{
    "mode": "man",
    "parameter": "ip-tcp_metrics",
    "section": "8",
    "url": "https://www.chedong.com/phpMan.php/man/ip-tcp_metrics/8/json",
    "generated": "2026-05-30T08:17:08Z",
    "synopsis": "ip [ OPTIONS ] tcpmetrics { COMMAND | help }\nip tcpmetrics { show | flush } SELECTOR\nip tcpmetrics delete [ address ] ADDRESS\nSELECTOR := [ [ address ] PREFIX ]",
    "sections": {
        "NAME": {
            "content": "ip-tcpmetrics - management for TCP Metrics\n",
            "subsections": []
        },
        "SYNOPSIS": {
            "content": "ip [ OPTIONS ] tcpmetrics { COMMAND | help }\n\n\nip tcpmetrics { show | flush } SELECTOR\n\nip tcpmetrics delete [ address ] ADDRESS\n\nSELECTOR := [ [ address ] PREFIX ]\n\n",
            "subsections": []
        },
        "DESCRIPTION": {
            "content": "ip tcpmetrics is used to manipulate entries in the kernel that keep TCP information for IPv4\nand IPv6 destinations. The entries are created when TCP sockets want to share information for\ndestinations and are stored in a cache keyed by the destination address. The saved informa‐\ntion may include values for metrics (initially obtained from routes), recent TSVAL for TIME-\nWAIT recycling purposes, state for the Fast Open feature, etc.  For performance reasons the\ncache can not grow above configured limit and the older entries are replaced with fresh in‐\nformation, sometimes reclaimed and used for new destinations. The kernel never removes en‐\ntries, they can be flushed only with this tool.\n\n\nip tcpmetrics show - show cached entries\naddress PREFIX (default)\nIPv4/IPv6 prefix or address. If no prefix is provided all entries are shown.\n\n\nThe output may contain the following information:\n\nage <S.MMM>sec - time after the entry was created, reset or updated with metrics from sock‐\nets. The entry is reset and refreshed on use with metrics from route if the metrics are not\nupdated in last hour. Not all cached values reset the age on update.\n\ncwnd <N> - CWND metric value\n\nfocookie <HEX-STRING> - Cookie value received in SYN-ACK to be used by Fast Open for next\nSYNs\n\nfomss <N> - MSS value received in SYN-ACK to be used by Fast Open for next SYNs\n\nfosyndrops <N>/<S.MMM>sec ago - Number of drops of initial outgoing Fast Open SYNs with\ndata detected by monitoring the received SYN-ACK after SYN retransmission.  The seconds show\nthe time after last SYN drop and together with the drop count can be used to disable Fast\nOpen for some time.\n\nreordering <N> - Reordering metric value\n\nrtt <N>us - RTT metric value\n\nrttvar <N>us - RTTVAR metric value\n\nssthresh <SSTHRESH> - SSTHRESH metric value\n\ntwts <TSVAL>/<SEC>sec ago - recent TSVAL and the seconds after saving it into TIME-WAIT\nsocket\n\n\nip tcpmetrics delete - delete single entry\naddress ADDRESS (default)\nIPv4/IPv6 address. The address is a required argument.\n\n\nip tcpmetrics flush - flush entries\nThis command flushes the entries selected by some criteria.\n\n\nThis command has the same arguments as show.\n\n",
            "subsections": []
        },
        "EXAMPLES": {
            "content": "ip tcpmetrics show address 192.168.0.0/24\nShows the entries for destinations from subnet\n\nip tcpmetrics show 192.168.0.0/24\nThe same but address keyword is optional\n\nip tcpmetrics\nShow all is the default action\n\nip tcpmetrics delete 192.168.0.1\nRemoves the entry for 192.168.0.1 from cache.\n\nip tcpmetrics flush 192.168.0.0/24\nRemoves entries for destinations from subnet\n\nip tcpmetrics flush all\nRemoves all entries from cache\n\nip -6 tcpmetrics flush all\nRemoves all IPv6 entries from cache keeping the IPv4 entries.\n\n",
            "subsections": []
        },
        "SEE ALSO": {
            "content": "ip(8)\n\n",
            "subsections": []
        },
        "AUTHOR": {
            "content": "Original Manpage by Julian Anastasov <ja@ssi.bg>\n\n\n\niproute2                                     23 Aug 2012                           IP-TCPMETRICS(8)",
            "subsections": []
        }
    },
    "summary": "ip-tcpmetrics - management for TCP Metrics",
    "flags": [],
    "examples": [
        "ip tcpmetrics show address 192.168.0.0/24",
        "Shows the entries for destinations from subnet",
        "ip tcpmetrics show 192.168.0.0/24",
        "The same but address keyword is optional",
        "ip tcpmetrics",
        "Show all is the default action",
        "ip tcpmetrics delete 192.168.0.1",
        "Removes the entry for 192.168.0.1 from cache.",
        "ip tcpmetrics flush 192.168.0.0/24",
        "Removes entries for destinations from subnet",
        "ip tcpmetrics flush all",
        "Removes all entries from cache",
        "ip -6 tcpmetrics flush all",
        "Removes all IPv6 entries from cache keeping the IPv4 entries."
    ],
    "see_also": [
        {
            "name": "ip",
            "section": "8",
            "url": "https://www.chedong.com/phpMan.php/man/ip/8/json"
        }
    ]
}