TCP window scaling and broken routers
Posted Jul 21, 2004 18:31 UTC (Wed) by schabi
In reply to: TCP window scaling and broken routers
Parent article: TCP window scaling and broken routers
"this case the nasty firewalls zero out the bits in the unknown option and people are complaining"
It's different. With ECN, the router had two different, valid options: Leave the bits in the flag word as they are, or clear them and thus deleting the option. ECN was designed carefully enough that both ways worked. Blocking or dropping the packed is no option.
The Window scaling is not bits in the flag word, but an separately added option field. There, the firewall has two valid options: let the packet pass as it is, or remove the window scaling option field entirely. Communication continues to work with both options. Fiddling around inside the header field and wildly mangling the values is no option.
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