Diameter Peer and Realm

Question

Probably is bigineer question. Diameter protocol maintains two table one is peer and other is realm. My question here is what is the requirement of having two tables here. We can have only one i.e. Peer Table which will tell us which peer to be reached. Looks that I am missing some part...

Answer 1

Realm routing table is used in routing of requests. Each request will have destination realm and application id. A lookup is performed on the realm table to pick up the next-hop peer for this combination of dest realm+application id. This step won't be necessary if the request specifically has destination-host name also, but in general, requests won't have this optional AVP filled.
Even when destination-host is present, note that it need not be a known peer. A peer is a host we can connect to and reach, but a request may take multiple hops to reach final destination.

Peer table maintains information about all known peers. So in general, peer table will be used for connection management while realm table will be used for forwarding.

Implementations may merge them (though I don't see why they would do that).
rk

Answer 2

The Diameter client could be common to multiple enterprises/departments with different domain names such as 1.abc.com, 2.abc.com, xyz.com. In the case where each of these domains have different AAA servers, the NAS client will need to route the request to the appropriate domain based on the NAI(in the format user@domain.com) received from the user.
Therefore the client needs to maintain a peer table (as configured).
The realm table will be required to map the target domain to the AAA servers, to help the client entity route the request based on the received NAI. Most NAS clients support NAS server grouping for redundancy/loadbalancing.
Sample config would be like,

Peer table

1.abc.com, 10.10.10.2 , Up
2.abc.com 10.10.10.3, Down
1.xyz.com 11.11.11.2 Up

NAS server group

abcgroup, 1.abc.com
abcgroup, 2.abc.com
xyzgroup, 1.xyz.com

Realm route

abc.com, abcgroup
xyz.com, xyzgroup