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02_02_引入帧模式MPLS中的典型标签分发

2019年7月27日 05:32 作者：金淼淋分类：MPLS  803

Label Assignment and Distribution
Introducing Typical Label
Distribution in Frame-Mode MPLS
llJIJ1üjtMPLS+
YES LAB
wwwveslabnet
YES LAB MPLS Unicast IP Routing
Arch itectu re (Cont.)
LSR
Control Plane
YES LAB
OSPF: 10.0.0.0/8
10.1.1.1
OSPF:
RIB:
LIB:
Data Plane
FIB:
LFIB:
10.0.0.0/8 + 1.2.3.4
10.0.0.0/8 + 1.2.3.4
10.0.0.0/8 +1.2.3.4
wwwveslabnet OSPF:
RIB:
LIB:
LDP: 10.0.0.0/8, I-=25
10.1.1.1
L=25 10.1.1.1
MPLS Unicast IP Routing
Arch itecture (Cont.)
LSR
Control Plane
L*23
10.0.0.0/8 + 1.2.3.4
10.0.0.0/8 1.2.3.4
10.0.o.0/8+Next-hop L=23, Local L=25
Data Plane
LAB:
YES LAB
LDP: 10.0.0.0/8, L=23
I L=23 10.1.1.1
1-=23 10.1.1.1
10.0.0.0/8+1.2.3.4,
L225+L=23
wwwveslabnet LSP Building
YES LAB
IP Routing
Protocol updates
The IP routing protocol determinesthe path.
wwwveslabnet LSP
77
LIB
10/8 77
10/8 77
LFIB
77 16
LIB
10/8 > 16
10/8 > 51
Building (Cont.)
YES LAB
LDP Updates
LFIB
10/8>NH
LIB
10/8 pop
LAB
16>34
LIB
10/8 +23
10/8 +34
NH = Next Hop
10/8 +51
LDP propagates labels to convert the path to an ISP.
wwwveslabnet PHP: After
The pop or implicit null
label is advertised.
MPLS Domain
10.0.0.0/8
10.0.0.0/8
L=18
10.0.0.0/8
L=pop
YES LAB
3
10.0.0.0/8
10.1.1.1
17
FIB
10/8>NH, 17
LAB
35*17
10.1.1.1
v
18
FIB
10/8+NH, 18
LAB
17>18
10.1.1.1
FIB
10/8>NH
LAB
18 *pop + int V
FIB
10/8
LFIB
One Single Lookup
NH = Next Hop
•A label is removed on the router before the last hop
within an MPLS
üfJ,
wwwveslabnet PH p
YES LAB
— Penultimate hop popping optimizes MPLS performance
(one less LFIB fit
— PHP does not work on ATM. (virtual path
identifier/virtual channel identifier cannot be removed.)
The pop or implicit null label uses a reserved value 3
when being advertised to a neighbor.
Pop implicit null
fldHmpls Idp explicit-null ,
wwwveslabnet Impact of IP Aggregation on L
Aggregation
Point
10.1.1.0/24
10M.0116
10.1.1.0/24
1-=33 —
YES LAB
10.1.1.0/24
LDP
L=pop
10.1.0.0/16
1--23
MPLS Domain
IP aggregation breaks an LSP into two segments.
Router C is forwarding packets based on Layer 3
wwwveslabnet Impact of IP Aggregation on LSPs
(Cont.)
YES LAB
— IP aggregation breaks an LSP into two segments. IP
0
— Aggregation should not be used where end•to•end
LSPs are required, such as
fi(J
• MPLSVPNs
• MPLSTEs
• Transit BGP where core routersare not running BGP
wwwveslabnet Label Allocation in a Frame-Mode MPLS Network:
Routing Table Of A
Building the IP Forwarding Table
Routing Table Of B Routing Table Of C
FIB on A
Network Next Hop
MPLS Domain
Label
Routing Table of E
Network Next HO
YES LAB
Network X
— IP routing protocols are used to build IP routingtables on all
LSRs.
Eh LSR_E P ,
— FIBS are initially built based on IP routingtables with no
labeling information. Label Allocation in a Frame-Mode
MPLS Network: Allocating Labels
Routing Table Of B
etwork Next Ho
Router B assigns label 25
to destination X.
Network X
1
x
FIB on B
Network Next Hop
MPLS Domain
c
Label
— Every LSR allocates a label for every destination in
the IP routing
— Labels have local
— Label allocations are Label Distribution and Advertisemen
YES LAB
LIB on B
Network LSR
local
MPLS Domain
Label
25
Network X
•The allocated label is advertised to all neighbor LSRs, regardless of whether
the neighbors are upstream or downstream LSRs for the destination. Populating the LFIB
YES LAB
LIB on B
FIB on B
Network Next Hop
Label
47
Network
47
LSR
local
Label
25
47
Network X
Label
25
MPLS Domain
I-FIB on B
Action Next Hop
47
— Router B has already assigned a label to network X and created an entry in the
jf-tELFlB4a@Jur
— The outgoing label is inserted in the LFIB after the label is received from the
next-hop Packet Propagation Across
an MPLS Network
YES LAB
2) Label lookup is performed
in the LFIB; label is switched.
Label
25
gab: 250
LAB on B
Action Next Ho
47
'Lab: 47'
IP:X
FIB on A
Network Next Ho
Label
25
MPLS Domain
Label
47
LFIB on C
Action Next Ho
pop
I) IP lookup is performed in
the FIB; packet is labeled.
3) Label lookup is performed
in the LFIB; label is removed. TTL and Loop Detection
1 AB
Label
TTL
TTL
Routing Loop
MPLS Domain
Labeled packets are dropped when the TTL is decreased to O.
wwwveslabnet Traceroute with Disabled TTL
Propagation
YES LAB
Label
IP TTL
TTL
MPLS Domain
TTL Exceeded
tra c eroute
1 10 ms
The first traceroute packet (ICMP or UDP) that
reaches the network is dropped on router A.
(ICMPÜI
UDP)
An ICMP TTL exceeded message is sent to the
source from router A. ICMP
wwwveslabnet
10.1. 1.1
A. acme.com Traceroute with Disabled
TTL Propagation (Cont.)
255 1
MPLS Domain
254 1
Label
TTL Exceeded
tracer oute
1 10 ms
2 10 ms
YES LAB
10.1. 1.1
A . acme com
The second traceroute packet that reaches
the network is dropped on router D.
An ICMP TTL exceeded message is sent to
the source from router D. ICMP
wwwveslabnet Per-Platform Label Allocatio
Label
25
25
MPLS Domain
YES LAB
LFIB on B
Action Next Hop
Network X
• An LFIB on a router usually does not contain an incominginterface.
• The same label can be used on any interface—per
platform label allocation.
LSR announcesa label to an adjacent LSR only once, even if there are parallel
links between them. LSRLA
wwwveslabnet

Work Blog » 02_02_引入帧模式MPLS中的典型标签分发

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