VPRN Service Overview
Page 858 7750 SR OS Services Guide
BGP Support
BGP is used with BGP extensions mentioned in Routing Prerequisites on page 857 to distribute
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.
Figure 2: Route Distinguisher
The three Type values are:
• Type 0: Value Field — Administrator subfield (2 bytes)
Assigned number subfield (4 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)
Assigned number subfield (2 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)
Assigned number subfield (2 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.
Type Field
(2-bytes)
Value Field
(6-bytes)
To Next Page
Loading...
