Ethernet
The AToM solution to carry Ethernet over MPLS is strictly point-to-point. In essence, all Ethernet frames are carried from one ingress PE to one egress PE router. This is the equivalent of LAN-to-LAN bridging over point-to-point WAN links. The connection is not multipoint, so no emulation of a LAN-like functionality occurs whereby one frame enters the ingress PE and is broadcast to all PE routers that belong to the same Layer 2 VPN. A LAN-like solution across MPLS in one VPN is possible; it is called VPLS, and it is covered in Chapter 11.
The AC can be an Ethernet port or an 802.1Q (dot1q) VLAN. For each of the two types of ACs, LDP signals a different VC Type or PW type in the PW ID FEC TLV via the targeted session between the PE routers. VC Type 5 is used for Ethernet Port mode, and VC Type 4 is used for Ethernet VLAN mode. In the Ethernet VLAN mode, a VLAN header that has some meaning to the PE routers is always present. In other words, the PE routers look at the VLAN header. In Ethernet Port mode, a VLAN header might or might not be present on the frame. In any case, if a VLAN header does exist, the PE router does not inspect it; rather, it carries the frame transparently. Running EoMPLS in Ethernet Port mode allows a complete Ethernet trunk to be transported over one pseudowire. To run Ethernet VLAN mode, configure the xconnect command on the VLAN interface or on the Ethernet subinterface.
This section describes some issues that pertain only to EoMPLS.
Ethernet Frame Format
Figure 10-16 shows the Ethernet II frame format. The first one is the Ethernet II frame. The second is the Ethernet II frame with an 802.1Q VLAN header. The 802.1Q VLAN header consists of the average nbr of cells peer rcvd in one pkt MNCP
22 28
average nbr of cells MCPT sent in one pkt (us)
22 400
tag protocol identifier (TPID) and tag control information (TCI) fields. These 4 extra bytes are referred to as the VLAN tag.
Figure 10-16 Ethernet II and Ethernet II with 802.1Q Frame Format
|
Preamble |
SFD |
DA |
SA |
Ethertype |
Data |
FCS |
||
|
7 Bytes |
1 Byte |
6 Bytes |
6 Bytes |
2 Bytes |
46-1500 Bytes |
4 Bytes |
||
|
Ethernet II With 802.1Q Frame Format |
||||||||
|
Preamble |
SFD |
DA |
SA |
TPID |
TCI |
Ethertype |
Data |
FCS |
7 Bytes 1 Byte 6 Bytes 6 Bytes 2 Bytes 2 Bytes 2 Bytes 46-1500 Bytes 4 Bytes
7 Bytes 1 Byte 6 Bytes 6 Bytes 2 Bytes 2 Bytes 2 Bytes 46-1500 Bytes 4 Bytes
The 4 bytes of the VLAN header are further divided into the following:
■ TPID (16 bits)—The TPID is set to 0x8100 to identify the tagged protocol as 802.1Q.
■ TCI (16 bits)—The TCI consists of the following fields:
Priority (3 bits)—The 3 priority bits are used as quality of service (QoS) bits to prioritize the Ethernet frames.
CFI (1 bit)—The canonical format indicator indicates whether the MAC address is in canonical format.
VID (12 bits)—The VID is the VLAN identifier. It is the number of the VLAN.
EoMPLS Forwarding
When the ingress PE router receives the Ethernet frame, it strips off the preamble, Start of Frame Delimiter (SFD), and FCS fields, adds a control word, labels the frame, and forwards it across the MPLS network. If the Ethernet frame is tagged with an 802.1Q tag, this tag is kept, too. On the egress PE router, the VC label is stripped off, the control word is removed, the Ethernet FCS is added, and the frame is sent toward the CE router or switch.
VLAN ID Rewrite
VLAN ID Rewrite is the feature whereby the 802.1Q tag might be rewritten in Ethernet VLAN mode if the 802.1Q VLAN ID is different at both sides of the AToM network. You might have VLAN 100 on the ingress PE router and VLAN 200 on the egress PE router, for example. The VLAN ID rewrite happens either on the imposition side or on the disposition side. The VLAN ID Rewrite is an automatically enabled feature, so no configuration is needed to enable it.
EoMPLS Scenario Examples
This section gives you an overview of some of the scenarios to create EoMPLS services. Notice that EoMPLS is either done in Ethernet Port mode or in Ethernet VLAN mode. In the examples, the Ethernet refers to Ethernet Port mode, and Eth VLAN refers to Ethernet VLAN mode.
