cisco DHCP.doc

CISCO的路由器（IOS12.0 T1以后），可以配置为dhcp的中继设备，DHCP的客户端设备，也可以配置为DHCP的服务器。Cisco设备上设置DHCP实例 一位客户想把DHCP SERVER迁移到6509交换机的MSFC上,要求还挺复杂: 1.同时为多个VLAN的客户机分配地址 2.VLAN内有部分地址采用手工分配的方式 3.为客户指定网关、Wins服务器等 4.VLAN 2的地址租用有效期限为1天,其它为3天 5.按MAC地址为特定用户分配指定的IP地址 最终配置如下： ip dhcp excluded-address 9 /不用于动态地址分配的地址 ip dhcp excluded-address 40 54 ip dhcp excluded-address 9 ! ip dhcp pool global /global是pool name， 由用户指定 network /动态分配的地址段 domain-name /为客户机配置域后缀 dns-server /为客户机配置dns服务器 netbios-name-server /为客户机配置wins服务器 netbios-node-type h-node /为客户机配置节点模式（影响名称解释的顺利,如h-node=先通过wins服务器解释.） lease 3 /地址租用期限: 3天 ip dhcp pool vlan1 network /本pool是global的子pool, 将从global pool继承domain-name等option default-router 00 01 /为客户机配置默认网关 ! ip dhcp pool vlan2 /为另一VLAN配置的pool network default-router 00 01 lease 1 ! ip dhcp pool vlan1_john /总是为MAC地址为.的机器分配.地址 host 1 client-identifier 010050.bade.6384 /client-identifier=01加上客户机网卡地址 ! ip dhcp pool vlan1_tom host 0 client-identifier 010010.3ab1.eac8 相关的DHCP调试命令： no service dhcp /停止DHCP服务默认为启用DHCP服务 sh ip dhcp binding /显示地址分配情况 show ip dhcp conflict /显示地址冲突情况 debug ip dhcp server events | packets | linkage /观察DHCP服务器工作情况 如果DHCP客户机分配不到IP地址，常见的原因有两个。第一种情况是没有把连接客户机的端口设置为Portfast方式。MS客户机开机后检查网卡连接正常，Link是UP的，就开始发送DHCPDISCOVER请求，而此时交换机端口正在经历生成树计算，一般需要30-50秒才能进入转发状态。MS客户机没有收到DHCP SERVER的响应就会给网卡设置一个169.169.X.X的IP地址。解决的方法是把交换机端口设置为Portfast方式：CatOS(4000/5000/6000): set spantree portfast mod_num/port_num enable; IOS(2900/3500): interface . ; spanning-tree portfast。 另外一种情况是DHCP服务器和DHCP工作站不在同一个VLAN，这时候通常通过设置ip helper-address来解决： interface vlan1 ip address 54 /假设DHCP服务器地址为 interface Vlan2 ip address 54 ip helper-address /假设这是DHCP客户机所在的VLAN1. 使用IP Helper Addresses命令提问 配置路由器对DHCP Request转发的支持回答Router1#configure terminal Enter configuration commands, one per line. End with CNTL/Z.Router1(config)#interface Ethernet0Router1(config-if)#ip helper-address Router1(config-if)#ip helper-address Router1(config-if)#exitRouter1(config)#endRouter1#注释 使用IP Helper Address命令把路由器配置成为一个DHCP代理服务器，转发客户端的DHCP Request至配置的ip helper address。2. 限制IP Helper Addresses命令的影响 提问 配置IP Helper Address命令以后导致链路利用率增高或者DHCP服务器负荷增高回答Router1#configure terminal Enter configuration commands, one per line. End with CNTL/Z.Router1(config)#no ip forward-protocol udp tftpRouter1(config)#no ip forward-protocol udp nameserverRouter1(config)#no ip forward-protocol udp domainRouter1(config)#no ip forward-protocol udp timeRouter1(config)#no ip forward-protocol udp netbios-nsRouter1(config)#no ip forward-protocol udp netbios-dgmRouter1(config)#no ip forward-protocol udp tacacsRouter1(config)#endRouter1#注释 缺省情况下IP Helper命令会转发很多UDP广播数据包，不仅仅是DHCP数据包，并且不能针对不同的服务器转发不同的广播包3. 