MPLS OVERVIEW
--------------
Multiprotocol Label Switching
Open Standard per RFC 3031
Previously Cisco Propetiary Tag Switching
MPLS OVERVIEW- Multiprotocol
------------------------------
Can transport different payloads
layer 2
- ethernet,hdlc,ppp,frame-relay & ATM
layer 3
- IPV4 & IPV6
Traffic is switched between interfaces based on locally significant label values
Similar to how frame-relay or ATM switch uses input/output DLCIS and VPI/VCIS
MPLS LABEL FORMAT
-----------------
4 byte header used to switch packets
20 bit label= local significant to rotuers
3 bit EXP = class off service
s bit = defines last label in label stack
8 bit ttl= time to live
MPLS PACKET WITH IP AS PAYLOAD
------------------------------------------------
HOW LABEL WORKS
----------------
MPLS Labels are bound to FECS
- forwarding equivlancy class
-ipv4 prefix for our purpose
Router uses MPLS LFIB to switch traffic
Essentially the LFIB is cef table + label
Switching Logic
- if traffic comes in if1 with label x send out if2 with label y
MPLS DEVICE ROLES
-----------------
PE/LER = provider edge router/label edge router, this connects to customer edge devices retrieves unlabelled packets and add label (pe) aka label pursh or label imposition. In l3VPN performs both IP routing & MPLS Lookup
P/LSR = provider router/label switch routers connect pe to P routers switches traffic based only on label
Label PUsh/POP/SWAP
-------------------
PE and P routers perform 3 major operations
- label push
- add a label to an incoming packet aka label imposition
- Label swap
- replace a label on incoming packet
- label pop- remove a label from outgoing packet aka label disposition
LABEL DISTRIBUTION
-------------------
Adjacent P/PE'S must agree on label per FEC
Label binding can be dynamic through
- Tag Distribution Protocol (TDP) - CIsco Propetiary legacy protocol
-Label Distribtuion Protocol (LDP)
-RRSVP (RESOURCE RESERVATIOB PROTOCOL)- use for mpls te (traffic engineering)
- Multiprotocol BGP (MPBGP)
LABEL DISTRIBUTION PROTOCOL (LDP)
----------------------------------
Standard Per RFC 3036
Neighbor discovery is done via udp port 646 to 224.0.0.2
Neighbor adjacency is TCP port 646
Label Advertisement
- Advertise FEC for connected IGP interfaces
- Advertise FEC for IGP learned routers (including static)
LDP router id is selected same process as OSPF router id
The labels are local link significant so labels get originated on per hop basis.They are significant to two neighboring routers
MPLS COMMANDS
--------------
ip cef
mpls label protocol ldp|tdp
mpls ip
show mpls ldp interface
show mpls ldp neighbor
show mpls forwarding-table
show ip cef [internal]
debug mpls packet
(config) ip cef
config ) mpls label protocol ldp
cofnig) mpls ip
debug mpls transport events
LAB
----
OK i am looking at the core of the network here r1-r6
I am going to enable mpls and i will use the ldp protocol
I have already configured the underlying topology with ospf so there is connectivity to loopbacks etc
r6
---
R6 is one of our pe I will start by configuring mpls and the ldp protocol
r6(config)#mpls ip
r6(config)#mpls label protocol ldp
r6(config)#int fa0/0.16
r6(config-subif)#mpls ip
r6#sh mpls int
Interface IP Tunnel Operational
FastEthernet0/0.16 Yes (ldp) No Yes
r6#
r1
---
r1(config)#mpls ip
r1(config)#mpls label protocol ldp
r1(config)#int fa0/0.16
r1(config-subif)#mpls ip
r1(config-subif)#
