I have decided to continue my education and dig deeper into the Cisco world. As an engineer that’s basically dedicated the past 4 years of his life into a Nokia IP/Routing world, I somtimes need to take a step back and spend time to understand other vendor’s platform and emerging technologies. I recently passed the Cisco DevNet exam and well, it made me realize there is a lot of gaps in my knowledge regarding Cisco. I’m currently studying for ENCORE and hope to grasp some of the unfamiliar knowledge and refresh up on all the basics, OSPF, BGP, STP, etc.. I hold a NRS II, which is basically a CCNP, but it involves a detailed 4 hour live router lab that must be performed in person under strict monitoring rules. My goal is to become a CCNP/NRS II by the end of the year. I’ve chosen to start labbing LISP, as SD-Access is an emplementation of VXLAN with LISP control plane. These are technologies I will be digging much deeper into as I have not had experience with them professionally.
Lets talk about Overlay Tunnels. An overlay network is a logical or virtual network on top of a physical transport network, which is also known as the underlay network.
Some overlay tunneling technologies include, GRE, IPsec, LISP, VxLAN and MPLS. In this POST, I want to concentrate on LISP.
The main goal of LISP is to address the scalability problems with the growing route table of the internet.
A few KeyTerms to remmember:
- Endpoint Identifier (EID) – The IP address of an endpoint within a LISP Site. EIDs are the same ip addresses in use today on endpoints (v4/v6).
- LISP Site – The name of the Site where EID’s and LISP routers live.
- Ingress Tunnel Router (ITR) – LISP Routers that LISP-encapsulate IP Packets coming from EIDs that are destined outside the LISP site.
- Egress tunnel router (ETR) – ETRs are LISP routers that de-encapsulate LISP-encapsulated IP packets coming from sites outside the LISP site and **destined to EIDs within the LISP site. **
- Tunnel Router (xTR) – Routers that perform ITR and ETR Functions. (Most routers wihtin an LISP domain)
- Proxy ITR (PITR) -PITRS are for non-LISP sites that send traffic to EID destinations
- Proxy ETR (PETR) – PETRS act just like ETRS, but for EIDs that send traffic to destinations at non-LISP sites.
- LISP Router – Any router that performs any LISP functions.
- Routing Location (RLOC) – RLOC is an IPv4/v6 address of an ETR that is Internet facing or core network facing.
- Map Server (MS) – This is a network device (Router) that learns EID to prefix mapping entries from an ETR and stores them in a local EID-to-RLOC mapping database.
- Map Resolver (MR) – Network device that receives LISP-encapsulated map requests from an ITR and finds the appropriate ETR to answer those requests by consulting the map server.
- Map Server/Map Resolver (MS/MR) – When MS and MR are implemented on the same device.
The advantage and key control plane feature of LISP is the efficiency and scalability of the on-deman routing, as it’s not a PUSH model such as BGP or OSPF. LISP utilizes a pull model where only the requested routing information is provided, instead of a full table.
This entire operation sure feels like a DNS query. I felt this way the second I was updating the MS/MS in my lab telling it what the EID’s prefixes within my LISP site was. It’s an easy way to think of LISP and maybe that will click easier in your head.
Lets review the registration process for Site: Avifi-A on the left, CSR-A12.
If the traffic flow is from Site Avifi – B to Site Avifi-A, the Avifi-A router will be the ETR in this instance(technically, the device is confiured as itr/etr as it’s providing both functions.). Avifi-A will need to adervtise it’s Lo0 address to the MS/MR.
The EID for Avifi-A : 192.168.1.0/24 – This includes the Lo0 that’s currently reachable on the router.
The RLOC is the interface address configured on Gi1 on the Avifi-A router. Although not displayed on the image, it’s 10.0.1.2.
Here is an example configuration snippet of the database-mapping command to include the EID and the RLOC.
R2-Avifi-A#show run | sec lisp
database-mapping 192.168.1.0/24 10.0.1.2 priority 1 weight 100
ipv4 itr map-resolver 10.0.1.1
The Lab has since expanded to add CPE’s with traditional OSPF routing between the xTR and the CPE. There is redistribution of connected subnets (loopbacks) and the xTR has an updated database to include this loopback.
I’ve also included an IPSEC via VTI that has an OSPF adjacency across a simulated ISP network with public IP addresses. This allows us to take advantage of a PxTR which is a PITR and PETR router collapsed into one device. I’ve uploaded this EVE-NG LAB into my blog for you to downoad and play with..who knows, maybe ever learn about LISP!
I’ve left fun exercise for your to practice, if you wish to use this lab.
Establish the underlay network for Site B’s CPE to the PE. Once that’s completed, ensure the EID is updated on the MS/MR and that the EID is reachable via LISP overlay network.