Profile 28 w/ Data MDTs
Continuing on from the previous lab, configure the PEs to switchover to data MDTs immediately for any customer traffic. Use up to 20 MDTs per PE.
Answer
Explanation
Profile 28 and 29 also allow for Data MDTs. These use a type 3 route to advertise a S-PMSI route.
In our network, the receivers have already joined the SSM group (1.1.1.1, 232.1.1.1). This prompts the type 3 route from XR5, even though there is currently no traffic.
Remember that the root PE must setup the p2mp tunnel. But how can XR5 know which PEs are interested in receiving traffic for a S-PMSI tunnel? It can’t simply assume that all PEs in total are interested, like it can with the default MDT.
The answer is that the route type 4 is used by the leaf PEs to signal interest in receiving the traffic advertised in the type 3 route. With SR-p2mp, the root needs to know which PEs are interested. It sets the “leaf-info-required” flag in the type 3 route.
0x01 means leaf info required:
XR7 and XR8 are interested in receiving this traffic and see the leaf-info-required flag. So they source their own type 4 routes which simply mean that they are interested in receiving the traffic for the specified (S, G) on the S-PMSI tree.
XR5 then requests the PCE to compute the S-PMSI tree rooted at itself with receivers XR7 and XR8. We can see that there are now two p2mp policies rooted at XR5.
Just as we’ve seen when using mLDP and P-PIM in the core for multicast tree building, the data MDTs optimize traffic flow, as the traffic is only delivered to PEs that are interested in receiving the traffic.
We can see information about the local data MDTs using the following command on the root. Notice that you can see the leafs which have advertised interest in joining the S-PMSI using the type 4 route.
We can see remote data MDTs using the following commands on the egress PEs. The remote keyword is a way to know if the PE has joined the MDT. If the PE has joined, you will see a non-zero value under “VRF Routes Using Cache.” The cache keyword also shows data MDTs the PE has learned about via type 3 routes.
Note that color and FRR are enabled on the data MDTs separately. You can use the same syntax as you saw in the last lab:
However, if you want to use particular colors for certain (S, G) flows, and enable FRR on only specific (S, G) flows, you can use an RPL.
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