EoMPLS Carrying Simple Ethernet
The PE routers are configured with the xconnect command on the main Ethernet interface and carry the nontagged Ethernet frames received from the CE routers over the pseudowire. The PE routers run EoMPLS in Ethernet Port mode. In Figure 10-17, you can see that the pseudowire with VCID 2000 carries the Ethernet frames across the MPLS network.
Figure 10-17 EoMPLS Carrying Simple Ethernet
Targeted LDP Session
Figure 10-17 EoMPLS Carrying Simple Ethernet
Targeted LDP Session
Example 10-12 shows the configuration needed for the network in Figure 10-17. The xconnect commands on the Ethernet interfaces of the PE routers specify the loopback IP address of the remote PE router as peer-router-id. The configured VCID is 2000.
Example 10-12 EoMPLS Carrying Simple Ethernet Example
interface FastEthernet0/1 ip address 10.100.100.1 255.255.255.0
PE2-ce interface FastEthernet0/1 ip address 10.100.100.2 255.255.255.0
hostname PE1
pseudowire-class one encapsulation mpls
interface FastEthernet9/0/0 no ip address xconnect 10.200.254.4 2000 pw-class one hostname PE2
interface FastEthernet4/1/0 no ip address xconnect 10.200.254.1 2000 pw-class one
PE1#show mpls l2transport vc 2000
Local intf Local circuit Dest address VC ID Status
Fa9/0/0 Ethernet 10.200.254.4 2000 UP
PE1#show mpls l2transport vc 2000 detail
Local interface: Fa9/0/0 up, line protocol up, Ethernet up Destination address: 10.200.254.4, VC ID: 2000, VC status: up Preferred path: not configured Default path: active
Tunnel label: 23, next hop 10.200.200.2 Output interface: Et0/0/0, imposed label stack {23 35} Create time: 00:02:26, last status change time: 00:02:26 Signaling protocol: LDP, peer 10.200.254.4:0 up MPLS VC labels: local 25, remote 35 Group ID: local 0, remote 0 MTU: local 1500, remote 1500 Remote interface description: Sequencing: receive disabled, send disabled Sequence number: receive 0, send 0 VC statistics:
packet totals: receive 107, send 67 byte totals: receive 10736, send 7818 packet drops: receive 0, seq error 0, send 0
EoMPLS Carrying an Ethernet Trunk
When the AC is an Ethernet trunk, the configuration on the PE routers is the same as in Example 10-12. The difference is that the CE routers are configured with 802.1Q subinterfaces; therefore, the Ethernet frames are tagged when the PE router receives them. The result is that the PE routers carry the whole 802.1Q trunk across the MPLS network in one pseudowire. The transported Ethernet frames across the pseudowire have the 802.1Q tags.
Figure 10-18 shows the two PE routers running EoMPLS in Ethernet Port mode. The CE routers have two subinterfaces: one for VLAN 100 and one for VLAN 200. Both VLANs are carried across the MPLS network over the pseudowire with VCID 2000.
Figure 10-18 EoMPLS Carrying an Ethernet Trunk
Targeted LDP Session
Figure 10-18 EoMPLS Carrying an Ethernet Trunk
Targeted LDP Session
- 100 and 200 100 and 200
The PE routers are running EoMPLS in Ethernet Port mode, indicated by the VC Type being Ethernet, as shown in Example 10-13.
Example 10-13 EoMPLS Carrying an Ethernet Trunk Example
PE1-ce
interface FastEthernet0/1 no ip address
interface FastEthernet0/1.1 encapsulation dotlQ 100 ip address 10.100.100.1 255.255.255.0
interface FastEthernet0/1.2 encapsulation dot1Q 200 ip address 10.100.200.1 255.255.255.0
PE2-ce
interface FastEthernet0/1 no ip address
interface FastEthernet0/1.1 encapsulation dot1Q 100 ip address 10.100.100.2 255.255.255.0
interface FastEthernet0/1.2 encapsulation dot1Q 200 ip address 10.100.200.2 255.255.255.0
PE1#show mpls l2transport vc
Local intf Local circuit Dest address VC ID Status
Fa9/0/0 Ethernet 10.200.254.4 2000 UP
PE1#show mpls l2transport vc detail
Local interface: Fa9/0/0 up, line protocol up, Ethernet up Destination address: 10.200.254.4, VC ID: 2000, VC status: up Preferred path: not configured Default path: active
Tunnel label: 23, next hop 10.200.200.2 Output interface: Et0/0/0, imposed label stack {23 21} Create time: 00:01:04, last status change time: 00:00:19 Signaling protocol: LDP, peer 10.200.254.4:0 up MPLS VC labels: local 24, remote 21 Group ID: local 0, remote 0 MTU: local 1500, remote 1500 Remote interface description: Sequencing: receive disabled, send disabled Sequence number: receive 0, send 0 VC statistics:
packet totals: receive 50, send 39 byte totals: receive 5712, send 5389 packet drops: receive 0, seq error 0, send 0
PE1#show mpls l2transport binding
Destination Address: 10.200.254.4, VC ID: 2000 Local Label: 24
Cbit: 1, VC Type: Ethernet, GroupID: 0 MTU: 1500, Interface Desc: n/a VCCV Capabilities: Type 1, Type 2 Remote Label: 21
Cbit: 1, VC Type: Ethernet, GroupID: 0 MTU: 1500, Interface Desc: n/a VCCV Capabilities: Type 1, Type 2
EoMPLS Carrying One VLAN
In the scenario of EoMPLS carrying one VLAN, you have an 802.1Q trunk between the CE and the PE routers. Each VLAN is mapped to one pseudowire. The advantage of this scenario compared to the previous scenario is that each VLAN has its own pseudowire and can be routed differently through the MPLS network, or the different pseudowires can be between different PE routers. Figure 10-19 shows an example of the two PE routers running two pseudowires between them, one for VLAN 100 and one for VLAN 200.