使用DHCP来动态配置路由器IP地址提问 配置路由器动态获得IP地址回答Router1#configure terminalEnter configuration commands, one per line. End with CNTL/Z.Router1(config)#interface FastEthernet0/1Router1(config-if)#ip address dhcp Router1(config-if)#endRouter1#Interface FastEthernet0/1 assigned DHCP address 7, mask Router1#注释 在12.2(8)T之前此命令仅仅适用于以太网接口。从12.3(8)T以后可以对DHCP选项进行控制，下例配置为不获得DNS服务器Router1#configure terminal Enter configuration commands, one per line. End with CNTL/Z.Router1(config)#interface FastEthernet0/1Router1(config-if)#no ip dhcp client request dns-nameserverRouter1(config-if)#end另外对于获得的缺省路由，管理距离为254S* /0 254/0 via 从12.3(4)T开始增加了对获得地址释放和重新获得的支持Router1#release dhcp FastEthernet0/1Router1#renew dhcp FastEthernet0/14. 通过DHCP来对客户端进行动态IP地址分配提问 配置路由器成为DHCP服务器回答Router1#configure terminal Enter configuration commands, one per line. End with CNTL/Z.Router1(config)#service dhcpRouter1(config)#ip dhcp pool /24Router1(dhcp-config)#network Router1(dhcp-config)#default-router Router1(dhcp-config)#dns-server Router1(dhcp-config)#exitRouter1(config)#ip dhcp excluded-address 0Router1(config)#ip dhcp excluded-address 00 55Router1(config)#endRouter1#注释 注意的是要配置excluded命令来排除某些地址，防止出现地址冲突5. 配置DHCP的配置选项提问 配置更多的DHCP配置选项提供给客户端回答Router1#configure terminal Enter configuration commands, one per line. End with CNTL/Z.Router1(config)#ip dhcp pool ORAserverRouter1(dhcp-config)#host 4 Router1(dhcp-config)#client-name bigserverRouter1(dhcp-config)#default-router Router1(dhcp-config)#domain-name Router1(dhcp-config)#dns-server Router1(dhcp-config)#netbios-name-server Router1(dhcp-config)#netbios-node-type h-nodeRouter1(dhcp-config)#option 66 ip Router1(dhcp-config)#option 33 ip Router1(dhcp-config)#option 31 hex 01Router1(dhcp-config)#lease 2Router1(dhcp-config)#exitRouter1(config)#endRouter1#注释 Option 66 定义TFTP服务器; Option 33定义静态路由; Option 31定义客户端使用IRDP.6. 配置DHCP的分配时长 提问 修改缺省DHCP分配时长回答Router1#configure terminal Enter configuration commands, one per line. End with CNTL/Z.Router1(config)#ip dhcp pool /24Router1(dhcp-config)#lease 2 12 30 Router1(dhcp-config)#exitRouter1(config)#endRouter1#注释 缺省分配为一天，配置选项为天，小时，分钟7. 分配静态IP地址提问 每次都分配给某个特定设备特定IP地址回答Router1#configure terminal Enter configuration commands, one per line. End with CNTL/Z.Router1(config)#ip dhcp pool IANRouter1(dhcp-config)#host 3 Router1(dhcp-config)#client-identifier 0100.0103.85e9.87Router1(dhcp-config)#client-name win2kRouter1(dhcp-config)#default-router Router1(dhcp-config)#domain-name Router1(dhcp-config)#dns-server Router1(dhcp-config)#exitRouter1(config)#endRouter1#注释 这里通过MAC地址来绑定某个IP地址。Client-identifier后面跟的是MAC地址，不过比传统MAC地址多了0100，代表是以太网，对于更多的媒介类型值参考RFC 3232中的Number Hardware Type部分Router1#show ip dhcp binding IP address Hardware address Lease expiration Type3 0100.0103.85e9.87 Infinite Manual2 0100.50da.2a5e.a2 Apr 11 2006 09:00 PM Automatic3 0100.0103.ea1b.ed Apr 11 2006 08:58 PM Automatic8. 