1. CÊu tróc MPLS

2. Néi dung Kh¸i niÖm MPLS Nh·n vµ LSR Ên ®Þnh nh·n vµ ph©n phèi
§­êng chuyÓn m¹ch nh·n
ATM LSR
Loops vµ TTL
Tæng quan LDP
Day in the Life of a Packet

3. Kh¸i niÖm MPLS MPLS: ChuyÓn m¹ch nh·n ®a giao thøc
MPLS chÝnh lµ chuyÓn m¹ch líp 2+
§­îc ph¸t triÓn ®Ó tæ hîp IP vµ ATM
ViÖc truyÒn gãi trong MPLS ®­îc thùc hiÖn theo c¸ch t­¬ng tù nh­ trong ATM switch
ViÖc göi gãi tin ®­îc thùc hiÖn dùa vµo nh·n

4. Kh¸i niÖm MPLS Gi¶I ph¸p cña c¸c h·ng
ý t­ëng ban ®Çu: Ipsilon – flow-driven
CSR cña Toshiba: 1994 chuyÓn m¹ch ATM - flow-driven
Tag Switching cña Cisco 1996: topology-driven
Aris cña IBM: 1996, topology-driven
C¸c gi¶i ph¸p kh¸c: FastIP (3Com), IP Navigator cña Ascend, VNS cña Nortel....

5. Kh¸i niÖm MPLS Nguyªn t¾c c¬ b¶n TÝch hîp ATM vµ IP trong mét thiÕt bÞ
TÝch hîp ®Þnh tuyÕn vµ chuyÓn m¹ch
Ph©n t¸ch ®Þnh tuyÕn vµ chuyÓn tiÕp

6. Kh¸i niÖm MPLS
Kh«ng nh­ IP, ViÖc ph©n líp vµ ®Æt gi¸ trÞ label cã thÓ dùa vµo:
§Þa chØ ®Ých
Traffic Engineering
VPN
QoS
FEC: Forwarding Equivalence Class
Mçi FEC cã thÓ biÓu thÞ: prefix cña ®Þa chØ ®Ých, VPN, Traffic Engineering tunnel, líp dÞch vô.

7. Kh¸i niÖm MPLS C¸c thµnh phÇn c¬ b¶n LSR: Label Switch Router
Lo¹i LSR
Chøc n¨ng thùc hiÖn
LSR
ChuyÓn tiÕp gãi cã nh·n
LSR biªn
KiÓm tra l¹i líp 3, ®Æt vµo ng¨n xÕp nh·n tr­íc khi göi gãi vµo m¹ng LSR.
NhËn gãi tin cã nh·n, lo¹i bá nh·n, kiÓm tra l¹i líp 3 vµ chuyÓn tiÕp gãi IP ®Õn nót tiÕp theo.
ATM-LSR
Sö dông giao thøc MPLS trong m¶ng ®iÒu khiÓn ®Ó thiÕt lËp kªnh ¶o ATM. ChuyÓn tiÕp tÕ bµo ®Õn nót ATM-LSR tiÕp theo
ATM-LSR biªn
NhËn gãi cã nh·n hoÆc kh«ng nh·n, ph©n vµo c¸c tÕ bµo ATM vµ göi c¸c tÕ bµo ®Õn nót ATM-LSR tiÕp theo.
NhËn c¸c tÕ bµo ATM tõ ATM-LSR cËn kÒ, t¸i t¹o c¸c gãi tõ c¸c tÕ bµo ATM vµ chuyÓn tiÕp gãi cã nh·n hoÆc kh«ng nh·n.

8. Nh·n vµ LSR LSR: Router chuyÓn m¹ch nh·n
Edge-LSR lµ LSR thùc hiÖn viÖc d¸n nh·n vµ bá nh·n
ATM-LSR: Bé chuyÓn m¹ch ATM chøa bé ®iÒu khiÓn chuyÓn m¹ch nh·n

