Bgp As Number Substitution And Soo Attribute - HP FlexNetwork 10500 Series Configuration Manual

Figure 58 Network diagram for sham link
Site 1
OSPF Area 1
VPN 1
A sham link is considered a virtual point-to-point link within a VPN and is advertised in a Type 1 LSA.
It is identified by the source IP address and destination IP address that are the local PE address and
the remote PE address in the VPN address space. Typically, the source and destination addresses
are loopback interface addresses with a 32-bit mask.
To add a route to the destination IP address of a sham link to a VPN instance, the remote PE must
advertise the source IP address of the sham link as a VPN-IPv4 address through MP-BGP. To avoid
routing loops, a PE does not advertise the sham link's destination address.

BGP AS number substitution and SoO attribute

BGP detects routing loops by examining AS numbers. If EBGP runs between PE and CE, you must
assign different AS numbers to geographically different sites or configure the BGP AS number
substitution feature to ensure correct transmission of routing information.
The BGP AS number substitution feature allows geographically different CEs to use the same AS
number. If the AS_PATH of a route contains the AS number of a CE, the PE replaces the AS number
with its own AS number before advertising the route to that CE.
After you enable the BGP AS number substitution feature, the PE performs BGP AS number
substitution for all routes and re-advertises them to connected CEs in the peer group.
Figure 59 Application of BGP AS number substitution and SoO attribute
EBGP_Update: 10.1.0.0/16
AS_PATH: 800
AS 800
Site 1
As shown in
enabled on PE 2 for CE 2. Before advertising updates received from CE 1 to CE 2, PE 2 substitutes
its own AS number 100 for the AS number 800. In this way, CE 2 can correctly receive the routing
information from CE 1.
MPLS backbone
PE 1
CE 12
PE 1
VPNv4_Update: 10.1.0.0/16
RD: 100:1
AS_PATH: 800
CE 1
Figure 59, both Site 1 and Site 2 use the AS number 800. AS number substitution is
Sham-link
CE 22
Backdoor-link
AS 100
PE 2
MPLS backbone
198
PE 2
Site 2
OSPF Area 1
VPN 1
CE 3
AS 800
Site 2
EBGP_Update: 10.1.0.0/16
AS_PATH: 100, 100
CE 2