Layer 2 virtual private network (×××) service is usually tested in the CisIE® Service Provider (SP) lab
exam. Configuring interworking service appears to be difficult for some candidates. Below is an example of how to configure Ethernet VLAN with Frame Relay interworking, followed by a description of common configuration problems. Candidates can use this tip sheet to help avoid such mistakes and to prepare for
the Layer 2 ××× portion of the CCIE SP lab exam.
The figure shows routers PE1 and PE2 establishing a Label Distribution Protocol (LDP) connection to
support Any Transport over MPLS (AToM). Here, router R1 connects PE1 by Ethernet VLAN, and router R2 connects PE2 by Frame Relay data-link connection identifier (DLCI). The question asks whether routers R1 and R2 can communicate this way on the same subnet. PE1 and PE2 configurations are listed in the table.
PE1:
mpls ip
mpls label protocol ldp
mpls ldp router-id Loopback0
!
pseudowire-class inter-ether encapsulation mpls
interworking ip
!
interface Loopback0
ip address 9.9.9.9 255.255.255.255
!
interface FastEthernet0/0
no ip address
!
interface FastEthernet0/0.1
encapsulation dot1Q 10
xconnect 8.8.8.8 123 pw-class inter-ether
!
PE2:
mpl s ip
mpls labe l pr otocol ld p
mpls ldp r out er-id L oopba ck0
frame-re lay sw itch ing
!
pseud ow ire-cla s s atom encap su lat i o n mp ls
interw orking ip
!
inter f ace Loo pback0
ip addre s s 8 . 8.8.8 255 .25 5 .255.2 55
!
inter f ace S e rial1/ 0
no ip addr ess
encapsula t io n frame-re lay clo ckra t e 20 16000
frame-re lay intf-ty pe dce
!
conne ct ato m Ser i al1/0 30 6 l2 tran sport xconne ct 9.9 . 9.9 1 23 pw -cla ss atom
Common Configuration Problems
The PE1 virtual circuit number does not match with the PE2 virtual circuit number. For the above example, PE1 defines virtual circuit number 123; PE2 should also define virtual circuit number 123 to match PE1.
“frame-relay switching” is missed on PE2.
“frame-relay intf-type dce” is missed on PE2.
“interworking ip” is missed under pseudowire-class.
Useful Commands for Verification
PE#show mpls ldp neighbor PE#show mpls forwarding-table PE#show mpls interface
PE#show mpls l2transport vc <num> detail
PE#show mpls l2transport binding