大家好，又见面了，我是你们的朋友全栈君。
前面已经知道了Floodlight Controller是通过从SW发送LLDP帧来获得链路信息的，链路层发现协议（L2）是通过在本地网络中广播LLDP报文来通告自己的设备信息，从而服务于拓扑计算，（wikipedia：LLDP information is sent by devices from each of their interfaces at a fixed interval, in the form of an Ethernet frame. Each frame contains one LLDP Data Unit (LLDPDU). Each LLDPDU is a sequence of type-length-value (TLV) structures.）报文格式如下：
type-length-value 的设计很常见（比如netlink中attribute也是这种格式），这里的TLV结构是：
此时再看代码就很容易理解：
public
class
LLDPTLV {
class
LLDPTLV {
protected
byte
type
;
protected
short
length
;
protected
byte
[]
value
;
public
byte
getType() {
return
type
;
}
public
LLDPTLV setType(
byte
type) {
this
.
type
= type;
return
this
;
}
public
short
getLength() {
return
length
;
}
public
LLDPTLV setLength(
short
length) {
this
.
length
= length;
return
this
;
}
public
byte
[] getValue() {
return
value
;
}
public
LLDPTLV setValue(
byte
[] value) {
this
.
value
= value;
return
this
;
}
// serialization – Turn data into a stream of bytes
public
byte
[] serialize() {
// type = 7 bits
// info string length 9 bits, each value == byte
// info string
short
scratch = (
short
) (((0x7f &
this
.
type
) << 9) | (0x1ff &
this
.
length
));
// 7+9 = 2B
byte
[] data =
new
byte
[2 +
this
.
length
];
ByteBuffer bb = ByteBuffer. wrap(data);
bb.putShort(scratch);
if
(
this
.
value
!=
null
)
bb.put(
this
.
value
);
this
.
value
);
return
data;
}
// deserialization – Turn a stream of bytes back into a copy of the original
// object.
public
LLDPTLV deserialize(ByteBuffer bb) {
short
sscratch;
sscratch = bb.getShort();
this
.
type
= (
byte
) ((sscratch >> 9) & 0x7f);
this
.
length
= (
short
) (sscratch & 0x1ff);
if
(
this
.
length
> 0) {
this
.
value
=
new
byte
[
this
.
length
];
// if there is an underrun just toss the TLV
if
(bb.remaining() <
this
.
length
)
return
null
;
bb.get(
this
.
value
);
this
.
value
);
}
return
this
;
}
}
public
class
LLDP
extends
BasePacket {
class
LLDP
extends
BasePacket {
protected
LLDPTLV
chassisId
;
protected
LLDPTLV
portId
;
protected
LLDPTLV
ttl
;
protected
List<LLDPTLV>
optionalTLVList
;
protected
short
ethType
;
//上述几个字段都是LLDP协议规定的
public
LLDP() {
this
.
optionalTLVList
=
new
ArrayList<LLDPTLV>();
this
.
ethType
= Ethernet.
TYPE_LLDP
;
// 0x88cc
}
public
LLDPTLV getChassisId() {
return
chassisId
;
}
public
LLDP setChassisId(LLDPTLV chassisId) {
this
.
chassisId
= chassisId;
return
this
;
}
public
LLDPTLV getPortId() {
return
portId
;
}
public
LLDP setPortId(LLDPTLV portId) {
this
.
portId
= portId;
return
this
;
}
public
LLDPTLV getTtl() {
return
ttl
;
}
public
LLDP setTtl(LLDPTLV ttl) {
this
.
ttl
= ttl;
return
this
;
}
public
List<LLDPTLV> getOptionalTLVList() {
return
optionalTLVList
;
}
public
LLDP setOptionalTLVList(List<LLDPTLV> optionalTLVList) {
this
.
optionalTLVList
= optionalTLVList;
return
this
;
}
@Override
public
byte
[] serialize() {
int
length = 2 +
this
.
chassisId
.getLength() + 2
+
this
.
portId
.getLength() + 2 +
this
.
ttl
.getLength() + 2;
this
.
portId
.getLength() + 2 +
this
.
ttl
.getLength() + 2;
for
(LLDPTLV tlv :
this
.
optionalTLVList
) {
length += 2 + tlv.getLength();
}
byte
[] data =
new
byte
[length];
ByteBuffer bb = ByteBuffer. wrap(data);
bb.put(
this
.
chassisId
.serialize());
this
.
chassisId
.serialize());
bb.put(
this
.
portId
.serialize());
this
.
portId
.serialize());
bb.put(
this
.
ttl
.serialize());
this
.
ttl
.serialize());
for
(LLDPTLV tlv :
this
.
optionalTLVList
) {
bb.put(tlv.serialize());
}
bb.putShort((
short
) 0);
// End of LLDPDU
short
) 0);
// End of LLDPDU
if
(
this
.
parent
!=
null
&&
this
.
parent
instanceof
Ethernet)
((Ethernet)
this
.
parent
).setEtherType(
ethType
);
this
.
parent
).setEtherType(
ethType
);
return
data;
}
@Override
public
IPacket deserialize(
byte
[] data,
int
offset,
int
length) {
ByteBuffer bb = ByteBuffer. wrap(data, offset, length);
LLDPTLV tlv;
do
{
tlv =
new
LLDPTLV().deserialize(bb);
new
LLDPTLV().deserialize(bb);
// if there was a failure to deserialize stop processing TLVs
if
(tlv ==
null
)
break
;
switch
(tlv.getType()) {
case
0x0:
// can throw this one away, its just an end delimiter
break
;
case
0x1:
this
.
chassisId
= tlv;
break
;
case
0x2:
this
.
portId
= tlv;
break
;
case
0x3:
this
.
ttl
= tlv;
break
;
default
:
this
.
optionalTLVList
.add(tlv);
break
;
}
}
while
(tlv.getType() != 0 && bb.hasRemaining());
while
(tlv.getType() != 0 && bb.hasRemaining());
return
this
;
}
}
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