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This chapter describes the L2VPN Autodiscovery and Signaling feature which enables the discovery of remote Provider Edge (PE) routers and the associated signaling in order to provision the pseudowires.
Autodiscovery refers to the process of finding the Provider Edge (PE) routers that participates in a given L2VPN instance. One of the protocols used for this is BGP.
Once the PE routers are discovered, pseudowires are signaled and established across each pair of PE routers. Signaling refers to the exchange of Virtual Circuit (VC) labels between the PE routers. The signaling protocol can be either LDP or BGP.
VPLS is a multipoint Layer 2 bridging service for which BGP-based autodiscovery is well suited. BGP-based VPLS autodiscovery eliminates the need to manually provision the VPLS neighbors. VPLS autodiscovery enables each VPLS PE router to discover the other provider edge (PE) routers that are part of the same VPLS domain. VPLS Autodiscovery also tracks when PE routers are added to or removed from the VPLS domain. When the discovery process is complete, each PE router has the information required to setup VPLS pseudowires (PWs).
Even when BGP autodiscovery is enabled, pseudowires can be manually configured for VPLS PE routers that are not participating in the autodiscovery process.
The BGP signaling and autodiscovery scheme have the following components:
A means for a PE to learn which remote PEs are members of a given VPLS. This process is known as autodiscovery.
A means for a PE to learn the pseudowire label expected by a given remote PE for a given VPLS. This process is known as signaling.
The BGP Network Layer Reachability Information (NLRI) takes care of the above two components simultaneously. The NLRI generated by a given PE contains the necessary information required by any other PE. These components enable the automatic setting up of a full mesh of pseudowires for each VPLS without having to manually configure those pseudowires on each PE.
This is the basic BGP and LDP configuration that is required before proceeding to configure BGP-based autodiscovery.
Router(config)# interface loopback-interface
Router(config-if)# ipv4 address ipv4-address subnet-mask
Router(config-if)# exit
Router(config)# mpls ldp
Router(config-ldp)# router-id ipv4-address
Router(config-ldp-if)# interface interface-name
Router(config-ldp-if)# exit
Router(config-ldp)# exit
Router(config)# router bgp as-number
Router(config-bgp)# address-family l2vpn vpls-vpws
Router(config-bgp-af)# exit
Router(config-bgp)# neighbor loopback ipv4 address of neighbor
Router(config-bgp-nbr)# remote-as remote-as-number
Router(config-bgp-nbr)# update-source loopback-interface
Router(config-bgp-nbr)# address-family l2vpn vpls-vpwsThe following figure illustrates an example of LDP and BGP network topology that is required for enabling BGP based autodiscovery.
interface Loopback1
ipv4 address 1.1.1.10 255.255.255.255
!
mpls ldp
router-id 1.1.1.1
interface GigabitEthernet0/1/0/0
!
router bgp 120
address-family l2vpn vpls-vpws
!
neighbor 2.2.2.20
remote-as 120
update-source Loopback1
address-family l2vpn vpls-vpws
interface Loopback1
ipv4 address 2.2.2.20 255.255.255.255
!
mpls ldp
router-id 2.2.2.2
interface GigabitEthernt0/1/0/0
!
router bgp 120
address-family l2vpn vpls-vpws
!
neighbor 1.1.1.10
remote-as 120
update-source Loopback1
address-family l2vpn vpls-vpwsBGP and LDP need to be configured as indicated in the section Configuring BGP and LDP for BGP-based Autodiscovery before proceeding to the configurations in this section.
Router(config)# l2vpn
Router(config-l2vpn)# bridge group bridge-group-name
Router(config-l2vpn-bg)# bridge-domain bridge-domain-name
Router(config-l2vpn-bg-bd)# vfi vfi-name
Router(config-l2vpn-bg-bd-vfi)# autodiscovery bgp
Router(config-l2vpn-bg-bd-vfi-ad)# vpn-id vpn-id
Router(config-l2vpn-bg-bd-vfi-ad)# rd auto
Router(config-l2vpn-bg-bd-vfi-ad)# route-target 1.1.1.1:100
Router(config-l2vpn-bg-bd-vfi-ad-sig)# signaling-protocol bgp
Router(config-l2vpn-bg-bd-vfi-ad-sig)# ve-id 1
l2vpn
bridge group gr1
bridge-domain bd1
interface GigabitEthernet0/1/0/1.1
vfi vf1
! AD independent VFI attributes
vpn-id 100
! Auto-discovery attributes
autodiscovery bgp
rd auto
route-target 2.2.2.2:100
! Signaling attributes
signaling-protocol bgp
ve-id 3
l2vpn
bridge group gr1
bridge-domain bd1
interface GigabitEthernet0/1/0/2.1
vfi vf1
! AD independent VFI attributes
vpn-id 100
! Auto-discovery attributes
autodiscovery bgp
rd auto
route-target 2.2.2.2:100
! Signaling attributes
signaling-protocol bgp
ve-id 5A PE router advertises an identifier through BGP for each VPLS instance. This identifier is unique within the VPLS instance and acts like a VPLS ID. The identifier enables the PE router receiving the BGP advertisement to identify the VPLS associated with the advertisement and import it to the correct VPLS instance. In this manner, for each VPLS, a PE router learns the other PE routers that are members of the VPLS.
