mii/libdatachannel
1
0
Fork 0
mirror of https://github.com/mii443/libdatachannel.git synced 2025-08-22 23:25:33 +00:00
Code Issues Packages Projects Releases Wiki Activity

Merge pull request #313 from paullouisageneau/disable-sctp-pmtud

Browse Source 
Disable SCTP Path MTU discovery
This commit is contained in:
Paul-Louis Ageneau
2021-01-24 19:52:27 +01:00
committed by GitHub
parent 329b133383 ea12530d30
commit 470d145a9a
1 changed files with 30 additions and 12 deletions
Download Patch File Download Diff File Expand all files Collapse all files

42
src/sctptransport.cpp
View File

@ -25,6 +25,19 @@
#include <thread>
#include <vector>
// The IETF draft says:
// SCTP MUST support performing Path MTU discovery without relying on ICMP or ICMPv6 as specified in
// [RFC4821] using probing messages specified in [RFC4820]. The initial Path MTU at the IP layer
// SHOULD NOT exceed 1200 bytes for IPv4 and 1280 for IPv6.
// See https://tools.ietf.org/html/draft-ietf-rtcweb-data-channel-13#section-5
//
// However, usrsctp does not implement Path MTU discovery, so we need to disable it for now.
// See https://github.com/sctplab/usrsctp/issues/205
#define USE_PMTUD 0
// TODO: When Path MTU discovery is supported, it needs to be enabled with libjuice as ICE backend
// on all platforms except Mac OS where the Don't Fragment (DF) flag can't be set:
/*
#if !USE_NICE
#ifndef __APPLE__
// libjuice enables Linux path MTU discovery or sets the DF flag
@ -34,15 +47,9 @@
#define USE_PMTUD 0
#endif
#else // USE_NICE == 1
#ifdef __linux__
// Linux UDP does path MTU discovery by default (setting DF and returning EMSGSIZE)
// It should be safe to enable discovery for SCTP.
#define USE_PMTUD 1
#else
// Otherwise assume fragmentation
#define USE_PMTUD 0
#endif
#endif
*/
using namespace std::chrono_literals;
using namespace std::chrono;
@ -161,21 +168,32 @@ SctpTransport::SctpTransport(std::shared_ptr<Transport> lower, uint16_t port,
std::to_string(errno));
struct sctp_paddrparams spp = {};
// Enable SCTP heartbeats
spp.spp_flags = SPP_HB_ENABLE;
// RFC 8261 5. DTLS considerations:
// If path MTU discovery is performed by the SCTP layer and IPv4 is used as the network-layer
// protocol, the DTLS implementation SHOULD allow the DTLS user to enforce that the
// corresponding IPv4 packet is sent with the Don't Fragment (DF) bit set. If controlling the DF
// bit is not possible (for example, due to implementation restrictions), a safe value for the
// path MTU has to be used by the SCTP stack. It is RECOMMENDED that the safe value not exceed
// 1200 bytes.
// See https://tools.ietf.org/html/rfc8261#section-5
#if USE_PMTUD
// Enable SCTP path MTU discovery
spp.spp_flags = SPP_PMTUD_ENABLE;
spp.spp_flags |= SPP_PMTUD_ENABLE;
#else
// Fall back to a safe MTU value.
spp.spp_flags = SPP_PMTUD_DISABLE;
spp.spp_pathmtu = 1200; // Max safe value recommended by RFC 8261
// See https://tools.ietf.org/html/rfc8261#section-5
spp.spp_flags |= SPP_PMTUD_DISABLE;
spp.spp_pathmtu = 1200;
#endif
if (usrsctp_setsockopt(mSock, IPPROTO_SCTP, SCTP_PEER_ADDR_PARAMS, &spp, sizeof(spp)))
throw std::runtime_error("Could not set socket option SCTP_PEER_ADDR_PARAMS, errno=" +
std::to_string(errno));
// The IETF draft recommends the number of streams negotiated during SCTP association to be
// 65535. See https://tools.ietf.org/html/draft-ietf-rtcweb-data-channel-13#section-6.2
// 65535.
// See https://tools.ietf.org/html/draft-ietf-rtcweb-data-channel-13#section-6.2
struct sctp_initmsg sinit = {};
sinit.sinit_num_ostreams = 65535;
sinit.sinit_max_instreams = 65535;