Mpls Frame Format - Avaya 8600 Technical Manual

Layer 2 header
(eg. PPP, 802.3)
Label stack
entry format
Within a VPN, there can be no overlapping addresses. However, if two VPNs have no common sites,
then they may have overlapping address spaces. It is up to the PE router to maintain the separate
forwarding routing tables. The PE router will have a default forwarding table – referred to as VRF0 in the
ERS8600 – and one or more Routing and Forwarding tables (VRF's) – referred to as VRF1 to VRF255 on
the ERS8600 as the ERS8600 supports up to 255 VRF instances.
PE routers use BGP to allow distribution of VPN routes to other PE routers. BGP Multiprotocol Extensions
(BGP-MP) is used to allow BGP to forward routes from multiple address families.
The BGP-MP address contains a 12-byte VPN-IPv4 address which in turn contains an 8-byte Route
Distinguisher (RD) and a 4-byte IPv4 address. The Route Distinguisher makes the IPv4 address globally
unique, hence the reason the same IPv4 address space can be used as each VPN is distinguished with
its own RD.
Route Distinguisher (RD)
00 00 ASN
00 02
00 01
July 2010
MPLS label stack entries (1-n)
•••
1
Label
Label: Label value, 20 bits (0-16 reserved)
Exp.: Experimental, 3 bits (used for Class of Service)
S: Bottom of Stack, 1 bit (1 = last entry in label stack)
TTL: Time to Live, 8 bits

MPLS Frame Format

64 bits
RD Formats
nn
4 byte ASN
IP address
IV-VPN (MPLS) for ERS 8600 Technical Configuration Guide
n
IP
Network layer header and packet
4 bytes
Exp.
IPv4 Address
32 bits
Both configured as ASN:nn
 Autonomous System Number (ASN)
of backbone; should be IANA
assigned that is unique per service
nn
provider
Both configured as IP-address:nn
nn
 Defined if backbone uses private AS
number
 Mandatory format on ERS8600
when doing IPVPN-Lite
avaya.com
Data
TTL
S
9