9. Nh·n vµ LSR Giao thøc ®Þnh tuyÕn IP ®­îc sö dông trong miÒn ®Þnh tuyÕn
IGP domain with a label distribution protocol
Giao thøc ®Þnh tuyÕn IP ®­îc sö dông trong miÒn ®Þnh tuyÕn
Giao thøc ph©n phèi nh·n ®­îc sö dông ®Ó thùc hiÖn viÖc chuyÓn ®æi ®Þa chØ/nh·n gi÷a c¸c node kÕ cËn nhau
LSR nèi vµo (Ingress) nhËn gãi IP, ph©n líp gãi, Ên ®Þnh nh·n råi göi gãi ®· ®­îc d¸n nh·n tíi m¹ng MPLS
LSR lâi (Core) chuyÓn m¹ch c¸c gãi/tÕ bµo dùa vµo gi¸ trÞ nh·n
LSR nèi ra (Egress) th¸o bá nh·n tr­íc khi göi gãi IP ra ngoµi m¹ng MPLS

10. Nh·n vµ LSR Sö dông c¸c gi¸ trÞ Ethertypes/PPP PIDs/SNAP míi/etc
Label | Exp|S| TTL
Nh·n (Label) = 20 bit
Exp (Experimental) 3 bit
S = Bottom of stack, 1bit
TTL = Time to live, 8 bit
Sö dông c¸c gi¸ trÞ Ethertypes/PPP PIDs/SNAP míi/etc
Cho phÐp sö dông hoÆc mét vµi Label -> Chång Label
MPLS LSR lu«n göi gãi tin ®i dùa vµo gi¸ trÞ cña nh·n trªn ®Ønh cña chång giao thøc (top of the stack)

11. M¹ch ao MPLS Mçi gãi ®Òu cã g¾n “label” ®Ó nhËn diÖn cuéc nèi.
Mçi node cã chøa tr¹ng th¸i m¹ch aá “state”.
Bang tr¹ng th¸i (state) bao gåm tËp hîp c¸c liªn kÕt gi­a nh·n, chÆng tiÕp theo vµ nh·n sö dông cho chÆng tiÕp theo.
Bang ®­îc tham chiÕu bëi label. X Y Z V W
Label a b c
Bang tr¹ng th¸i U d
Virtual circuit is another packet transport paradigm. Asynchronous transfer mode (ATM) is an example of Virtual Circuit paradigm. Virtual circuit is established between the source and the destination.
Once the circuit is established, the packet is switched along with it. Each packet is identified by the label attached to it.
The label is unique within each link. The label value used on each link is determined in a distributed manner. That is, different labels are used on different links.
Each node keeps the circuit state. The state is a association between the label value, the next hop, and the new label value used on the next link. When a packet arrives at a node, the state table of the node is examined and the next hop is resolved.
The most important point is that the label is unique within a link, which results in small label length. The next hop is determined by looking up the state table using the label as a index. Thus the short label length simplifies table lookup procedure.
Remember that in datagram paradigm, the next hop is determined by the destination address. The destination address needs to be unique through the entire network, which results in long network address and complicated table lookup.

12. Göi ®i c¸c gãi cã g¾n nh·n MPLS
3 giai ®o¹n xö lý gãi
T¹o vµ g¾n nh·n
®äc, thay ®æi label vµ göi ®i
T¸ch bá nh·n
IP packet 1
IP packet
IP packet L1
IP packet L3 7
IP packet L2 2 4 6
§äc gi¸ trÞ L3
Label ®­îc t¹o ra vµ g¾n vµo. 8 3 5
§äc gi¸ trÞ Label
Label ®­îc t¸ch bá.
§äc gi¸ trÞ L3.
Label lookup is done.
Label is swapped.
®äc label
Thay ®æi label.

13. ChuyÓn m¹ch nh·n víi chång nh·n (label stack)
Nh·n bªn ngoµi ®­îc sö dông ®Ó truyÒn gãi. 1 2 3 4 6 7 8 5
IP packet L0
Outer label is swapped. L1 L2 L3
Inner label is intact.
Nh·n trong vÉn d­ nguyªn
Nh·n ngoµi ®­îc thay ®æi
Both labels are prepended by R1.
Nh·n ngoµi ®­îc R4 Ên ®Þnh
Nh·n trong ®­îc R7 Ên ®Þnh

14. T¸ch bá nh·n ë chÆng cuèi1 2 3 4 6 7 8 5
Gãi IP L1 L2 L3
®äc gi¸ trÞ label
Label ®­îc t¸ch bá

15. LSP: ®­êng chuyÓn m¹ch nh·n
C¸c gãi ®· d¸n nh·n ®­îc chuyÓn m¹ch trªn ®­êng LSP. #2 #3 In
Out
inf
label #1 #2 #1 #2 #1 #2 #1 #2 #3 #3 #3 #3 #1 #3 In
Out
inf
label #1 #3 In
Out
inf
label #1 #2 #2 #3 #3 #1