*Mar 1 01:33:49.067: mpls: Add mpls app; FastEthernet0/0.16
*Mar 1 01:33:49.067: mpls: Add mpls app; FastEthernet0/0.16
*Mar 1 01:33:49.067: mpls: Add mpls app; i/f status change; FastEthernet0/0.16
*Mar 1 01:33:49.067: ldp: enabling ldp on FastEthernet0/0.16
*Mar 1 01:33:49.123: ldp: i/f status change: FastEthernet0/0.16; cur/des flags 0x2/0x2mcast 1
*Mar 1 01:33:49.123: mpls: Enable MPLS forwarding on FastEthernet0/0.16
*Mar 1 01:33:49.123: ldp: enabling ldp on FastEthernet0/0.16
*Mar 1 01:33:49.123: ldp: i/f status change: FastEthernet0/0.16; cur/des flags 0x2/0x2mcast 1
*Mar 1 01:33:49.127: mpls: Allocate router id, select 1.1.1.1
*Mar 1 01:33:54.011: tagcon: (Default-IP-Routing-Table) Assign peer id; 6.6.6.6:0: id 0
*Mar 1 01:33:54.015: %LDP-5-NBRCHG: LDP Neighbor 6.6.6.6:0 is UP
*Mar 1 01:33:54.015: tagcon: peer 6.6.6.6:0 (pp 0x83C87FD0): advertise 155.0.3.1
*Mar 1 01:33:54.015: tagcon: peer 6.6.6.6:0 (pp 0x83C87FD0): advertise 155.0.5.1
*Mar 1 01:33:54.015: tagcon: peer 6.6.6.6:0 (pp 0x83C87FD0): advertise 155.0.2.1
*Mar 1 01:33:54.015: tagcon: peer 6.6.6.6:0 (pp 0x83C87FD0): advertise 1.1.1.1
*Mar 1 01:33:54.019: tagcon: peer 6.6.6.6:0 (pp 0x83C87FD0): advertise 1.1.1.1/32, label 3 (imp-null) (#2)
*Mar 1 01:33:54.019: tagcon: peer 6.6.6.6:0 (pp 0x83C87FD0): advertise 2.2.2.2/32, label 16 (#4)
*Mar 1 01:33:54.019: tagcon: peer 6.6.6.6:0 (pp 0x83C87FD0): advertise 155.0.3.0/24, label 3 (imp-null) (#6)
*Mar 1 01:33:54.019: tagcon: peer 6.6.6.6:0 (pp 0x83C87FD0): advertise 155.0.2.0/24, label 3 (imp-null) (#8)
*Mar 1 01:33:54.019: tagcon: peer 6.6.6.6:0 (pp 0x83C87FD0): advertise 155.0.7.0/24, label 17 (#10)
*Mar 1 01:33:54.023: tagcon: peer 6.6.6.6:0 (pp 0x83C87FD0): advertise 155.0.5.0/24, label 3 (imp-null) (#12)
*Mar 1 01:33:54.023: tagcon: peer 6.6.6.6:0 (pp 0x83C87FD0): advertise 155.0.4.0/24, label 18 (#14)
*Mar 1 01:33:54.023: tagcon: peer 6.6.6.6:0 (pp 0x83C87FD0): advertise 4.4.4.4/32, label 19 (#16)
*Mar 1 01:33:54.023: tagcon: peer 6.6.6.6:0 (pp 0x83C87FD0): advertise 6.6.6.6/32, label 20 (#18)
r1(config-subif)#exit
we can see when we configure r1 the mpls ldp neighbor relationship comes up with router 6.6.6.6 r6
r1#sh mpls ldp neigh
Peer LDP Ident: 6.6.6.6:0; Local LDP Ident 1.1.1.1:0
TCP connection: 6.6.6.6.21310 - 1.1.1.1.646
State: Oper; Msgs sent/rcvd: 14/15; Downstream
Up time: 00:02:29
LDP discovery sources:
FastEthernet0/0.16, Src IP addr: 155.0.2.6
Addresses bound to peer LDP Ident:
155.0.2.6 6.6.6.6
We see that we have a tcp connection to 6.6.6.6 using 646 tell us what int and what the source address of our neighbor is and the uptme
r1#sh mpls ldp par
Protocol version: 1
Downstream label generic region: min label: 16; max label: 100000
Session hold time: 180 sec; keep alive interval: 60 sec
Discovery hello: holdtime: 15 sec; interval: 5 sec
Discovery targeted hello: holdtime: 90 sec; interval: 10 sec
Downstream on Demand max hop count: 255
Downstream on Demand Path Vector Limit: 255
LDP for targeted sessions
LDP initial/maximum backoff: 15/120 sec
LDP loop detection: off
r1#
we can see our session parameters
I will configure the rest of the mpls ldp neighbors on r1
r1(config)#int fa0/0.12
r1(config-subif)#mpls ip
r1(config-subif)#int fa0/0.13
r1(config-subif)#mpls ip
r1(config-subif)#int fa0/0.16
r1(config-subif)#mpls ip
r2
---
r2#config t
Enter configuration commands, one per line. End with CNTL/Z.
