github.com/fafucoder/cilium@v1.6.11/pkg/mtu/detect_linux.go (about)

     1  // Copyright 2018 Authors of Cilium
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //     http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  //
    15  // +build linux
    16  
    17  package mtu
    18  
    19  import (
    20  	"fmt"
    21  	"net"
    22  
    23  	"github.com/vishvananda/netlink"
    24  )
    25  
    26  const (
    27  	externalProbeIPv4 = "1.1.1.1"
    28  	externalProbeIPv6 = "2606:4700:4700::1111"
    29  )
    30  
    31  func getRoute(externalProbe string) ([]netlink.Route, error) {
    32  	ip := net.ParseIP(externalProbe)
    33  	if ip == nil {
    34  		return nil, fmt.Errorf("unable to parse IP %s", externalProbe)
    35  	}
    36  
    37  	routes, err := netlink.RouteGet(ip)
    38  	if err != nil {
    39  		return nil, fmt.Errorf("unable to lookup route to %s: %s", externalProbe, err)
    40  	}
    41  
    42  	if len(routes) == 0 {
    43  		return nil, fmt.Errorf("no route to %s", externalProbe)
    44  	}
    45  
    46  	return routes, nil
    47  }
    48  
    49  func autoDetect() (int, error) {
    50  	var routes []netlink.Route
    51  	var err error
    52  
    53  	routes, err = getRoute(externalProbeIPv4)
    54  	if err != nil {
    55  		prevErr := err
    56  		routes, err = getRoute(externalProbeIPv6)
    57  		if err != nil {
    58  			return 0, fmt.Errorf("%v, %v", err.Error(), prevErr.Error())
    59  		}
    60  	}
    61  
    62  	link, err := netlink.LinkByIndex(routes[0].LinkIndex)
    63  	if err != nil {
    64  		return 0, fmt.Errorf("unable to find interface of default route: %s", err)
    65  	}
    66  
    67  	if mtu := link.Attrs().MTU; mtu != 0 {
    68  		log.Infof("Detected MTU %d", mtu)
    69  		return mtu, nil
    70  	}
    71  
    72  	return EthernetMTU, nil
    73  }