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detect_linux.go
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detect_linux.go
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// SPDX-License-Identifier: Apache-2.0
// Copyright 2018 Authors of Cilium
//go:build linux
// +build linux
package mtu
import (
"fmt"
"net"
"github.com/cilium/cilium/pkg/logging/logfields"
"github.com/sirupsen/logrus"
"github.com/vishvananda/netlink"
)
const (
externalProbeIPv4 = "1.1.1.1"
externalProbeIPv6 = "2606:4700:4700::1111"
)
func getRoute(externalProbe string) ([]netlink.Route, error) {
ip := net.ParseIP(externalProbe)
if ip == nil {
return nil, fmt.Errorf("unable to parse IP %s", externalProbe)
}
routes, err := netlink.RouteGet(ip)
if err != nil {
return nil, fmt.Errorf("unable to lookup route to %s: %w", externalProbe, err)
}
if len(routes) == 0 {
return nil, fmt.Errorf("no route to %s", externalProbe)
}
return routes, nil
}
func autoDetect() (int, error) {
var routes []netlink.Route
var err error
routes, err = getRoute(externalProbeIPv4)
if err != nil {
prevErr := err
routes, err = getRoute(externalProbeIPv6)
if err != nil {
return 0, fmt.Errorf("%v, %v", err.Error(), prevErr.Error())
}
}
if routes[0].Gw == nil {
return 0, fmt.Errorf("unable to find default gateway from the routes: %s", routes)
}
link, err := netlink.LinkByIndex(routes[0].LinkIndex)
if err != nil {
return 0, fmt.Errorf("unable to find interface of default route: %w", err)
}
if mtu := link.Attrs().MTU; mtu != 0 {
log.Infof("Detected MTU %d", mtu)
return mtu, nil
}
return EthernetMTU, nil
}
// getMTUFromIf finds the interface that holds the ip and returns its mtu
func getMTUFromIf(ip net.IP) (int, error) {
ifaces, err := netlink.LinkList()
if err != nil {
return 0, fmt.Errorf("unable to list interfaces: %w", err)
}
for _, iface := range ifaces {
addrs, err := netlink.AddrList(iface, netlink.FAMILY_ALL)
if err != nil {
log.WithFields(logrus.Fields{
logfields.Device: iface.Attrs().Name,
}).Warning("Unable to list all addresses")
continue
}
for _, addr := range addrs {
if addr.IPNet.IP.Equal(ip) == true {
myMTU := iface.Attrs().MTU
log.WithFields(logrus.Fields{
logfields.Device: iface.Attrs().Name,
logfields.IPAddr: ip,
logfields.MTU: myMTU,
}).Info("Inheriting MTU from external network interface")
return myMTU, nil
}
}
}
return 0, fmt.Errorf("No interface contains the provided ip: %v", ip)
}