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Message-ID: <CAK3+h2zLGGA2w38mRwpf5Ww+d8ZdtESp1zix82OZODG7o=Rsbg@mail.gmail.com> Date: Thu, 25 Oct 2012 15:52:10 -0700 From: Vincent Li <vincent.mc.li@...il.com> To: Eric Dumazet <eric.dumazet@...il.com> Cc: "netdev@...r.kernel.org" <netdev@...r.kernel.org> Subject: Re: Disable tcp MSS option in three way handshake? On Thu, Oct 25, 2012 at 3:42 PM, Eric Dumazet <eric.dumazet@...il.com> wrote: > On Thu, 2012-10-25 at 15:27 -0700, Vincent Li wrote: >> Hi, >> >> this sounds crazy, we have a weird situation that an unknown tcp >> implementation not putting tcp MSS option in the SYN/ACK which caused >> us some issue. I am tasked to mimic the unknown tcp immplementation on >> not sending MSS in tcp SYN/ACK, I am wondering if I can achieve that >> by modifying linux kernel tcp code, there is socket option >> TCP_MAXSEG, but that seems only affecting the size of MSS, not >> removing the MSS option. do you have any pointer on how to do that in >> kernel tcp code? > > You'll have to patch the code. > > Or else, you could add a new feature to net/netfilter/xt_TCPMSS.c > > (We already have > > #define XT_TCPMSS_CLAMP_PMTU 0xffff > > You could add > > #define XT_TCPMSS_REMOVE 0xfffe > > and replace MSS option by NOP > > > thanks for the reply, I did a quick look at the code, as a quick dirty hack, can I change the 699 /* Set up TCP options for SYN-ACKs. */ 700 static unsigned int tcp_synack_options(struct sock *sk, 701 struct request_sock *req, 702 unsigned int mss, struct sk_buff *skb, 703 struct tcp_out_options *opts, 704 struct tcp_md5sig_key **md5, 705 struct tcp_extend_values *xvp) 706 { .................. 730 /* We always send an MSS option. */ 731 opts->mss = mss; <---------here set opts->mss = 0 ? would that work? -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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