r2(config)#ip cef
r2(config)#mpls ip
r2(config)#mpls label protocol ldp
r2(config)#int fa0/0.12
r2(config-subif)#mpls ip
r2(config-subif)#int fa0/
*Mar 1 01:44:18.231: %LDP-5-NBRCHG: LDP Neighbor 1.1.1.1
r2(config-subif)#int fa0/0.23
r2(config-subif)#mpls ip
r2(config-subif)#int fa0/0.24
r2(config-subif)#mpls ip
r2(config-subif)#
r4
--
r4(config)#mpls ip
r4(config)#mpls label protocol ldp
r4(config)#int fa0/0.24
r4(config-subif)#mpls ip
r4(config-subif)#
r4#sh mpls ldp ne
Peer LDP Ident: 2.2.2.2:0; Local LDP Ident 4.4.4.4:0
TCP connection: 2.2.2.2.646 - 4.4.4.4.55869
State: Oper; Msgs sent/rcvd: 26/26; Downstream
Up time: 00:09:58
LDP discovery sources:
FastEthernet0/0.24, Src IP addr: 155.0.7.2
Addresses bound to peer LDP Ident:
155.0.3.2 155.0.4.2 155.0.7.2 2.2.2.2
r4#
notice on r4 it has the address the directly connected neighbor has 155.0.3.2 which link between r2 - r1 155.0.4.2 which is the link between r3 - r2
155.0.7.2 - which is the link between r4 and r2 it will use these when building it mpls forwarding table, i will finish off the config and we will look at the forwarding table
r3
---
r3(config)#mpls ip
r3(config)#mpls label protocol ldp
r3(config)#int fa0/0.13
r3(config-subif)#mpls ip
r3(config-subif)#int fa9
*Mar 1 01:57:41.676: %LDP-5-NBRCHG: LDP Neighbor 1.1.1.1:
r3(config-subif)#int fa0/0.23
r3(config-subif)#mpls ip
r3(config-subif)#int fa0/0.23
*Mar 1 01:57:59.341: %LDP-5-NBRCHG: LDP Neighbor 2.2
r3(config-subif)#int fa0/0.35
r3(config-subif)#mpls ip
r3(config-subif)#
r5
---
r5(config)#mpls ip
r5(config)#mpls label protocol ldp
r5(config)#ip cef
r5(config)#do sh ip int brief
Interface IP-Address OK? Method Status Protocol
FastEthernet0/0 unassigned YES TFTP up up
FastEthernet0/0.35 155.0.6.5 YES manual up up
FastEthernet0/1 unassigned YES NVRAM administratively down down
Serial0/0/0 unassigned YES TFTP up down
Serial0/1/0 unassigned YES TFTP up up
Loopback0 5.5.5.5 YES NVRAM up up
r5(config)#int fa0/0.35
r5(config-subif)#mpls ip
r5(config-subif)#
*Jan 30 20:49:12.583: %LDP-5-NBRCHG: LDP Neighbor 3.3.3.3:0 (1) is UP
r5#sh mpls ldp neigh
Peer LDP Ident: 3.3.3.3:0; Local LDP Ident 5.5.5.5:0
TCP connection: 3.3.3.3.646 - 5.5.5.5.18064
State: Oper; Msgs sent/rcvd: 15/15; Downstream
Up time: 00:00:29
LDP discovery sources:
FastEthernet0/0.35, Src IP addr: 155.0.6.3
