file: /proc/sys/net/ipv4/tcp_retrans_collapse
variable: net.ipv4.tcp_retrans_collapse
Official reference

Bug-to-bug compatibility with some broken printers. On retransmit try to send bigger packets to work around bugs in certain TCP stacks.

tcp_retries1 - INTEGER This value influences the time, after which TCP decides, that something is wrong due to unacknowledged RTO retransmissions, and reports this suspicion to the network layer. See tcp_retries2 for more details.

RFC 1122 recommends at least 3 retransmissions, which is the default.

tcp_retries2 - INTEGER This value influences the timeout of an alive TCP connection, when RTO retransmissions remain unacknowledged. Given a value of N, a hypothetical TCP connection following exponential backoff with an initial RTO of TCP_RTO_MIN would retransmit N times before killing the connection at the (N+1)th RTO.

The default value of 15 yields a hypothetical timeout of 924.6 seconds and is a lower bound for the effective timeout. TCP will effectively time out at the first RTO which exceeds the hypothetical timeout.

RFC 1122 recommends at least 100 seconds for the timeout, which corresponds to a value of at least 8.

tcp_rfc1337 - BOOLEAN If set, the TCP stack behaves conforming to RFC1337. If unset, we are not conforming to RFC, but prevent TCP TIME_WAIT assassination. Default: 0

tcp_rmem - vector of 3 INTEGERs: min, default, max min: Minimal size of receive buffer used by TCP sockets. It is guaranteed to each TCP socket, even under moderate memory pressure. Default: 4K

default: initial size of receive buffer used by TCP sockets. This value overrides net.core.rmem_default used by other protocols. Default: 87380 bytes. This value results in window of 65535 with default setting of tcp_adv_win_scale and tcp_app_win:0 and a bit less for default tcp_app_win. See below about these variables.

max: maximal size of receive buffer allowed for automatically selected receiver buffers for TCP socket. This value does not override net.core.rmem_max. Calling setsockopt() with SO_RCVBUF disables automatic tuning of that socket’s receive buffer size, in which case this value is ignored. Default: between 87380B and 6MB, depending on RAM size.