Juniper关于某双层dhcprelay结构问题分析报告

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1、实用标准文案Juniper双层dhcp-relay结构问题分析一、拓扑图说明：如上图，PC-1和PC-2都配置自动获取IP,但PC-1获取IP是在MX-1上做的DHCP中继，而PC-2是在R5上做的DHCP中继。二、配置文件1、R1配置interfaceFastEthernet0/0ipaddress12.1.1.2255.255.255.0servicedhcpipdhcppoolvlan-2network172.17.17.0255.255.255.0精彩文档实用标准文案default-router172.17.17.1ipdhcppoolvlan-121networ

2、k172.20.3.0255.255.255.0default-router172.20.3.1iproute0.0.0.00.0.0.012.1.1.12、R5配置interfaceFastEthernet0/0ipaddress172.16.16.2255.255.255.0interfaceFastEthernet1/0switchportaccessvlan2interfaceVlan2ipaddress172.17.17.1255.255.255.0iphelper-address12.1.1.2iproute0.0.0.00.0.0.0172.16.16.13

3、、R2配置interfaceFastEthernet0/0ipaddressdhcp4、R6配置interfaceFastEthernet0/0ipaddressdhcp5、MX1配置interfaces{精彩文档实用标准文案ge-0/0/1{unit0{familyinet{address12.1.1.1/24;}}}ge-0/0/4{unit0{familyinet{address172.16.16.1/24;}}}ge-0/0/5{unit0{familybridge{interface-modeaccess;vlan-id121;forwarding-option

4、s{server-group{dhcp-1{12.1.1.2;}}active-server-groupdhcp-1;groupgroup-1interfaceirb.121;精彩文档实用标准文案routing-options{static{route172.17.17.0/24next-hop172.16.16.2;bridge-domains{vlan-121{vlan-id121;routing-interfaceirb.121;三、问题描述通过上述配置后，则R2能正常获取IP,但PC-2则无法获取。1、在PC-2debug信息精彩文档实用标准文案2、MX-1查看d

5、hcprelay包统计四、故障处理通过上述抓包和MX-1上dhcprelay包统计可以看出，在MX-1上对dhcprelay过来的单播包进行了丢弃处理，这个是juniper设备独有的特性，其他厂商不需要额外处理，但juniper自身作为dhcprelay后，则默认对dhcprelay过来的单播报文作丢弃处理。若需要接受这种报文，则需要开启。forwarding-options{dhcp-relay{forward-snooped-clientsall-interfaces;通过如上命令后，R6才可以正常获取到IP地址。英文解释（http://blog.ip.fi/）The

6、rearetwodifferentwaystoconfigureDHCPinJunos,bootphelperanddhcprelay.Theseworkinverydifferentmanner,bootphelperisbeingphasedoutandisnotsupportedforexampleinQFX10k.Behaviourofbootphelperisobvious,itworkslikeitworksineveryothersensibleplatform.Behaviourofdhcp-relayisveryconfusingandit'snotdo

7、cumentedatallanywhere.精彩文档实用标准文案Ifit'spossibleinyourplatformtoconfigurebootphelper,doit.Ifnot,complaintoJunosaboutdhcp-relayimplementationandaskthemtofixit.Themainproblemwithdhcp-relayimplementationisthatonceyou'veconfiguredit,you'repuntingalldhcptrafficinallinterfa