Monday, March 14, 2011

Cisco equipment opened MPLS VPN unable to visit a web page fault analysis


Network topology1.1.2 description:Anhui zhengfa webmaster dry cisco equipment opened MPLSVPN, user reflect located in the city’s experience-rich PC cannot open the provincial experience-rich WEB server page, but can the Ping tong, FTP and network share fail. Backbone cisco equipment for …

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Network topology1.1.2 description:Anhui zhengfa webmaster dry cisco equipment opened MPLSVPN, user reflect located in the city’s experience-rich PC cannot open the provincial experience-rich WEB server page, but can the Ping tong, FTP and network share fail. Backbone cisco equipment for PE, our router for CE. C7206 and C7513 passed between 2 * 2M adopts MP means interconnection.1.1.3 problem analysisAccording to the fault phenomena, eliminate network connectivity problem. Through observation, in ShengTing local can normal visit server page, eliminate server IIS Settings, issues in factories use same machine access to itsHis site isOften, ruled out the IE browser Settings problem. In ShengTing and factories to server and PC flow separately caught, below image and found server received end-to-end launched a TCP connection request, normal connection is established, and alreadyAfter the HTTP packet out, but end-to-end PC just caught TCP handshake message has not caught the HTTP server message that message during transmission is discarded.According to preliminary mastery of the phenomena and from similar case experience, preliminary judgment is forwarding path MTU Settings are problem. Equipment Sequential examination forwarding paths equipment configuration, found no set up any ends CE equipmentACL rules, wan interface for 1500 MTU, and never change, won’t cause problems, Check the cisco equipment and our equipment, also be the default 1500 interconnection interface. Examination revealed C7513 and ciscoC7206 interconnections interface multilink 1 Int MTU for 1500, because the two interconnection interface open MPLSVPN, so its interface MTU should MTU1500 more than normal 8 bytes (increase MPLS and VPN two layers of label). Without open MPLSThe interface is 1500 MTU bytes, so open MPLS interface MTU should be greater than or equal to 1508, and caught the server of a message for 1514=1500 frame size (IP packet longDegrees) + 14 (dcli), this message arrived backbone became 1508 bytes, thus judgment cisco equipment MPLS interface MTU default values set too small cause 1508 bytes of HTTP message is discarded.The PC by following commands above ShengTing WEB server: Ping Ping &; ndash F &; ndash L 1472 172.18.17.4Unable to connect, the PING – f not subdivision, for the data length, plus 1472 20 bytes IP head and 8 byte ICMP head just to 1500 bytes. To reduce packet length Ping&; ndash F &; ndash L 48-53 (1500MTU – 8 bytes tags – 28 bytes baotou 172.18.17.4 can ping general).Bt4 cracked wireless networksIn order to further confirm the judgment, the cisco equipment two interconnection MP interface MTU change for 1508 bytes, bureau PC is able to normal visit ShengTing server page, and troubleshooting! Orders for: meta – switchingMtu 1508,Equipment configuration is as follows:C7513 configuration:With Multilink1Description to_wuhushiIP after *. *. 255.255.255.252 1.1Meta – mtu 1508 switchingMeta – switching IPThe PPP multilinkThe PPP multilink group 1C7206 configuration:With Multilink1IP after *. *. 1.2 255.255.255.252Meta – mtu 1508 switchingMeta – switching IPThe PPP multilinkThe PPP multilink group 1Cisco ios download





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