What is the purpose of the MR in LISP?

[Mitrixsen]

Hello, everyone.

I don’t really understand what role the Map Resolver (MR) performs in LISP.

If MS is the main one that handles registrations and maintains mappings, why did they invent MR in the first place? Apparently, if the ITR does not have a mapping in the local cache, it asks the MR for it first.

MR also checks its local database and either replies or asks the MS.

The use of MR seems a bit redundant to me at the moment, maybe a bit unnecessary? If the MS contains all the necessary information, why should the ITR routers bother asking the MR device? What function does such a router actually perform? Does it also have any actual mappings or what is there for?

Thank you.
David

[Torbjørn]

LISP is very similar to DNS in many ways - the MR has the same role as a DNS resolver.

In DNS you might want to have resolvers close to your clients in large networks. This way you will distribute the load and shield your DNS authoritative servers as the DNS resolvers can cache DNS records and send DNS replies to the client without querying the authorative servers again. The Map-Resolver works in the same fashion for LISP, it allows LISP to be resilient and can support huge scale. In practice the MR and MS is usually co-located like it is in an SDA fabric.

I'm curious as I saw your other LISP post, are you studying for the CCIE?

[Mitrixsen]

Hi Torbjorn.

In DNS you might want to have resolvers close to your clients in large networks. This way you will distribute the load and shield your DNS authoritative servers as the DNS resolvers can cache DNS records and send DNS replies to the client without querying the authorative servers again. The Map-Resolver works in the same fashion for LISP, it allows LISP to be resilient and can support huge scale. In practice the MR and MS is usually co-located like it is in an SDA fabric.

So if I understand this right, the MR can also cache LISP records and reply to the routers without asking the MS all the time?

I'm curious as I saw your other LISP post, are you studying for the CCIE?

Maybe in a few years! I am currently studying for my CCNP ENCOR exam which requires you to be able to describe LISP to a certain point

Thank you!

[Torbjørn]

I had to check and must correct myself - I assumed that the LISP MR was caching but it turns out that it is not, as mentioned in section 1 of RFC9301. You can find a good description of exactly what the map resolver does in section 8.4 of the same RFC.

Keep up the good work! You'll be there in no time - and I suspect that you'll do well on your ENCOR based on your questions.

[M02@rt37]

Hello David,

no more to say that @Torbjørn perfectly explain.

Just a little post I wrote with a basic configuration as concerned LISP: https://community.cisco.com/t5/documents-de-routage-et-commutation/lisp-locator-id-separation-protocol/ta-p/5134577

Good luck for your ENCOR exam.