The signaling of pseudowires between provider edge devices, uses targeted LDP sessions to exchange label values and attributes. Forwarding Equivalence Class (FEC) 129 is used for the signaling. The information carried by FEC 129 includes the VPLS ID, the Target Attachment Individual Identifier (TAII) and the Source Attachment Individual Identifier (SAII).
The LDP advertisement also contains the inner label or VPLS label that is expected for the incoming traffic over the pseudowire. This enables the LDP peer to identify the VPLS instance with which the pseudowire is to be associated and the label value that it is expected to use when sending traffic on that pseudowire.
BGP and LDP need to be configured as indicated in the section Configuring BGP and LDP for BGP-based Autodiscovery before proceeding to the configurations in this section.
The below code block shows the basic configuration steps required for BGP-based VPLS autodiscovery with LDP Signaling.
Router(config)# l2vpn
Router(config-l2vpn)# bridge group {bridge group name}
Router(config-l2vpn-bg)# bridge-domain {bridge domain name}
Router(config-l2vpn-bg-bd)# vfi {vfi name}
Router(config-l2vpn-bg-bd-vfi)# autodiscovery bgp
Router(config-l2vpn-bg-bd-vfi-ad)# vpn-id 10
Router(config-l2vpn-bg-bd-vfi-ad)# rd auto
Router(config-l2vpn-bg-bd-vfi-ad)# route-target 1.1.1.1:100
Router(config-l2vpn-bg-bd-vfi-ad)# signaling-protocol ldp
Router(config-l2vpn-bg-bd-vfi-ad-sig)# vpls-id 120:200
Router(config-l2vpn-bg-bd-vfi-ad-sig)# commitThe following figure illustrates an example of configuring VPLS with BGP autodiscovery (AD) and LDP Signaling.
l2vpn
router-id 10.10.10.10
bridge group bg1
bridge-domain bd1
vfi vf1
vpn-id 100
autodiscovery bgp
rd 1:100
router-target 12:12
signaling-protocol ldp
vpls-id 120:200
l2vpn
router-id 20.20.20.20
bridge group bg1
bridge-domain bd1
vfi vf1
vpn-id 100
autodiscovery bgp
rd 2:200
router-target 12:12
signaling-protocol ldp
vpls-id 120:100
BGP-based autodiscovery is possible even for point-to-point L2VPN services such as VPWS. However, true autodiscovery is not possible in VPWS as it is in VPLS. In VPWS, in order to connect the Customer Edge (CE) routers, an explicit configuration has to be done at each PE. Only the existence of other PEs can be indicated by autodiscovery.
The two primary functions of the VPWS control plane are: auto-discovery and signaling. Both of these functions are accomplished with a single BGP Update advertisement.
When a VPWS cross-connect is configured with BGP autodiscovery and signaling enabled, BGP distributes NLRI for the cross-connect with the PE as the BGP next-hop and appropriate CE-ID. Additionally, the cross-connect is associated with one or more BGP export Route Targets (RTs) that are also distributed (along with NLRI).
BGP and LDP need to be configured as indicated in the section Configuring BGP and LDP for BGP-based Autodiscovery before proceeding to the configurations in this section.
The below code block shows the basic configuration steps required for BGP-based VPWS autodiscovery with BGP Signaling.
Router(config)# l2vpn
Router(config-l2vpn)# xconnect group {xconnect group name}
Router(config-l2vpn-xc)# mp2mp {instance name}
Router(config-l2vpn-xc-mp2mp)# vpn-id {vpn-id}
Router(config-l2vpn-xc-mp2mp)# l2-encapsulation vlan
Router(config-l2vpn-xc-mp2mp)# autodiscovery bgp
Router(config-l2vpn-xc-mp2mp-ad)# rd auto
Router(config-l2vpn-xc-mp2mp-ad)# route-target 2.2.2.2:100
Router(config-l2vpn-xc-mp2mp-ad)# signaling-protocol bgp
Router(config-l2vpn-xc-mp2mp-ad-sig)# ce-id 1
Router(config-l2vpn-xc-mp2mp-ad-sig-ce)# interface GigabitEthernet0/1/0/1.1 remote-ce-id 2The following figure illustrates an example of configuring VPWS with BGP autodiscovery and BGP Signaling.