16. LDP LSP ®­îc thiÕt lËp sö dông giao thøc LDP 1.1.1.1 1.1.1.2 1.1.1.4
Label request
For #2
Label request
For #2
Label request
For #2
Label request
For #2 #1 #2 #1 #2 #1 #2 #1 #2 #3 #3 #3 #3
Label mapping #1 #2 #2 #3
Label mapping
Label mapping #3 #1
Label mapping

17. C¸c LSR vµ Label PPP Header Shim Header Layer 3 Header Ethernet Hdr
PPP Header(Packet over SONET/SDH)
PPP Header
Shim Header
Layer 3 Header
Ethernet
Ethernet Hdr
Shim Header
Layer 3 Header
Frame Relay
FR Hdr
Shim Header
Layer 3 Header
GFC
VPI
VCI PT
CLP
HEC
DATA
ATM Cell Header
Label
Subsequent cells
GFC
VPI
VCI
PTI
CLP
HEC
DATA
Label

18. Ên ®Þnh vµ ph©n phèi Label
Label chØ cã gi¸ trÞ côc bé tõng chÆng
Mçi LSR cã mét c¬ chÕ nhËn biÕt vµ chuyÓn ®æi nh·n riªng
Mçi LSR chñ ®éng Ên ®Þnh label cho c¸c FEC cña m×nh
Label ®­îc Ên ®Þnh vµ trao ®æi gi÷a c¸c LSR kÕ cËn nhau

19. Ên ®Þnh vµ ph©n phèi Label
C¸c LSR Upstream vµ Downstream
/24
/24
Rtr-A
Rtr-B
Rtr-C
Router-C lµ downstream neighbor cña Rtr-B víi ®Þa chØ ®Ých lµ /24
Rtr-B lµ downstream neighbor cña Rtr-A víi ®Þa chØ ®Ých lµ /24
LSR biÕt ®­îc c¸c downstream neighbor cña nã th«ng qua giao thøc ®Þnh tuyÕn IP
§Þa chØ next-hop chÝnh lµ downstream neighbor

20. Ên ®Þnh vµ ph©n phèi Label
Unsolicited Downstream Distribution
Sö dông label 30 øng víi ®Ých /24
Sö dông label 40 øng víi ®Ých /24
/24
/24
Rtr-A
Rtr-B
Rtr-C
Next-Hop In
Lab -
...
Address
Prefix
Out
I/F 1 30
Next-Hop In
Lab 30
...
Address
Prefix
Out
I/F 1 40
Next-Hop In
Lab 40
...
Address
Prefix
Out
I/F 1 -
C¸c tuyÕn x¸c ®Þnh bëi IGP
C¸c LSR ph©n phèi label ®Ó truyÒn gãi tíi c¸c node kÕ cËn

21. Ên ®Þnh vµ ph©n phèi Label
On-Demand Downstream Distribution
Use label 40 for destination /24
Use label 30 for destination /24
/24
/24
Rtr-A
Rtr-B
Rtr-C
Request label for destination /24
Request label for destination /24
C¸c Upstream LSR yªu cµu downstream neighbor ph©n bæ label
C¸c Downstream LSR ph©n bæ label theo yªu cÇu

22. Ên ®Þnh vµ ph©n phèi Label
Label Retention Mode
Liberal retention mode
LSR l­u gi÷ c¸c gi¸ trÞ label tõ tÊt c¶ c¸c node kÕ cËn
C¶i thiÖn thêi gian héi tô, when next-hop is again available after IP convergence
Require more memory and label space
Conservative retention mode
LSR chØ l­u gi÷ l¹i c¸c gi¸ trÞ label tõ c¸c node chÆng kÕ tiÕp
LSR discards all labels for FECs without next-hop
Free memory and label space

