On Wednesday, September 15, 2010 10:04:45 am Andre Oppermann wrote: > Below is the wording proposed by Lawrence: > /* > * The default Maximum Segment Size (MSS) to use when we do not have specific > * knowledge (e.g. via path MTU discovery) that the destination host is > prepared > * to accept larger datagrams. The smallest allowable IP datagram MTU and > * optionless IP/TCP header lengths are used for the calculation as per > RFC879. > * For IPv4 (RFC791): 576 - 20 - 20 = 536. > * For IPv6 (RFC2460): 1280 - 40 - 20 = 1220. > */ > #define TCP_MSS 536 > #define TCP6_MSS 1220
I think the existing text is fine for this comment, with one nit: * For IPv4 the MSS is 576 - sizeof(struct tcpiphdr) I would find it clearer if it was 'sizeof(struct ip) - sizeof(struct tcphdr)' instead. > * Limit the lowest MSS we accept for path MTU discovery and the TCP SYN MSS > * option. Allowing low values of MSS can consume significant resources and > be > * used to mount a resource exhaustion attack. Connections requesting lower > MSS > * values will be rounded up to this value and the IP_DF flag will be > cleared to > * allow fragmentation along the path. > * > * See tcp_subr.c tcp_minmss SYSCTL declaration for more comments. Setting > this > * SYSCTL to "0" disables the minmss check. > * > * The default value is fine for TCP over IPv4 across the Internet's smallest > * known link MTU (256 bytes for AX.25 packet radio). However, a connection > is > * very unlikely to come across such low MTU interfaces (anno domini 2003). > */ > #define TCP_MINMSS 216 I actually prefer the above text for this block. The 'amounts of resources' phrase is certainly redundant and just 'resources' is clearer. -- John Baldwin _______________________________________________ svn-src-all@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/svn-src-all To unsubscribe, send any mail to "svn-src-all-unsubscr...@freebsd.org"