l2vpn
xconnect group gr1
mp2mp mp1
vpn-id 100
l2 encapsulation vlan
autodiscovery bgp
rd auto
route-target 2.2.2.2:100
! Signaling attributes
signaling-protocol bgp
ce-id 1
interface GigabitEthernet0/1/0/1.1 remote-ce-id 2
l2vpn
xconnect group gr1
mp2mp mp1
vpn-id 100
l2 encapsulation vlan
autodiscovery bgp
rd auto
route-target 2.2.2.2:100
! Signaling attributes
signaling-protocol bgp
ce-id 2
interface GigabitEthernet0/1/0/2.1 remote-ce-id 1PE1:
PE1# show l2vpn discovery xconnect
Service Type: VPWS, Connected
List of VPNs (1 VPNs):
XC Group: gr1, MP2MP mp1
List of Local Edges (1 Edges):
Local Edge ID: 1, Label Blocks (1 Blocks)
Label base Offset Size Time Created
---------- ------ ---- -------------------
16030 1 10 01/24/2009 21:23:04
Status Vector: 9f ff
List of Remote Edges (1 Edges):
Remote Edge ID: 2, NLRIs (1 NLRIs)
Label base Offset Size Peer ID Time Created
---------- ------ ---- --------------- -------------------
16045 1 10 1.1.1.1 01/24/2009 21:29:35
Status Vector: 7f ff
PE1# show l2vpn xconnect mp2mp detail
Group gr1, MP2MP mp1, state: up
VPN ID: 100
VPN MTU: 1500
L2 Encapsulation: VLAN
Auto Discovery: BGP, state is Advertised (Service Connected)
Route Distinguisher: (auto) 3.3.3.3:32770
Import Route Targets:
2.2.2.2:100
Export Route Targets:
2.2.2.2:100
Signaling protocol:BGP
CE Range:10
….
Group gr1, XC mp1.1:2, state is up; Interworking none
Local CE ID: 1, Remote CE ID: 2, Discovery State: Advertised
AC: GigabitEthernet0/1/0/1.1, state is up
Type VLAN; Num Ranges: 1
VLAN ranges: [1, 1]
MTU 1500; XC ID 0x2000013; interworking none
PW: neighbor 1.1.1.1, PW ID 65538, state is up ( established )
PW class not set, XC ID 0x2000013
Encapsulation MPLS, Auto-discovered (BGP), protocol BGP
MPLS Local Remote
------------ ------------------------------ -----------------------------
Label 16031 16045
MTU 1500 1500
Control word enabled enabled
PW type Ethernet VLAN Ethernet VLAN
CE-ID 1 2
------------ ------------------------------ -----------------------------
...
PE1# show bgp l2vpn vpws
BGP router identifier 3.3.3.3, local AS number 100
BGP generic scan interval 60 secs
BGP table state: Active
Table ID: 0x0
BGP main routing table version 913
BGP NSR converge version 3
BGP NSR converged
BGP scan interval 60 secs
Status codes: s suppressed, d damped, h history, * valid, > best
i - internal, S stale
Origin codes: i - IGP, e - EGP, ? - incomplete
Network Next Hop Rcvd Label Local Label
Route Distinguisher: 1.1.1.1:32775
*>i2:1/32 1.1.1.1 16045 nolabel
*>i3:1/32 1.1.1.1 16060 nolabel
Route Distinguisher: 3.3.3.3:32770 (default for vrf gr1:mp1)
*> 1:1/32 0.0.0.0 nolabel 16030
*>i2:1/32 1.1.1.1 16045 nolabel
*>i3:1/32 1.1.1.1 16060 nolabel
Processed 5 prefixes, 5 pathsPE2:
PE2# show l2vpn discovery xconnect
Service Type: VPWS, Connected
List of VPNs (1 VPNs):
XC Group: gr1, MP2MP mp1
List of Local Edges (2 Edges):
Local Edge ID: 2, Label Blocks (1 Blocks)
Label base Offset Size Time Created
---------- ------ ---- -------------------
16045 1 10 01/24/2009 21:09:14
Status Vector: 7f ff
Local Edge ID: 3, Label Blocks (1 Blocks)
Label base Offset Size Time Created
---------- ------ ---- -------------------
16060 1 10 01/24/2009 21:09:14
Status Vector: 7f ff
List of Remote Edges (1 Edges):
Remote Edge ID: 1, NLRIs (1 NLRIs)
Label base Offset Size Peer ID Time Created
---------- ------ ---- --------------- -------------------
16030 1 10 3.3.3.3 01/24/2009 21:09:16
Status Vector: 9f ff
PE2# show l2vpn xconnect mp2mp detail
Group gr1, MP2MP mp1, state: up
VPN ID: 100
VPN MTU: 1500
L2 Encapsulation: VLAN
Auto Discovery: BGP, state is Advertised (Service Connected)
Route Distinguisher: (auto) 1.1.1.1:32775
Import Route Targets:
2.2.2.2:100
Export Route Targets:
2.2.2.2:100
Signaling protocol:BGP
CE Range:10
...