23. Ên ®Þnh vµ ph©n phèi Label
Label Distribution Modes
§iÒu khiÓn LSP ®éc lËp
LSR g¾n mét gi¸ trÞ Label cho mét FEC mét c¸ch ®éc lËp, bÊt kÓ LSR cã nhËn ®­îc nh·n chÆng tiÕp theo cho FEC ®ã hay kh«ng
LSR sau ®ã qu¶ng b¸o gi¸ trÞ Label cho c¸c node kÕ cËn nã
§iÒu khiÓn LSP theo yªu cÇu
LSR only binds and advertise a label for a particular FEC if:
it is the egress LSR for that FEC or
it has already received a label binding from its next-hop

24. Ên ®Þnh vµ ph©n phèi Label
Mét sè giao thøc trao ®æi label
LDP
T¹o gi¸ trÞ label theo ®Þa chØ IP ®Ých
RSVP, CR-LDP
Sö dông cho traffic engineering
BGP
External label (VPN)
PIM
For multicast states label mapping

25. §­êng chuyÓn m¹ch nh·n (LSP)
IGP domain with a label distribution protocol
IGP domain with a label distribution protocol
LSP follows IGP shortest path
LSP diverges from IGP shortest path
LSP ®­îc t¹o ra tõ c¸c th«ng tin ®Þnh tuyÕn IGP
LSPs may diverge from IGP shortest path
LSP tunnels (explicit routing) with TE
LSPs are unidirectional
Return traffic takes another LSP

26. §­êng chuyÓn m¹ch nh·n (LSP) T¸ch bá nh·n ë chÆng cuèi
Label ngoµi cïng cña chång nh·n (top of the stack) ®­îc t¸ch bá ®i bëi upstream neighbor cña egress LSR
Egress LSR yªu cÇu “popping” th«ng qua giao thøc ph©n phèi nh·n
Egress LSR advertises implicit-null label
Egress LSR sÏ kh«ng cÇn ph¶i xem xÐt råi tach bá nh·n n÷a
One lookup is saved in the egress LSR

27. §­êng chuyÓn m¹ch nh·n (LSP) T¸ch bá nh·n ë chÆng cuèi
Address
Prefix and mask
/24
Next-Hop
Interface
Serial1
/24
Serial2
171.68/16
...
Null
Next-Hop In
Lab
Address
Prefix
Out
I/F -
171.68/16 1 4
...
Next-Hop In
Lab
Address
Prefix
Out
I/F 4
171.68/16 2
pop
...
Summary route for /16
Summary route for /16 1 1
/24
Use label 4 for FEC /16
Use label “implicit-null” for FEC /16
/24
Summary route is propagate through the IGP and label is assigned by each LSR
Egress LSR summarises more specific routes and advertises a label for the new FEC
Egress LSR needs to do an IP lookup for finding more specific route
Egress LSR need NOT receive a labelled packet

28. ATM LSR Bé chuyÓn m¹ch ATM göi ®i c¸c cell (not packet)
ViÖc ph©n phèi Label lµ Downstream on-demand, Ordered
IGP label trïng víi gi¸ trÞ VPI/VCI trong Cell header
Merging LSR:
Ability to use the same label for different FECs if outgoing interface is the same
Save label space on ATM-LSRs
Cell interleave problem
Non Merging LSR:
ATM-LSR requests one label per FEC and per incoming interface (upstream neighbors)
Downstream LSR may request itself new label to its downstream neighbors

29. ATM LSRs Non-Merging Downstream on Demand
Lab 5 8
...
Address
Prefix
171.68
Out
I/F 3 4 1 2
ATM-LSR requested additional label for same FEC in order to distinguish between incoming interfaces (Downstream on Demand)
ATM cell 5
IP Packet
ATM cell 5
171.68
ATM cell 4
ATM cell 3
ATM cell 4
ATM cell 3
ATM cell 4
IP Packet
ATM cell 8
ATM cell 8
ATM cell 8

30. ATM LSRs VC-Merging Downstream on Demand
Lab 5 8
...
Address
Prefix
171.68
Out
I/F 3 1 2
ATM-LSR transmitted cells in sequence in order for the downstream LSR to re-assembling correctly the cells into packets
ATM cell 5
IP Packet
ATM cell 5
171.68
ATM cell 3
ATM cell 3
ATM cell 3
ATM cell 3
ATM cell 3
IP Packet
ATM cell 8
ATM cell 8
ATM cell 8

31. Loops and TTL
In IP networks TTL is used to prevent packets to travel indefinitely in the network
MPLS may use same mechanism as IP, but not on all encapsulations
TTL is present in the label header for PPP and LAN headers (shim headers)
ATM cell header does not have TTL

