SWITCH交换机基础知识(2)

Half Duplex (CSMA/CD)

? Unidirectional data flow ? Higher potential for collision ? Hubs connectivity

Full Duplex

? Point-to-point only ? Attached to dedicated switched port ? Requires full-duplex support on both ends ? Collision-free

? Collision detect circuit disabled 监听的功能就关掉了

冲突检测用的是本地环电路(local loop circuit)检测CSMA/CD

Nodes that are attached to hubs that share their connection to a switch port must operate in half-duplex mode because the end stations must be able to detect collisions.

4、管理mac-address-table 1）Show mac-address-table

wg_sw_a(config)#mac-address-table aging-time ? <10-1000000> Aging time value The default is 300 sec.

The MAC address table is also referred to as the CAM table (Content Address Memory) on some switches.

2）配置永久的mac地址

wg_sw_1900&2950(config)#mac-address-table permanent {mac-address type module/port}

wg_sw_2950_only(config)#mac-address-table static mac_addr {vlan vlan_id} [interface int1 [int2 ... int15]]

3）Setting a Restricted Static MAC Address on the Catalyst 2950

这个端口只能接这个mac地址的机器。就是mac和端口绑定??? 对于EI版ios还可以规定由谁可以给它发数据

wg_sw_2950(config)#mac-address-table secure mac-addr interface [vlan vlan-id] ————

wg_sw_2950#mac-address-table secure 0003.3333.3333 fa 0/1 vlan 1 wg_sw_2950#show mac-address-table

Dynamic Address Count: 1 Secure Address Count: 1 Static Address (User-defined) Count: 1 System Self Address Count: 25 Total MAC addresses: 28

Maximum MAC addresses: 8192 Non-static Address Table:

Destination Address Address Type VLAN Destination Port ------------------- ------------ ---- --------------------

0050.0f02.3372 Dynamic 1 FastEthernet0/2 0003.3333.3333 Secure 1 FastEthernet0/1

5、配置端口安全

wg_sw_2950(config)#interface fa0/1 wg_sw_2950(config-if)#port security

wg_sw_2950(config-if)#port security max-mac-count 10 这个端口只能接10个mac地址

port secure max-mac-count 1：这个端口只能和1个mac地址进行捆绑。 默认时一个接口下可以接132个mac。 Port security 或者portswitch security

校验交换机端口安全设置：

wg_sw_2950#show mac-address-table secure

wg_sw_2950(config-if)#port security action {shutdown | trap} wg_sw_2950#show port-security

port security action {shutdown | trap} 关闭/陷阱－你没有任何感觉，但是交换机把该信息传到管理员哪里了。如果你用了ciscoworks之类的软件。

怎么设置，监视哪些信息，trap什么：ccna不要求掌握。要设置snmp（基于udp。有v1、v2、v3三个版本）服务器。 6、

wg_sw_2950#copy startup-config tftp://host/dst_file

wg_sw_2950#erase startup-config ；删除startup-config，回复到出厂模式

7、show spantree 8、show vlan

What type of errors can indicate a duplex mode mismatch?

--FCS and late collision errors

What happens if a frame arrives at a switch destined for a MAC address that is not already in the MAC table,and the table is full?

-- the frame is forwarded through all ports except the receiving port.

Which two functions can LAN switches and bridges provide?(choose two)

a. packet routing b.jitter avoidance c.address learning d.store and forward decision e.loop avoidance using the Spanning Tree Protocol answer:c e

what feature do switches and bridges implement so that they can receive and transmit frames independently on each port?

a.loop avoidance b.buffering memory c.strore and forward mode d.spanning tree protocol answer:b

collisions usually happen within the first ? bytes of a frame. a.16 b.32 c.64 d.128 answer:b

which three frame types are flooded to all ports except the source port on a switch? a.unicast frames b.multicast frames c.broadcast frames d.frames with a known destination address e.frames with an unknown destination address answer:b.c.e

with STP, how is the designated port selected on a segment? a.the port that has the lowest path cost to the root bridge b.the port that has the highest path cost to the root bridge

c.the port that has the lowest path cost to the closest nonroot bridge d. the port that has the highest path cost to the closest nonroot bridge

if a Catalyst switch port is in autonegotiate mode and an attached device that does NOT support autonegotiation is operating in full-duplex mode,whtat will the switch do?

a.disable the port b.suspend the port c.set the port to full-duplex d.set the port to half-duplex answer:d

what does the mac-addrress-table restricted static 1111.2222.1111 e0/3 e0/1 command do?

Answer: specifies that traffic to the address 1111.2222.1111 on e0/3 will be allowed only from interface e0/1

What is the default maximum number of address allowed on a secure port? Answer:256

Which three frame types are flooded to all ports except the source port on a switch? a.unicast frames b.multicast frames c.broadcast frames

d.frames with a known destination address e.frames with an unknown destination address flood是在交换机mac表里面找不到目的地址的时候的一种处理方式 ???

CCNA笔记：2层交换

Layer 2 Switching Switching Services

路由协议有在阻止层3的循环的过程.但是假如在你的switches间有冗余的物理连接,路由协议并不能阻止层2循环的发生,这就必须依靠生成树协议(Spanning Tree Protocol,STP)

不像bridges使用软件来创建和管理MAC地址过滤表,switches使用ASICs来创建和管理MAC地址表,可以把switches想象成多端口的bridges

层2的switches和bridges快于层3的router因为它们不花费额外的时间字查看层3包头信息,相反,它们查看帧的硬件地址然后决定是转发还是丢弃.每个端口为1个冲突域,所有的端口仍然处于1个大的广播域里

层2交换提供:

1.基于硬件的桥接(ASIC) 2.线速(wire speed) 3.低延时(latency) 4.低耗费

Bridging vs. LAN Switching

桥接和层2交换的一些区别和相似的地方: 1.bridges基于软件,switches基于硬件 2.switches和看作多端口的bridges

3.bridges在每个bridge上只有1个生成树实例,而switches可以有很多实例

4.switches的端口远多于bridges 5.两者均转发层2广播

6.两者均通过检查收到的帧的源MAC地址来学习 7.两者均根据层2地址来做转发决定 Three Switch Function at Layer 2

2层交换的一些功能:

1.地址学习(address learning):通过查看帧的源MAC地址来加进1个叫做转发/过滤表的MAC地址数据库里

2.转发/过滤决定(forward/filter decisions):当1个接口收到1个帧的时候,switch在MAC地址数据库里查看目标MAC地址和出口接口,然后转发到符合条件的那个目标端口去

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