Hello, i just wanted to know if Cluster-ID is really obsolete or if there are any scenarios where we want to configure the same cluster-id on different routers to avoid routing loops??
Most cost companies care about uptime. To get more uptime, they implement fault tolerance and redundancy. If they implement redundancy regarding route reflectors, they will also need to use the cluster-id, so that a route reflector in the same cluster, can identify an update from another router reflector in the same cluster.
i am confused, because i read a site where it says it is obsolete, please read lines below
Cisco IOS implementation of route reflector functionality supports the bgp cluster-id parameter, which is used in the Cluster list attribute instead of the Router ID. The cluster-id parameter is useful in redundant route reflector scenarios where multiple route reflectors serve the same set of clients, but can lead to partial connectivity when multiple IBGP sessions are disrupted.
The revised BGP route selection rules ensure that a route reflector in a cluster always prefers route from a client (with shorter Cluster list) over a reflected route, thus making the bgp cluster-id parameter obsolete. You should not use the bgp cluster-id in new designs to increase the resilience of your network.
If you are taking the certification, stick with the cluster-id.
When a route is reflected, it is possible through misconfiguration to
form route re-distribution loops. The route reflection method
defines the following attributes to detect and avoid routing
CLUSTER_LIST is a new, optional, non-transitive BGP attribute of Type
code 10. It is a sequence of CLUSTER_ID values representing the
reflection path that the route has passed.
When an RR reflects a route, it MUST prepend the local CLUSTER_ID to
the CLUSTER_LIST. If the CLUSTER_LIST is empty, it MUST create a new
one. Using this attribute an RR can identify if the routing
information has looped back to the same cluster due to
misconfiguration. If the local CLUSTER_ID is found in the
CLUSTER_LIST, the advertisement received SHOULD be ignored.
9. Impact on Route Selection
The BGP Decision Process Tie Breaking rules (Sect. 22.214.171.124, ) are
modified as follows:
If a route carries the ORIGINATOR_ID attribute, then in Step f)
the ORIGINATOR_ID SHOULD be treated as the BGP Identifier of the
BGP speaker that has advertised the route.
In addition, the following rule SHOULD be inserted between Steps
f) and g): a BGP Speaker SHOULD prefer a route with the shorter
CLUSTER_LIST length. The CLUSTER_LIST length is zero if a route
does not carry the CLUSTER_LIST attribute.
On the service providers networks that I have worked with, they use the cluster ID in their redundant clusters.
It is true that the cluster related items, in the route selection process, are somewhere in the bottom 3 of a 13 step selection process.
Any input from others is very welcome.
Best wishes on your CCIP,
If I were going to implement route reflectors in clusters, I'd use cluster IDs to be safe. It takes minutes of extra planning. I have recently spoken with engineers at other organizations running large iBGP networks specifically about route reflection, and none of them were talking about removing their cluster ids. As Keith points out, it's pretty far down the selection process, and most networks are designed such that BGP never gets to make a decision with those criteria.
I'll also point out that RFC4456 only says "should" and not "must." It's better to be safe than sorry.