L2VPN Advanced Concepts

L2VPN Advanced Concepts

With L2VPN Pseudowires, the PE routers are not aware of the VLAN used by the other end.

In the BGP update message, there is no such field to carry the VLAN information. So, even if both PEs are using different VLANs, the Pseudowire stays up.

BUM traffic will pass through the PEs, though the VLAN IDs are different.

With L2VPN, one bridge domain is not equal to one VLAN. L2VPN does not understand VLANs. From L2VPN point of view, VLAN number is not to restrict traffic flow to same VLAN.

With L2VPN, one bridge domain = one broadcast domain (irrespective of the VLAN number)

Topics to be familiar with:

• L2VPN Multihoming

• Martini Encapsulation

• VLAN normalization (vlan swapping)

• Traffic Policing, Out-of-band route reflection, route target constraint

From bgp.l2vpn.0 to <instance-name>.l2vpn.0 , will the RD be there or stripped off?

Route Distinguisher (RD) is still maintained in the customer instance.

Instance specific routing tables

L2VPN advertisements go through three stages of processing

bgp.l2vpn.0 to <instance-name>.l2vpn.0 to <instance-name>.l2id.0

RD will be there in first two tables, but will be removed in the 3rd table (l2id.0)

Multihoming

Two ways

1. Multichassis LAG or similar
2. tag one site as primary and keep the backup circuit in a down site

root@Juniper#set routing-instances <name> protocols l2vpn site <name> site-preference <primary|backup>

On both PEs, same site-identifieris used, similarly same remote-site-id.

Primary site uses BGP Local preference to 65535 and backup uses Local Preference of 1.

We will see RN -- remote site not designated and LN -- local site not designated in the show l2vpn connections output.

Martini Encapsulation

Martini Encapsulation is different from Martini Circuits (LDP based).

Martini Encapsulation describe encapsulating different Layer 2 protocols in MPLS.

Control Word

Defined in RFC 4448

32-bit header for the Control Word

FR/ATM makes great use of it but in Ethernet its mostly not required/used.

`MPLS Transport Label > MPLS VPN Label > Control Word > Customer Layer 2 Frame`

Ethernet Control word is mainly 0s, but still performs a vital function.

Junos load-balances based on hash of fields in layer 3 header.

First half set to all zeros. Second half is for sequence number.

4 bits + 12 bits + 16 bits

Swapping VLAN Tags in L2VPN

Solution to mismatched VLANs

[edit interfaces <interface-name>]

unit <> {
  vlan-id X;
	input-vlan-map {
		swap;
		vlan-id Y;
}
  output-vlan-map swap;
}

Encapsulation VLAN-CCC

For example, In (swap .100) Out (swap .200)

Traffic Policing

root@PE#set interfaces <interface-name> unit <unit-no> family ccc policer input <policer-name>

Route Distinguisher ID

To automatically generate a unique RD for each VPN based on the PE’s loopback IP

set routing-options route-distinguisher-id 192.168.1.1

Route Reflectors

bgp.l2vpn.0

For protocol next-hop resoltion, uses inet.3 by default.

RRs usually dont participate in LSPs, so no inet.3 table.

We can tell RR to resolve L2VPN next-hops in inet.0 instead of inet.3

by using

set routing-options resolution rib bgp.rtarget.0 resolution-ribs inet.0

Route Target Filtering

BGP neighbors indicate route targets they are interested in

Neighbor routers only send advertisements for those route targets

Route Target BGP family

set protocols bgp group <group-name> family route-target

Add this family in addition to family l2vpn signaling

bgp.rtarget.0 table gets populated ; This table will serve as export policy as well (to filter unnecessary routes)

show route table bgp.rtarget.0

[RTarget/5]