Addresses bound to peer LDP Ident:
155.0.5.3 155.0.4.3 155.0.6.3 3.3.3.3
r5#
r5#sh mpls forwarding-table
Local Outgoing Prefix Bytes tag Outgoing Next Hop
tag tag or VC or Tunnel Id switched interface
16 16 1.1.1.1/32 0 Fa0/0.35 155.0.6.3
17 17 2.2.2.2/32 0 Fa0/0.35 155.0.6.3
18 18 155.0.3.0/24 0 Fa0/0.35 155.0.6.3
19 19 155.0.2.0/24 0 Fa0/0.35 155.0.6.3
20 20 155.0.7.0/24 0 Fa0/0.35 155.0.6.3
21 Pop tag 155.0.5.0/24 0 Fa0/0.35 155.0.6.3
22 Pop tag 155.0.4.0/24 0 Fa0/0.35 155.0.6.3
23 Pop tag 3.3.3.3/32 0 Fa0/0.35 155.0.6.3
24 21 4.4.4.4/32 0 Fa0/0.35 155.0.6.3
25 23 6.6.6.6/32 0 Fa0/0.35 155.0.6.3
r5#
r5#sh mpls ldp bindingS 6.6.6.6 255.255.255.255
tib entry: 6.6.6.6/32, rev 24
local binding: tag: 25
remote binding: tsr: 3.3.3.3:0, tag: 23
r5#
Lets take r6 loopback and trace the path to it
we router 5 has assigned a local label of 25 to the network 6.6.6.6 if we recieve traffic for 6.6.6.6 we will send it out fa0/0.35 with a label of 23
r3
--
r3#sh mpls forward
Local Outgoing Prefix Bytes tag Outgoing Next Hop
tag tag or VC or Tunnel Id switched interface
16 Pop tag 1.1.1.1/32 0 Fa0/0.13 155.0.5.1
17 Pop tag 2.2.2.2/32 0 Fa0/0.23 155.0.4.2
18 Pop tag 155.0.3.0/24 0 Fa0/0.13 155.0.5.1
Pop tag 155.0.3.0/24 0 Fa0/0.23 155.0.4.2
19 Pop tag 155.0.2.0/24 0 Fa0/0.13 155.0.5.1
20 Pop tag 155.0.7.0/24 0 Fa0/0.23 155.0.4.2
21 19 4.4.4.4/32 0 Fa0/0.23 155.0.4.2
22 Pop tag 5.5.5.5/32 0 Fa0/0.35 155.0.6.5
23 20 6.6.6.6/32 0 Fa0/0.13 155.0.5.1
r3#
ok on r3 if we recieve an incoming label of 23 we will swap the label putting on label 20 and send it out int fa0/0.13 which is the link to r1
r1
---
r1#sh mpls forwarding
Local Outgoing Prefix Bytes tag Outgoing Next Hop
tag tag or VC or Tunnel Id switched interface
16 Pop tag 2.2.2.2/32 0 Fa0/0.12 155.0.3.2
17 Pop tag 155.0.7.0/24 0 Fa0/0.12 155.0.3.2
18 Pop tag 155.0.4.0/24 0 Fa0/0.12 155.0.3.2
Pop tag 155.0.4.0/24 0 Fa0/0.13 155.0.5.3
19 19 4.4.4.4/32 0 Fa0/0.12 155.0.3.2
20 Pop tag 6.6.6.6/32 0 Fa0/0.16 155.0.2.6
21 Pop tag 155.0.6.0/24 0 Fa0/0.13 155.0.5.3
22 Pop tag 3.3.3.3/32 0 Fa0/0.13 155.0.5.3
23 22 5.5.5.5/32 0 Fa0/0.13 155.0.5.3
if we recieve a label of 20 we will remove the label and send it out fa0/0.16 which is the link to r6
we will reach r6 6.6.6.6 so the mpls switching is done
r1#sh mpls ldp bind