32. Loops and TTL LSR ë chÕ ®é ATM kh«ng cã kh¶ n¨ng TTL
Some suggested options:
- hop-count object in LDP
- Path Vector object in LDP

33. Loops and TTL
LSR-1
LSR-2
LSR-3
IP packet TTL = 10
IP packet TTL = 6
Label = 25
IP packet TTL = 6
Label = 39
LSR-6 --> 25 Hops=4
LSR-6
IP packet TTL = 6
Label = 21
IP packet TTL = 6
IGP domain with a label distribution protocol
Egress
LSR-4
LSR-5
TTL is decremented prior to enter the non-TTL capable LSP
If TTL is 0 the packet is discarded at the ingress point
TTL ®­îc kiÓm tra t¹i LSP nèi ra

34. C¸c kh¸i niÖm trong LDP LDP - Label Distribution Protocol
Label ®­îc t¹o ra t­¬ng øng víi FEC (Unicast Destination Prefix)
LDP works between adjacent/non-adjacent peers
C¸c phiªn LDP ®­îc thiÕt lËp gi÷a c¸c peers

35. C¸c b¶n tin LDP C¸c b¶n tin ph¸t hiÖn (Discovery)
§­îc sö dông ®Ó ph¸t hiÖn vµ duy tr× sù hiÖn diÖn cña c¸c peer míi
C¸c Hello packet (UDP) ®­îc göi tíi tÊt c¶ c¸c ®Þa chØ routers multicast
Mét khi node kÕ cËn ®­îc ph¸t hiÖn, phiªn LDP ®­îc thiÕt lËp trªn TCP

36. C¸c b¶n tin LDP C¸c b¶n tin vÒ phiªn C¸c b¶n tin qu¶ng b¸
ThiÕt lËp, duy tr× vµ gi¶i to¶ c¸c phiªn LDP
C¸c b¶n tin qu¶ng b¸
T¹o, thay ®æi, xo¸ gi¸ trÞ label
C¸c b¶n tin th«ng b¸o
B¸o hiÖu lçi

37. Day in the life of a Packet
Address
Prefix and mask
/24
Next-Hop
Interface
Serial1
/24
Serial2
171.68/16
...
Null
Next-Hop In
Lab
Address
Prefix
Out
I/F -
171.68/16 1 4
...
Next-Hop In
Lab
Address
Prefix
Out
I/F 4
171.68/16 1 7
...
Next-Hop In
Lab
Address
Prefix
Out
I/F 7
171.68/16 2
pop
... P P 1 1 2 PE PE
Use label “implicit-null” for FEC /16
Use label 4 for FEC /16
Use label 7 for FEC /16
/24
Summary route for /16
Summary route for /16 CE
/24
Summary route is propagate through the IGP and label is assigned by each LSR
Egress LSR summarises more specific routes and advertises a label for the new FEC
Egress LSR needs to do an IP lookup for finding more specific route

38. Day in the life of a Packet Basic Layout

39. Day in the life of a Packet Database Layout

40. Day in the life of a Packet

41. Day in the life of a Packet

42. KÕt luËn LSR göi c¸c gãi tin dùa vµo gi¸ trÞ nh·n
IP header vµ quyÕt ®Þnh göi gãi tin ®­îc t¸ch riªng ra ®Ó t¨ng tÝnh linh ®éng
Gi¸ trÞ Label cã thÓ ®­îc t¹o ra tõ nhiÒu nguån kh¸c nhau
C¸c giao thøc ®Þnh tuyÕn IP
§Þa chØ Multicast
Traffic Engineering
QoS
VPN

43. KÕt luËn
MPLS cho phÐp ph©n líp linh ®éng c¸c gãi tin vµ tèi ­u ho¸ tµi nguyªn m¹ng
Label ®­îc ph©n bæ bëi c¸c giao thøc kh¸c nhau
LDP, RSVP, BGP, PIM
C¸c giao thøc ph©n phèi kh¸c nhau cã thÓ cïng tån t¹i trªn mét LSR
Label chØ cã gi¸ trÞ côc bé
Kh«ng cÇn ph¶i ®¸nh sè hay ph©n bæ gi¸ trÞ nh·n trªn ph¹m vi toµn cÇu