Bgp Support; Route Distinguishers - Alcatel-Lucent 7750 SR OS Service Manual

VPRN Service Overview

BGP Support

BGP is used with BGP extensions mentioned in
VPRN routing information across the service provider's network.
BGP was initially designed to distribute IPv4 routing information. Therefore, multi-protocol
extensions and the use of a VPN-IPv4 address were created to extend BGP's ability to carry
overlapping routing information. A VPN-IPv4 address is a 12-byte value consisting of the 8-byte
route distinguisher (RD) and the 4-byte IPv4 IP address prefix. The RD must be unique within the
scope of the VPRN. This allows the IP address prefixes within different VRFs to overlap.

Route Distinguishers

The route distinguisher (RD) is an 8-byte value consisting of 2 major fields, the Type field and
value field. The type field determines how the value field should be interpreted. The TiMOS
implementation must support the three (3) type values as defined in the internet draft.
The three Type values are:
•
•
•
Page 858
Type Field
(2-bytes)
Figure 2: Route Distinguisher
Type 0: Value Field — Administrator subfield (2 bytes)
The administrator field must contain an AS number (using private AS numbers is
discouraged). The Assigned field contains a number assigned by the service provider.
Type 1: Value Field — Administrator subfield (4 bytes)
The administrator field must contain an IP address (using private IP address space is
discouraged). The Assigned field contains a number assigned by the service provider.
Type 2: Value Field — Administrator subfield (4 bytes)
The administrator field must contain a 4-byte AS number (using private AS numbers is
discouraged). The Assigned field contains a number assigned by the service provider.
Routing Prerequisites on page 857
Value Field
(6-bytes)
Assigned number subfield (4 bytes)
Assigned number subfield (2 bytes)
Assigned number subfield (2 bytes)
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