Date: Fri, 10 Aug 2001 16:32:20 -0500 From: Pandurangi Venkatesh-AVP028 <venkatesh.pandurangi@motorola.com> To: "'freebsd-questions@FreeBSD.ORG'" <freebsd-questions@FreeBSD.ORG> Subject: Does anybody noticed TCP checksum problem while tunneling? Message-ID: <796456A0F96AD511A0AC009027B0F7412D0782@IL27EXM08.cig.mot.com>
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Hello, We are using a CMU mobile IPv4 code, for enhancing the Mobile IPv4 functions on a FreeBSD platform. We are seeing some problems related to TCP checksum, when a TCP packet is encapsulated (IP in IP) and sent from CN (Correspondent Node) to MN (Mobile Node) via FA (Foreign Agent). There is a telnet session initiated from CN to MN when MN is in Foreign Domain. CN sends a TCP packet to FA's IP address using IP in IP tunneling. Looks like CN is calculating the TCP checksum twice 1) using CN's IP address as source and FA's IP address as destination (inner IP packet). 2) it is calculated again using outer IP packet using CNs IP address as source and MNs IP address as destination. When this packet reaches FA, FA reports TCP checksum error, which breaks the telnet session initiated from CN to MN. Example : MN's home IP address : 77.1.63.2 CN's IP address : 77.1.61.2 FA's IP address : 77.1.59.1 These are connected using CISCO routers. The way the packets are routed from CN to MN is via FA using Mobile IP route optimization. When a ping is made from CN to MN, we can see the ping (ICMP) messages encapsulated by CN and sent to FA. FA de-capsulates and sends it to MN. MN sends the ping reply back to CN using normal IP routing. This was ping works fine without any problems. When a telnet/ftp session is initiated from CN to MN it does not work and FA reports check sum error. Does anyone noticed this problem? Or anybody has a solution to this problem? Thanks in advance. Regards Venkatesh To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message
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