Group gr1, XC mp1.2:1, state is up; Interworking none
Local CE ID: 2, Remote CE ID: 1, Discovery State: Advertised
AC: GigabitEthernet0/1/0/2.1, state is up
Type VLAN; Num Ranges: 1
VLAN ranges: [1, 1]
MTU 1500; XC ID 0x2000008; interworking none
PW: neighbor 3.3.3.3, PW ID 131073, state is up ( established )
PW class not set, XC ID 0x2000008
Encapsulation MPLS, Auto-discovered (BGP), protocol BGP
MPLS Local Remote
------------ ------------------------------ -----------------------------
Label 16045 16031
MTU 1500 1500
Control word enabled enabled
PW type Ethernet VLAN Ethernet VLAN
CE-ID 2 1
------------ ------------------------------ -----------------------------
...
PE2# show bgp l2vpn vpws
BGP router identifier 1.1.1.1, local AS number 100
BGP generic scan interval 60 secs
BGP table state: Active
Table ID: 0x0
BGP main routing table version 819
BGP NSR converge version 7
BGP NSR converged
BGP scan interval 60 secs
Status codes: s suppressed, d damped, h history, * valid, > best
i - internal, S stale
Origin codes: i - IGP, e - EGP, ? - incomplete
Network Next Hop Rcvd Label Local Label
Route Distinguisher: 1.1.1.1:32775 (default for vrf gr1:mp1)
*>i1:1/32 3.3.3.3 16030 nolabel
*> 2:1/32 0.0.0.0 nolabel 16045
*> 3:1/32 0.0.0.0 nolabel 16060
Route Distinguisher: 3.3.3.3:32770
*>i1:1/32 3.3.3.3 16030 nolabel
Processed 4 prefixes, 4 pathsSignaling of pseudowires requires exchange of information between two endpoints. LDP is better suited for point-to-point signaling.
A PE router advertises an identifier through BGP for the VPWS instance. The signaling of pseudowires between provider edge devices uses targeted LDP sessions to exchange label values and attributes and to configure the pseudowires. FEC 129 is used for the signaling. The information carried by FEC 129 includes the xconnect ID, the Target Attachment Individual Identifier (TAII) and the Source Attachment Individual Identifier (SAII).
BGP and LDP need to be configured as indicated in the section Configuring BGP and LDP for BGP-based Autodiscovery before proceeding to the configurations in this section.
The below code block shows the basic configuration steps required for BGP based VPWS autodiscovery with LDP Signaling.
Router(config)# l2vpn
Router(config-l2vpn)# xconnect group {xconnect group name}
Router(config-l2vpn-xc)# mp2mp {instance name}
Router(config-l2vpn-xc-mp2mp)# vpn-id {vpn-id}
Router(config-l2vpn-xc-mp2mp)# l2-encapsulation vlan
Router(config-l2vpn-xc-mp2mp)# autodiscovery bgp
Router(config-l2vpn-xc-mp2mp-ad)# rd auto
Router(config-l2vpn-xc-mp2mp-ad)# route-target 2.2.2.2:100
Router(config-l2vpn-xc-mp2mp-ad)# signaling-protocol ldp
Router(config-l2vpn-xc-mp2mp-ad-sig)# ce-id 1
Router(config-l2vpn-xc-mp2mp-ad-sig-ce)# interface GigabitEthernet0/1/0/1.1 remote-ce-id 2The following figure illustrates an example of configuring VPWS with BGP autodiscovery and LDP Signaling.
l2vpn
xconnect group gr1
mp2mp mp1
vpn-id 100
l2 encapsulation vlan
autodiscovery bgp
rd auto
route-target 2.2.2.2:100
! Signaling attributes
signaling-protocol ldp
ce-id 1
interface GigabitEthernet0/1/0/1.1 remote-ce-id 2
l2vpn
xconnect group gr1
mp2mp mp1
vpn-id 100
l2 encapsulation vlan
autodiscovery bgp
rd auto
route-target 2.2.2.2:100
! Signaling attributes
signaling-protocol ldp
ce-id 2
interface GigabitEthernet0/1/0/2.1 remote-ce-id 1
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