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// Copyright 2019 The gVisor Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package header
import (
"encoding/binary"
"time"
)
// NDPRoutePreference is the preference values for default routers or
// more-specific routes.
//
// As per RFC 4191 section 2.1,
//
// Default router preferences and preferences for more-specific routes
// are encoded the same way.
//
// Preference values are encoded as a two-bit signed integer, as
// follows:
//
// 01 High
// 00 Medium (default)
// 11 Low
// 10 Reserved - MUST NOT be sent
//
// Note that implementations can treat the value as a two-bit signed
// integer.
//
// Having just three values reinforces that they are not metrics and
// more values do not appear to be necessary for reasonable scenarios.
type NDPRoutePreference uint8
const (
// HighRoutePreference indicates a high preference, as per
// RFC 4191 section 2.1.
HighRoutePreference NDPRoutePreference = 0b01
// MediumRoutePreference indicates a medium preference, as per
// RFC 4191 section 2.1.
//
// This is the default preference value.
MediumRoutePreference = 0b00
// LowRoutePreference indicates a low preference, as per
// RFC 4191 section 2.1.
LowRoutePreference = 0b11
// ReservedRoutePreference is a reserved preference value, as per
// RFC 4191 section 2.1.
//
// It MUST NOT be sent.
ReservedRoutePreference = 0b10
)
// NDPRouterAdvert is an NDP Router Advertisement message. It will only contain
// the body of an ICMPv6 packet.
//
// See RFC 4861 section 4.2 and RFC 4191 section 2.2 for more details.
type NDPRouterAdvert []byte
// As per RFC 4191 section 2.2,
//
// 0 1 2 3
// 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// | Type | Code | Checksum |
// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// | Cur Hop Limit |M|O|H|Prf|Resvd| Router Lifetime |
// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// | Reachable Time |
// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// | Retrans Timer |
// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// | Options ...
// +-+-+-+-+-+-+-+-+-+-+-+-
const (
// NDPRAMinimumSize is the minimum size of a valid NDP Router
// Advertisement message (body of an ICMPv6 packet).
NDPRAMinimumSize = 12
// ndpRACurrHopLimitOffset is the byte of the Curr Hop Limit field
// within an NDPRouterAdvert.
ndpRACurrHopLimitOffset = 0
// ndpRAFlagsOffset is the byte with the NDP RA bit-fields/flags
// within an NDPRouterAdvert.
ndpRAFlagsOffset = 1
// ndpRAManagedAddrConfFlagMask is the mask of the Managed Address
// Configuration flag within the bit-field/flags byte of an
// NDPRouterAdvert.
ndpRAManagedAddrConfFlagMask = (1 << 7)
// ndpRAOtherConfFlagMask is the mask of the Other Configuration flag
// within the bit-field/flags byte of an NDPRouterAdvert.
ndpRAOtherConfFlagMask = (1 << 6)
// ndpDefaultRouterPreferenceShift is the shift of the Prf (Default Router
// Preference) field within the flags byte of an NDPRouterAdvert.
ndpDefaultRouterPreferenceShift = 3
// ndpDefaultRouterPreferenceMask is the mask of the Prf (Default Router
// Preference) field within the flags byte of an NDPRouterAdvert.
ndpDefaultRouterPreferenceMask = (0b11 << ndpDefaultRouterPreferenceShift)
// ndpRARouterLifetimeOffset is the start of the 2-byte Router Lifetime
// field within an NDPRouterAdvert.
ndpRARouterLifetimeOffset = 2
// ndpRAReachableTimeOffset is the start of the 4-byte Reachable Time
// field within an NDPRouterAdvert.
ndpRAReachableTimeOffset = 4
// ndpRARetransTimerOffset is the start of the 4-byte Retrans Timer
// field within an NDPRouterAdvert.
ndpRARetransTimerOffset = 8
// ndpRAOptionsOffset is the start of the NDP options in an
// NDPRouterAdvert.
ndpRAOptionsOffset = 12
)
// CurrHopLimit returns the value of the Curr Hop Limit field.
func (b NDPRouterAdvert) CurrHopLimit() uint8 {
return b[ndpRACurrHopLimitOffset]
}
// ManagedAddrConfFlag returns the value of the Managed Address Configuration
// flag.
func (b NDPRouterAdvert) ManagedAddrConfFlag() bool {
return b[ndpRAFlagsOffset]&ndpRAManagedAddrConfFlagMask != 0
}
// OtherConfFlag returns the value of the Other Configuration flag.
func (b NDPRouterAdvert) OtherConfFlag() bool {
return b[ndpRAFlagsOffset]&ndpRAOtherConfFlagMask != 0
}
// DefaultRouterPreference returns the Default Router Preference field.
func (b NDPRouterAdvert) DefaultRouterPreference() NDPRoutePreference {
return NDPRoutePreference((b[ndpRAFlagsOffset] & ndpDefaultRouterPreferenceMask) >> ndpDefaultRouterPreferenceShift)
}
// RouterLifetime returns the lifetime associated with the default router. A
// value of 0 means the source of the Router Advertisement is not a default
// router and SHOULD NOT appear on the default router list. Note, a value of 0
// only means that the router should not be used as a default router, it does
// not apply to other information contained in the Router Advertisement.
func (b NDPRouterAdvert) RouterLifetime() time.Duration {
// The field is the time in seconds, as per RFC 4861 section 4.2.
return time.Second * time.Duration(binary.BigEndian.Uint16(b[ndpRARouterLifetimeOffset:]))
}
// ReachableTime returns the time that a node assumes a neighbor is reachable
// after having received a reachability confirmation. A value of 0 means
// that it is unspecified by the source of the Router Advertisement message.
func (b NDPRouterAdvert) ReachableTime() time.Duration {
// The field is the time in milliseconds, as per RFC 4861 section 4.2.
return time.Millisecond * time.Duration(binary.BigEndian.Uint32(b[ndpRAReachableTimeOffset:]))
}
// RetransTimer returns the time between retransmitted Neighbor Solicitation
// messages. A value of 0 means that it is unspecified by the source of the
// Router Advertisement message.
func (b NDPRouterAdvert) RetransTimer() time.Duration {
// The field is the time in milliseconds, as per RFC 4861 section 4.2.
return time.Millisecond * time.Duration(binary.BigEndian.Uint32(b[ndpRARetransTimerOffset:]))
}
// Options returns an NDPOptions of the the options body.
func (b NDPRouterAdvert) Options() NDPOptions {
return NDPOptions(b[ndpRAOptionsOffset:])
}
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