VPRN Service Overview
Page 414 7705 SAR OS Services Guide
BGP Support
BGP is used with BGP extensions, as mentioned in Routing Prerequisites, to distribute
VPRN routing information across the service provider’s network.
BGP was initially designed to distribute IPv4 routing information. Therefore, multiprotocol
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.
BGP is configured through the config>router>bgp context.
Route Distinguishers
The route distinguisher (RD) is an 8-byte value consisting of two major fields: the Type field
and Value field. The Type field determines how the value field should be interpreted. The
7705 SAR OS implementation supports the three (3) Type-Value combinations, as defined
in RFC 2547bis. Figure 42 illustrates the RD structure.
The three Type-Value combinations supported are described in Table 55.
Figure 42: Route Distinguisher Structure
20950
Value Field
(6-bytes)
Type Field
(2-bytes)
Table 55: Route Distinguisher Type-Value Fields
Type Field Value Field Notes
Type 0 Administrator subfield (2 bytes) The Administrator field must contain an AS number (using
private AS numbers is discouraged)
Assigned number subfield (4 bytes) The Assigned field contains a number assigned by the
service provider
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