Service provider story about tracking down TCP RSTs

Re:Service provider story about tracking down TCP RSTs by frnkblk on Monday September 03, 2018 @01:51AM (#17900608)

To clarify, the Arista routers are the ISP's border routers. It was the residential/business customers' SOHO routers, of various makes and models, that were not decrementing the initial TCP SYN.

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Re:Service provider story about tracking down TCP RSTs by xkgt on Monday September 03, 2018 @12:13PM (#17903358)

Thanks for pointing out. Sorry I overlooked that part. Perhaps I got primed by the opening statements which implied that problem happened only after placing new Arista routers and hastily assumed that it was Arista's routers that mangled the bits.

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Re:Service provider story about tracking down TCP RSTs by frnkblk on Monday September 03, 2018 @03:06PM (#17904329)

You are correct, the problem started only after placing new Arista border routers. The previous border routers were not doing ECMP. The issue was a combination of the use of anycast, diverse Internet transit egress, this model of Arista defaulting to using the packet's TTL in its ECMP hash calculations, and the end-customer router CPE egressing packets that are part of the same TCP connection with variable TTL values. Change any one of those items and the issue would not have shown up.

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