Date: Wed, 06 Jan 1999 20:21:10 -0500 From: "Louis A. Mamakos" <louie@TransSys.COM> To: Wes Peters <wes@softweyr.com> Cc: Joe Abley <jabley@clear.co.nz>, freebsd-hackers@FreeBSD.ORG Subject: Re: setting DF bit Message-ID: <199901070121.UAA47729@whizzo.transsys.com> In-Reply-To: Your message of "Wed, 06 Jan 1999 18:13:40 MST." <36940A44.89628F8B@softweyr.com> References: <19990107135107.B12785@clear.co.nz> <36940A44.89628F8B@softweyr.com>
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> Joe Abley wrote: > > > > Hi, > > > > How do arrange for the DF bit in the IP header to be set for a given > > connected socket? > > > > I was expecting to find a sockopt, but I can't find one... > > And won't. "sysctl -w net.inet.ip.sourceroute 1" will turn on DF > system-wide, setting it to zero (the default) will turn it back off. > This doesn't seem right. I think the only place the kernel networking code generates packets with "DON'T FRAGMENT set in the header is when doing path MTU discovery in the TCP code. I suppose you could generate packets using a SOCK_RAW kinda socket, but that's probably not what was had in mind. If you had a socket option to enable this on e.g., UDP sockets, then you'd have to have a socket that was connect()'ed so you might get notified of MTU exceeded ICMP messages. The problem is that I don't think there's a good way of returning any of the useful data up to the application, other than listening in with an ICMP raw socket. louie To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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