配置一个DHCP 数据库客户端提问 在另一个设备上备份当前的DHCP数据库回答FTP方式Router1#configure terminal Enter configuration commands, one per line. End with CNTL/Z.Router1(config)#ip dhcp database ftp:/dhcp:bindsave/dhcp-leasesRouter1(config)#endRouter1#TFTP 方式Router1#configure terminal Enter configuration commands, one per line. End with CNTL/Z.Router1(config)#ip dhcp database t/dhcp-leasesRouter1(config)#endRouter1#RCP方式Router1#configure terminal Enter configuration commands, one per line. End with CNTL/Z.Router1(config)#ip dhcp database rcp:/dhcp/dhcp-leasesRouter1(config)#endRouter1#注释 通常DHCP数据库保存于内存，如果重启就会丢失，可以使用上述方式进行备份从而不会丢失，通过下述命令验证Router1#show ip dhcp database URL : ftp:/dhcp:bindsave/dhcp-leasesRead : NeverWritten : Apr 09 2006 10:24 PMStatus : Last write succeeded. Agent information is up-to-date.Delay : 300 secondsTimeout : 300 secondsFailures : 1Successes: 309. 在同一子网配置多个DHCP服务器提问 在同一子网配置多个DHCP服务器来增加可用性回答Router1:Router1#configure terminal Enter configuration commands, one per line. End with CNTL/Z.Router1(config)#ip dhcp pool /24Router1(dhcp-config)#network Router1(dhcp-config)#default-router Router1(dhcp-config)#domain-name Router1(dhcp-config)#dns-server Router1(dhcp-config)#exitRouter1(config)#ip dhcp excluded-address 9Router1(config)#ip dhcp excluded-address 50 54Router1(config)#ip dhcp database ftp:/dhcp:bindsave/dhcp-leases-rtr1Router1(config)#endRouter1#Router2:Router2#configure terminal Enter configuration commands, one per line. End with CNTL/Z.Router2(config)#ip dhcp pool /24 Router2(dhcp-config)#network Router2(dhcp-config)#default-router Router2(dhcp-config)#domain-name Router2(dhcp-config)#dns-server Router2(dhcp-config)#exitRouter2(config)#ip dhcp excluded-address 49Router2(config)#ip dhcp database ftp:/dhcp:bindsave/dhcp-leases-rtr2Router2(config)#endRouter2#10. DHCP静态映射提问 根据某个文本文件来进行IP地址的静态指配回答先在TFTP服务器上创建此文本文件Freebsd% cat /tftpboot/dhcp.static *time* Aug 17 2006 03:52 PM*version* 2!IP address Type Hardware address Lease expiration6 /24 id 0100.104b.33da.74 Infinite7 /24 id 0100.0dbc.eff6.38 Infinite8 /24 id 0100.0a5e.4001.27 Infinite9 /24 id 0100.0331.327e.41 Infinite0 /24 id 0100.0d60.b21a.4c Infinite *end*Freebsd%路由器配置Router1#configure terminal Enter configuration commands, one per line. End with CNTL/Z.Router1(config)#ip dhcp pool OREILLYRouter1(dhcp-config)#origin file t/dhcp.staticRouter1(dhcp-config)#default-router Router1(dhcp-config)#dns-server Router1(dhcp-config)#domain-name Router1(dhcp-config)#lease 3Router1(dhcp-config)#endRouter1#注释 7讲到的静态地址分配需要一个特定的DHCP Pool，扩展性不强，从12.3(11)T以后可以使用特定的文本文件来进行指配，不过必须遵照一定的格式。如果文本文件修改后需要生效，必须先no service dhcp 来停止DHCP服务然后ser