diff options
| -rw-r--r-- | net/ipv4/syncookies.c | 22 | ||||
| -rw-r--r-- | net/ipv6/syncookies.c | 15 |
2 files changed, 20 insertions, 17 deletions
diff --git a/net/ipv4/syncookies.c b/net/ipv4/syncookies.c index b6ea297..15e0241 100644 --- a/net/ipv4/syncookies.c +++ b/net/ipv4/syncookies.c @@ -136,22 +136,22 @@ static __u32 check_tcp_syn_cookie(__u32 cookie, __be32 saddr, __be32 daddr, } /* - * MSS Values are taken from the 2009 paper - * 'Measuring TCP Maximum Segment Size' by S. Alcock and R. Nelson: - * - values 1440 to 1460 accounted for 80% of observed mss values - * - values outside the 536-1460 range are rare (<0.2%). + * MSS Values are chosen based on the 2011 paper + * 'An Analysis of TCP Maximum Segement Sizes' by S. Alcock and R. Nelson. + * Values .. + * .. lower than 536 are rare (< 0.2%) + * .. between 537 and 1299 account for less than < 1.5% of observed values + * .. in the 1300-1349 range account for about 15 to 20% of observed mss values + * .. exceeding 1460 are very rare (< 0.04%) * - * Table must be sorted. + * 1460 is the single most frequently announced mss value (30 to 46% depending + * on monitor location). Table must be sorted. */ static __u16 const msstab[] = { - 64, - 512, 536, - 1024, - 1440, + 1300, + 1440, /* 1440, 1452: PPPoE */ 1460, - 4312, - 8960, }; /* diff --git a/net/ipv6/syncookies.c b/net/ipv6/syncookies.c index 13ca0a0..d703218 100644 --- a/net/ipv6/syncookies.c +++ b/net/ipv6/syncookies.c @@ -24,15 +24,18 @@ #define COOKIEBITS 24 /* Upper bits store count */ #define COOKIEMASK (((__u32)1 << COOKIEBITS) - 1) -/* Table must be sorted. */ +/* RFC 2460, Section 8.3: + * [ipv6 tcp] MSS must be computed as the maximum packet size minus 60 [..] + * + * Due to IPV6_MIN_MTU=1280 the lowest possible MSS is 1220, which allows + * using higher values than ipv4 tcp syncookies. + * The other values are chosen based on ethernet (1500 and 9k MTU), plus + * one that accounts for common encap (PPPoe) overhead. Table must be sorted. + */ static __u16 const msstab[] = { - 64, - 512, - 536, - 1280 - 60, + 1280 - 60, /* IPV6_MIN_MTU - 60 */ 1480 - 60, 1500 - 60, - 4460 - 60, 9000 - 60, }; |