Figure 10-19 EoMPLS Carrying One VLAN
PE1-ce
Loopback 0 10.200.254.1/32
FastEth 9/0/0.1 VLAN 100: VCID 2000
Targeted LDP Session
Targeted LDP Session
Loopback 0 10.200.254.1/32
Loopback 0 10.200.254.4/32
Loopback 0 10.200.254.4/32
FastEth 4/1/0.1 VLAN 100: VCID 2000
PE2-ce
FastEth 9/0/0.2 VLAN 200: VCID 2001
FastEth 4/1/0.2 VLAN 200: VCID 2001
The PE routers are running EoMPLS in VLAN mode, indicated by the VC Type being Eth VLAN, as shown in Example 10-14.
Example 10-14 EoMPLS Carrying One VLAN Example hostname PE1
interface FastEthernet9/0/0 no ip address
interface FastEthernet9/0/0.1 encapsulation dotlQ 100 xconnect 10.200.254.4 2000 pw-class one
interface FastEthernet9/0/0.2 encapsulation dot1Q 200 xconnect 10.200.254.4 2001 pw-class one
hostname PE2
interface FastEthernet4/1/0 no ip address
interface FastEthernet4/1/0.1 encapsulation dotlQ 100 xconnect 10.200.254.1 2000 pw-class one
interface FastEthernet4/1/0.2 encapsulation dot1Q 200 xconnect 10.200.254.1 2001 pw-class one
PE1#show mpls l2transport vc
Local intf Local circuit Dest address VC ID Status
Fa9/0/0.1 Eth VLAN 100 10.200.254.4 2000 UP
Fa9/0/0.2 Eth VLAN 200 10.200.254.4 2001 UP
PE1#show mpls l2transport vc 2001 detail
Local interface: Fa9/0/0.2 up, line protocol up, Eth VLAN 200 up Destination address: 10.200.254.4, VC ID: 2001, VC status: up Preferred path: not configured Default path: active
Tunnel label: 23, next hop 10.200.200.2 Output interface: Et0/0/0, imposed label stack {23 22} Create time: 00:10:33, last status change time: 00:03:46 Signaling protocol: LDP, peer 10.200.254.4:0 up MPLS VC labels: local 24, remote 22 Group ID: local 0, remote 0 MTU: local 1500, remote 1500 Remote interface description: Sequencing: receive disabled, send disabled Sequence number: receive 0, send 0 VC statistics:
packet totals: receive 91, send 43 byte totals: receive 8686, send 4906 packet drops: receive 0, seq error 0, send 0
PE1#show mpls l2transport binding
Destination Address: 10.200.254.4, VC ID: 2000 Local Label: 20
Cbit: 1, VC Type: Eth VLAN, GroupID: 0 MTU: 1500, Interface Desc: n/a
Example 10-14 EoMPLS Carrying One VLAN Example (Continued)
VCCV Capabilities: Type 1, Type 2 Remote Label: 21
Cbit: 1, VC Type: Eth VLAN, GroupID: 0 MTU: 1500, Interface Desc: n/a VCCV Capabilities: Type 1, Type 2 Destination Address: 10.200.254.4, VC ID: 2001 Local Label: 24
Cbit: 1, VC Type: Eth VLAN, GroupID: 0 MTU: 1500, Interface Desc: n/a VCCV Capabilities: Type 1, Type 2 Remote Label: 22
Cbit: 1, VC Type: Eth VLAN, GroupID: 0 MTU: 1500, Interface Desc: n/a VCCV Capabilities: Type 1, Type 2
Continue reading here: Dot1q Tunneling QinQ over AToM
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