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Multilayer Switching (MLS)是与现有的路由器一道 提供第三层交换机的Cisco的基于以太网的路由交换技术。本 文包括仅IP MLS; IPX MLS 和组播MLS是超出本文的范围之外。
传统路由器典型地执行二个主要功 能:根据路由表和信息包交换的路由处理计算(媒体访问控制 (MAC)地址重写,再做检查和、存活时间(TTL)减少量等等)。路由器和第三层交换机的之间主要区别是信息包交换在路由器在软 件完成由基于微处理机的引擎,而第三层交换机它由特定特定应用 集成电路(ASIC)完成在硬件。
MLS要求三个不同的组件:
MLS-RP:多层交换路由处理器。 它通知MLS-SE MLS配置并且用路由协 议(RP)为路由计算。
MLS-SE:多层交换引擎。它负责对信息包交换和重写功能在自定义 ASIC,并且能识别第三层流。
MLSP: 多层交换协议:MLS-RP 传送的组播协议信息通知 MLS-RP MAC地址使用的MLS-SE、路由和访问控制列表更改等等。 MLS-SE将使用该信息编程自定义ASIC。
惯例
请参阅 Cisco技术提示惯例。
网络图
此跟随的示例 使用路由交换模块(RSM) 显示一IP-MLS示例配置:

MLS运行
在上面的例子,PC-A想要与PC-B联络。 他们 用不同的VLAN因此数据流通过RSM (默认网关将被路由为个人计算机 )。第一个信息包将由PC-A发送并且由RSM路由往 PC-B; 快捷方式,PC-A --> PC-B,将被创建并且所有后续 信息包将是MLS-SE交换的第三层(Supervisor=NFFC)。
注意: 当PC-B 与PC-A时,联络条目为快捷方式是单向的,另一个条目将被创建。
下面的语法显示PC通信、MLS快捷方 式和其他MLS信息。
PC-A#ping 12.12.12.12
!-- pinging PC-B
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 12.12.12.12, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 1/3/4 ms
在交换机:
switch-MLS-SE (enable) show mls entry
Destination IP Source IP Prot DstPrt SrcPrt Destination Mac Vlan Port
--------------- --------------- ---- ------ ------ ----------------- ---- -----
MLS-RP 11.11.11.1:
11.11.11.11 12.12.12.12 ICMP - - 00-d0-58-43-9f-60 11 6/11
!-- As in the note above we have two shortcuts A->B and B->A
12.12.12.12 11.11.11.11 ICMP - - 00-00-0c-07-ac-01 12 6/12
switch-MLS-SE (enable)
switch-MLS-SE (enable) show mls
Multilayer switching enabled
!-- By default, MLS is enabled on the switch
Multilayer switching aging time = 256 seconds
Multilayer switching fast aging time = 0 seconds, packet threshold = 0
Current flow mask is Destination flow
Configured flow mask is Destination flow
Total packets switched = 8
!-- Five echos and five replies were sent; the first echo and reply went
!-- through the RSM and subsequent were Layer 3 switched, which gives us a total of
!-- eight Layer 3 switched packets and two shortcuts.
Active shortcuts = 2
Netflow Data Export disabled
Total packets exported = 0
MLS-RP IP MLS-RP ID XTAG MLS-RP MAC-Vlans
---------------- ------------ ---- ---------------------------------
11.11.11.1 00100b108800 2 00-10-0b-10-88-00 11-12
switch-MLS-SE (enable)
switch-MLS-SE (enable) show mls statistics rp
Total packets switched = 8
Active shortcuts = 2
Total packets exported= 0
Total switched
MLS-RP IP MLS-RP ID packets bytes
--------------- ------------ ---------- ------------
11.11.11.1 00100b108800 8 944
switch-MLS-SE (enable)
RSM-MLS-RP#sho mls rp
multilayer switching is globally enabled
mls id is 0010.0b10.8800
mls ip address 11.11.11.1
!-- IP address of MLS-RP
mls flow mask is destination-ip
number of domains configured for mls 1
vlan domain name: sales
current flow mask: destination-ip
current sequence number: 3150688457
current/maximum retry count: 0/10
current domain state: no-change
current/next global purge: false/false
current/next purge count: 0/0
domain uptime: 1d00h
keepalive timer expires in 8 seconds
retry timer not running
change timer not running
1 management interface(s) currently defined:
vlan 11 on Vlan11
2 mac-vlan(s) configured for multi-layer switching:
mac 0010.0b10.8800
vlan id(s)
11 12
!-- VLANs, interfaces participating in MLS
router currently aware of following 1 switch(es):
switch id 0050.d133.2bff
!-- MAC address of the MLS-SE
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