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Also clamp MSS on IPv6

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Some routers erratically drop "Packet too big" icmp messages, and PMTU
discovery then doesn't work. We can however easily clamp MSS on IPv6 too.
This commit is contained in:
Samuel Thibault 2023-11-05 17:21:14 +01:00
parent 7514eecf68
commit 3667bdfe80
3 changed files with 42 additions and 10 deletions
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10
ppp.c
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@ -1803,7 +1803,7 @@ void processipin(sessionidt s, tunnelidt t, uint8_t *p, uint16_t l)
{
int ihl = (p[0] & 0xf) * 4; // length of IP header
if (l >= ihl + 20 && (p[ihl + 13] & TCP_FLAG_SYN) && ((p[ihl + 12] >> 4) > 5))
adjust_tcp_mss(s, t, p, l, p + ihl);
adjust_tcp4_mss(s, t, p, l, p + ihl);
}
// Add on the tun header
@ -2284,6 +2284,14 @@ void processipv6in(sessionidt s, tunnelidt t, uint8_t *p, uint16_t l)
return;
}
// adjust MSS on SYN and SYN,ACK packets with options
if (p[6] == IPPROTO_TCP)
{
int ihl = 40; // length of IPv6 header
if (l >= ihl + 20 && (p[ihl + 13] & TCP_FLAG_SYN) && ((p[ihl + 12] >> 4) > 5))
adjust_tcp6_mss(s, t, p, l, p + ihl);
}
// Check if it's a Router Solicition message.
if (*(p + 6) == 58 && *(p + 7) == 255 && *(p + 24) == 0xFF && *(p + 25) == 2 &&
*(uint32_t *)(p + 26) == 0 && *(uint32_t *)(p + 30) == 0 &&