tib entry: 1.1.1.1/32, rev 2
local binding: tag: imp-null
remote binding: tsr: 6.6.6.6:0, tag: 16
remote binding: tsr: 2.2.2.2:0, tag: 16
remote binding: tsr: 3.3.3.3:0, tag: 16
tib entry: 2.2.2.2/32, rev 4
local binding: tag: 16
remote binding: tsr: 6.6.6.6:0, tag: 17
remote binding: tsr: 2.2.2.2:0, tag: imp-null
remote binding: tsr: 3.3.3.3:0, tag: 17
tib entry: 3.3.3.3/32, rev 22
local binding: tag: 22
remote binding: tsr: 6.6.6.6:0, tag: 24
remote binding: tsr: 2.2.2.2:0, tag: 22
remote binding: tsr: 3.3.3.3:0, tag: imp-null
tib entry: 4.4.4.4/32, rev 16
local binding: tag: 19
remote binding: tsr: 6.6.6.6:0, tag: 22
remote binding: tsr: 2.2.2.2:0, tag: 19
remote binding: tsr: 3.3.3.3:0, tag: 21
tib entry: 5.5.5.5/32, rev 24
local binding: tag: 23
remote binding: tsr: 6.6.6.6:0, tag: 25
remote binding: tsr: 2.2.2.2:0, tag: 23
remote binding: tsr: 3.3.3.3:0, tag: 22
tib entry: 6.6.6.6/32, rev 18
local binding: tag: 20
remote binding: tsr: 6.6.6.6:0, tag: imp-null
remote binding: tsr: 2.2.2.2:0, tag: 20
remote binding: tsr: 3.3.3.3:0, tag: 23
tib entry: 155.0.2.0/24, rev 8
local binding: tag: imp-null
remote binding: tsr: 6.6.6.6:0, tag: imp-null
remote binding: tsr: 2.2.2.2:0, tag: 17
remote binding: tsr: 3.3.3.3:0, tag: 19
tib entry: 155.0.3.0/24, rev 6
local binding: tag: imp-null
remote binding: tsr: 6.6.6.6:0, tag: 18
remote binding: tsr: 2.2.2.2:0, tag: imp-null
remote binding: tsr: 3.3.3.3:0, tag: 18
tib entry: 155.0.4.0/24, rev 14
local binding: tag: 18
remote binding: tsr: 6.6.6.6:0, tag: 21
remote binding: tsr: 2.2.2.2:0, tag: imp-null
remote binding: tsr: 3.3.3.3:0, tag: imp-null
tib entry: 155.0.5.0/24, rev 12
local binding: tag: imp-null
remote binding: tsr: 6.6.6.6:0, tag: 20
remote binding: tsr: 2.2.2.2:0, tag: 18
remote binding: tsr: 3.3.3.3:0, tag: imp-null
tib entry: 155.0.6.0/24, rev 20
local binding: tag: 21
remote binding: tsr: 6.6.6.6:0, tag: 23
remote binding: tsr: 2.2.2.2:0, tag: 21
remote binding: tsr: 3.3.3.3:0, tag: imp-null
tib entry: 155.0.7.0/24, rev 10
local binding: tag: 17
remote binding: tsr: 6.6.6.6:0, tag: 19
remote binding: tsr: 2.2.2.2:0, tag: imp-null
remote binding: tsr: 3.3.3.3:0, tag: 20
r1#
we will locally generate label for each network in the cef table see above.
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