Hi,
Basically we would use "independet-domain", when the customer route attributes has to be transparently fowarded across the VPN network
even without having the service-provider AS path in the routes.
Let's say we have a netwoek like this:
|<-----VPN-------->|
internal internal
routes +-----+ +-----+ +-----+ +-----+ routes
======> | CE1 |----------| PE1 |************| PE2 |-----------| CE2 | <========
+-----+ +-----+ +-----+ +-----+
|<---EBGP------>| |<---EBGP------>|
If the administrator of customer site wants to make routing decisions based on their own route attributes,
then with VPN network (without "independet-domain") would not help.
Say on CE1, we have a internal route as below,
suryak@CE1# run show route protocol bgp 110.1.1.1/32 detail
inet.0: 40 destinations, 40 routes (39 active, 0 holddown, 1 hidden)
110.1.1.1/32 (1 entry, 1 announced)
*BGP Preference: 170/-101
Next hop type: Indirect
Next-hop reference count: 3
Source: 200.10.0.1
Next hop type: Router, Next hop index: 547
Next hop: 200.10.0.1 via ge-5/1/0.0, selected
Protocol next hop: 200.20.0.1
Indirect next hop: 8e23240 1048574
State: <Active Int Ext>
Local AS: 100 Peer AS: 100
Age: 1 Metric: 10 Metric2: 2
Task: BGP_100.200.10.0.1+179
Announcement bits (3): 0-KRT 4-BGP RT Background 5-Resolve tree 1
AS path: I (Originator) Cluster list: 33.33.33.33
AS path: Originator ID: 10.255.178.60
Accepted
Localpref: 100
Router ID: 200.10.0.1
When the same is advertised across the VPN network to CE2, it appreas as
suryak@CE2# run show route protocol bgp 110.1.1.1/32 detail
inet.0: 35 destinations, 35 routes (34 active, 0 holddown, 1 hidden)
110.1.1.1/32 (1 entry, 1 announced)
*BGP Preference: 170/-101
Next hop type: Router, Next hop index: 513
Next-hop reference count: 4
Source: 20.0.0.1
Next hop: 20.0.0.1 via ge-3/1/1.0, selected
State: <Active Ext>
Local AS: 100 Peer AS: 200
Age: 36:40
Task: BGP_200.20.0.0.1+179
Announcement bits (1): 0-KRT
AS path: 200 200 I
Communities: target:100:100
Accepted
Localpref: 100
Router ID: 20.0.0.1
If we analyse the customer route attributes like Originator ID, Cluster list, Metric, AS path are not transparent from CE1 to CE2.
In this case we like to have a transprancy for route attribute, then we can use "independet-domain".
|<-----VPN-------->|
internal internal
routes +-----+ +-----+ +-----+ +-----+ routes
======> | CE1 |----------| PE1 |************| PE2 |-----------| CE2 | <========
+-----+ +-----+ +-----+ +-----+
|<---IBGP------>| |<---IBGP------>|
Taking the same route on CE1, we can see the difference.
suryak@CE1# run show route protocol bgp 110.1.1.1/32 detail
inet.0: 40 destinations, 40 routes (39 active, 0 holddown, 1 hidden)
110.1.1.1/32 (1 entry, 1 announced)
*BGP Preference: 170/-101
Next hop type: Indirect
Next-hop reference count: 3
Source: 200.10.0.1
Next hop type: Router, Next hop index: 547
Next hop: 200.10.0.1 via ge-5/1/0.0, selected
Protocol next hop: 200.20.0.1
Indirect next hop: 8e23240 1048574
State: <Active Int Ext>
Local AS: 100 Peer AS: 100
Age: 5:31 Metric: 10 Metric2: 2
Task: BGP_100.200.10.0.1+179
Announcement bits (3): 0-KRT 4-BGP RT Background 5-Resolve tree 1
AS path: I (Originator) Cluster list: 33.33.33.33
AS path: Originator ID: 10.255.178.60
Accepted
Localpref: 100
Router ID: 200.10.0.1
suryak@CE2# run show route protocol bgp 110.1.1.1/32 detail
inet.0: 35 destinations, 35 routes (34 active, 0 holddown, 1 hidden)
110.1.1.1/32 (1 entry, 1 announced)
*BGP Preference: 170/-101
Next hop type: Indirect
Next-hop reference count: 6
Source: 20.0.0.1
Next hop type: Router, Next hop index: 513
Next hop: 20.0.0.1 via ge-3/1/1.0, selected
Protocol next hop: 20.0.0.1
Indirect next hop: 91740e4 2097150
State: <Active Int Ext>
Local AS: 100 Peer AS: 100
Age: 18 Metric: 20 Metric2: 0
Task: BGP_100.20.0.0.1+179
Announcement bits (2): 0-KRT 3-Resolve tree 1
AS path: I (Originator) Cluster list: 33.33.33.33
AS path: Originator ID: 10.255.178.60
Accepted
Localpref: 100
Router ID: 20.0.0.1