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142 CHAPTER 5: IP ROUTING PROTOCOL OPERATION
Two Measures to Avoid Looping Inside an AS
As route reflector is imported, it is possible that path looping will be generated in
AS. Path update packets that already left the cluster may attempt to return to the
cluster. The conventional AS path method can not detect the internal AS looping,
because the path update packet has not left AS. Upon configuring route reflector,
BGP provides the following measures to avoid internal AS looping:
1 Configure the Originator_ID of the route reflector
The Originator_ID is established by the route reflector. The originator drops the
update packet and returns it to the originator if it is an improper configuration.
The parameter is not necessarily configured, and it will automatically function after
BGP is enabled.
2 Configure the Cluster_ID of the route reflector
Configuring BGP AS Confederation Attributes
Confederation provides a method to handle the booming IBGP network
connections inside AS. It divides the AS into multiple sub-AS, in each, all IBGP
peers are fully connected, and are connected with other sub-AS of the
confederation.
The shortcomings of confederation: it is required that the route be re-configured
upon switching from non-confederation to confederation solution, and that the
logic topology be basically changed. Furthermore, the path selected via
confederation may not be the best path if there is no manually set BGP policy.
Configuring the Confederation ID
In the eye of the BGP speakers that are not part of the confederation, multiple
sub-AS’s that belong to the same confederation appear as a single unit. The
external network does not need to know the status of internal sub-AS’s, and the
confederation ID is the AS number identifying the confederation as a whole.
Perform the following configurations in BGP view..
By default, the confederation_ID is not configured.
Configure a Sub-AS Within the Confederation
Configure the confederation_ID first, and then configure the sub-AS that belongs
to the confederation. One confederation can include up to 32 sub-AS’s. The
AS-number that is used when configuring the sub-AS as part of the confederation
is valid within the confederation.
Perform the following configurations in BGP view..
Table 125 Configuring the Confederation ID
Operation Command
Configure confederation_ID confederation id as-number
Canceling confederation_ID undo confederation id
Table 126 Configuring a Sub-AS Belonging to the Confederation
Operation Command
Configure a confederation consisting of
sub-ASs
confederation peer-as as-number-1 [ ...
as-number-n ]