SD-WAN

Ok everyone, I think I have a tricky one for you this time. 

What is the purpose of "metadata" with the SSR?

#Trivia

Metadata is typically inserted with the first packet of a session. It is used by the SSR to inform the peer SSR about the characteristics of the session created -  e.g. the tenant of the source endpoint, the service selected for the session, authentication information, the session key information comprising of the source/destination addresses, source/destination ports etc. .. The receiving peer then makes a routing decision based on the information received in the metadata. It also sends reverse metadata to the originating SSR containing the information about the decision made by the receiving SSR.

Regards

Well said, @SHEETANSHU SHEKHAR! To add to that, the metadata also includes a cryptographic signature using credentials that are known by both the original and receiving SSR. This allows the receiving SSR to authenticate that the sender is a trusted source. This is just one of the many ways that the SSR enforces Zero Trust Security. <u5:p></u5:p>

Nice answers @Sheetanshu and @Jenna!

There are three main types of metadata in use within the SSR:

1. Session metadata. This is the 'signaling exchange' sent between routers. It occurs at the outset of a session, during a metadata handshake, and will reoccur when properties of the session change and need to be re-signaled.
2. Per-packet metadata. This type of metadata is mostly associated with changes made to packets regardless of what session they are associated with. An example of this is when an SSR needs to fragment packets destined for another SSR; in this case, it adds "fabric fragmentation" metadata to each of the pieces, telling the egress node how to reassemble them.
3. BFD metadata. In a unique category unto itself, BFD metadata appears in every BFD packet exchanged between routers. It is a lightweight payload used to communicate service changes (e.g., when an active node fails and activity is resumed by a highly available counterpart), used as part of the BFD application to measure link quality.

For more info on how the SSR uses metadata, check out this article.