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Unicast Routing Overview

Unicast Routing Overview

Posted on Jan 27, 2020 (0)

Unicast Routing Overview

In Cisco Viptela Solution, the Overlay network is managed and controlled by Overlay Management Protocol (OMP).  This OMP protocol establish and maintain the Viptela Control plane and provides following Services:

  • Orchestration of
    • Routing and secure connectivity between sites
    • Service chaining
    • VPN topologies (Segmentation)
  • Distribution of Routes
  • Distribution of data-plane security parameters
  • Central Control and Distribution of routing policies

OMP is the Control plane protocol which exchanges the routing, policy, and management information between vSmart, vEdge. This Protocol is enabled by default and upon device restart, it establish or initiates the OMP peering between themselves via DTLS, AES-256 key encryption over System IP address. Once the routing, Policy, security services are propagated to vEdge, this are used by vEdge for data plane connectivity and transport.

OMP Route Advertisements

As soon as vEdge learns the routes are services from local site, it advertises these all information to vSmart controller along with its transport location mapping called as TLOC which are further called as OMP routes or routes.

It is due to OMP routes, vSmart learn the topology of the overlay network and services available in that network. As all vEdge devices advertises its imported to vSmart Controller and based on policy decisions the controller further distributes the routing information to other edge devices. The Edge devices will never advertises its routing information directly to another vEdge devices.

OMP Route Types

There are Three Types of Routes

OMP Routes (vRoutes)

  • Prefixes learned from site-local (i.e. service side)
  • Like prefixes of BGP

TLOC’s

  • Transport Locator
  • Ties OMP route to physical location (i.e. vEdge)
  • Like next-hop of BGP

Service Routes

  • Service Chaining
  • Ties OMP route to an advertised network service

OMP routes (vRoutes)

OMP routes are those routes or prefixes which are used to establish the reachability between end points. These OMP routes represent a services in DC, Service in Branch Office or it is a collection of hosts in any location of overlay network.

At each site, vEdge router advertise the OMP routes to vSmart controller and these routes contain routing information that vEdge has learned from that local site.

Following are OMP routes that is advertised by vEdge at local site.

  • Connected (Direct)
  • Static
  • BGP
  • OSPF

OMP routes advertises the following attributes:

  • TLOC—Transport location identifier of the next hop for the route. It is similar to the BGP NEXT_HOP attribute. A TLOC consists of three components:
    • System IP address of the OMP speaker that originates the OMP route
    • Color to identify the link type
    • Encapsulation type on the transport tunnel
  • Origin—Source of the route, such as BGP, OSPF, connected, and static, and the metric associated with the original route.
  • Originator—OMP identifier of the originator of the route, which is the IP address from which the route was learned.
  • Preference—Degree of preference for an OMP route. A higher preference value is more preferred.
  • Service—Network service associated with the OMP route.
  • Site ID—Identifier of a site within the Viptela overlay network domain to which the OMP route belongs.
  • Tag—Optional, transitive path attribute that an OMP speaker can use to control the routing information it accepts, prefers, or redistributes.
  • VPN—VPN or network segment to which the OMP route belongs.

With the Help of following command, we will be able to see the OMP Routes

vEdge1# show ip route

TLOC Routes:

TLOC route are those routes which identify the transport location. A TLOC identify location that connect the physical WAN transport to WAN interface on vEdge Router. TLOC is identified by 3-tuple which is

  • System IP
  • Color
  • Encapsulation

TLOC advertises the following attributes:

  • TLOC private address—Private IP address of the interface associated with the TLOC.
  • TLOC public address—NAT-translated address of the TLOC.
  • Carrier—An identifier of the carrier type, which is generally used to indicate whether the transport is public or private.
  • Color—identifies the link type.
  • Encapsulation type—Tunnel encapsulation type.
  • Preference—Degree of preference that is used to differentiate between TLOCs that advertise the same OMP route
  • Site ID—Identifier of a site within the Viptela overlay network domain to which the TLOC belongs.
  • Tag—Optional, transitive path attribute that an OMP speaker can use to control the flow of routing information toward a TLOC. When an OMP route is advertised along with its TLOC, both or either can be distributed with a community TAG, to be used to decide how send traffic to or receive traffic from a group of TLOCs.
  • Weight—Value that is used to discriminate among multiple entry points if an OMP route is reachable through two or more TLOCs.

IP address used in TLOC is fixed system IP address of vEdge Router. Let’s understand the TLOC

The encapsulation is that used on the tunnel interface. It can be either IPsec or GRE. vEdge router that has two WAN connections and it has two TLOCs. The system IP address of the router is 1.1.1.1. The TLOC on the left is uniquely identified by the system IP address 1.1.1.1, the color metro-ethernet, and the encapsulation IPsec, and it maps to the physical WAN interface IP address 143.143.143.143. The TLOC on the right is identified by the system IP address 1.1.1.1, the color biz-internet, and the encapsulation IPsec, and it maps to the WAN IP address 88.88.88.88.

Service Routes

Service routes are those routes that represent any services that are connected to local sites. Routes of network-services connected to vEdge

Attributes of Service Routes:

  • VPN id
  • Service-id:
  • FW, IDS, IDP, VPN or generic net-svc
  • Label
  • Originator-id
  • Path-id

Below is the figure that describes all routes in one diagram.

OMP Routes: Route Distribution

When OMP is enabled, it automatically redistributes following routes that it learn either locally or from its routing peers.

  • Connected
  • Static
  • OSPF intra-area routes
  • OSPF inter-area routes

In order to avoid routing loops, and less optimal routing, when redistribution is done following types of routes requires explicit configuration.

  • BGP
  • OSPF external routes

Now to avoid distributing very large number of routing information from an Edge to overlay network, Routes learned from on vEdge via OMP are not automatically redistributed in to another routing protocols on that routers. If redistribution is desired redistribution must be enabled locally on each vEdge router.

To indicate the route origin, OMP includes or set the origin and sub-origin type in its advertisement and while selecting routes, vEdge and vSmart considers the origin a sub-origin types.

OMP also carries the metric of original routes with Metric 0 is said as directly connected routes.

OMP Best-Path Algorithm and Loop Avoidance

In Network topology, it can be possible that, some network prefix are advertised from multiple vEdge routers. In order to choose best path, Viptela perform the following operation.

  • Check: OMP routes are valid or not, if not ignore it.
  • If OMP routes are valid, and if the routes are learned, select the OMP routes which has lower AD.
  • Select the OMP with higher OMP route preference
  • Select the OMP route with higher TLOC preference value.
  • Compare the origin types and select if first match order.
    • Connected
    • Static
    • EBGP
    • Ospf Intra-area
    • Ospf inter-area
    • OSPF external
    • IBGP
    • Unknown
  • If Origin type is same , Select the OMP with lower Metric
  • Select the OMP with higher router ID
  • Select the OMP with higher Private IP address.

A vEdge router installs the OMP routes in its FIB only when its TLOC is active. For TLOC to be active, it must have active BFD session associated to it. If the BFD session becomes inactive, the vSmart controller removes all the OMP routes that points to TLOC from FIB table.


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