Cisco Support Community
cancel
Showing results for 
Search instead for 
Did you mean: 
Announcements

Welcome to Cisco Support Community. We would love to have your feedback.

For an introduction to the new site, click here. If you'd prefer to explore, try our test area to get started. And see here for current known issues.

Bronze

EoMPLS ( port -based) VC 5,dot1q tag

Hi everybody

Please consider the scenario on EoMpls ( port based)

EoMpls.png

R2 has loopback 1.1.1.1,R3, 3.3.3.3, R4,4.4.4

R2  and R4 are PE routers while R3 is P.

R1 and R5 are acting as customer CE routers.

R1 connects to R2 with 10.10.10.1

R5 Connects to R4 with 10.10.10.2

R1 configuration:

interface FastEthernet0/0.1

encapsulation dot1Q 200

ip address 10.10.10.1 255.255.255.0

R2 configurations:

interface FastEthernet0/0 ( going to R1)

no ip address

duplex auto

speed auto

xconnect 4.4.4.4 100 encapsulation mpls

R2#show mpls forwarding-table

Local  Outgoing    Prefix            Bytes tag  Outgoing   Next Hop

tag    tag or VC   or Tunnel Id      switched   interface

16     Pop tag     200.200.200.0/24  0          Fa0/1      199.199.199.3

17     Pop tag     3.0.0.0/8         0          Fa0/1      199.199.199.3

19     19          4.4.4.4/32        0          Fa0/1      199.199.199.3

20                 l2ckt(100)        35694      none       point2point

Since we are using port based EoMPLs, Vc type 5 is negotiated as shown below:

R2#show mpls l2transport binding

  Destination Address: 4.4.4.4,  VC ID: 100

    Local Label:  20

        Cbit: 1,    VC Type: Ethernet,    GroupID: 0

        MTU: 1500,   Interface Desc: n/a

        VCCV: CC Type: CW [1], RA [2]

              CV Type: LSPV [2]

    Remote Label: 20

        Cbit: 1,    VC Type: Ethernet,    GroupID: 0

        MTU: 1500,   Interface Desc: n/a

        VCCV: CC Type: CW [1], RA [2]

              CV Type: LSPV [2]

+++++++++++++++++++++++++++++++++++++++++

Based on the following link, this is what I understand,

http://www.cisco.com/en/US/docs/switches/lan/catalyst6500/ios/15.0SY/configuration/guide/eompls.html

If we have VC 5, then R2 will remove dot1q tag from the frame it receives from R1 before sending it to the core.

Quote from the above link:

EoMPLS Overview

EoMPLS is one of the AToM transport types. EoMPLS works by encapsulating  Ethernet PDUs in MPLS packets and forwarding them across the MPLS  network. Each PDU is transported as a single packet.  Cisco IOS Release 15.0SY supports two EoMPLS modes:

VLAN  mode—Transports Ethernet traffic from a source 802.1Q VLAN to a  destination 802.1Q VLAN through a single VC over an MPLS network. VLAN  mode uses VC type 5 as default (no dot1q tag) and VC type 4 (transport  dot1 tag) if the remote PE does not support VC type 5 for subinterface  (VLAN) based EoMPLS.

Port mode—Allows all traffic on a port to share a single VC across an MPLS network. Port mode uses VC type 5.

++++++++++++++++++++++++++++++++++++++++++++

However I performed the lab, I found R2 is not doing that.  R1 sends a ARP message which is received by R2. R2 sees a Vlan tag 200 on the the ARP message from R1. R2 even though has negotiated Vc type 5, did not remove dot1q tag 200 as it should based on the above Cisco.s link

Below is wireshark capture Between R2 and R3

No.     Time        Source                Destination           Protocol Length Info

    277 161.435000  c0:00:14:c4:00:00     Broadcast             ARP      90     Who has 10.10.10.2?  Tell 10.10.10.1

Frame 277: 90 bytes on wire (720 bits), 90 bytes captured (720 bits)

Ethernet II, Src: c0:01:14:c4:00:01 (c0:01:14:c4:00:01), Dst: c0:02:14:c4:00:01 (c0:02:14:c4:00:01)

MultiProtocol Label Switching Header, Label: 19, Exp: 0, S: 0, TTL: 255

MultiProtocol Label Switching Header, Label: 20, Exp: 0, S: 1, TTL: 255

PW Ethernet Control Word

Ethernet II, Src: c0:00:14:c4:00:00 (c0:00:14:c4:00:00), Dst: Broadcast (ff:ff:ff:ff:ff:ff)

802.1Q Virtual LAN, PRI: 0, CFI: 0, ID: 200

Address Resolution Protocol (request)

I appreciate your help.

Thanks

1 REPLY
Bronze

EoMPLS ( port -based) VC 5,dot1q tag

This is what I found. I putting this info so it might help others with the similar questions.  Found a great link on L2 VPN architecture.

http://www.dcfcpug.org/sponsors/l2vpn.pdf

From the above link:

Another difference between the port-tunneling mode and VLAN-tunneling mode is in the

handling of VLAN IDs. In port-tunneling mode, the VLAN ID is transparently passed from the

ingress PE to the egress PE over MPLS in a single VLAN.

This is exactly what I observed in my lab, regardless if  the frame is tagged or untagged, PE router simply encapsulates the whole frame except for preamble and FCS in new ethernet with two mpls labels and control word and sends it over the pseudowire eventhough VC type was 5( Ethernet)

++++++++++++++++++++++++++++++++

Thanks.

461
Views
0
Helpful
1
Replies