Route Bridges
- This however cannot keep up with the fast-trend networking is
taking and thus switches are used for token ring segmentation.
- Collisions do not occur
- What is Switched Token Ring?
- The Token Ring siwtch supports source-route (SR), transparent,
and source-route transparent (SRT) bridging protocols.
- The switch makes forwarding decisions based on simple rules
and table lookups performed at high speed.
Token Ring Token Ring
\ o o /
o O ---- Switch ---- O o
o o
- Token Ring Switching Advantages:
- Increases bandwidth
- Requires no end-system changes
Bridging Modes:
---------------
- Bridging Modes (Type) Review:
- Transparent Bridging (TB):
- Forwarding decisions are made based on the destination MAC
address in a frame.
- Source-Route Bridging (SRB):
- Forwarding decisions are made based on the routing information
field (RIF) in a frame. The switch modifies RIFs for
explorer frames.
- Source-Route/Transparent Translational Bridging (SR/TLB):
- Forawrding decisions require conversion of SRB frames with
or without RIF to transparent bridging (TB) frames, which
includes converting the source address/destination address
(SA/DA) format.
- Used to go from one media to another (Ethernet -> Token Ring)
- Source-Route Switching (SRS):
- Forwarding decisions are made based on the RIF in a frame, if
present. However, the switch does not modify RIFs.
Transparent Bridging:
---------------------
- Switch decision based on destination MAC address (parallel paths
eliminated by IEEE spanning tree.)
- Primarily used in Ethernet 802.3 environments
- Cannot support multiple parallel paths
- IEEE
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